Instrumentation Flashcards
7 cards from real EETC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Instrumentation flashcards as text
What is the standard live zero signal range used in industrial 4-20mA current loops?
Answer: 4-20mA
The 4-20mA standard uses 4mA as the live zero, allowing detection of broken wires (which read 0mA, below the live zero).
A thermocouple produces a voltage based on which physical principle?
Answer: Seebeck effect
The Seebeck effect describes the generation of an EMF at the junction of two dissimilar metals exposed to a temperature difference.
An RTD (Resistance Temperature Detector) measures temperature by:
Answer: Changing resistance with temperature
RTDs exploit the predictable, repeatable increase in electrical resistance of metals (typically platinum) as temperature rises.
Which instrument measures the true RMS value of a non-sinusoidal AC waveform most accurately?
Answer: True RMS voltmeter
A true RMS meter computes the square root of the mean of the squared instantaneous values, correctly handling distorted waveforms.
In a differential pressure (DP) flow transmitter, flow rate is proportional to:
Answer: The square root of differential pressure
Bernoulli's equation relates flow velocity to the square root of pressure difference, so volumetric flow = K × √ΔP.
A loop-powered transmitter receives its operating power from:
Answer: The 4-20mA signal loop itself
Loop-powered (2-wire) transmitters draw their operating current (typically ≤3.6mA) from the same 4-20mA loop, requiring no separate power wiring.
What does the term 'span' refer to in instrument calibration?
Answer: The difference between upper and lower range values
Span is the algebraic difference between the upper range value (URV) and lower range value (LRV) of the calibrated range.