234B Series TEC TO-Can
LaserMount
U
ser’s Manual
· Page 11
As can be seen be the graph, the resistance of the thermistor drops very quickly.
In the typical control range (0°C to 40°C), typical 10K thermistors offer good
sensitivity to changes in temperature, and this is the range in which most 10K
thermistors are typically used. 10K thermistors can be used at much higher
temperatures, but will suffer poorer temperature stability performance because
of the lower sensitivity.
All Arroyo temperature controllers support operation using a 10
μ
A or 100
μ
A
thermistor bias, which limits the upper control range to 450k
Ω or
45k
Ω
,
respectively. To minimize noise and maximize stability, you should select
highest current while still allowing you full operation across your required
temperature range. The typical setting is 100
μ
A, but your application will
determine the actual needs.
The Steinhart-Hart Equation
As can be seen from the temperature versus resistance graph above, resistance
varies inversely with temperature in a non-linear fashion. This relationship can be
accurately modeled by polynomial equations, and one such being the Steinhart-
Hart equation:
3
)
ln(
*
)
ln(
*
1
R
C
R
B
A
T
+
+
=
The coefficients for the BetaTHERM 10K3A1 thermistor are:
A = 1.12924x10
-3
B = 2.34108x10
-4
C = 0.87755x10
-7
These are the default coefficients for Arroyo Instruments temperature controllers,
but can be changed in the
Sensor
menu, or by selecting the appropriate
234B
mount from the
Mount
menu setting.
