•- oUNITED STATES DEPARTMENT OF THE INTERIOR

BUREAU OF RECLAMATION

PROCEDURE FOR

CALIBRATING PRESSURE GAUGES

(DUSBR 1040-89

INTRODUCTION

This procedure is under tile jurisdiction of the Geotechnical Services Branch, code D-3760, Research and Laboratory ServicesDivision, Denver Office, Denver, Colorado. The procedure is issued under the fixed designation USBR 1040. The number immediatelyfollowing the designation indicates the year of acceptance or the year of last revision.

1. Scope

1.1 This designation outlines the procedure forcalibrating pressure gauges used for standard laboratorytesting. It is recommended that any adjustments to apressure gauge be made only by experienced personnelor the manufacturer.

1.2 This calibration procedure is limited to pressuregauges as classified in Federal Specification GG-G-76E.

2. Applicable Documents

2.1 American National Standard, ANSI B40.1-1980,Gauges-Pressure Indicating Dial Type -- Elastic Element

2.2 Federal Specification GG-G-76E, Gauges, Pressure,and Vacuum, Dial Indicating, 1981

3. Summary of Method

3.1 A master gauge is calibrated using a primarypressure standard (see subpar. 9.2, figs..1 and 3a). Thepressure gauge to be calibrated is connected to the mastergauge as shown on figure 3b. Pressure is applied to thepressure gauge at predetermined pressure increments overits full operating range. The value indicated by the pressuregauge is compared to the corresponding value indicatedby the master gauge at each pressure increment. Thepercent error between the two values is calculated andthe gauge is adjusted as necessary.

4. Significance and Use

4.1 Pressure gauges used in the laboratory must becalibrated to ensure reliable test results.

4.2 This calibration procedure is to be performed uponreceipt of a pressure gauge and annually thereafter.

5. Apparatus

5.1 Pressure Gauge.-A pressure gauge meetingrequirements of Federal Specification GG-G-76E and theAmerican National Standard ANSI B40.1-1980.

5.2 Primary Pressure Standard (fig. 1).-A highaccuracy, deadweight tester designed for precision meas-urement of applied gas pressure. The device consists ofa weighted piston which becomes suspended in staticequilibrium when a prescribed gas pressure is introduced.Calibrated masses are used for a range of pressures.

5.3 Tubing.-High-pressure tubing of appropriate sizeand length to connect pressure gauges and the primarypressure standard to the pressure source.

5.4 Pressure Regulator.-A pressure regulator..capableof maintaining the desired pressure to the gauges andprimary pressure standard.

5.5 Valves.-Appropriate size valves, two required;bleed and pressure cutoff.

6. Precautions

6.1 SaFety Precaucions.-Safety glasses are to be wornwhen applying pressure to the gauges.

7. Calibration and Standardization

7.1 Verify that the primary pressure standard has beencurrently calibrated in accordance with manufacturerspecifications. If the calibration is not current, it is to beperformed before using the primary pressure standard forthis calibration procedure.

8. Conditioning

8.1 Not applicable; special conditioning requirementsare not needed for this procedure.

9. Procedure

9.1 All data are to be recorded on the "Pressure GaugeCalibration" form as shown on figure 2.

9.2 Master Gauge Calibration:9.2.1 Connect the master gauge to the primary pres-

sure standard and pressure source as shown on figure 3a.9.2.2 Apply pressure to the master gauge in incre-

ments (a minimum of five) over the full range of themaster gauge.

9.2.3 Record the value of pressure indicated by theprimary pressure standard and the corresponding valueof pressure indicated by the master gauge for each pressureincrement.

9.2.4 Compute the percent error for each pressureincrement and compare the values obtained withpermissible error values in table 1.

9.2.5 Adjust the master gauge if necessary (seesubpar. 1.1) and repeat subparagraphs 9.2.2 through 9.2.4

70

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USBR 1040

7-2328 (10-85)Bureau of Reclamation PR ESSU R E GAUG E CA LIBRATION

DesignationUSBR 1040 89MANUFACTURER

EXAMPLE

GAUGE RANGE ACCURACY GRADE SERIAL NO.

70-1400 kPa 3AMASTER GAUGE RANGE ACCURACY GRADE

O-1500kPa 3ACALIBRATED BY DATE ICHECKED BY,

IFULL SCALE MASTER GAUGE INDICATION (FCM) 1500 kPa

Master gauge calibration

PressureappliedIbf/in2 []kPa []

(1)

0

200

400

600

Mastergauge reading (MGR)Ibf/in2 [] kPa []

Trial

(A) (B) (C)

0 0 0

200 200 200

401 400 402

598 600

800 801 801

1000 1000 1000

599

801

I000

1200 1202 1201 1200

1400 1400 1398 1399

1500 1502 1500 1500

SERIAL NO.

45787DATE

i D•t%error -(1)-IMGn' X 100

(FCM)Trial

(A) (B) (C)

0.0 0.0 0.0

0.0 0.0 0.0

-0.07 0.0 -0. 13

O. 13 0.0 0.07

-0.07 -0.07

0.00.0

-0.07

0.0

-0.13 -0.07 0.0

0.0 O. 13 0.07

-0. 13 0.0 0.0

FULL SCALE MASTER GAUGE INDICATION (FCG) 1400 kPoGauge calibration

Master gaugereading [] Ibf/in2

[] kPa

Gauge reading (GR)Ibf/in2 [] kPa []

Trial

%error -(1)-(GR) X 100(FCG)Trial

(1) (A) (B) (C) (A) (B) (C)

0 0 0.0

200 202 -0. 14

400 402 - 0. 14600 602

-0. 14800 802 -0.14

I000 I000 0.0

1200 1200 0.0

1400 1400 0.0

Remarks Trial A indicales •auge meets permissible error percentages given

Accept [] in Table I for 3A accurac), grade.Reject []

GPO 849-232

Figure 2. - Pressure gauge calibration -- example.

72

USBR 1040

atmosphere

Bleed valve (• (

Pressureregulator

Pressure source

Primary PressureStandardPressure

cutoff valve

(a) Schematic of master gauge calibration

Gauge to be calibrated

Bleed valve (•)I Pressure

(•J) cutoff valve

Pressureregulator (

Pressure source

(b) Schematic of gauge calibration

Figure 3. - Schematics of calibration assemblies.

73