Appendix C Thermistor Temperature Probes; Thermistor Temperature Probes; What Are Thermistors; Et Series Temperature Probes - ACR Electronics SmartReader Plus Reference Manual

SmartReader Plus Data Loggers
79
1.17

APPENDIX C Thermistor Temperature Probes

1.17.1

Thermistor Temperature Probes

The SmartReader Plus 1, 2, 4 and 8 data loggers can record temperature from a wide variety
of external thermistor temperature probes. You can use the standard thermistor probes ACR
makes available or you can use your own.
1.17.2

What are Thermistors?

Thermistors are temperature-sensitive resistors. The most common are those classified as
the NTC (Negative Temperature Coefficient) type, which, at high temperatures, have a
relatively low electrical resistance. At low temperatures their resistance is much higher. In
between, the resistance varies with temperature at a predictable rate that can be made linear
by a mathematical equation (refer to Equations in the TrendReader guide).
Thermistors provide a rugged, highly stable and accurate means of measuring temperature.
They can be used for very low temperature applications down to -80°C (-112°F) or with special
probe configurations, in environments up to 450°C (850°F).
Thermistors with consistent properties, for a given type, are readily available. These
interchangeable thermistors can be substituted without recalibrating the logger.
1.17.3

ET Series Temperature Probes

The ET Series External Temperature Probes provide added versatility to the temperature
measuring capabilities of your SmartReader Plus 1, 2, 4 and 8 data loggers. Accurate,
interchangeable and suitable for various defined temperature ranges, they interface easily to
the terminal connector block on each logger. Each ET Series Temperature Probe consists of a
NTC thermistor potted into the tip of a short length of stainless steel tubing.
Equations
Each ET series thermistor probe is associated with a standard linearizing equation in
TrendReader software. The equation converts the resistance values of the thermistor to
accurate temperature readings, depending on the specific characteristics of the thermistor
type.
Why the Different Types?
Individual thermistor types are most effectively used over specific and defined temperature
Thermistor Temperature
Probes
Copyright © 2010 ACR Systems Inc. All Rights Reserved.