Transducer: Thermistor & LDR

Transducers are devices that transform energy from one form to another. They are used in control systems, instrumentation and electronic communications.

Input transducers are transducers that change non-electrical energy to electrical energy. 
  Examples of such transducers are
  • Solar cells
  • Microphones
  • Thermistors
  • Light Dependent Resistors (LDR)
    •   

    Thermistor

    A thermistor is a device that has a resistance changes with temperature. When temperature increases, the resistance of thermistor decreases. Therefore, it can be used for temperature control.

    Vout = R⁄(R + RTH) X V

    Vout = RTH⁄(R + RTH) X V
    When temperature rises, what happen to Vout?
    When temperature rises,
    RTH decreases;
    Effective R decreases;
    Current increases as V = IR;
    Vout increases as Vout = IR    		 When temperature rises,
    RTH decreases;
    Effective R decreases;
    Current increases as V = IR;
    V1 increases as V1 = IR and R is a fixed resistor.
    Vout decreases as V1 + Vout = V
    It could be used to activate a fire alarm, if Vout rises above a certain threshold value. It could be used to switch on a heater, if Vout fall below a certain threshold value.

    LDR

    LDR is a device that has a resistance changes with light intensity (amount of light) shining on it. When light intensity increases, its resistance decreases.

    Vout = R⁄(R + RLDR) X V

    Vout = RLDR⁄(R + RLDR) X V
    When light intensity rises, what happen to Vout?
    When light intensity rises,
    RLDR decreases;
    Effective R decreases;
    Current increases as V = IR;
    Vout increases as Vout = IR    		 When light intensity rises,
    RLDR decreases;
    Effective R decreases;
    Current increases as V = IR;
    V1 increases as V1 = IR and R is a fixed resistor.
    Vout decreases as V1 + Vout = V
    It could be used to activate a burglar alarm, if Vout rises above a certain threshold value. It could be used to switch on the street lamp, if Vout fall below a certain threshold value.
    Excel@Physics