After a short holiday break, we’re finally back with the new part of the DAQ dictionary. This time, the R takes the whole article for itself. Enjoy the new page on your quest to learn more about data acquisition.
Ramp Voltage
A steadily rising voltage.
Range
The maximum and minimum allowable full-scale signal (input or output).
Reed Relay
Consists of two thin magnetic strips (reeds). When a coil close to the reeds is energized, they are magnetized and drawn together making a connection between leads attached to the reeds.
Relay
An electromechanical device that opens or closes contacts when a current is passed through a coil.
Relative Accuracy
How accurately a change in signal is measured.
Repeatability
The ability of an instrument to give the same reading under repeated identical conditions.
Reproducibility
The precision with which a measured value can be repeated.
Resistance Temperature Device (RTD)
Resistance temperature devices (or detectors) rely on the principle that the resistance of a metal increases with temperature. When made of platinum, they may be known as platinum resistance thermometers (PRTs).
Resolution
A measure of the smallest change that can be detected.
Response Time
The time a system takes to respond to a given input. For example the time between software sending a message to an instrument and the instrument sending a reply, or the time a sensor takes to indicate a change in conditions.
Rise Time
The time a signal takes to change from a specified low value to a specified high value. Usually measured as the time to rise from 10% to 90% of the step height or maximum amplitude, but sometimes over 5 to 95%.
RMS
Root mean square. The square root of the sum of the squares of a set of quantities divided by the total number of quantities. Used when monitoring AC (alternating current) signals. Many power supplies, for example, issue an AC signal. This needs to be converted to a dc (direct current) signal for the PC interface. The solution is a signal conditioning input that produces a dc signal proportional to the RMS of the amplitude of the input signal. The RMS operation means the reading will always be positive.
RTU
Remote Terminal Unit. A data acquisition device at a remote location which transmits data back to, and accepts commands from, a central PC (or another controller).
