helium leak test

PORTABLE HELIUM LEAK DETECTOR HLD-1112 Diffusion Version

HLD-1112

• Readily Portable • Digital Display For Leak Rate • No Liquid Nitrogen • Excellent Sensitivity • Electromagnetic Valve Operation • Easy To Maintain

HLD-1112

Mass Spectrometer Helium Leak Detector

FACTORY CALIBRATION DATA

odel Number: HLD-1112 Date: __________________

erial Number:

djustments are left untouched and calibration may be ver

changes may occur when using filament No. 2 or after an ion source placement.

ilament No. 1

M S

Your HLD-1112 Mass spectrometer Leak Detector has been thoroughly checked out prior to shipment. It is shipped tuned to helium on filament No. 1. Normally, once set, the tuning a

ified daily or as required. The data recorded below are readings taken during the final check prior to

shipment. They are convenient for reference purposes if tuning adjustments are altered. Slightre F

uning Parameters and other settings T

e : V B. Repeller Voltage : V

. Focus Voltage : V D. Emission Current : Amp

. Sensitivity : 2 x 10-10 cc/s/div E: Min Range Select : 10-9

. DP Temp Setting : oC F: Background : cc/s

alibrated By Approved By

ignature Signature

ame Name

Date Date

A. Ion Voltag C D E C S N

HLD-1112 Helium Leak Detector

INDEX

SECTION 1 INTRODUCTION………………………………………………. 1 1-1 SCOPE ……………………………………………………………………. 1 1-2 NEED FOR TESTING ……………………………………………………. 1 1-3 GLOSSARY OF TERMS…………………………………………………. 1 1-4 METHODS OF TESTING………………………………………………… 2 1-4.1 WATER IMMERSION……………………………………………. 2 1-4.2 DYE PENETRANT………………………………………………... 3 1-4.3 ULTROSONICS…………………………………………………… 3 1-4.4 HALOGEN………………………………………………………… 3 1-4.5 RADIOISOTOPE………………………………………………….. 3

1-4.6 HELIUM METHOD……………………………………………….. 3 1-5 HELIUM MASS SPECTROMETER LEAK DETECTION……………….. 3 1-5.1 PRINCIPLES OF MASS SPECTROMETRY 1-5.2 APPLICATION AS LEAK DETECTOR…………………………. 4 1-6 NATURE OF FLOW IN VACUUM……………………………………….. 4 1-7 HELIUM MASS SPECTROMETER LEAK DETECTION METHODS….. 4

1-7.1 Tracer Probe Technique………………………………………………….. 5 1-7.2 Tracer Probe technique (Hood Technique)……………………………... 6 1-7.3 Tracer Probe Technique (Test Object sealed)…………………………… 7 1-7.4 Tracer Probe Technique (Bombing)……………………………………… 8 1-7.5 Detector Probe Technique (Sniffer Probe)………………………………… 8

SECTION 2 DESCRIPTION…………………………………………………….. 10 2-1 HLD-1112 LEAK DETECTOR…………………………………………….. 10 2-2 VALVE BLOCK……………………………………………………………. 10 2-3 SPECIFICATIONS…………………………………………………………. 12 2-4 VACUUM SYSTEM……………………………………………………….. 12 2-5 DIFFUSION PUMP DESCRIPTION………………………………………. 12 2-5.1 Conter flow principle……………………………………………….. 13 2-6 MECHANICAL VACUUM PUMP………………………………………… 13 2-6.1 Mechanical Pump Specifications……………………………………. 13 2-7 SPECTROMETER TUBE…………………………………………………… 13 2-7.1 Ion Source……………………………………………………………. 13 2-7.2 Preamplifier Assembly……………………………………………….. 14 2-7.3 Analyzing Magnets…………………………………………………… 14


SECTION 3 RECEIVING AND INSTALLATION…………………………….. 15 3-1 DESCRIPTION……………………………………………………………… 15 3-2 UNPCKING…………………………………………………………………. 15 3-3 SERVICES REQUIRED FOR OPERATION………………………………. 15 3-4 PREPRATION FOR OPERATION…………………………………………. 15 3-5 INSTALLATION……………………………………………………………. 15 SECTION 4 OPERATION………………………………………………………. 16 4-1 GENERAL INTRODUCTION…………………………………………….. 16 4-2 OPERATING CONTROLS AND INDICATORS…………………………. 16

4-2.1 TUNING CONTROLS……………………………………………… 17 4-3 STARTING PROCEDURES………………………………………………… 17 4-4 OPERTING START AND VENT CYCLES………………………………… 18 4-5 SHUTDOWN PROCEDURES………………………………………………. 18 4-6 STATUS OF VALVES IN VARIOUS MODES……………………………. 19

4-6.1 VENT MODE………………………………………………………… 19 4-6.2 START MODE……………………………………………………….. 19 4-6.3 TEST MODE…………………………………………………………. 20 4-6.4 HOLD MODE………………………………………………………… 20

SECTION 5 CALIBRATION, TUNING AND MEASURING BACKGROUND.. 21 5-1 CALIBRATION CHECK……………………………………………………. 21 5-2 TUNING ADJUSTMENTS………………………………………………….. 21 5-3 CALIBRATION ADJUSTMENTS………………………………………….. 22

5-3.1 Correction of Exponent………………………………………………. 22 5-3.2 Correction of mantissa………………………………………………… 23

5-4 CHECKING BACKGROUND……………………………………………….. 23 SECTION 6 MASS SPECTROMETER IN HLD-1112………………………….. 24 6-1 ION SOURCE………………………………………………………………… 25 6-2 MAGNETIC FIELD…………………………………………………………… 25 6-3 PREAMPLIFIER ASSEMBLY……………………………………………….. 25 6-4 COLD CATHODE GAUGE………………………………………………….. 26 6-5 ADJUSTABLE SOURCE MAGNETS……………………………………….. 26

SECTION 7 EXPLANATION OF TUNING CONTROLS……………………….. 27 7-1 FOCUS CONTROL…………………………………………………………… 29 7-2 ION CONTROL……………………………………………………………….. 29 7-3 REPELLER CONTROL………………………………………………………. 30 7-4 EMISSION CONTROL……………………………………………………….. 31 7-5 ZERO CONTROL…………………………………………………………….. 31 7-6 SECTOR MAGNET…………………………………………………………… 31


7-7 ION SOURCE MAGNET CONTROL………………………………………… 32 7-7 CALIBRATION CONTROL………………………………………………….. 32 7-8 DIFFUSION PUMP CONTROL………………………………………………. 32 SECTION 8 INTERPRETATION OF SENSITIVITY…………………………… 33 8-1 SENSITIVITY………………………………………………………………….. 33 8-2 MEASUREMENTS OF LEAK RATE………………………………………… 33 8-3 SHIFTING OF SCALES………………………………………………………. 33

8-3.1 MIN RANGE SELECT AT 10-9………………………………………. 34 8-3.2 MIN RANGE SELECT AT 10-8………………………………………. 34 8-3.3 MIN RANGE SELECT AT 10-7………………………………………. 34

SECTION 9 USING SNIFFER……………………………………………………… 35 9-1 TROUBLESHOOTING SNIFFER…………………………………………….. 36 SECTION 10 TROUBLESHOOTING……………………………………………….. 37 10-1 TROUBLESHOOTING CHART………………………………………………. 37 SECTION 11 MAINTEANCE………………………………………………………. 39 11-1 DAILY CHECKUPS…………………………………………………………. 39 11-2 WEEKLY MAINTENANCE…………………………………………………. 39 SECTION 12 GENERL SUGGESTIONS………………………………………….. 40

HLD-1112, Helium Leak Detector

SECTION 1 INTRODUCTION

1-1 SCOPE

This manual provides information concerning the historical need for leak testing, a glossary of terms, testing methods and information, as well as alternative applications. Further, it provides equipment description, receiving and installation procedures, and complete operating instructions, calibration procedures, troubleshooting. The degree of Information provided is sufficient for normal operation of Fillunger make leak detector and its intended leak testing modes. 1-2 NEED FOR TESTING

The need for leak testing with helium leak detector has been established by its success throughout the domestic and foreign manufacturing complex. All of these industries that either use or manufacture sealed or leak proof enclosures that carry a guarantee or such, have a need for leak testing. The Fillunger HLD-1112 mass spectrometer leak detectors is capable of detecting leaks from 2 x 10-10 std cc/sec to 1 x 10-4 std cc/sec. A partial list typical users includes

• Manufacturer using tubular elements such as refrigeration equipment manufacturer, petroleum cracking plants, chemical plants etc

• Any industrial pressure vessel manufacturer. • Industrial aerosol container manufacturer • Beverage canning industry • Hermetically sealed instrument manufacturers. • Any manufacturer using bellows in his product. • Vacuum chamber manufacturer • General R & D laboratory users • Hermetically sealed electronic component manufacturers producing relays, connectors,

quartz crystals, reed relays • Vacuum tube manufacturers

1-3 GLOSSARY OF TERMS LEAK

A leak may be defined as an unintended crack, hole or porosity in a containing wall that allows the admission or escape of fluid or gas. LEAK DETECTOR

Instrument or system designed to locate and measure leaks. FLOW

Std cc/sec = one cubic centimeter of gas per second at a pressure differential of one standard atmosphere (760 Torr at 0" C).

