Application Note 14:Temperature Measurement with the
A lot of people want to measure medium temperatures like IAT
and CT with the LM-1. The following document shows how to do
that for temperatures between -50 deg C (-58 deg F) and ~200
deg C (400 degF)
The devices of choice for these measurements are called NTC
thermistors. NTC stands for Negative Temperature Coefficient.
NTC thermistors are resistors whose resistance value gets lower
with rising temperature. Unfortunately the resistance over temperature
curve is non linear.
The exact resistance over temperature curve is dependent on the
material used to manufacture the thermistors. Each material has
a different curve.
Thermistors are usually specified by their resistance at 25
deg C (77 deg F) and the temperature curve. This curve or table
shows the change in resistance relative to the resistance of
the thermistor at 25 deg C (77 deg F).
Resistance curves for different materials can be found here:
NTC resistors can be found here:
Recommended part# is KC009G-ND
This thermistor has a resistance at 25 deg C of 10 kOhm. Material
The circuit is very simple. It just requires a thermistor, a
zener diode and 2 resistors.
Calculation of Voltage/Temperature for LogWorks
Download this spreadsheet to
calculate an output voltage curve for thermistors.
1. In the column "Rth/R25", enter the material data
for the thermistor used. The spreadsheet is already filled out
for the thermistor material GE9.7
2. In the field G5, enter the nominal resistance of the thermistor
at 25 deg C in kOhm.
3. In the field G2, enter the value of the load resistor in kOhm.
4. In the field G8, enter the zener voltage measured where indicated
in the schematic above.
5. In the field G11, enter the Dissipation constant for the thermistor.
This constant indicates how many milliWatts is required to heat
up the thermistor by 1 deg C. The current flowing through the
thermistor will heat it up and therefore indicate a higher temperature
that the actual measured temperature.
6. In Field A1, enter “degC” for a Centigrade scale
or “degF” for a Fahrenheit scale.
Column A and B are then show the output voltage/temperature curve
for the circuit.
Column D shows the error expected due to internal heating by
the measurement current in deg C.
By reducing the load resistor you can shift the area of maximum
sensitivity to higher temperatures. Do not reduce the load resistor
below 0.5 kOhm.
After everything is set up, save the spreadsheet first in the
normal .xls format. Then save it again in .dif format.
The resulting .dif file can be directly loaded in LogWorks in
the Input Configuration/Load Edit Table custom setup for the