TABLE OF CONTENTS John Fontes, Senior Applications Engineer, Honeywell Sensing and Control
Because temperature can have such a significant effect on materials and processes at the molecular level, it is the most widely sensed of all variables. Temperature is defined as a specific degree of hotness or coldness as referenced to a specific scale. It can also be defined as the amount of heat energy in an object or system. Heat energy is directly related to molecular energy (vibration, friction and oscillation of particles within a molecule): the higher the heat energy, the greater the molecular energy.
Temperature sensors detect a change in a physical parameter such as resistance or output voltage that corresponds to a temperature change. There are two basic types of temperature sensing:
Contact temperature sensing requires the sensor to be in direct physical contact with the media or object being sensed. It can be used to monitor the temperature of solids, liquids or gases over an extremely wide temperature range.
Non-contact measurement interprets the radiant energy of a heat source in the form of energy emitted in the infrared portion of the electromagnetic spectrum. This method can be used to monitor non-reflective solids and liquids but is not effective with gases due to their natural transparency.
Temperature sensors comprise three families: electro-mechanical, electronic, and resistive. The following sections discuss how each sensor type is constructed and used to measure temperature and humidity.
Bi-metal thermostats are exactly what...