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Atm cc/sec =one cubic centimeter of gas per second at ambient atmospheric pressure and temperature (used interchangeably with Std cc/sec). Because the difference is usually insignificant for leak testing purposes. RATE OF RISE

In vacuum systems, this is defined as the rate of increase in absolute pressure per unit time with the vacuum pumps isolated from the system, and is the sum of actual leakage and internal out gassing. Rate of rise is usually expressed in Torr or miliiTorr (microns) per hour. The flow rate is expressed in Torr-liters/second. CONVERSIONS

lit/secmbar 1

lit/sec1000

1mbar x 1000

cc/sec Atm 1 cc/sec Std 1

=

=

=

lit/secTorr 0.76

lit/sec1000

1Torr x 760

cc/sec Atm 1 cc/sec Std 1

=

=

=

NUMERICAL NOTATION, EXPONENTIAL SYSTEM

Most leak rates of commercial significance are very small fractions of std cc/s Therefore, negative powers often are used as convenient system of numerical notation. Following illustration shows the relationship of exponents and multipliers (to the base 10) to the arithmetic form. and the equivalent decimal notations. Multiplier Arithmetic Form Decimal Notation 1x102 1x10x10 100 1 x 101 1 x10 10 1x100 1 1 1x10-1 1x1/10 0.1 1x10-2 1x1/10x1/10 0.01 1 x 10-3 1 x 1/10 x 1/10 x 1/10 0.001 5x 10-3 5x 1/10x 1/10 x 1/10 0.005 1-4 METHODS OF TESTING

There are many methods of testing for leaks in enclosures either systems or containers. The more commonly used methods, along with their ranges of accuaracy, are listed below. 1-4.1 WATER IMMERSION (AIR BUBBLE OBSERVATION)

This method is accurate to approximately 10-4 std cc/sec and can be more sensitive If Internal pressure is increased or vacuum created above water. This method is limited because of difficulty in differentiating between leakage bubbles and surface desorption bubbles. It Is used

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to test industrial items such as valves, hydraulic components, castings, automotive, and air conditioning components. 1-4.2 DYE PENETRANT

A special dye applied to one side of a surface suspected to contain a leak seeps through the leak and appears on the other side. This method can take an hour or more for a 10-4 std ccIsec leak to show up. This test is inexpensive but destructive in some applications, as well as slow and messy. 1-4.3 ULTRASONIC

This method is accurate to approximately 10-4 std CC/sec. This method tests for ultrasonic sounds coming from a gas leak and is used for testing of high-pressure lines. 1-4.4 HALOGEN (SENSITIVE TO HALOGEN ELEMENTS OR COMPOUNDS.

ESPECIALLY REFRIGERANT GASES) This method is good to approximately 10-5 std cc/sec in most current applications. but

extendable to 10-9 std cc/sec under some limited situations. It is critically dependent on operator Judgment If leaks are below 10-5 std cc/sec and requires a constant now of fresh air In the test area because of the tendency of tracer gas to hang in the area. The detector used in this method is sensitive to a variety of gases (other than the selected tracer gas) from external sources such as cigarette smoke and solvent fumes which may produce erroneous indications of leakage. 1-4.5 RADIOISOTOPE

This method is useful only for testing hermetically -sealed cavities. It has approximately the same range as the helium method but it involves an expensive installation (from four to ten times the cost of a helium installation depending on degree of isolation of radiation required). It also requires a radiation safety officer. 1-4.6 HELIUM METHOD

This method is accurate to 10-11 std cc./sec and is capable of finding leaks of any size larger. This method is useful for testing hermetic seals. vacuum enclosures and vacuum systems. and is the most versatile of industrial and laboratory leak detection testing methods. 1-5 HELIUM MASS SPECROMETER LEAK DETECTION

Helium is an excellent tracer gas because it is the lightest of the inert gases and. as such readily penetrates small leaks. In addition, Its minute presence in the atmosphere (5 PPM or 4 mill Torr absolute), ease in being detected by a simple mass spectrometer (has a mass of 4 so that adjacent peaks- of 3 and 6 are easily separated by this technique), and relatively low cost, make it particularly suited to this application.

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1-5.1 PRINCIPLES OF MASS SPECTROMETRY

A mass spectrometer sorts gases by their molecular weights (mass number) to determine the quantity of each gas present. With the helium mass spectrometer leak detector, the gas of interest is primarily helium (although such a device can be adjusted to indicate other gases such as hydrogen, argon, or neon). The mass spectrometer tube is relatively simple. The principle is to ionize the gases in a vacuum; electro statically accelerates the various ions. and then separate the ions by passing them through a magnetic field which is set to bend the helium ion beam exactly 90 (See Figure). The light ions bend more than 90 and the heavy ions bend less than 90°. A slit properly placed, allows only helium ions to pass through and be collected. The resulting current is amplified and a meter indicates the presence and amount of helium. 1-5.2 APPLICATION AS A LEAK DETECTOR

A mass spectrometer leak detector consists of a spectrometer tube, the electronics to operate and interpret it, and a high-vacuum system to maintain proper vacuum. In addition, means are provided for connecting a test object to pump and valve systems necessary to evacuate the test object for connection to the spectrometer tube. If it is a sealed object containing helium then accessory known as sniffer probe can be used. 1-6 NATURE OF HELIUM FLOW IN A VACUUM

It should be noted that the purpose of vacuum system in helium leak detector is to support operation of the analyzing spectrometer tube. Helium molecules entering through a leak individually reach spectrometer tube in a few milliseconds. Helium molecules as well as molecules of other gases are continuously removed by the vacuum system. If helium is continuously applied to a leak, the concentration in a spectrometer tube will rise sharply at first then it will reach equilibrium when it is being pumped out at the same rate as it is entering. When helium is completely removed from a leak, the input will drop to zero as the helium tracer gas is pumped out of the system. Thus, a leak is indicated as a rise and fall in output signal of the spectrometer tube. 1-7 HELIUM MASS SPECTROMETER LEAK DETECTION METHODS

The use of helium leak detectors in commercial, industrial, scientific and research

organizations is expanding at an ever-increasing rate. These organizations have discovered that

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modern helium leak detection techniques improve operating efficiency, product reliability, and reduce costs. A random listing of typical helium leak detector applications is provided in Table-I. Industry Products or Systems that requires Leak Testing Semiconductor-Electronic Aerospace Research and Development Nuclear Packaging-Food and drug Medical

• Hermetically sealed devices, such as Relays, Connectors, Displays, quartz crystals, Reed Relays

• Feedthroughs, Heaters, Bellows, Transducers • Cryogenic parts • Nuclear Reactors, Heat exchangers • Foil Packs, Containers • Cardiac Pacemakers.

Air Conditioning and Refrigeration Automotive Packaging Miscellaneous

• Evaporator coils, Condenser coils, compressors.

• Control valves, bellows, Assemblies and complete systems

• Tubing, Accumulators, Beverage containers and ends, Aerosol Containers, Foil packs,

• Battery cases, Heat Exchangers . Vacuum Systems • Coaters, Metallizers, Furnaces.

• Surface Analysis. • E.B. Welders. • Ion Implanters. • MBE systems. • EM, SEM etc.

Vacuum, Pressure or other • Nuclear Power Stations. • Chemical Plants. • Petro-Chemical towers. • Underground lines. • Radio TV cables. • Cryogenic Components and Systems.

