Job-readiness and assessment field guide
CCST practical 006 loop-current assessment: readiness checklist
Direct answer
The candidate can explain where current flows, choose a suitable measurement method, interpret live zero and locate an open, saturated or mis-scaled boundary.
Written for controls-technician candidates practicing safe, referenced current-loop diagnosis across transmitter and receiving input.
Role scope
Loop source, transmitter and receiver type, series current path, polarity, test point, expected range, live zero, fault current, input raw value and engineering scale.
Skills map
Physical stimulus through transmitter conversion, series loop current, receiving resistor or input electronics, raw data, quality and displayed value.
Core exercise
Known lower, middle and upper stimuli produce coherent current, raw counts and engineering units without interrupting the declared process boundary.
Stretch case
Open loop, short, reversed polarity, inadequate supply, 3.6 mA fault, 21 mA saturation, wrong meter mode, blown meter fuse and scale mismatch.
Troubleshooting
A stimulus, transmitter, supply, conductor, test method, receiver, raw value, quality or scale mismatch.
Portfolio evidence
The physical loop tested with approved procedures, exact device data and suitable traceable instruments.
How is current measured in a 4–20 mA loop?
Current is measured in series or with an approved loop-capable method, which may require opening the circuit; follow exact procedures and verify the meter setup first.
Why is 4 mA called a live zero?
It represents the configured lower-range value while leaving current below the normal range available to indicate some loop or instrument faults.