CAS Automation Specialist Instrumentation & Sensors Flashcards

What does the '4-20 mA' standard represent in industrial instrumentation?

Answer: A current loop signal range where 4 mA represents 0% and 20 mA represents 100% of span

The 4–20 mA current loop is the industry-standard analog signal where 4 mA = live zero (0% of range) and 20 mA = full scale (100%).

Which type of flowmeter measures flow by detecting the frequency of vortices shed by an obstruction in the flow stream?

Answer: Vortex flowmeter

A vortex flowmeter uses the von Kármán effect: vortices shed from a bluff body at a frequency proportional to flow velocity.

What is the primary advantage of a Coriolis mass flowmeter over a volumetric flowmeter?

Answer: It directly measures mass flow, independent of fluid density, temperature, or pressure

Coriolis meters measure mass flow directly by detecting the Coriolis force effect, making them independent of process conditions that affect density.

An RTD (Resistance Temperature Detector) operates on which physical principle?

Answer: The predictable change in electrical resistance of a metal with temperature

RTDs use the known, repeatable relationship between a metal's (typically platinum) electrical resistance and temperature.

In process instrumentation, what does the term 'rangeability' refer to?

Answer: The ratio of maximum to minimum flow that an instrument can measure accurately

Rangeability (or turndown ratio) is the ratio of the maximum to minimum measurable value within the instrument's specified accuracy.

Which pressure measurement term describes pressure referenced to absolute zero (perfect vacuum)?

Answer: Absolute pressure

Absolute pressure is measured relative to absolute zero pressure (perfect vacuum) and equals gauge pressure plus atmospheric pressure.