The mass spectrometer leak detector operates with helium as a tracer gas therefore it is necessary either to fill objects with helium or spray objects with helium when leak testing is involved. There are two basic methods of leak testing popularly known as Tracer Probe Technique and Detector Probe Technique. 1-7.1 Tracer Probe Technique (Evacuated Test Object):

Object to be tested is evacuated with MSLD and the surface of test object is sprayed with a small jet of helium to locate individual leaks. If leak exits helium passes through leak, enters MSLD and quantity of helium leaked through is measured in form of LEAK RATE.

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In this technique since job is directly connected to MSLD leaks of the order of minimum detectable leak of MSLD can be located. For example HLD-1112 will detect 2 x 10


Fig 1. Test Piece Evacuated: Helium spray is used to detect a leak

-10 cc/s leak using this technique. 1-7.2 Tracer Probe Technique (Hood technique):

This technique is similar to evacuation technique. Evacuated test object is further wrapped in a enclosure and flooded with helium. This measures TOTAL leak rate in a object. Technique does not pin point location of leak but is suitable to determine acceptance of object for acceptable leak rates quickly if object is in final stage of manufacturing and can not be rectified even if leaks are located.

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Fig. 2. Test Piece Evacuated and hooded with helium atmosphere

1-7.3 Tracer Probe Technique (Test object already sealed):

Sometimes it is necessary to leak test completely sealed object. Placing helium inside object does this. This may be done by placing helium inside object before complete sealing (either 100 % or mixed with other gas used for backfilling). The object is then placed in a vacuum chamber connected to the leak detector. Helium escaping from the object in to the vacuum chamber is detected by MSLD. Sensitivity depends upon partial pressure of helium in the object.

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Fig.3. Test Object sealed with helium: Vacuum envelope is used to determine leak rate.

1-7.4 Tracer Probe Technique (BOMBING Technique): If the presence of helium in the finished object is undesirable, units already sealed may

first be placed in a container that is then pressurized with helium for a specific time at a known pressure. Sufficient helium soaking time is required and high pressure of helium is recommended so that it penetrates through leak. Helium will enter the object through leaks and may be detected later as per above method. This method of testing is called as BOMBING, and is very popular to test hermetically sealed parts such as IC’s, quartz crystal oscillators, cardiac pacemakers, etc. Gross leaks may sometimes not be detected, since, all helium entering through a leak may be lost prior to testing. Also spurious signal may be given by helium not entering the object but entering surface fissures and remaining long enough to be detected. 1-7.5 Detector Probe Technique (Sniffer Probe Technique):

Test object which can not be evacuated or objects which are used for pressure applications are normally tested by this method. In this mode of testing object is pressurized by helium. If object volume is too high then helium can be mixed with nitrogen/dry air (Helium concentration should be at least 15 % by volume). MSLD equipped with accessory SNIFER PROBE is then scanned over surface of object. Some of the helium escaping from a leak is captured through the sniffer probe and enters the MSLD thus locating the leak. Sensitivity of this

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type of testing is limited to about 5 x 10-7 cc/s, since most of the helium diffuses in to the surrounding atmosphere. The sensitivity also limited by operator technique and variation in ambient helium concentration in the vicinity of the testing.

Fig.3 Test Object pressurized, sniffer probe used to detect leak.

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SECTION 2 DESCRIPTION

2-1 HLD-1112 leak Detector Fillunger’s HLD-1112 is portable helium mass spectrometer leak detector. This unit consists of a diffusion pumped vacuum system, single piece aluminum valve block and spectrometer tube, and electronic system to drive spectrometer tube and various manifolds in valve block. Operation of HLD is controlled by push buttons at front panel and suitable indicating lamps indicate each mode of operation. Leak Rate is expressed in terms of bar graph and exponent digit. Object pressure is also indicated by bar graph at front panel. When unit is in operating condition, the object to be leak tested is connected to the test port and START switch is pressed. HLD will evacuate object under test and access it to a spectrometer tube. Glowing of TEST lamp at the front panel indicates this status. When object is sprayed with helium and if object is leaking, helium entering through leak instantly diffuses in to vacuum system. A constant pressure ratio is always maintained between the fore line and the spectrometer tube, which measures the amount of helium in the system. This amount of helium entered into the vacuum system is then ionized, accelerated, mass separated in spectrometer tube. Helium ions that hits preamplifier’s inverting terminal will give rise electrical signal, which then is represented as leak rate at the front panel of HLD. When the helium source is removed from the leak, the helium remaining in the system is rapidly pumped away. Thus the effect is a rise and fall of the leak rate indication. 2-2 VALVE BLOCK Valve Block used in HLD-1112 is made up of single aluminum block with inbuilt directly acting two numbers of solenoid valves. One valve (V3) is roughing valve, which will evacuate object under test when opened, and other valve (V4) is test valve, which provides, baking to the Turbo Pump. There are manifolds for Test Port, Vent Valve, Optional Accessory, TC gauge and baking line.

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Valves V3 and V4 will operate at signal voltage 24 V dc, when voltage is applied valve is opened. Separate Valve control logic is board controls operating sequence, which has following operating modes. Each mode is selected from front panel.

Fig. 2.2 Shematic diagram of HLD-1112

VENT MODE: Vents object under test • •

•

•

START MODE: Pumps object under test and transfers valves in TEST mode if test port pressure is below 0.1 mbar

HOLD: Revert back to VENT mode without venting the object in case job volume is high

TEST: Establishes vacuum connection between object and spectrometer tube

Color-coded mode identification is provided on front panel itself, which indicates current

status of operation. One-piece electronics board that provides driving voltages to ion source, power supply to preamplifier, controls spectrometer tube operation. This board also drives thermocouple gauge and cold cathode gauge that controls operation. Leak rate and test port pressure is displayed by using separate display board, which also has filament status indicator and range selection switch.

Diffusion pump is started when it is heated using PID controlled power regulator. This pump has separate switch inside door. After set temperature is achieved DP ready is indicated on front panel.

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2-3 SPECIFICATIONS Following table lists operating specifications of the model HLD-1112 Sensitivity :

2 x 10-10 atm cc/s for helium 8 x 10-11 atm cc/s for air

Leak Detection Range : 2 x 10-10 atm cc/s to 1 x 10-4 atm cc/s Start up time : Less than 35 minutes Response Time : Less than 2 sec. Vacuum Pump Forepump

: :

80 l/s oil diffusion pump Two stage, tri-vane , 168 lpm.

Valve Block : Electromagnetic valves inbuilt in single piece block. Spectrometer Tube :

90 degree constructed in one piece quality aluminum alloy with demountable pole pieces, easy access to cold cathode, ion source and preamplifier.

Test Port Pressure :

Monitored by thermocouple gauge and indicated as horizontal bar graph from Atm to 0.001 mbar

Spectrometer Tube Pressure

:

Monitored by cold cathode penning gauge and indicated by analog meter in from 10-3 to 10-5 mbar.

Leak Indicator :

Mantissa part is indicated by vertical bar graph and exponent is indicated in terms of seven segment display

Test Port : NW 25 KF quick coupling or 1.125” compression coupling Power : 220/240 V; 50 Hz single phase Weight : 30 kg. Size : 560 x220 x 380 mm (Length x width x height) 2.4 VACUUM SYSTEM

The Vacuum System provides the necessary vacuum, and the valving system, with the roughing pump, evacuates the object to be tested and properly sequences the testing operation. The vacuum system consists of diffusion pump, mechanical pump, a spectrometer tube, valve and interconnecting pipe. The system serves two functions: it maintains the required vacuum in the spectrometer tube, it connects objects under test and establishes vacuum connection to spectrometer tube if START switch is pressed.

2.5 DIFFUSION PUMP DESCRIPTION

The HLD-1112 uses 80 l/s oil diffusion pump. It evacuates spectrometer tube to 10-5 cc/s from atmosphere together with two-stage rotary vacuum pump. It features two numbers of high speed aluminum jets and uses Santovac 5 oil which is oxidation resistant . Oil is heated with PID controlled ceramic heater which ensures excellent stability in vacuum.

