ILX Lightwave LDT-5416 User Manual page 22

Use of the Steinhart-Hart Equation - The Steinhart-Hart equation accurately models the non-
linear R-T characteristic curve of a negative temperature coefficient (NTC) thermistor. When the
correct constants for a thermistor are known, the Steinhart-Hart equation can be used to convert
between resistance and temperature. This method offers the advantage of accurately
calculating R-T values at any point on the curve, not just those supplied by the manufacturer.
There are several forms of the Steinhart-Hart equation. The form of the Steinhart-Hart equation
which is used by ILX Lightwave is:
Where R is the resistance in ohms; C
particular thermistor.
These constants may be derived specifically for each thermistor, or the nominal value for a
thermistor may be used (see ILX Lightwave Application Note #4 Thermistor Calibration and the
Steinhart-Hart Equation). ILX Lightwave supplies the Steinhart-Hart constants when a TS-510
calibrated thermistor is purchased.
Linearized Thermistor Mode – For users wanting to display a calculated temperature without
using one of the methods above the LDT-5416 has a unique mode that when selected will
display and control to a calculated temperature. To use this mode the LDT-5416 sensor select
switch must be set to °C LINEARIZED FOR 10k. This mode can only be used with 10kΩ
thermistors with 1% accuracy and a Beta of 3900 to 4050. In this mode, the display will show
temperature with an accuracy of ±1.0°C. For users requiring higher accuracy or not using a
10k thermistor one of the other methods above should be used.
Use of 10kΩ thermistors with accuracy greater than 1% and a Beta value outside of the
range of 3900 to 4050 can result in temperature readings exceeding ±1.0°C of set point.
Potential damage to the load may occur due to inaccurate set points.
November 2016
Table 2.4 Typical Thermistor R/T Data
°C
Temperature in
10
11
12
13
14
15
1
( ���� �� ) + ��
= �� + ��
1 2
��
, C , and C
1 2
12
R /R
T 25
1.990
1.897
1.809
1.726
1.646
1.571
3
(���� ��)
3
are the Steinhart-Hart constants for a
3
LDT-5416