Page 20 ·
TECPak
User’s Manual
The
TECPak
supports operation using a 10
μ
A or 100
μ
A constant current
source, which limits the upper control range to 450k
Ω
and
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 6be 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 A, B, and C can usually be obtained from the thermistor
manufacturer. The
TECPak
defaults to the coefficients for the BetaTHERM
10K3A1 thermistor (A = 1.12924x10
-3
, B = 2.34108x10
-4
, C = 0.87755x10
-7
). You
can change the coefficients using the TEC:CONST command, or through the
Settings…
dialog within
Arroyo Control
.
