Data Acquisition Systems

The acquisition chain is: sensor → signal conditioning → multiplexer → sample-and-hold → ADC → processor. The Nyquist criterion sets the minimum sampling rate at twice the highest signal frequency; an anti-aliasing low-pass filter removes components above f_s/2 before sampling.

ADC resolution is full-scale divided by 2ⁿ, so more bits give finer steps. The ideal signal-to-noise ratio is about 6.02n + 1.76 dB, improving 6 dB per added bit.

(avoid aliasing)

(ideal n-bit ADC)

Relation 1 —

(avoid aliasing)

Write this relation with symbols exactly as in A Course in Electrical & Electronic Measurements — AK Sawhney before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Relation 2 —

Write this relation with symbols exactly as in A Course in Electrical & Electronic Measurements — AK Sawhney before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Relation 3 —

(ideal n-bit ADC)

Write this relation with symbols exactly as in A Course in Electrical & Electronic Measurements — AK Sawhney before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Quantisation replaces the continuous signal with discrete levels; the maximum error is half the least-significant-bit (LSB) step. Increasing bits reduces this error but demands a more precise converter and reference.

A sample-and-hold freezes the input during conversion so the ADC sees a steady value; without it, a fast-changing signal would corrupt the conversion.

SCADA systems extend acquisition to remote sites, combining RTUs, communication links and a central master for monitoring and control of power and process plants.

State assumptions explicitly before using any relation for data acquisition systems — steady state, uniform properties, linear elastic material, ideal gas, incompressible flow, etc., as applicable.

Wrong assumptions invalidate the entire solution even when the formula is correct. In Instrumentation viva and GATE descriptive questions, listing valid assumptions often earns separate marks.

1. Read the question and list given data with SI units (common in Instrumentation papers).
2. Draw a neat labelled diagram where applicable — examiners in Indian universities award diagram marks even when arithmetic slips.
3. Identify which relation from this topic applies to data acquisition systems.
4. Use equation 1: .
5. Use equation 2: .
6. Substitute values, compute, and verify units and sign (direction).
7. State conclusion in one line — e.g. safe/unsafe, stable/unstable, feasible/infeasible.

Data Acquisition Systems appears in process control and labs. In Indian electrical curricula this topic is tested because it connects theory to measurement and transducers.

GATE and semester exams often combine data acquisition systems with earlier units — revise prerequisites before attempting mixed problems.

Industry interview panels sometimes ask: "Where did you use data acquisition systems?" — answer with a lab, mini-project, or plant visit example if possible.

• Sampling at exactly f_max instead of ≥ 2f_max (aliasing)
• Omitting the anti-aliasing filter before the ADC
• Using 2ⁿ⁻¹ for the number of levels (it is 2ⁿ)
• Forgetting the sample-and-hold for fast signals

Before attempting data acquisition systems problems, confirm you can:

1. Multiplexer, sample-and-hold, ADC, processor, display chain
2. Anti-aliasing filter before ADC
3. SCADA for remote monitoring and control

Revise the solved examples in A Course in Electrical & Electronic Measurements — AK Sawhney and one previous-year GATE or university paper for this unit.