Sensors; Thermistor And Thermistor Current Selection; Table 5 - Tec Link Conditions - Newport 8000 User Manual

Chapter 4
See the section in the main Model 8000 manual of linking for a complete description
of the linking process.
4.5

Sensors

4.5.1

Thermistor and Thermistor Current Selection

4.5.1.1 Introduction
Choosing the right sensing current depends on the range of temperature you want to
measure and the resolution you require at the highest measured temperature. To
correctly set the thermistor current you must understand how the thermistor and the
8000 interact and how temperature range and resolution values are inherent in the
nature of thermistors.
4.5.1.2 Thermistor Range
Thermistors can span a wide temperature range, but their practical range is limited by
their non-linear resistance properties. As the sensed temperature increases, the
resistance of the thermistor decreases significantly and the thermistor resistance
changes less for an equivalent temperature change. Consider the temperature and
sensitivity figures below.
Temperature
-20°C
25°C
50°C
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Temperature Controller Module Operation
Conditi Description
on
TEC output is on
On
Off TEC output is off
Out Tol TEC is out of tolerance
In Tol TEC is in tolerance
I Lim TEC is current limiting
V Lim TEC has reached its voltage limit
T Lim TEC has exceeded temperature limit (low or
high)
TEC has exceeded high temperature limit
Th Lim
TEC has exceeded low temperature limit
Tl Lim
TEC has exceeded R limits (high or low)
R Lim
TEC module is open
Open

Table 5 - TEC Link Conditions

Sensitivity
5600 ohms/°C
439 ohms/°C
137 ohms/°C
53