Solution: Types of Signal Conditioning in DAQ Systems

Signal conditioning prepares a sensor signal for accurate measurement and ADC conversion.

1. Amplification

Weak sensor outputs are increased to a suitable voltage range.

$$V_{out}=G V_{in}$$

Operational amplifiers and instrumentation amplifiers are commonly used.

2. Filtering

Filters remove unwanted frequency components and noise.

• Low-pass: removes high-frequency noise.
• High-pass: removes unwanted low-frequency/DC components.
• Band-pass: passes a selected frequency band.
• Notch: rejects a narrow interfering frequency such as 50/60 Hz.

3. Isolation

Electrical isolation prevents unwanted current paths and protects the measurement system. Isolation amplifiers and opto-isolators are common methods.

4. Linearization

Some sensors have nonlinear input-output characteristics. Linearization converts the response into a more convenient relationship, either using analog circuits or software.

5. Level Shifting and Scaling

The signal is shifted or scaled to match the ADC input range. For example, a 0–100 mV sensor can be amplified to 0–5 V.

6. Excitation

Resistive and bridge-type sensors may require a stable excitation voltage or current before their output can be measured.

7. Signal Conversion

A conditioning stage may convert one signal form to another, such as current-to-voltage conversion for a 4–20 mA transmitter.

8. Sample-and-Hold / Anti-Aliasing

A sample-and-hold circuit maintains the signal during conversion, while an analog anti-aliasing filter limits frequencies above the useful measurement bandwidth.

Conclusion

The major conditioning functions are amplification, filtering, isolation, linearization, scaling, excitation and signal conversion. Proper conditioning improves signal-to-noise ratio, ADC utilization, accuracy and reliability.