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2.5.1 Counter-flow principle

Counter flow technique takes advantage of the differences in compression ratios (Outlet pressure divided by inlet) produced by the diffusion pump for gases of different molecular weights. For example, the maximum compression ratio of helium may be 10 or 100, while for oxygen, nitrogen and other gases contained in air, the ratios are normally far in excess of one million. This principle is implemented in the leak detector by introducing helium in to diffusion pump outlet (fore line) rather than into the normal pump inlet as has been done in conventional leak detectors. Helium having much lower compression ratio than other gases contained in air, diffuses backwards through the diffusion pump to reach the spectrometer tube where it is detected in the normal manner. Although the mechanical forepump is also attached to the diffusion pump foreline and removes all inlet gases, including some helium , there is no appreciable loss of sensitivity in the counterflow detector. In fact at higher test port pressures, it is more sensitive than the conventional method. 2-6 MECHANICAL VACUUM PUMP The 10 m3/hr (166 lpm) pump serves as foreline pump. This pump maintains the proper low vacuum (10-3 mbar) required for operation of spectrometer tube. This rough pump also evacuates object under test up to 10--3 mbar. 2-6.1 Mechanical Pump Specifications Type of Pump :Two stage tri-vane type, VKC-series from Precise Vacuum

System, model no. VKC-8 Nominal Speed : 10 m3/hr (168 lpm) Water vapor tolerance : 40 mbar Ultimate pressure : 2.5 10-4 mbar Power :230 V ac Weight : 36 kg Dimensions :440 x 180 x 290 2-7 SPECTROMETER TUBE

Spectrometer tube is the heart of leak detector. The spectrometer tube and leak rate indicator provide a visual representation of the helium concentration in the vacuum system. The spectrometer tube consists tungsten ion source preamplifier assembly cold cathode gauge analyzing magnets and enhancement magnets. 2-7.1 Ion Source

The ion source consists of two filaments, two halves of an ion chamber, a pair of focus plates, and a ground slit. The top half of the chamber (the repeller plate) is held at a positive potential (repeller voltage) with respect to the bottom half of the ion chamber. The bottom half of the ion chamber is held at a positive potential (ion voltage) with respect to the exit ground slit.

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Two focus plates are also held positive (Variable focus and fix focus) with respect to the ground slit. When the filament is electrically heated, electron emission with help of the enhancement magnets divides the electrons into the ion chamber. Electrons colliding with molecules produce positive ions. These ions are forced through the bottom of the ion chamber, the grounded potential exit slit, and enter the analyzing magnetic field. This magnetic field separates and allows only the helium ions to reach the preamplifier. The repeller, variable focus, and ion chamber require adjustment when ion sources are changed. This fine-tuning procedure will produce an efficient, helium-sensing spectrometer tube. 2-7.2 Preamplifier Assembly

The preamplifier assembly consists of an ion collector assembly and a sensitive electrometer amplifier. The ion collector assembly includes: (a) Ground potential electrodes to guide the beam of helium ions. (b) A suppressor electrode to exclude any other ions. (c) An ion collector electrode mounted on a low-leakage feed-through.

2-7.3 Analyzing Magnet The magnetic field is provided by single block of Alnico-V magnet material, which is

bounded to a mild steel yoke. The yoke connects three pole pieces that define the magnetic field for cold cathode gauge, ion source and deflection pole pieces.

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SECTION 3

RECEIVING AND INSTALLATION 3-1 DESCRIPTION

The Fillunger HLD-1112 mass spectrometer helium leak detector is carefully packed in thermo Cole and enclosed by wooden container. Upon receipt, inspect the container for evidence of damage in shipment. Do not discard any evidence of rough handling. Leak Detector and its accessories should be inspected immediately and any damage should be reported to the carrier without delay. 3-2 UNPACKING INSTRUCTIONS 1. To unpack the leak detector open wooden enclosure by unplugging nails from top. 2. Carefully lift helium leak detector, which is packed, in thermo Cole box. 3. Carefully cut the strapping holding the detector in standing position only. 4. Remove top portion of thermocole box. 5. Lift Helium Leak Detector and gently lower it onto the floor. 6. Unpack other accessories such as rotary pump, trolley and voltage stabilizer. 7. Unpack spares and verify the list as per packing list. 3-3 SERVICES REQUIRED FOR OPERATION 1. Power :230 V, 50 Hz, single phase 15 A service 2. Helium :Welding commercial grade standard cylinder with pressure regulating

valve and tube. 3-4 PREPARATION FOR OPERATION 1. Helium Leak Detector : Open access door and check HLD from inside. 2. Rotary Vacuum Pump: The rotary vacuum pump is shipped with the proper initial oil

charge and both inlet and exhaust port blanked. Remove both blanks and discard these closing clamps and blanks. Check oil level when pump is not running. The oil level should be in the middle of sight glass.

3-5 INSTALLATION 1. Locate trolley and place it on flat suitable place. 2. Place HLD-1112 on top portion of trolley and align four fixing holes. 3. Mount fixing screws from bottom and ensure that all four screws are tightened and firmly

seated. Turn service valve (back side) fully inside then 1/2 turn out. 4. Mount voltage stabilizer on bottom portion of trolley. 5. Mount Rotary vacuum pump on bottom portion of trolley. 6. Connect QC-25 hose between HLD-1112 and rotary vacuum pump (INLET PORT) 7. Connect power cord of HLD-1112 to the output of voltage stabilizer. 8. Connect power cords of voltage stabilizer and rotary pump to the distribution box

provided on trolley.

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SECTION 4

OPERATION 4-1 GENERAL INTRODUCTION

Operation of the HLD-1112 leak detector is carried out by a procedures known as a “start cycle” and “vent cycle”. The purpose of the test cycle is to establish a connection between the test object and the leak detector, so that helium passing through a leak will reach the spectrometer tube and be detected. The purpose of vent cycle is to vent the object that was connected to HLD. Before operating your HLD-1112, study the controls and indicators listed as following. 4-2 OPERATING CONTROLS AND INDICATORS

CONTROL / INDICATOR

FUNCTION

VENT Switch Vents object under test

START Switch Evacuates object under test and transfers HLD in to TEST mode if pressure reaches in green band.

TEST indicator Indicates that HLD is ready to test object. HOLD Switch (when pressed before object pressure is in green band)

Stops evacuation of object under test and recovers pressure of spectrometer tube. (If large volume object is connected).

HOLD Switch (when pressed after object pressure is in green band)

Isolates object under test from HLD which enables measurement of residual background of helium.

DP ready Indicates that DP temperature is achieved. DP heater Switches ON DP heater and PID. Pressure Bar graph Indicates Pressure at the Test Port. Leak Rate Bar graph Indicates a Signal Proportional to the Helium Pressure in the

Spectrometer Tube. (Mantissa Part) Seven segment display Indicates exponent value of leak rate. Range Switch / Min range select switch

Selects exponent value of leak rate.

Zero Knob Adjusts leak rate bar graph to zero. Fil. Lamp Indicates that the Filament is on (Emission is present). Service Valve Isolates spectrometer tube for service and for shipping. Also

used when evacuating the spectrometer tube after service.

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4-2.1 TUNING CONTROLS AND INDICATORS

CONTROL / INDICATOR

FUNCTION

Main Power (back side switch)

Controls All Electrical Power to the Leak Detector

Elect. (Switch) Controls Electrical Power to the Electronics Only. Spectrometer Tube (Meter) Indicates Pressure in the Spectrometer Tube. Focus Adjusts the Focus-Plate-to-Chamber Voltage (Tuning). EMIS Adjusts the Emission by Varying the Filament Current

(Tuning). Repeller Adjusts the Repeller-to-Chamber Voltage (Tuning). Ion Adjusts the Ion Source Chamber Voltage (Tuning). Coarse / Zero Adjusts the LEAK RATE BAR GRAPH to Zero indication. Calibrate Adjusts the Amplifier Gain to Make the Leak-Rate Reading

Agree with the standard Calibrated leak value. Threshold Sets the Point above which the Audible Alarm Sounds. Volume Adjusts the Volume of the Audible Alarm. Select min. range Selects appropriate min. range in three position. FIL. ON-OFF Switches Filament ON/OFF. FIL. 1-2 Selects One of Two Filaments in the Ion Source. EMISSION TP-5 TP-6 With Voltmeter Plugged into TP-5 and TP-6 the Emission

Current Can be read. TP-1 to GND To Read Chamber Voltage. TP-2 to GND To Read Repeller Voltage. TP-3 to GND To Read Focus Voltage. PID Control Controls Electrical Power to the Diffusion Pump

(Proportional control) 4-3 STARTING PROCEDURES

This is the procedure that makes the HLD-1112 ready for actually conducting leak tests.

Choice of procedure depends upon previous shutdown or standby.Checking of calibration and background is described. Normally, the leak detector remains in calibration. If retuning and calibration is required. (total absence of response to helium) see Section IV, Tuning and Calibration. 1.0 Ensure that HLD is connected with rotary vacuum pump. Switch ON mechanical pump. 2.0 Switch ON mains Power of HLD-1112.

