# Characteristics of sensors and transducers

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

Let’s go through transducer characteristics that describe the performance of sensors.

One of the characteristics that describe the functional relationship between physical input and electrical output is the Transfer Function, which shows the relationship between the input and output signal. Depending on the details of this characteristic, it may be a complete description of sensor characteristics. The transfer function may be used as a calibration curve. For instance, let’s take an example of the infrared temperature sensor.

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

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

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

Another actual parameter is the Sensitivity of the transducer. This describes the relationship between input and output signals. Sensitivity is a ratio between a change in the electrical signal to a change of input physical signal. As mentioned above, temperature sensor sensitivity would be described in units Volts/Kelvin. High sensitivity would be when a 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 don’t return to the same value during cyclic changes of input (Units: % if FSO);

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.