EQUIPMENT--Discontinuance of field use of mercury liquid-in-glass thermometers

In Reply Refer To:                              November 22, 1993
Mail Stop 412


Subject:  EQUIPMENT--Discontinuance of field use of mercury liquid-in-glass

The purpose of this memorandum is to announce that mercury liquid-in-glass 
thermometers are no longer to be used in the field.  Alternatives are 
thermistor thermometers, digital hand-held thermometers, and red safety liquid-
in-glass (alcohol) thermometers.  The reasons for this change are to prevent 
contamination of samples, vehicles, and the environment resulting from broken 
mercury thermometers and to limit exposure of field personnel to mercury vapors 
resulting from spills.  Mercury-filled NIST-calibrated thermometers can be used 
to calibrate thermometers in the laboratory only.  The NIST thermometers should 
not be taken into the field.  Water-quality monitors can be calibrated using 
lab-calibrated thermometers.

The Hydrologic Instrumentation Facility (HIF) recently tested the Cole-Parmer 
Model No. 90201-10 hand-held thermometer in hopes that it could provide an 
alternative to more expensive thermistor thermometers.  The test results (see 
Attachment 1) show that the thermometer meets the manufacturer's specification 
for accuracy of +/- 0.2 degrees Celsius (C) in the range tested, and that the 
unit performs well concerning environmental effects on accuracy and tolerance 
towards temperature change.  Please note the recommendations regarding the care 
and handling of this thermometer.  The Cole-Parmer thermometers can be 
purchased from HIF for $60, or individually from the company.

Other liquid-in-glass or thermistor thermometers with accuracies of at least 
+/- 0.5 C can also be used to measure temperatures in the field.  Temperature 
measurements made with multi-parameter units such as the Hydrolab are also 
acceptable.  Thermistors on other meters, such as dissolved-oxygen meters, must 
be calibrated and checked for accuracy before being used.  As with other field 
meters, all thermometer calibrations should be recorded in a dedicated log 
book.  Read Quality of Water Branch Technical Memorandum No. 79.16 for 
information on quality assurance of temperature measurements.

Data-quality objectives should be taken into consideration when selecting a 
thermometer.  Current basic-data requirements are to report air and water 
temperatures to the nearest 0.5 C.  The liquid-in-glass pocket thermometers 
generally have 1 degree divisions and, therefore, cannot be read as accurately 
as a digital or thermistor thermometer, but they can be read to the nearest 
0.5 C.

If the need arises, the HIF will test additional digital thermometers as 
requested by the Office of Water Quality or through the HIF Instrument Test 

                            David A. Rickert
                            Chief, Office of Water Quality

This memorandum does not supersede any other Office of Water Quality Technical 

Key Words:  Temperature, Thermometers, Thermistors, Mercury

Distribution:  A, B, S, FO, PO, AH

                                                              ATTACHMENT 1

(Modified from WRD Instrument News, Issue No. 62, September 1993)


The HIF has completed testing and evaluating the Cole-Parmer Digital 
Thermometer, Model 90201-10 to determine whether it can be used as an 
alternative to the mercury thermometer.  The following test report indicates 
that this digital thermometer meets the accuracy specifications, performs well 
within a specified range of environmental conditions, and is tolerant of 
temperature change within a specified range.  Please read the conclusions and 

                        TEST AND EVALUATION REPORT

               Cole-Parmer Digital Thermometer Model 90201-10

General Discussion

Two Cole-Parmer model 90201-10 digital thermometers were evaluated.  Three 
tests were used in the evaluation.

