Overview
Data acquisition computer boards:
- Are self-contained printed circuit boards (PCBs) that plug into backplanes and motherboards, or interface directly with computer buses.
- Receive multiple electrical or electronic inputs from devices such as sensors and translate analog data into a digital format that computers can process.
- Are an integral part of data acquisition systems (DAQ) for monitoring, analyzing, and /or controlling systems and processes. These devices include random access memory (RAM) and may include software that supports real-time graphing, mathematical functions such as averaging, and statistical calculations such as deviation.
Inputs
Data acquisition computer boards can receive:
- AC voltage
- DC voltage
- AC current
- DC current
- charges from piezoelectric devices
- frequency inputs
Data acquisition printed circuit boards (PCBs) work with:
- accelerometers
- thermocouples
- thermistors
- resistance temperature detectors (RTDs)
- strain gauges
- linear rotary and variable differential transformers (LVDTs and RVDTs)
Data acquisition computer boards may also receive specialized inputs from:
- encoders
- tachometers
- timers
- relays
Outputs
Data acquisition computer boards may also output :
- voltage (e.g., 0 – 10 VDC)
- current loops (e.g., 0 – 20 mA)
- frequencies (e.g., AM or FM)
- timer, counter, relay, and resistance signals
Analog-to-Digital Conversion (ADC)
There are several types of analog-to-digital converters (ADC) for data acquisition computer boards. They include:
- Flash ADCs apply the input in parallel to many fast comparators whose thresholds are spaced equally throughout a range of input voltages.
- Half-flash ADCs (combine the results of two sequentially performed, lower-resolution flash conversions to determine the output code).
- Integrator ADCs (provide an output code that represents the average value of the input voltage over a time interval)
- Successive approximation ADCs (sequentially compare a series of binary-weighted values with an analog input to produce an digital output in a series of steps.)
- Voltage-to-frequency ADCs (convert an input voltage to an output pulse train with a frequency proportional to the input voltage.)
- Delta-sigma circuits (sample at a rate and frequency that pushes the quantization noise out of range.)
Filtering
Data acquisition computer boards provide filtering that allow for myriad functions. Types include:
- integral
- multi-pole
- analog
- digital filters
Some devices DAQ boards provide:
- programmable filters
- anti-aliasing filters (that include a low pass cutoff frequency and a high pass cutoff frequency)
Filter types include:
- Bessel (do not provide a relatively fast response or roll-off)
- Butterworth (do not provide a relatively fast response or roll-off)
- Cauer (provide a relatively fast response or roll-off)
- Chebyshev (provide a relatively fast response or roll-off)
- linear phase (preserve the phase characteristics of a signal by time-delaying the signal components equally)
Some data acquisition computer boards include an integral amplifier with programmable gain and a variable bandwidth.
Bus Types and Networking
Data acquisition computer boards work with virtually all computer bus types:
- universal serial bus (USB)
- peripheral component interconnect (PCI) and PCI Express
- industry standard architecture (ISA)
Supported network topologies include:
- Ethernet
- DeviceNet
- smart distributed system (SDS)
Applications
Data acquisition computer boards are common in the following applications:
- environmental
- vehicular
- marine
- aerospace
- military
- seismic
- meteorological applications.
- medical imaging and other biomedical applications