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3.0 Switch ON Diffusion Pump heater. 4.0 Wait 30 minutes till DP ready lamp illuminates. This switch will illuminate indicating that preset

temperature of diffusion pump is achieved. 5.0 Switch ON Elect. ON/OFF switch. 6.0 Flip FIL switch to ON position momentary. FIL will be lighted and its status will be indicated on

front panel. 7.0 HLD-1112 is now ready to operate. 4-4 OPERATING START AND VENT CYCLES 1.0 Ensure that HLD is in VENT mode. If not then press VENT. 2.0 Connect STD leak/Object under test at TEST port and Push START switch. Object/std leak will

be evacuated at this stage, vacuum at object under test will be indicated on pressure bar. When Pressure reaches below preset value. TEST switch will be illuminated.

3.0 When TEST is illuminated. (a) If std leak is mounted then some leak rate will be indicated. Verify that this leak rate agrees

with std used. If necessary tune and calibrate HLD. (b) If object mounted then wait till leak rate drops below acceptable leak rate and then spray

object with helium to identify leaks. 4.0 If object volume is too high and it takes beyond 3 minutes to evacuate, push HOLD switch

momentary for 30 sec then release. Wait till TEST indicator illuminates. After TEST lamp is illuminated sparay helium.

5.0 Push VENT to vent that object/std leak. 6.0 After pressure bar indicates Atmosphere pressure then remove object under test. 4-5 SHUTDOWN PROCEDURE 1.0 Press VENT and remove object under test or std leak. 2.0 Plug test port and press START. 3.0 Flip fil switch to OFF position. 4.0 Switch OFF electronics switch. 5.0 Switch OFF DP heater. 6.0 After 30 min switch OFF mains of HLD-1112.

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4-6 STATUS OF VALVES IN VARIOUS MODES 4-6.1 VENT MODE

This mode of operation allows connection of object under test. In this mode following is status of valves V1: Vent : OPEN V3: Roughing : CLOSE V4: Test : OPEN

Fig. 3.1 VENT Mode 4-5.2 START MODE

This mode of operation evacuates object under test and access the object to spectrometer tube. Vacuum connection will be established when Test Port pressure falls (G1) below 0.01 mbar is achieved. In this mode following is status of valves. V1: Vent : CLOSE V3: Roughing : OPEN V4: Test : CLOSE

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Fig. 3.2 START Mode 4-6.3 TEST MODE

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This mode follows START

mode if test port pressure reaches below 0.01 mbar. In this mode Object under test is accesses to spectrometer tube and vacuum connection between object under test and spectrometer is established. When object is sprayed with helium, helium penetrate through leaks and will be detected at spectrometer tube. In this mode following is status of valves V1: Vent : CLOSE V3: Roughing : OPEN V4: Test : OPEN

Fig. 3.3 TEST Mode 4-6.4 HOLD MODE

In START mode foreline of diffusion pump is closed. If evacuation of object takes more than 3 min. This mode is selected by pressing HOLD switch. This mode will hold vacuum in object and provide baking to diffusion pump which will recover vacuum in spectrometer tube till HOLD switch is pressed. In this mode status of valves is as follows V1: Vent : CLOSE V3: Roughing : CLOSE V4: Test : OPEN

Fig. 3.4 HOLD Mode


SECTION 5

CALIBRATION, TUNNING AND MEASURING BACKGROUND 5-1 CALIBRATION CHECK Usually the first step, before beginning the day’s testing, is to verify that the HLD-1112 is sensitive to helium and properly tuned. HLD-1112 is tuned to helium prior shipment. However slight tuning may be necessary before actual leak testing work is carried out. Using a standard reference leak of known value called a “calibration leak” does this, proceed as follows:

1. Push VENT to vent test port. 2. Remove plug and place calibration leak in test port and tighten. 3. Open valve of standard leak.

Note

It is normal practice to leave calibration leak valve in open condition always

4. Push START switch. Mechanical pump will sound louder for a brief interval. (This is the “rough” pumping stage)

5. When TEST PORT PRESSURE reaches below. 0.08 mbar (green band), TEST lamp will glow indicating that HLD is in TEST mode.

6. Verify that FIL is ON, if it becomes OFF during start cycle then switch ON again using FIL ON switch. (You may select FIL 2 if FIL 1 is not working).

7. Turn range-selector switch to an appropriate range to observe LEAK RATE indication. 8. Leak rate indicated on HLD should exactly match with value on std leak. If necessary do

minor adjustment with CAL. 9. If exponent is same and leak rate indicated on HLD is less than value on std leak even

though CAL is at full maximum then increase EMIS slightly. 10. If exponent is same and leak rate indicated on HLD is higher than value on std leak even

though CAL is at minimum then decrease EMIS slightly. 11. If exponent indicated on HLD does not match with value on std leak then perform tuning

adjustment. 12. Close valve on calibration leak and adjust LEAK RATE bar to zero indication, using ZERO

control. 13. Reopen calibration leak valve and make minor adjustments with CAL to agree HLD with std

leak. 5-2 TUNNING ADJUSTMENTS

This procedure will tune HLD-1112 so that it will be sensitive to only helium. As a source of helium std calibrated source of helium is to be used. Such std leaks are available in

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many exponential ranges with various values. Typically std leaks leaking in the exponential range of 10-7, 10-8 are used. 1.0 Perform steps 1-6 from section 5-2. 2.0 Reduce ION fully counterclockwise. 3.0 Keep REP at full maximum. 4.0 Keep FOCUS at the middle. 5.0 Use a multimeter and set EMIS at 0.25 V across TP5-TP6. Note that filament should be

ON, if it is OFF then flip FIL switch to ON position. If multimeter is not available set EMIS at 2 O clock position.

6.0 Set zero using ZERO knobs. If zero is not possible keep both ZERO fully counterclockwise.

7.0 Verify that Std leak valve is open, increase ION very slowly and observe LEAK RATE indication. If LEAK RATE decreases follow increase of ION voltage. If it increases then continue increase of ION till peak in Leak Rate is achieved. IF LEAK RATE falls below zero then use ZERO so that LEAK RATE always remains above zero in 10-9 range.

8.0 IF peak is detected then close valve of std leak and verify that this LEAK RATE is due to helium inside std leak. (LEAK RATE will drop to zero if this is helium peak).

9.0 If LEAK RATE does not drop to zero then continue increase of ION in same direction. 10.0 IF another peak is detected then verify that this is helium peak. 11.0 Use FOCUS to maximize LEAK RATE. For this turn FOCUS in both directions. Up to this point HLD-1112 is set to detect only helium that is available from std leak with known leak rates. 5-3 CALIBRATION ADJUSTMENTS

This procedure will set HLD-1112 to display LEAK RATE exactly given on std leak . For simplicity let us assume that we have 2.0 x 10-7 cc/s std leak available for calibration. 5-3.1 Correction of Exponent 1.0 If exponent value indicated on HLD is higher than exponent value on std leak (e.g.

exponent indicated on HLD is 10-6 cc/s and exponent on std leak rate is 10-7 cc/s), increase DP temperature by 5-10 degrees.

2.0 If exponent value indicated on HLD is lower than exponent value on std leak (e.g. exponent indicated on HLD is 10-8 cc/s and exponent on std leak rate is 10-7 cc/s), decrease DP temperature by 5-10 degrees.

3.0 You may use EMIS control. Decrease EMIS if exponent to be shifted from 10-7 cc/s to 10-8 cc/s. Increase EMIS if exponent is to be shifted from 10-8 cc/s to 10-7 cc/s. However this adjustment is effective only when range switching is at the boundary between these ranges.

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5-3.2 Correction of mantissa 1.0 Once exponent is corrected use CAL to correct value of mantissa part of LEAK RATE. 2.0 If CAL is fully clockwise and mantissa value indicated on HLD is still less than mantissa

on std leak; increase EMIS slightly and readjust CAL. 3.0 If CAL is fully counterclockwise and mantissa value indicated on HLD is higher than

mantissa on std leak; decrease EMIS slightly and readjust CAL.

Once both exponent and mantissa corrections in LEAK RATE is done close valve of std leak and verify that LEAK RATE drops to zero in lowest 10-9 cc/s range. Adjust Zero and again open valve of std leak to verify indicated leak rate. If necessary adjust CAL. Perform opening and closing of std leak 2-3 times to ensure zero and LEAK RATE.

