iWorX TM-100 Technical Note

TM-100 Temperature Sensor
Technical
Note
TM-100

Overview

The TM-100 Temperature Sensor is a sensor that can monitor temperatures
between 15°C above and 15°C below room temperature. The TM-100 is capable of
responding to changes in temperature within a few seconds because of its small
size (1mm x 3mm) and mass. The TM-100 is suitable for monitoring the
temperature of nasal airflow, changes in skin temperature that indicate evaporative
cooling, and changes in atmospheric temperature and temperature in
environmental chambers. Since the sensor element is water-resistant, the tip of the
TM-100 can be immersed in aqueous solutions, including saline solutions, for a
few hours.

How It Works

The sensor element in the TM-100 that responds to temperature changes is a
thermistor, which is a type of resistor that changes resistance with changes in
temperature. The thermistor in the TM-100 has a negative temperature coefficient
(NTC) which means that the resistance of the thermistor decreases as the
iWorx Systems, Inc.
temperature goes up. Thermistors with positive temperature coefficients also exist.
Table 1 at the end of this Technical Note shows the resistances of the thermistor in
www.iworx.com
the TM-100 over a range of temperatures from 0°C to 50°C.
The thermistor in the TM-100 is wired into the circuit of the sensor as one leg of a
Wheatstone bridge. On the other three legs of the bridge circuit, selected resistors
LabScribe is a trademark of
are used to give the TM-100 a linear output over a range that is 15°C above and
iWorx Systems, Inc.
below room temperature.
©2015 iWorx Systems, Inc.