Contact
temperature sensors measure their own temperature. One infers the temperature
of the object to which the sensor is in contact by assuming or knowing that the
two are in thermal equilibrium, that is, there is no heat flow between them.
Many potential measurement error sources exist, as you can appreciate, especially
from too many unverified assumptions. Temperatures of surfaces are especially
tricky to measure by contact means and very difficult if the surface is moving.
It is wise to be very careful when using such sensors on new applications.
The Measurements (or Applications) page can lead
you to many well-known solutions or examples of ones possibly similar to the one
you are trying to solve. Why re-invent the wheel?
Two
excellent reference by Baker et al. are listed in the References
page and worth reading to get an idea of the complexities that can arise,
how to test and get around them.
Surface temperature measurent problem can
be solved in many cases through the use of non-contact sensors; they are almost
ideal for those types of applications and are in use in many industrial plants
worldwide in great numbers.
However, all sensors have their own set of complexities.
It is an imperfect world, after all, but many imperfections can be expertly improved
upon and overcome if one is diligent and resourceful.
Thermocouples
Thermocouples are among the easiest temperature sensors to use. They are widely applied in science and industry. They are based on the Seebeck effect that occurs in electrical conductors when they experience a temperature gradient along their length. NB: They do NOT measure at either the hot or cold junction!
Thermistors
Thermistors are tiny bits of inexpensive semiconductor materials with highly temperature sensitive electrical resistance. They are used in many applications where they are never seen because they are buried inside something else, There are also a special group of very precise thermistors that are used as the sensors in Electronic thermometers for taking the temperature of people.
Liquid-In-Glass Thermometers
The thermometer that checked your fever when you were young was a specialized version of this oldest and most familiar temperature sensor.
Resistance Temperature Detectors (RTDs)
RTDs are among the most precise temperature sensors commercially used. They are based on the positive temperature coefficient of electrical resistance.
Filled System Thermometers
In the USA, most home thermal cooking ovens are controlled by little temperature sensors that look like small metal tubes with bulges on the end-filled system thermometers-much like liquid-in-glass-but different.
Bimetallic Thermometers
The simple mechanical sensor that works in most "old-fashioned" thermostats based on the fact that two metals expand at different rates as a function of temperature.
Semiconductor Temperature Sensors
Commercial temperature sensors have been made from semiconductors for a number of years now. Working over a limited temperature range, they are simple, linear, accurate and low cost devices with many uses.
Other Temperature Sensors
Temperature measurement occasions often seem to stretch the capabilities of existing sensors and inventive minds continue to create new and/or better ways to measure those temperatures. There's quite a list of them, the "Other" devices, already and it's sure to grow.
Other Resources Other pages on the site, but some of the key related ones are the following:
Also
noteThe Temperature Sensors
Community Web Site, a companion site set up to enable direct inputs from
temperature sensor users and makers. Vendors, do visit there. Sign in and enter
your own company data, product and service offerings and news-It's been Improved!
Users can post reports & reviews of companies, news, products and services.
Note that inputs are moderated for propriety and excess zeal! Best of all, it
is freely available and "self service".
