Loading…
Skip to main content
Engineering Toolbox/Loop Source vs Readback Error

Instrumentation & Calibration

Loop Source vs Readback Error

Check a sourced 4–20 mA signal against either measured loop current or the engineering-unit value displayed by an HMI, DCS or PLC.

Loop-check data

Source a known signal with approved test equipment and record the actual receiving-end indication.

mA
mA
±% span

Loop-check use

Verify the receiving end, not just the source.

A known mA source can verify the analog input path and scaling through the receiving system. Use the engineering-value mode when the control-system display is what operators actually depend on.

Interpretation

A mismatch can originate from the test setup, wiring, loop resistance, analog input card, scaling/configuration, transmitter output trim or another part of the signal chain. This calculator quantifies the mismatch; it does not assign the root cause.

Engineering readback error (% span) = (Actual readback − Expected readback) / |URV − LRV| × 100

Continue in Instrumentation & Calibration

View category →
4–20 mA Signal Scaling Convert loop current to percentage of span and engineering units, or calculate the expected mA from a process value. 3–15 psi Pneumatic Signal Convert a standard pneumatic control signal between psi and percentage output without hiding underrange or overrange conditions. Five-Point Calibration Check Evaluate 0, 25, 50, 75 and 100% points against a defined tolerance in percentage of calibrated span. Calibration Error Calculate signed error in engineering units and percentage of span, with a clear pass/fail result against tolerance.