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 primary purpose of a signal isolator in an instrumentation loop?
Answer: To break ground loops and provide electrical isolation between circuits
Isolators break conductive paths between circuits, eliminating ground loop currents that would otherwise cause measurement offset or noise.
A vortex flow meter operates on the principle that vortices shed by a bluff body occur at a frequency that is:
Answer: Proportional to fluid velocity
The Strouhal number relates vortex-shedding frequency to fluid velocity and bluff-body width: f = St × V / d, making frequency a direct velocity indicator.
During a field calibration of a pressure transmitter, 'zero suppression' means:
Answer: Raising the lower range value above zero so the 4mA point is above zero
Zero suppression sets the 4mA (LRV) point above zero, such as calibrating 50-150 psig, so the instrument ignores pressure below 50 psig.
What does SIL (Safety Integrity Level) classify in process instrumentation?
Answer: The reliability level required for a safety function to reduce risk
SIL (defined in IEC 61511) quantifies the required probability of failure on demand (PFD) for a safety instrumented function to reduce process risk to tolerable levels.
A magnetic (electromagnetic) flow meter requires the process fluid to be:
Answer: Electrically conductive (minimum ~5 µS/cm)
Mag meters induce a voltage in the flowing fluid per Faraday's law, which requires the fluid to be conductive enough to complete the circuit between the electrodes.
In process control, hysteresis in a control valve causes problems because:
Answer: The valve position lags behind the controller signal, causing control offsets
Hysteresis (stiction and backlash) means the valve does not move until the signal overcomes internal friction, creating a dead zone and limit cycling in control loops.
What is the function of a thermowell in temperature measurement installations?
Answer: To protect the temperature sensor from process pressure, flow, and corrosion
A thermowell is a closed-end tube inserted into the process that allows the temperature sensor to be installed, removed, or replaced without shutting down or depressurizing the process.