CAS Automation Specialist Instrumentation & Sensors Flashcards

What is the primary limitation of a thermocouple compared to an RTD for temperature measurement?

Answer: Thermocouples require a reference junction and have lower accuracy than RTDs

Thermocouples require cold junction (reference) compensation and typically have lower accuracy and repeatability than RTDs.

In a differential pressure (DP) transmitter used for level measurement, what does an increase in DP typically indicate?

Answer: An increase in liquid level

In a DP level transmitter, higher hydrostatic head from more liquid increases the differential pressure reading, indicating higher level.

What does HART (Highway Addressable Remote Transducer) protocol allow that a standard 4–20 mA loop does not?

Answer: Two-way digital communication superimposed on the 4–20 mA signal

HART superimposes a digital FSK signal on the 4–20 mA analog current, enabling configuration, diagnostics, and additional variables.

Which type of level sensor uses guided microwave pulses along a probe to measure liquid level?

Answer: Guided Wave Radar (GWR)

Guided Wave Radar (GWR) sends TDR (Time Domain Reflectometry) microwave pulses along a probe; the reflection time indicates the level.

In an orifice plate flow measurement system, the relationship between differential pressure (ΔP) and volumetric flow rate (Q) follows which relationship?

Answer: Q is proportional to the square root of ΔP

For an orifice plate, Q ∝ √ΔP (derived from Bernoulli's principle), meaning flow varies with the square root of differential pressure.

What is the purpose of a 'two-wire transmitter' configuration in process instrumentation?

Answer: To carry both power and the 4–20 mA signal on the same pair of wires

A two-wire transmitter draws its operating power from the loop current (4–20 mA), eliminating the need for a separate power supply cable.