Transducers A transducer is a device that converts energy from one form to another. Ex : (Oscilloscope, since it can be used for several types of measurements, force, acceleration, pressure, temperature,…..etc)

Transducers may be self-generating or externally powered which come with different types such as (capacitive , inductive , resistive) Most transducers fit into one of the following types: 1- Resistive changing: Light dependent resistor: resistance falls when increasing light level).

B)Thermister( resistance falls when increasing temperature) B)Thermister( resistance falls when increasing temperature). C) Strain gauge( resistance falls with force). D) Moisture detector( resistance falls when wet).

2- Self-generating. 3- Inductance changing. 4- Capacitive changing. Selection of Transducers: 1- sensitivity: must be as high enough for the resolution of the system. (S) 2- Range: (max , min).

3- Physical properties 4- Loading effect & distortion )energy use) 5- Electrical output format (be compatible). 6- Power. 7- Calibration. 8- Accuracy. 9- Cost.

Resistive Changing Transducers In this type resistance of the transducers is changeable to produce an electrical output. The resistance changing element is made part of a voltage divider. Vo=R1/(R1+R2)*Vin.

Type of Resistive Changing Transducers Resistive Temperature Detector (RTD) RT= Ro[1+α(T-To)]. Ro= RTD at a standard Temperature. To= Standard Temperature. T= RTD Temperature. α= Temperature coefficient.

B) Thermistor : This is more Sensitive to Temperature than RTD.

Self Generating Transducers Produce their own output voltage from external stimulus. (Motion,….) Common Types are magnetic induction Piezoelectric , photo, voltage device.

Magnetic- Induction Transducers: Here , any movement of the magnet with respect to the coil induces voltage across the coil.

Inductive Transducers They work on changing the magnetic path of an Inductor which is modified by the movement of an armature Located on the magnetic path. Here , by changing the force, the air gape length is changed ,and in return , causes a change in the inductance.

As an example , the linear transformer which is used for mechanical position measure. Notes: * A minimum output is obtained when the 2nd wining is perpendicular to the primary. Min Also , a maximum output is obtained when the 2nd winding is parallel with the primary. Max

One of the ways to measure the inductance change is to make the inductance transducers part of an unbalanced inductance bridge (Maxwell , Hay).

Capacitive transducers We knew C= Kεo A/d Where, K: dielectric constant εo: 8.854*10^-12 F/m d: distance between the plate area. A: overlapping plate area.

Since the capacitance is inversely proportional to the spacing between the two plates, any variation in (d) causes a corresponding variation in the capacitance. A forced Applied to a diaphram that function as one plate of a simple capacitor changes the distance between the (DF) and the static plat.

(sensitivity to temperature variation) The resultant change in C is usually measured with an oscillator circuit. The transducers as a part of the oscillating circuit , causes a change in the frequency of the oscillator. This change in frequency is a measure the magnitude of the applied force. The capacitive transducer has excellent frequency response. It’s disadvantages are (sensitivity to temperature variation)