Characteristics of sensors and transducers

Sensor ir transducer is a device which converts one type of energy to another – usually electric. They are used for various purposes including measurement or information transfer. Generally speaking sensor or transducer is a device that converts a signal from one to another.

Lets go through transducer characteristics that describe a performance of sensors.

One of characteristics, that describes the functional relationship between physical input and electrical output is Transfer Function Transfer function is a graph that shows relationship between the input and output signal. Depending details of this characteristic it may be a complete description of sensor characteristics. Transfer function may be used as a calibration curve. For instance lets take an example of infrared temperature sensor.

 

IR_Transducer.jpg

Its transfer function can be represented as 3D function of a thermal radiation. It is because sensor is affected by two temperatures: Tb – absolute temperature of object and Ts – Absolute temperature of transducer sensor surface. Then output Voltage:

V=G(Tb4-Ts4), where G- constant. Then we can represent transfer function in 3D space:

 

3D transfer function of a thermal radiation sensor.jpg

Another characteristic is Dynamic Range of sensor. This term defines the input signal that can be converted to electrical. Signals outside the range may cause large inaccuracy. Dynamic Range of transducer is typically defined by manufacturer with other characteristics as well.

Another actual parameter is Sensitivity of transducer. This describes the relationship between input and output signals. Sensitivity is a ration between change in electrical signal to a change of input physical signal. As mentioned above temperature sensors sensitivity would be described in units Volts/Kelvin. High sensitivity would be when small temperature change would result in a large voltage change.

Other characteristics that are used are:

Accuracy – the largest expected error between actual and ideal output signals(Units: % if FSO(Full Scale Output));

Hysteresis – when sensors doesn’t return to the same value during cyclic changes of input (Units: % if FSO);

 

hysteresis_transducer.JPG

Linearity – a deviation from linear transfer function over dynamic range;

Noise – output noise that adds to output signal;

Resolution – minimal detectable signal fluctuation.

Bandwidth – defines a response time to a instant change of physical signal.

 

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