Chip resistors are usually designed in a manner to allow for measurement of various properties such as temperature, strain, position, pressure and presence. A thick film is usually suited for the sensor applications and used in a variety of sensors as indicated below:
When temperature changes, the value of resistance for resistors also changes. The resistor value returns to normal once temperature also goes back to normal. Changes in temperature usually have two consequences on the level of resistance of the resistors. Firstly, an increase in temperature causes an increase in the cross-sectional area of the resistor wire as well as the length. In addition to that it affects the resistivity value of the material.
The coefficient of temperature is a property of the material used to look at the effects of temperature changes which are referred to as Temperature Coefficient Resistance (TCR) in this case. This is actually the fractional difference in the amount of resistance per degrees Celsius. An increase in temperature indicates a positive result with the TCR and a negative when the temperature lowers. Usually a low temperature coefficient is needed to maintain persistent values of resistance but sometimes Thermistors could be used to guarantee a larger resistor temperature coefficient making them useful I over-current protection.
Industrial resistors on the other hand are used in power generation and distribution applications such as load banks, dynamic braking resistors and grounding resistors among others. Many resistors manufacturers have come up with special types of resistors based on thick film technology which provide a high integration density required for high power dissipation in a particular area.
In this case, also the thick film resistor technology is applicable whereby pressure sensors with a high stability are used. The Thick Film Resistor network will remain stable without any considerable change in resistance even in cases of temperature cycling. A thick film resistor network that is appropriately designed is thus useful in a range of sensor applications. However the right experience in manufacturing and materials are required to come up with the best performance devices under various environmental stress conditions such as pressure.
Electrical resistance is most widely used characteristic that varies in proportion to the strain. Strain sensors can thus be formed from thick film resistors since the thick film structure can be made sensitive to strain causing resistance changes. The manufactured strain gauges would only change resistance when there is deformation of the surface to which the sensors are attached. The detected resistance however too depends with the stability of the metal, temperature, material properties and adhesive that bonds the surface with the gauges.
Temperature is a vital consideration as it causes a variety of effects such as the size of the object due to thermal expansion and consequently the resistance of the gauge and the connecting wires resulting to a misreading of the applied strain. Strain gauges are most likely to change with temperature variations thus changing resistance greatly too.