Variable resistance transducer
- 1. MECHANICAL VIBRATIONS VARIABLE RESISTANCE TRANSDUCERS BY, GAGAN.N
- 2. VARIABLE RESISTANCE TRANSDUCERS These are one of the most commonly used types of transducers, also called as resistive transducers or resistive sensors. It used for measuring various physical quantities like temperature, pressure, displacement, force, vibrations etc. These transducers are usually used as the secondary transducers, where the output from the primary mechanical transducer acts as the input for the variable resistance transducer. The output obtained from it is calibrated against the input quantity and it directly gives the value of the input. 9/30/2019 Dept. of MECHANICAL ENGINEERING MECHANICAL VIBRATIONS 2
- 3. PRINCIPLE OF WORKING The variable resistance transducer elements work on the principle that the resistance of the conductor is directly proportional to the length of the conductor and inversely proportional to the area of the conductor. Thus if L is the length of the conductor (in m) and A is its area (in m square), R its resistance (in ohms) is given by: R = ρL/A where ρ is called as resistivity of the material and it is constant for the materials and is measured in ohm-m The resistance of some materials also changes with the change in their temperature. This principle is primarily used for the measurement of temperature. 9/30/2019 Dept. of MECHANICAL ENGINEERING MECHANICAL VIBRATIONS 3
- 4. SOME EXAMPLES 1) Sliding contact devices: In this type there is a long conductor whose effective length is variable. One end of the conductor is fixed, while the position of the other end is decided by the slider or the brush that can move along the whole length of the conductor. The slider is connected to the body whose displacement is to be measured. When the body moves the slider also moves along the conductor so its effective length changes, due to which it resistance also changes. The effective resistance is measured as the resistance between the fixed position of the conductor and the position of the sliding contact. The value of the resistance is calibrated against the input quantity, whose value can be measured directly. One of most popular sliding contact type of variable resistance transducer is the potentiometer. These devices can be used to measured linear as well as angular displacement. 9/30/2019 Dept. of MECHANICAL ENGINEERING MECHANICAL VIBRATIONS 4
- 5. 2) Thermistors: Thermistors work on the principle that resistance of some materials changes with the change in their temperature. When the temperature of the material changes, its resistance changes and it can be measured easily and calibrated against the input quantity. The commonly used thermistors are made up of the ceramic like semiconducting materials such as oxides of manganese, nickel and cobalt. Thermistors can be used for the measurement of temperature, as electric power sensing devices and also as the controls for various processes. 9/30/2019 Dept. of MECHANICAL ENGINEERING MECHANICAL VIBRATIONS 5
- 6. 3) Thermocouple: The thermocouples work on the principle of Seeback effect, Peltier effect and Thomson effect. The voltage output from the thermocouple changes as its temperature changes or the temperature of the body in whose contact it is changes. The voltage output is calibrated against the temperature of the body that can be measured easily. Thermocouple is a very popular devise used for measurement of temperature. 9/30/2019 Dept. of MECHANICAL ENGINEERING MECHANICAL VIBRATIONS 6
- 7. REFERENCES Book: Mechanical Measurements by Thomas G. Beckwith and N. Lewis Buck https://www.brighthubengineering.com/hvac/53335- variable-resistance-transducers/ www.wikipedia.com 9/30/2019 Dept. of MECHANICAL ENGINEERING MECHANICAL VIBRATIONS 7
- 8. 9/30/2019 Dept. of MECHANICAL ENGINEERING MECHANICAL VIBRATIONS 8