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7.9.13 THERM
The THERM type is for thermistors that have unique calibration coefficients or
do not match the YSI-400 specification. This type of probe generally has mod
-
erate cost, a limited operating range (–40°C to 150°C), excellent accuracy
(0.005°C to 0.01°C) and excellent resolution (0.002°C). This type uses the
Steinhart-Hart equation in the following form:
RTK b bT bT bT( [ ])[ ] exp[ ]Ω= + + +
−−−
01
1
2
2
3
3
The coefficients b0 through b3 are usually found on the calibration certificate
of the probe. These coefficients are set with the functions “b0", ”b1", “b2", and
”b3". In some cases the equation is used without the b2 term. For this case, the
“b2" coefficient should be set to 0. Consider the following examples.
Example 1:
A thermistor has coefficients for the equation ln(R) as a function of T given as
a, b, c, and d. Set the instrument's coefficients to the Report of Calibration val
-
uesasfollows:
Coefficients Report of Calibration Value
b0 a
b1 b
b2 c
b3 d
Example 2:
A thermistor has coefficients for the equation ln(R) as a function of T given as
a, b, and c. Set the instrument's coefficients to the Report of Calibration values
as follows:
Coefficients Report of Calibration Value
b0 a
b1 b
b2 0.0
b3 c
7.9.14 Probe Wires
This function sets the number of connecting wires in the probe. The instrument
can be used with probes that have two, three, or four wires. Three wires con
-
necting the probe sensor instead of two allows the instrument to partially cancel
1522 Handheld Thermometer Readout
User’s Guide
44