1. Turn the Range Selector to the 10-9 range (Lowest range). 2. Using ZERO control, adjust the LEAK RATE meter to zero and return the REPELLER to

its original setting, fully clockwise. The resulting reading is background.

5-4 CHECKING BACKGROUND

Once helium is no longer entering the leak detector through the leak, the vacuum system rapidly removes the remaining helium. However, a small residual amount is usually present, called background. Normally, background is steady and it can be cancelled by setting the LEAK RATE bar indication to zero. It is sometimes useful to measure background. Proceed as follows:

1. Verify that the leak detector is tuned and calibrated. 2. Install the test port plug. 3. Proceed with normal cycle to TEST status. 4. Now turn the REPELLER control fully counterclockwise. 5. Turn the Range Selector to the 10-9 range (Lowest range). 6. Using ZERO control, adjust the LEAK RATE meter to zero and return the REPELLER to

its original setting, fully clockwise. The resulting reading is background. 7. Re-zero LEAK RATE METER before using leak detector. At the time of shipment,

background is about 5 divisions or less.

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SECTION 6

MASS SPECTROMETER IN HLD-1112

HLD-1112 uses spectrometer tube to detect and analyze helium. This is mass

spectrometer, which is made sensitive to helium after proper tuning of electronic voltages. The spectrometer tube (Figure 6.1) is the heart of the leak detector. In spectrometer tube helium entering through object or std leak is first ionized using electron bombardment from hot filament, then these ions are accelerated and passed through a sector magnet for mass separation. After mass separation only helium ions with mass 4 amu will be available for detection. Preamplifier used in spectrometer tube will detect these “only helium” ions and generate corresponding electrical signal. This signal in form of voltage (usually in µV) is further amplified using amplifier that drives leak rate bar.

The electronic control card operates this spectrometer tube and the leak rate indicator provides visual and optional audible interpretation of the helium ion signal. The vacuum system provides the necessary vacuum, 1 x 10-5 mbar mbar or less. The valve system and roughing pump evacuate the object to be tested and properly sequence the testing operation.

Figure 6.1 Cut-way View of Spectrometer Tube

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The spectrometer tube also a cold cathode vacuum gauge, which continuously monitors vacuum, required for operation of spectrometer tube. If vacuum falls beyond operating range of spectrometer tube, ion source filaments will be switched OFF for protection. It is surrounded by a magnetic field provided by two large pole pieces fastened to a block of Alnico V Magnet. Brief description of each component in spectrometer is listed below:

6-1 ION SOURCE

The ion source is a one-piece expendable unit, consisting of the following parts: a. Two permanently-aligned tungsten filaments (one used as a spare) that provide a source

of electrons. b. An ionization chamber into which electrons are “beamed” in order to strike gas

molecules to create positive ions. c. A repeller electrode that repels these positive ions, forcing them out through a slit in

the ion chamber. d. Two focus plates that direct the ion beam toward a slit in a ground-potential plate.

The parts are welded to eight rods that extend through individual glass seals in a round flange to form the male portion of a standard octal connector. A special clamp and O-Rings are used to seal the assembly into the spectrometer tube. This construction permits easy servicing of the spectrometer tube. The spare filament allows the user to continue working after one filament burns out until it is convenient to discard the entire source assembly. In addition, no cleaning or disassembly of the source is necessary. It is inexpensively and easily replaced as a unit. All parts of the unit are pre-aligned, and the unit itself is keyed to the spectrometer tube so that no special skill is required to replace it. 6-2 MAGNETIC FIELD

A block of Alnico V, which is mounted permanently between two large rectangular, soft iron plates, provides the magnetic fields. Inserts in these plates direct the flux into two pole pieces that define the magnetic field, which separates the helium from other ions. Made of nickel-plated mild steel, the two pieces are identical, keyed for proper insertion, and O-Ring sealed to the spectrometer tube to facilitate service. Other inserts provide fields for the cold cathode vacuum gauge (2-1.1.4) and for the ion source. 6-3 PREAMPLIFIER ASSEMBLY

The preamplifier assembly contains an ion collector assembly and a preamplifier stage. The ion collector assembly includes ground-potential electrodes to guide the beam of helium ions, a suppressor electrode to exclude any other ions and an ion collector electrode to translate helium ions into an electrical signal. The preamplifier stage includes a solid-state operational amplifier and a feedback resistor. Having the preamplifier in vacuum protects the electrical signal from external interference and stabilizes the leak rate meter. Like the ion source, the entire assembly is mounted as a unit on eight rods that extend through individual glass seals in a round

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flange to form the male portion of the preamplifier section connector. It is factory pre-aligned and is of all-welded construction. It is sealed in place with a clamp and O-Ring. Removal and replacement require no special skill. Special care should be taken in handling the preamplifier assembly, being particularly careful not to subject the preamplifier to a static voltage discharge. 6-4 COLD CATHODE VACUUM GAUGE

The cold cathode gauge monitors the vacuum (absolute pressure*) and triggers the

protective system if the pressure exceeds 2 X 10 -4 mbar. It consists of two pole pieces, a liner that forms the cathode, and nichrome loop mounted on a single ceramic insulator for an anode. A disc shield prevents sputtered conductive deposits from causing leakage paths across the anode feedthrough insulator. The assembly seals in place with an O-Ring. The common magnet provides the magnetic field. 6-5 ADJUSTABLE SOURCE MAGNETS

Rotatable external eccentric magnetic pole pieces on each side of the ion source enclosure

allow adjustment of the electron beam direction for maximum ionization and sensitivity.

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Typically, once properly tuned and calibrated, your HLD-1112 leak detector will remain in calibration, with only minor adjustments. Calibration should be checked at least once a day. It may be checked any time. The procedure is simple and is described in SECTION V. In this section theory of tuning is explained. As will be seen from the diagram, electrons “boiling” out of the hot filament are driven through the slit into the ion chamber. Inside the chamber, they create positive ions by bombarding neutral molecules. Positive ions of many different gases are ejected through a slit in the bottom of the ion chamber. They are then accelerated and passed through a ground potential slit. After this they travel at constant velocity through a magnetic field at right angles to their path. This causes the ions to follow different paths according to their mass, heavier ions being deflected less and lighter ions more.


SECTION 7

EXPLANATION OF TUNNING CONTROLS

Tuning (“Peaking”) a leak detector means optimizing its sensitivity to helium. This is somewhat like selecting the best dial position for reception of a particular radio station - but in a leak detector there are several interacting steps. Controls affecting tuning are: 1. Focus Control 2. Ion Control 3. Repeller Control 4. Emission Control 5. Ion Source Magnet

Control

Calibrating means adjusting the reading on the LEAK RATE meter to agree with an accepted standard reference leak (calibrating leak). This is somewhat analogous to adjusting the volume on your radio to a desired level. Controls affecting calibration are: 1. Diffusion Pump Control 2. Calibrate Control

Figure 7.1 Schematic of Mass Separation

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When properly tuned helium ions are deflected 90o so that they alone enter the collector (where they cause an electrical current to flow in proportion to the number of ions collected per second).

This is what happens when the HLD-1112 is properly tuned to helium. To understand the tuning procedure, it is helpful to understand how the formation, acceleration and separation of ions are actually brought about. It is done with DC voltages, which affect ions in much the same way as gravity affects a ball in a pinball machine - with an important difference. Gravity exhibits attraction only, whereas DC voltages can attract or repel ions. Some of these voltages are fixed, while others are adjustable to permit external control.

The table below shows the adjustments available to the user and the typical range of DC voltages in these adjustments:

Parameter Adjustment Control Adjustment

Range Electrons Entering Ion Chamber

a. Quantity per unit time b. Direction

Emission Control Black knobs on Spect tube

0-2 Amp 360 rotation

Ions Leaving Ion Chamber a. Energy b. Quantity per unit time c. Direction

Ion control Repeller Control Focus Control

160-330 Volt 260-430 Volt 250-310 Volt

The following pages explain the various controls by individual diagrams.

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7.1 FOCUS CONTROL

(ION-72 to ION+22)

Figure 7.3 Ion Control

The focus control

determines the direction taken by the beam of ions emerging from the ion chamber. In the correct position the ions pass through the exit slit into the magnetic field. The focus control is the most critical tuning adjustment. Unless all of the ions pass through the exit slit, no indication will appear on the LEAK RATE BAR regardless of the other adjustments. Focus voltage varies relative to ION voltage. Var FOCUS=(ION-72) - (ION+22)

For instances if ION voltage is 205 V, then FOCUS voltage will vary from 133 to 227 V.

