6.0 CHECKING CALIBRATION
6.1
The Thermalert TH-5 thermometer incorporates an automatic zeroing amplifier which produces
near-perfect stability of calibration. A calibration check is not necessary before each use. Under nor-
mal circumstances, the instrument will provide years of service without requiring recalibration.
6.2
Should it be suspected that the instrument is out of calibration, it may be checked with the
Physitemp type T calibrator (Model CT-3), or if this is unavailable, with an NIST calibrated thermome-
ter. Verifying instrument calibration with an NIST calibrated thermometer requires extremely careful
technique, an accurate reference standard thermometer, and a reasonably draft-free location. The fol-
lowing apparatus and supplies are needed:
1 - quart thermos flask with 2-hole cork
Stirrer
NIST traceable mercury in glass thermometer, 0.05°
graduations, partial immersion, 25-50°C (78-122°F)
with ice point scale.
Physitemp type T temperature probe
Ice made from distilled water
Distilled water
6.3
Preparation:
a) Crush the ice and place it in the thermos flask, at least 3/4 full. Add distilled water. Leave for
30 minutes to allow temperature to stabilize, stirring periodically.
b) Immerse the standard mercury-in-glass thermometer in the ice bath to the immersion
mark on the stem. Stir the bath well and compare with thermometer reading at 0°C with the
correction table supplied with the thermometer. If the error is greater than 0.0°C, wait 10
minutes, stir the water bath and remeasure. If the error remains greater, test with another
standard thermometer.
6.4
A complete calibration check requires two different measurements, one for each of the
temperature ranges of the TH-5.
6.5
Checking low end of temperature range:
Fill a thermos flask with a mixture of hot and cold water to produce a temperature of
approximately 25
°
C. Attach any Physitemp type T thermocouple probe to the standard
mercury thermometer so that the sensor is at the same level as the mercury bulb, and
immerse in the flask to the immersion depth marked on the stem. Do not allow probe or
thermometer to touch the sides of the flask. Connect the probe to the TH-5 and switch it
ON. Stir the bath well and wait 5 - 10 minutes. Ensure the flashing colon (battery warning)
is not visible before reading the instrument and then the mercury thermometer to .05°C.
Make a note of both readings.
5
Содержание TH-5
Страница 2: ......
