PROGRAMS AND PLANS--Quality Assurance of Temperature Measurements



In Reply Refer To:                             September 28, 1979 
EGS-Mail Stop 412


QUALITY OF WATER BRANCH TECHNICAL MEMORANDUM NO. 79.16

Subject: PROGRAMS AND PLANS--Quality Assurance of Temperature 
Measurements

This is to remind you that it is the field office's responsibility 
to assure that only accurate thermometers are used to make 
temperature measurements in the field and in district 
laboratories. Frequently new thermometers are found to be in error 
when checked against ASTM standard thermometers.

Thermometers that are used in making general temperature 
measurements should be accurate to +/- 0.5 degrees C. They should 
be calibrated before they are used and periodically during their 
usage. TWRI Book 1, Chapter Dl should be referred to for proper 
procedures to follow in calibrating thermometers. Although the 
method described on page 28 requires two constant-temperature 
water baths, other stable reference sources may be used. A mixture 
of water and ice agitated by a magnetic stirrer makes a good low 
temperature reference solution and an insulated container of water 
at room temperature makes a good second calibration point. 
Thermometers that read within + 0.5!C of an ASTM standard 
thermometer at two reference calibration points are acceptable for 
field use. It is advisable to mark these thermometers as 
acceptable. A dot or ring of paint or finger nail polish on the 
thermometer has been found to be satisfactory for this. 
Thermometers that are unacceptable should be destroyed or returned 
to the supplier for replacement.

Many of the electronic field instruments have a thermister system 
that can be Used to make temperature measurements. These systems 
should also be checked frequently at several points over their 
operating range to assure proper operation.

Units that do not perform to the manufacturer's specifications or 
to +/- 0.5 degrees C should not be used or returned to the 
manufacturer for repair or adjustment.

Remember that it takes both good equipment and proper technique to 
make a valid temperature measurement. TWRI Book 1, Chaper Dl is an 
excellent source of information on this subject, and all field 
personnel should be familiar with it.



                             R. J. Pickering

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