thermocouple reference tables

8/8/2019 Thermocouple Reference Tables

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THERMOCOUPLE REFERENCE TABLES

The N.I.S.T. (National Institute of Standards and Technology) is the U.S. standardssetting agency. They have determined the output millivoltage of all type thermocouples,at all temperatures, within their range. The resulting tabulations are called

"Thermocouple Reference Tables" and the thermocouple output millivoltage is shownfor each degree of temperature

The junction of each type thermocouple produces a specific millivoltage across it at aspecific temperature. A thermocouple consists of two junctions connected in opposition.One is the measuring junction and the other is the reference junction. VD is themillivoltage resulting from the difference between the millivoltages generated by the twoopposing junctions. VD is the millivoltage read when a meter is connected across thethermocouple as shown below.

HOW TO DETERMINE THE MEASURING JUNCTION TEMPERATURE

1. Measure the "VD" millivoltage as shown above.2. Measure the actual temperature of the reference junction with a thermometer. 3. Go to the table for the thermocouple being used and look up the millivoltage

produced at that temperature.4. Add that millivoltage to the millivoltage measured as "VD" to get a total.5. Find that millivoltage total in the reference table. The corresponding temperature

is the temperature of the measuring junction.

Example #1 Type "T" Thermocouple

Measured "VD" = 3.41 mV

Reference Junction Temperature = 22C (71.6F)

1. From the table; 22C = 0.87 mV.2. Adding 0.87 mV to 3.41 mV = 4.28 mV.3. Finding 4.28 mV In the table; the corresponding temperature is 100C

(212F) and is the temperature of the measuring junction.

Example #2 Type "T" Thermocouple

Measured "VD" = 4.47 mV

Reference Junction Temperature = -5C (23F) (lower than the table reference of 0C)

1. From the table; 5C = -0.193 mV2. Adding -0.193 mV to +4.47 mV = +4.28 mV


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3. Finding 4.28 mV In the table; the corresponding temperature is 100C (212F)and is the temperature of the measuring junction

Metric/English Scale Conversion C = F 32 F = 1.8C + 32

ANSILETTER

LEG*METALLIC

COMPOSITION

MEETINGPOINT

USABLETEMPERATURE

RANGE

(LONG TERM)

TOLERANCES (THE GREATEROF BASE OR % OF READING) REFERENCE

TABLEDATASHEET

NUMBER F C ** STANDARD PREMIUM

B

P

N

PLATINUM +30%RHODIUM

PLATINUM +6%RHODIUM

3320 1825

400 TO 3050 F

200 TO 1680 C

0.5% NOT SET AN-HTP08

C ***PN

(TUNGSTEN+5% RHENIUM)

(TUNGSTEN+26% RHENIUM)

4500 248030 TO 4200 F0 TO 2300 C

NOTESTABLISHEDSEE IPTS-90

N.A. AN-HTP13

EPN

CHROMEL,

CONSTANTAN

2230 1220-300 TO 850 F

-200 TO +450 C

1.7 C

o r 0.5%

1.0 C or

0.4%

N.A.

JPN

IRON

CONSTANTAN

2230 122030 TO 700 F0 TO 400 C

2.2 C

or 0.75%

1.1 C or0.4%

N.A.

KPN

CHROMEL,

ALUMEL,

2550 1400-300 TO 1800 F-200 TO 1000 C

2.2 C

or 0.75%

1.1 C or 0.4%

AN-HTP12

NPN

NICROSIL****

NISIL

2440 134030 TO 1800 F0 TO 1000 C

2.2 C

or 0.75%

1.1 C

or 0.4%

N.A.

R

P

N


PURE

PLATINUM

3215 1770

400 TO 2700 F

200 TO 1500 C

1.5 C

or 0.25%

0.6 C

or 0.1%

AN-HTP09

SPN


PUREPLATINUM

3215 1770400 TO 2700 F200 TO 1500 C

1.5 C

or 0.25%

0.6 C or 0.1%

AN-HTP10

TP

COPPER 1980 1080-450 TO 660 F 1.0 0.5 C or

0.4%AN-HTP11


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N

CONSTANTAN,

-270 TO 350 C or 0.75%

* P=Positive Leg N = Negative Leg

**"Standard" grade wire is sufficiently accurate for most applications. The purity andcomposition of "premium" grade wire is more closely controlled, and its millivoltageoutput is closer to the NIST standard chart and therefore reads somewhat moreaccurately than the "standard" grade does.

*** Not an ANSI symbol, but is commonly used as a designated name; also sometimesreferred to as a Type "W".

****Trademark of Hoskins Mfg

NOTE: Individual T/C units may be calibrated by measuring their output at severalknown temperatures and preparing an error correction chart. This chart is used toeliminate any deviation from the "standard" output millivoltage versus temperaturereadings inherent in this particular thermocouple. The result is known as an "NIST"traceable thermocouple.


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