1.  Accuracy. -- Both units were tested in water baths at various temperatures 
between 5 and 100 C); a NIST-traceable thermometer was used as a reference. The 
differences between temperature readings from both the NIST-traceable 
thermometer and readings from both units are generally equal to or less than 
+/- 0.2 C (table 1).  Both Cole-Parmer units met the manufacturer's 

2.  Environmental Effects On Accuracy. -- The ambient temperature is commonly 
different from the water temperature.  Checking the performance of the units 
under these conditions is essential for the evaluation.  The units were placed 
in an environmental chamber in which both temperature and humidity were 
controlled; the temperature sensors were placed outside the chamber in the 
water bath.  Water temperatures were measured with both Cole-Parmer units.  
Measurements made with a NIST-traceable thermometer were used as reference  
Both units performed well (table 2).

3.  Tolerance Toward Temperature Change. -- Both units, including the 
temperature sensors,  were placed in an environmental chamber for 50 hours.  
The chamber was set in 5-hour cycles with temperature changes from 5 to 35 to 5 
C; humidity was kept between 40 and 50 percent.  After 10 cycles, the units 
were taken out of the chamber, and function tests were performed at 5, 15, and 
25 C.    Both units functioned well (table 2).

Conclusions and Recommendations

  Both Cole-Parmer units met the manufacturer's specification for accuracy (+/- 
0.2 C) in the range tested.

  The outer package of the unit is not physically strong and  users should  
exercise special care in handling the unit.  The plate holding the battery 
becomes detached and breaks off easily.  Users should verify that the batteries 
are making good contact.

  The unit itself cannot take freezing temperatures and is not waterproof--

TABLE 1.--Water bath temperatures (C) as measured by a reference thermometer 
and two Cole-Parmer model 90201-10 digital thermometers in thermometer accuracy 

[C, degrees C]


          BATH      NIST-Traceable   Cole-Parmer    Cole-Parmer
                     Thermometer       Unit 1         Unit 2


           0.0           0.05            0.2            0.4

           5.0           5.10            5.1            5.3

          10.0          10.10           10.0           10.2

          15.0          15.10           15.0           15.2

          20.0          20.00           19.9           20.1

          25.0          25.00           24.9           25.1

          30.0          30.05           30.0           30.2

          35.0          35.05           34.9           35.2

          50.0          50.00           50.1           50.3

          75.5          75.50           75.5           75.8

          98.4          98.40           98.7           98.6


TABLE 2.--Water bath temperatures (C) as measured by a reference thermometer 
and two Cole-Parmer model 90201-10 digital thermometers, whose meters were 
placed in an environmental chamber at a temperature different from that of the 
water bath, in thermometer accuracy test

[C, degrees C]
Meter in         |                        Sensor
environmental    |                     in water bath (degrees C)
chamber          |
                 |    NIST-Traceable   Cole-Parmer     Cole-Parmer
Temperature (C)  |     Thermometer       Unit 1          UNIT 2
     5.0         |          0.0            0.1            0.3
                 |          5.1            5.1            5.3
                 |         15.0           14.9           15.1
                 |         25.0           24.9           25.1
                 |         34.9           34.8           35.1
     15.0        |          0.0            0.2            0.4
                 |          5.1            5.0            5.3
                 |         15.0           14.9           15.1
                 |         24.9           24.8           25.0
                 |         34.9           34.6           34.9
     25.0        |          0.1            0.2            0.4
                 |          5.1            5.2            5.4
                 |         15.0           14.9           15.2
                 |         25.0           25.0           25.2
                 |         35.0           34.8           35.0
     35.0        |          0.2            0.3            0.5
                 |          5.0            5.0            5.2
                 |         15.0           14.9           15.1
                 |         25.0           24.9           25.0
                 |         35.0           34.8           35.0
            Note: The humidity was kept between 40 and 50 percent.


The HIF has placed an order for 50 units to be sold at $60 each.  The price 
includes HIF overhead.  The units are not on GSA schedule, but WRD offices can 
buy them if they keep their order under $300.  The normal price of the unit is 
$39.50.  HIF will alert the field when its units are available.

                          FOR FURTHER INFORMATION

For further explanation/discussion, contact Doreen Tai (DYTAI) at 601-688-1518.

                                 Vito J. Latkovich
                                 Chief, Hydrologic Instrumentation Facility