Instrumentation Flashcards

A transmitter with a 0.1% accuracy specification on a 0-100 psi range has a maximum error of:

Answer: 0.1 psi

0.1% of full span (100 psi) = 0.1 psi maximum allowable error across the calibrated range.

What does 'turndown ratio' describe in flow measurement?

Answer: The ratio of maximum to minimum measurable flow with acceptable accuracy

Turndown (rangeability) is the ratio of the maximum flow the meter measures accurately to the minimum, e.g., 10:1 means it reads correctly from 10% to 100% of full scale.

In a PLC analog input module, a broken 4-20mA signal wire most commonly causes the reading to go to:

Answer: 0mA, triggering a below-range fault

An open circuit allows no current to flow (0mA), which falls below the live zero (4mA) and should trigger a wire-break alarm in the control system.

An ultrasonic level transmitter using the time-of-flight (TOF) method measures:

Answer: The reflection time of a sound pulse from the liquid surface

TOF ultrasonic sensors measure the time for an emitted pulse to travel to the liquid surface and return, then calculate distance using the speed of sound.

Which ISA instrument tag designation indicates a flow indicating controller?

Answer: FIC

Per ISA-5.1, F=Flow, I=Indicating, C=Controller, so FIC is a flow instrument that both displays the measured value and provides control output.

Intrinsically safe (IS) instrumentation limits electrical energy in hazardous areas to prevent ignition by:

Answer: Restricting voltage and current to levels below ignition thresholds

IS design ensures that under normal and fault conditions, the maximum spark energy available is insufficient to ignite the specified flammable atmosphere.

A deadband (dead zone) in a control instrument refers to:

Answer: The range of input signal over which output does not change

Deadband is the range through which the input can change without producing a change in output, used deliberately to prevent hunting in on/off controls.