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Sensor Selection Guides

Temperature Sensor Overview

There are two temperature sensing methods:

Contact sensing brings the sensor in physical contact with a substance or object. It can be used with solids, liquids or gases. Non-contact (infrared) temperature sensing reads temperature by intercepting a portion of the infrared energy emitted by an object or substance, and detecting its intensity. Non-contact is used to sense the temperature of solids and liquids. Non-contact cannot be used on gases due to their transparent nature.

Contact Temperature Sensor Types and Comparisons

Contact sensors, aside from capillary/bulb thermometers and bi-metal sensors, use varying voltage signals or resistance values.

Voltage Signals

Thermocouple sensors generate varying voltage signals. The different metal and alloy combinations in the thermocouple's legs produce a predictable voltage for a given temperature.

Resistance Values

Resistance temperature detectors (RTDs) generate varying resistance values. RTDs as a class are divided into two types:

RTDs work by producing a predictable resistance at a given temperature. Resistance wire RTDs (generally platinum) have a positive coefficient by increasing resistance with temperature increase. Thermistors are generally negative coefficient by decreasing resistance with temperature increase. Each of these three contact sensor types (RTDs, thermocouples, and thermistors) have advantages and disadvantages depending on application, desired response time and accuracy. A presentation of general benefits can help determine the most suitable contact sensor type.

Thermocouple Advantages

RTD Advantages

Thermistor Advantages

Due to wide performance and cost variations among thermistors, generalized advantages and disadvantages may not always apply. Common benefits include:

Contact Sensor Conclusions

Non-Contact Sensors

A non-contact (infrared) sensor intercepts and converts emitted infrared heat into a voltage signal. Construction characteristics of non-contact sensors use a lens to concentrate radiated infrared energy onto a thermopile. The voltage signal produced by the thermopile is sent onto an electronics package for amplification and conditioning before being retransmitted as either a voltage or current signal. Non-contact temperature sensors generally react and register (respond) faster than contact temperature sensors.

Non-Contact Temperature Sensor Advantages

The reasons for using non-contact over contact temperature sensing are:

Contact vs. Non-contact Sensor Comparisons

Contact Temperature Sensors



Non-contact Temperature Sensors