7.2 ION CONTROL

(160V-330V) By adjusting voltage

between ion chamber and ground slit plate, the ion control determines the rate of acceleration of the ions. All ions will move at certain velocity determined by acceleration voltage and their masses. Relation between acceleration voltage and velocity is

Figure 7.2 Focus Control

mv qV2=

where q :charge of ion V:Voltage ,m: mass of ion

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After this acceleration all ions will enter sector magnet for mass separation. ION CONTROL will determine velocity of ions. It has range of 160 V to 330 V.

7-3 REPELLER CONTROL

(ION to ION+100)

Repeller control causes the ejection of ions from the ion chamber. Normally it is in the fully clockwise position. This puts an extra 100 volts on repeller electrode with respect to ION potential. This positive DC potential on the repeller electrode repels the positive ions out through the exit slit at the bottom of the ion chamber.

When fully counter-clockwise, the repeller control removes the extra 100 volts and restores the repeller electrode to exactly the same DC voltage as the ion chamber. Virtually no ions emerge. This is useful for determining residual helium (background) in the leak detector

Under special operating conditions the repeller control becomes a tuning control. This is usually associated with operation at reduced sensitivity to measure larger leaks. Repeller voltage is always function of ION voltage (REP=ION+100) in normal operation. Under special operating conditions repeller can be varied from ION+0 to ION+100. For instance if ION is held at 160 V, repeller can be varied from 160 V to 330 V.

Fig. 7.4 Repeller Control

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7-4 EMISSION CONTROL

(0.2 A to 2.2 A)

Controls leak detector sensitivity by controlling the rate of electron emission from the filament. In general, when the emission is increased, more ions are formed, hence a greater leak rate reading results. This control us useful when leak rates are to be set at correct exponential values. When emission is decreased less ions will be formed and hence leak rate will decrease. When emission is increased more ions will be formed causing leak rate to increase.

This control will set filament current from 0.2 Amp to 2.2 Amp. Any set value is maintained using constant emission circuit available on main electronics board.

Figure 7.5 Emission Control 7-5 ZERO CONTROL

Zero control is established by adjusting offset of amplifier used in preamplifier. This offset can be set to zero using ZERO controls available on board. For zero adjustment, either source of helium is stopped (close valve of std. Leak) or REP is set equal to ION (REP fully counterclockwise). 7-6 SECTOR MAGNET

(FACTORY SET NO CONTROL IS AVAILABLE)

Sector magnet in spectrometer tube plays important role in tuning. When all ions enters into magnetic field of sector magnet, every ion will experience lorentz force and depending upon their masses every different ion will move in different circular orbit. Heavier ions will have larger radius whereas lighter ions will have smaller radius. Since Lorents force causes ions with mass m to move in circular orbit, one can equate this force to centripetal force as

Lorentz Force=Centripetal Force

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RmvqvB

2

=

Where, q-charge of ion, m-mass of ion, R-radius of circle at which ion will move

For Helium q=1 (singly charged), m=4 amu, same equation for v becomes

4BRv =

Helium ions will move with circular orbit of radius R inside sector magnetic having

magnetic field B. Since B and R are fixed. If velocity can be adjusted to B.R/4 then it is possible to separate only helium ions. As defined in ION CONTROL it is possible to set velocities using ION voltages within 160 V and 330 V. As shown in geometry in the figure only quarter portion of full magnet is used therefore helium ions are separated and then ejected out of sector magnet without completing a circle. 7-7 ION SOURCE MAGNET CONTROL

The knobs on the spectrometer tube turn through 360 and maximize the production of

helium ions by magnetically optimizing the electron flow into the ionization chamber. 7-7 CALIBRATION CONTROL

After HLD-1112 is properly tuned indicated leak rate can be adjusted according to the std used. To set the calibration, knob on electronic panel can be used. This alters the amplifier gain (Post amplifier available on board) from factor 1 to 7 times. For instance if leak rate is 1 x 10-7 cc/s at CAL fully counterclockwise, same will be shown at 7 x 10-7 cc/s when CAL is set fully clockwise. In some applications, product acceptance may be based upon a leak rate less than a specified value. Here it is convenient to adjust the sensitivity (up or down) so that the LEAK RATE reading agrees with the calibrating leak. 7-8 DIFFUSIN PUMP CONTROL

(TEMPERATURE +/- 5 DEGRRES)

The rate of flow of helium into the spectrometer tube for a given concentration depends upon the operating temperature of the diffusion pump. At full temperature PID controller provides maximum power to the diffusion pump heater. This minimizes the access of helium to the spectrometer tube and reduces sensitivity. At the minimum position power is at a minimum, helium access is at a maximum and therefore sensitivity is highest.

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SECTION 8

INTERPRETATION OF SENSITIVITY AND MEASURMENTS OF LEAKS 8-1 SENSITIVITY

In normal operating conditions HLD-1112 is set to operate at maximum sensitivity (2 x 10-10 cc/s/div). This mode of operation will enable leak testing in the ranges 10-9 cc/s, 10-8 cc/s, 10-7cc/s, 10-6 cc/s. Sensitivity of HLD in any range is defined as follows

rangein divisions of Norangein Leak Detectable MaximumYSENSITIVIT =

Following table shows sensitivity in various ranges and leak rate measurement possibilities

Measurement Range cc/s

Minimum and Maximum Detectable Leak Rate cc/s

Sensitivity Std cc/s/div(minor)

10-9 1 x 10-9 to 10 x 10-9 2 x 10-10 10-8 1 x 10-8 to 10 x 10-8 2 x 10-9 10-7 1 x 10-7 to 10 x 10-7 2 x 10-8 10-6 1 x 10-6 to 10 x 10-6 2 x 10-7 10-5 1 x 10-5 to 10 x 10-5 2 x 10-6 10-4 1 x 10-4 to 10 x 10-4 2 x 10-5

For example if 10-9 cc/s range is selected. Sensitivity of HLD in this range is 10x 10-9

cc/s/50 div. That means 2 x 10-10 cc/s/div is the sensitivity for 10-9 cc/s range. This also indicates that if leak rate changes within one minor division in 10-9 cc/s range, 2 x 10-10 cc/s leak rate is detected by HLD-1112. 8-2 MEASUREMENTS OF LEAK RATE

Leak rates are indicated directly at the front panel on vertical bar graph and seven-segment display. Mantissa is read from bar graph while exponent is read from seven segment display. For example if leak rate bar indicates 2.6 and exponent indicates 10-8 then resultant leak rate is 2.6 x 10-8 cc/s. 8-3 SHIFTING OF SCALES USING REPELLER CONTROL

As discussed in section 7-3, when repeller is held at fully clockwise position extra 100 volts are applied to REPELLER plate w.r.t. ION plate. This causes ejection of all ions that are formed during ionization. This means that all helium ions are available for

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detection. This is normal mode operation that can detect leaks in most sensitive range (10-9 cc/s). When repeller is reduced less quantity of ions will be ejected and leak rate indicated will be less. This mode of operation with reduced repeller will enable measurements of leak rates in the higher ranges although sensitivity of the unit is reduced. When repeller is reduced position of “MIN RANGE SELECT” needs to be changed.

8-3.1 MIN RANGE SELECT SWITCH AT 10-9

At this operating mode measurement in the ranges 10-9, 10-8, 10-7, 10-6 are possible. Repeller is kept fully clockwise and HLD is calibrated with given std leak in a normal way. 8-3.2 MIN RANGE SELECT SWITCH AT 10-8

At this operating mode measurement in the ranges 10-8, 10-7, 10-6, 10-5 are possible. Repeller should be adjusted as under:

1. Ensure that HLD is tuned and calibrated. 2. Keep std leak open and verify that indicated leak rate matches with value on std leak. 3. Reduce repeller so that indicated leak rate shifts one decade below. (For example if

2.0 x 10-7 cc/s std leak shows 2.0 x 10-7 cc/s on HLD; reduce repeller so that indication on HLD now is 2.0 x 10-8 cc/s).

