7.9.13 THERM
The THERM type is for thermistors that have unique calibration coefficients or
do not matchthe YSI-400 specification. This type of probe generally has mod-
erate cost, a limited operating range (–40°C to 150°C), excellentaccuracy
(0.005°C to0.01°C) and excellent resolution (0.002°C). This type uses the
Steinhart-Hartequation in the following form:
RTK b bT bT bT( [ ])[ ] exp[ ]Ω= + + +
−−−
01
1
2
2
3
3
The coefficientsb0 through b3 are usually found on the calibration certificate
of the probe. These coefficientsare set with the functions “b0", ”b1", “b2", and
”b3". In some cases theequation is used without the b2 term. For this case, the
“b2" coefficientshould be set to 0. Consider the following examples.
Example 1:
A thermistorhas 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 Reportof Calibration Value
b0 a
b1 b
b2 c
b3 d
Example2:
A thermistorhas coefficients for the equation ln(R) as a function of T given as
a, b, and c. Set theinstrument's coefficients to the Report of Calibration values
as follows:
Coefficients Reportof Calibration Value
b0 a
b1 b
b2 0.0
b3 c
7.9.14 Probe Wires
This functionsets the number of connecting wires in the probe. The instrument
can be used with probes that havetwo, 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