Signal Conditioning

Table of Contents

Signal conditioning is a process of data acquisition, and an instrument called a signal conditioner is used to perform this process.
Data acquisition is the process of sampling signals that measure real world physical conditions and converting the resulting samples into digital numeric values that can be manipulated by a computer.
Signal conditioning is a process of data acquisition, and an instrument called a signal conditioner is used to perform this process.
This instrument converts one type of electrical or mechanical signal (input-signal) into another (output-signal).

Need of Signal Conditioning

The purpose is to amplify and convert this signal into an easy to read and compatible form for data-acquisition or machine-control.
A signal conditioner helps to provide precise measurements, which are essential for accurate data acquisition and machine-control. These instruments can perform an additional number of different functions.

Amplification increases a voltage signal to a level suitable for digitization by the DAQ equipment. Typically a data acquisition device is calibrated for input voltages in the 0 to 10 V range. A small voltage, such as that coming from a thermocouple or strain gauge bridge may need to be amplified 1000 times to make it between 0 and 10 V.
If your signal is larger than the maximum input range then you will have to divide the signal down using a resistor network.

Many transducers, like strain gauges and RTDs (resistance temperature devices), need a power supply. The signal from these transducers is either a voltage or a mA current. For many transducers the supply will be low voltage DC, but for transducers based on capacitance measurement an AC supply may be required.
The information needed includes voltage range and current requirements, and for AC excitation voltages, the frequency used.
Excitation is commonly needed for measuring force, pressure, relative humidity, temperature, level, light level, concentration and vibration.

Linearization is needed when the signals produced by a sensor don’t have a straight-line relationship with the physical measurement, as is the case when using thermocouples to measure temperature.
Linearization is sometimes achieved using signal conditioning.

Filtering reduces noise errors in the signal.
For most applications a low-pass filter is used. This allows through the lower frequency components but attenuates the higher frequencies.
The cut-off frequency must be compatible with the frequencies present in the actual signal (as opposed to possible contamination by noise) and the sampling rate used for the A-D conversion.

A high transient voltage at one input may damage not only the input circuit, but an also propagate to other equipment connected to that input.
You can prevent this type of damage by providing isolation between inputs.

Certain types of transducer have a very high output impedance and are not able to supply enough current to use a normal voltage input.
When connected to a normal amplifier, the currents drawn from the transducer can seriously distort the input signal.
Typically glass electrodes used to measure pH, or gas concentration probes, are of this type.
You should connect them to a voltage measuring circuit with a very high input impedance.