EQUIPMENT--Discontinuance of field use of mercury liquid-in-glass thermometers
In Reply Refer To: November 22, 1993
Mail Stop 412
OFFICE OF WATER QUALITY TECHNICAL MEMORANDUM NO. 94.02
Subject: EQUIPMENT--Discontinuance of field use of mercury liquid-in-glass
thermometers
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
Program.
David A. Rickert
Chief, Office of Water Quality
This memorandum does not supersede any other Office of Water Quality Technical
Memorandum.
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)
ATTENTION--A REPLACEMENT FOR THE MERCURY THERMOMETER
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
recommendations carefully. THE DIGITAL THERMOMETER UNIT SHOULD BE HANDLED WITH
CARE.
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
specifications.
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--
HANDLE WITH CARE.
TABLE 1.--Water bath temperatures (C) as measured by a reference thermometer
and two Cole-Parmer model 90201-10 digital thermometers in thermometer accuracy
test
[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.
PURCHASING
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