4. Set MIN RANGE SELECT switch to 10-8. Exponential digit value will now change. 5. Select appropriate range and set CAL to agree with std leak. 6. If necessary set EMIS to lower or higher value. 7. Close std leak valve and set zero if necessary. Open valve and readjust CAL to agree

value of std leak on HLD. 8. HLD-1112 is now ready to operate within ranges 10-8, 10-7, 10-6 and 10-5 cc/s. 9. With this setting leak rates up to 10 x 10-5 cc/s can be measured.

8-3.3 MIN RANGE SELECT SWITCH AT 10-7

At this operating mode measurement in the ranges 10-7, 10-6, 10-5, 10-4 are possible. Repeller should be adjusted as under:

1. Ensure that HLD is tuned and calibrated. 2. Keep std leak open and verify that indicated leak rate matches with value on std leak. 3. Reduce repeller so that indicated leak rate shifts two decades below. (For example if

2.0 x 10-7 cc/s std leak shows 2.0 x 10-7 cc/s on HLD; reduce repeller so that indication on HLD now is 2.0 x 10-9 cc/s).

4. Set MIN RANGE SELECT switch to 10-7. Exponential digit value will now change. 5. Select appropriate range and set CAL to agree with std leak. 6. If necessary set EMIS to lower or higher value. 7. Close std leak valve and set zero if necessary. Open valve and readjust CAL to agree

value of std leak on HLD. 8. HLD-1112 is now ready to operate within ranges 10-7, 10-6, 10-5 and 10-4 cc/s. 9. With this setting leak rates up to 10 x 10-4 cc/s can be measured.

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SECTION 9

USING SNIFFER PROBE WITH HLD-1112

Sniffer Probe is an accessory of HLD-1112, which consists of precise leak valve, PVC Tube and Vacuum adapter. This is used to detect leaks from Helium pressurized vessels when used with HLD-1112 leak detector. Sniffer probe is factory set to detect leaks in 10-6 cc/s before shipment but use following procedure if sniffer does not detect any leak or does not indicate residual helium background in the range 10-7 cc/s.

1. Start HLD-1112 as per given procedure. 2. Calibrate HLD-1112 with given standard leak. 3. Press VENT switch and remove plug or std leak. 4. Connect end of Sniffer Probe 1.125” metal inlet to test port. 5. Close valve of Sniffer probe (clockwise, do not over tight) 6. Press START switch. 7. When test port bar reaches in green band TEST lamp will illuminate. 8. Ensure that Filament is in “ON” condition. 9. Note down reading at test port pressure bar. 10. Open valve of Sniffer very slowly and gently so that pressure bar graph reading

drops up to 0.01 mbar. 11. You will also observe leak rate indication rising from zero. Select appropriate

range for leak rate measurements. 12. Continue opening till leak rate between 2 x 10-7 cc/s and 5 x 10-7 cc/s is

indicated.

This is leak rate corresponding to helium present in the atmosphere, which normally is 5 ppm.

13. Sniffer probe now is ready to detect leaks from pressurized objects.

Pressurization is normally done at 1.5-2.0 kg/cm2 for small objects. If large object is involved then helium inside object can be mixed with nitrogen or compressed air. Concentration of He should be at least 15 % w.r.t. mixed gas.

14. Move sniffer slowly on weld joints.

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9-1 TROUBLE SHOOTING OF SNIFFER PROBE

Sr. No.

Symptom Corrective action

1. Valve is being opened but test port pressure bar is not responding

a Open SNIFFER fully counterclockwise and let air flow through sniffer valve.

b Close probe again and reopen slowly. 2. During opening TEST lamp

goes off but there is no indication of leak rate.

Set transfer pressure to 0.1 mbar using R8 on main electronics board.

3. After sniffer is opened spectrometer pressure rises beyond green band and filament goes OFF.

a Increase temperature of diffusion pump by 5 degees. b Recalibrate HLD-1112

3. Probe does not respond to

Helium Gas Recalibrate HLD-1112.

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SECTION 10

TROUBLESHOOTING

Careful maintenance will ensure proper operation of your HLD-1112 Mass Spectrometer Leak Detector, but occasionally a problem will arise. The Troubleshooting Chart lists various symptoms with appropriate corrective actions to be taken. The leak Detector system is to be serviced by trained personnel only. Failure to comply will result in Warranty termination (please read the Warranty Certificate). Contact out Sales/Service department for failures other than those mentioned in the troubleshooting chart.

10-1 TROUBLESHOOTING CHART No. Symptoms Cause Corrective Action

1

Rotary pump gives out fumes even when test port is blanked off

Loose connection on hose and/or clamps

Check Connection hose and clamps for proper fitment

2

Vacuum level is OK in START mode but drops above green band when HLD-1112 is in TEST mode

Need stabilization on diffusion pump.

If Diffusion Pump is just started allow some time to settle vacuum level for 30 min.

3

Pressure does not rise to ATM VENT switch is pressed.

Vent valve is not opened.

Check vent valve Check fuses on relay board.

4 When START is pressed pressure bar does not indicate pressure.

Valve V4 does not open

Check fuses on relay board.

5 Even if Test port pressure bar is full scale,TEST indicator does not glow

Valve V4 does not open together with valve V3

Check fuses on relay board. Adjust pressure transfer of TC gauge on main electronics board.

6 When START is pressed spectrometer tube pressure goes beyond green band and FIL becomes OFF.

Vent valve does not close

Check Vent valve

4

Test port pressure drops slowly and Test port bar fluctuates back and forth.

Rotary pump oil contaminated orsaturated with water vapour

Open ballast valve for 15 min.

5 Diffusion pump does not get hot.

PID controller is OFF Replace 1A fuse at the back side.

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6 No Sensitivity to helium

HLD out of Helium tuning. DP is excessively hot

Retune HLD as per procedure. Reduce temperature and retry.

No. Symptoms Cause Corrective Action HLD saturated with helium through gross leak.

Open ballast of rotary pump and wait for 15-20 min. Remove object under test and keep HLD in VENT mode.

Rotary pump oil contaminated.

Open ballast valve for 15 min.

7 High background.

Ion source contaminated. Switch to other filament. Retune HLD.

8 Filament Indicator Does not light when FIL switch is flipped ON

Blown fuse Check 1A fuse at back side of the cabinet. If blown replace

9 Does not stay lighted when FIL switch is released

Blown out Filament Switch to other filament and retry. If both filaments are blown, replace ion source.

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SECTION 11

MAINTENANCE

Like other quality test equipment, a mass spectrometer leak detector requires maintenance to insure continued reliable operation. For simplicity, in this section, the maintenance functions are grouped by recommended frequency as shown in Figure 7-1 below. All of them can be carried out at routine intervals, as indicated. The sensitivity should always be checked at least once a day. However, other functions may be carried out either more or less often than shown, depending upon the extent of use of the leak detector. The fully solid-state electronic system does not require preventive maintenance. Due to a rigorous 5-day operating check before shipment, component failure is rare and reliability is high.

Paragraph Description Daily Weekly 6 Mos.

12 Mos.

1 Check calibration and tuning X 2

Auxiliary Mechanical Vacuum Pump Check oil level

X

3

Auxiliary Mechanical Vacuum Pump Change oil

X

4

Complete overhaul, including Diffusion Pump Spectrometer Tube Valve Block Assembly

X

11-1 DAILY CHECKUPS 1. Check from back side of HLD that diffusion cooling fan rotates and PID controller

is powered up. 2. Check Tuning and calibration at least once a day or before job is to be tested for

leak. 3. Check position of Min range select switch. This switch should be at 10-9 position for

maximum sensitive measurements. 11-2 WEEKLY (AUXILIARY MECHANICAL VACUUM PUMP ONLY)

Check sight glasses. If the level is low, add mechanical pump oil until the level is between the marks in the sight glass, when running.

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SECTION12

GENERAL SUGGESTIONS

The following suggestions apply whether leak checking components, systems, or the leak detector itself 1) When spraying suspected leak locations, always apply helium starting at the

highest points first since helium rises. If drafts, such as from a cooling blower, exist in the area, apply helium downstream from source first, or deflect draft until leak checks are completed.

2) If vent grooves exist at flanges or other assembled seals, apply helium to these

points, (rather than a general spray), to obtain the most positive response, minimize use of helium and save time in checking.

3) Locate and repair large leaks before attempting to locate extremely small leaks. 4) Limit the search to a general area of test piece by isolation methods. Bagging,

masking or shielding with tape, plastic film or duct seal (if applied properly) will shorten the time required to locate both large and small leaks.

5) Use only enough helium to reach the leaks. DON’T flood the area.

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helium leak test

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