Signal Conditioning Circuits

We know that signal conditioning is a process in which signals from different sensors are transferred into a form necessary to interface with other modules of system.

For example, we know that thermocouple produces very low output voltage and this voltage is not sufficient to operate the other controlling modules. Therefore there is need to amplify such signals. For this purpose we use different signal conditioning circuits. In case of thermocouple, we have to use amplifier, linearization circuits, etc. the purpose of using linearization circuits is that, thermocouple has non linear characteristics but in most of the cases we need linear controlling action.

Signal conditioning circuit
Measurement System Block Diagram

 

Signal Conditioning Circuits:

There are different types of signal conditioning operations such as amplification, filtering, isolation, linearization, excitation, etc. we will discuss all these operation one by one.

Amplification

We know that most of the sensors produce output in the form of change in resistance, voltage or current. All these parameters are having very low strength i.e. very small voltage in case of thermocouple, small change in resistance in case of RTD, etc. Therefore we have use current or voltage amplifiers in case of sensors which produces output in the form of current or voltage.

If the sensor produces output in the form of change in resistance (such as resistance thermometer) we have to use bridge amplifiers. We can make use of operational amplifiers to amplify the signal.

Filtering

Another important signal conditioning circuit is filter. As mentioned earlier most of the sensor produces very low output and therefore electromagnetic noise may get added in the original output. To remove the electromagnetic noise from sensor output we have to use different filter circuits. Filter circuits eliminates noise i.e. undesired frequency components from original signal without affecting it.

Active filters, passive filters, bypass filters are the common types of filter circuits.

Isolation

Isolation circuits are required to differentiate signals from unwanted common mode voltages. Another advantage of isolation circuit is that, it protects measuring devices (sensors) if high voltage is applied to other circuit. It also breaks ground loops.

Linearization

There are many sensors which produces non linear output such as thermocouple, thermistor, etc. linearization circuits are used to convert non linear signal into linear one. It can be achieved by varying the gain of an amplifier as a function of input signal.

Excitation

Another signal conditioning operation is current or voltage excitation. Signal conditioning circuits provide the required voltage or current excitation to some passive sensors such as strain gauge, RTD, etc.

In the upcoming posts we will see signal conditioning of RTD, thermistor and thermocouple.

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