Duct Temperature Sensor - Thermistor Temperature Sensing DeviceDuct Temperature Sensor - The duct static temperature sensor measures air temperature in the ductwork. The solid state temperature sensing devices are commonly used in HVAC applications that are controlled by direct digital control or a modern building automation system. At the base of the box is a probe which sticks into the air stream of the ductwork. As the air passes over the probe the probe changes resistance.

Duct Temperature Sensor

A small current which passes through the thermistor either increases or decreases depending on how the temperature changes. The controller reads this change and registers this temperature change and compares it to a table in the DDC program. The table has a sliding scale which matches a temperature to the set amount of current returning from the thermistor. This is how a thermistor is a reliable temperature sensing device.

There are millions of these temperature sensors in use today and they reliably measure temperatures and cause DDC programs to react to the temperature these thermistors read. Thermistors are not only used in ductwork but also used in reading temperatures in pipes and mechanical equipment. Thermistors are not only used in HVAC application, computers use thermistors to read the temperature of your processor and turn the fan on to cool it when the temperature rises above a certain set point determined by the manufacturer. Chances are, there are several thermistors in your home and vehicle which read temperature to start an automatic process.

Duct Temperature Sensor

Modern digital thermostats use thermistors for temperature sensing. These temperature sensors are typically not calibrated after installation so if and when they go bad it is necessary to replace the entire device. That includes the thermostat installed in your home if it is a digital thermostat. It is not impossible to replace or repair these temperature sensors but it is usually easier and less time-consuming to replace the thermostat rather than repair it.

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Duct Temperature Sensor - Thermistor Temperature Sensing Device

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