Types Of Over Temperature Switches

By Author: Control Products
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Temperature control is essential for industrial manufacturers. This article discusses the types of temperature sensors to help you make the right choice next time you’re seeking a temperature control switch.

There are two types of temperature sensing methods that are classified by their functionality, contact or non-contact. Contact temperature sensors need to be in constant physical contact with a material. These temperature sensors can work effectively to control solid, liquid or gaseous temperatures. The non-contact temperature sensors calculate temperatures by absorbing the infrared energy emitted by a material. They control the temperatures by detecting the degree of infrared energy and are used with solids and liquids but cannot be used for gaseous temperature control.

Types of Contact Temperature Sensors

Contact temperature sensors are further classified by their voltage signals and resistance values. The thermal switches that generate varying voltage signals are called Thermocouples. Thermocouples have varying metal and alloy blends allowing them to give out a predictable voltage for a given temperature. ...
... Thermocouples are most often used for controlling extremely high temperatures. Thermocouples made of noble metals can control temperature ranges up to 3100°F. These thermal sensors have gained popularity due to their immediate response to temperature changes when grounded.

The second type of contact temperature sensors are Resistance Temperature Detectors (RTDs). These generate different resistance values and are further segregated into two types: resistance wire RTD and Thermistor.

RTDs of platinum metal are preferred to be used in high temperature settings because they increase their resistance with an increase in temperature. The functionality of RTDs involves the production of a predictable resistance at a given temperature. They are used for a very wide temperature range- usually from -328 to 1200°F. They have a high output and the current drop in RTD gives a bigger signal than the thermocouple voltage output.

Thermistors are used for low sensor costs because the majority of thermistors in their raw form are quite inexpensive, compared to RTDs. They have a high resistance that can reach up to several thousand ohms. They are preferred because they are effective in removing lead-wire resistance issues.

RTDs are considered the most suited for a majority of industrial setups which may experience a wide range of temperature. Thermistors are favored for low cost applications but they do not possess the same temperature capabilities.

Non-Contact Sensors

Non-contact or infrared sensors work on the basis of infrared emissions. They intercept and change the sent out infrared heat into a voltage signal. These sensors use a lens to target the radiated infrared energy which is then transferred into a thermopile. The thermopile then produces a voltage signal and is transported to an electronics package and amplified before being resent as a voltage or current signal.

From viewing the types of an over temperature switch, it’s important to make an informed decision on which switch works best for your specific situation.

The writer is associated with Control Products Inc the leading provider of quality control switches for all uses including: freeze switches, momentary switches, sealed limit switches, and other products of high performance.