Essential components of a DAQ system

A data acquisition system (DAQ) measures real-world physical quantities and converts them into digital data for a computer to process, display and store.

Block diagram

 Physical   +--------+  +------------+  +-----+  +-----+
 quantity ->| Sensor |->| Signal     |->| MUX |->| S/H |->
 (temp,     |/Transd.|  | conditioner|  +-----+  +-----+
 pressure)  +--------+  +------------+
        +-----+     +-----------------+     +--------------------+
     -> | ADC |---> | Computer / uP   |---> | Display, storage,  |
        +-----+     | + DAQ software  |     | network, printer   |
                    +--------+--------+     +--------------------+
                             | DAC / digital out -> Actuator (control)

Essential components

1. Sensors/transducers: convert physical quantity to electrical signal (thermocouple, strain gauge, LDR).
2. Signal conditioning: amplification, filtering (anti-aliasing), isolation, linearisation, excitation, cold-junction compensation, level shifting.
3. Multiplexer: selects one of several channels for one ADC.
4. Sample and hold: keeps the input stable during conversion.
5. ADC: converts the analog signal into digital form (resolution, speed chosen from signal bandwidth).
6. Computer / microprocessor / DAQ card: timing and control, processing, and the bus interface (USB, PCI).
7. Software: drivers, acquisition, analysis, display (LabVIEW, MATLAB).
8. Storage and display units, and optional DAC/actuator outputs for control.
9. Power supply and clock/timing.