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. It’s simple in most cases, but can be difficult in some uses.
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.
Applications collections 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?
Surface temperature measurement 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.
Many of the use cases for contact temperature sensors are well-proven and well-known, such as oral body temperature, oven and furnace atmospheric temperature, temperature of well-stirred liquids, local air temperature, etc.
However, as any expert on these measurement situations will be able to explain, the temperature measurement uncertainty and the requirements of the sensor used can be very specific and non-obvious to an unskilled user.
However, each sensor type has its 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.
Selecting from among the many types of contact sensor sensors requires a certain knowledge of each prospective application requirements in terms of precision, acceptable measurement error, response time, and other application parameters, and then matching those requirements with the detailed properties of the candidate devices and possible required accessories.
Most of the limitations on contact sensor use are in situations where the sensor may be damaged or destroyed or the object of the measurement contaminated or its temperature distribution changed.
Types of Contact Temperature Sensors
* Thermocouples (TCs)
* Resistance Thermometers (RTDs PRTs, SPRTs)
* Liquid in Glass Thermometers (LIGs)
* Filled System Thermometers (Filled)
* Bimetallic Thermometers (Bimetals)
* Semiconductor Temperature Sensors (Semi, ICs)
* Labels, Crayons, Paints, Tabs (Phase Change Devices)