CAS CAS Automation Specialist Instrumentation & Sensors

Question 1

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

Accepted Answer

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

Answer

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%).

Question 2

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

Accepted Answer

Vortex flowmeter

Answer

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

Question 3

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

Accepted Answer

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

Answer

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

Question 4

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

Accepted Answer

The predictable change in electrical resistance of a metal with temperature

Answer

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

Question 5

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

Accepted Answer

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

Answer

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

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