How 4–20 mA Scaling Works
Wanneer dit van toepassing is
Use this guide when loops read correctly at the transmitter but HMI numbers disagree because span and zero were never written down.
Te gebruiken tool
Browser-based preliminary check for Four Twenty MA Converter — fast estimates, not code or stamped design output.
Four Twenty MA Converter openen →Stappen
- 1Confirm whether 4 mA represents live zero or indicates fault depending on device policy.
- 2Define engineering value at 4 mA and at 20 mA for the measured variable.
- 3Solve linear relationship between mA and engineering units.
- 4Cross-check mid-scale points with a calibrator if disputes persist.
- 5Document alarm thresholds with the same scaling basis.
Voorbeelden
- Tank level 4 mA empty, 20 mA full.
- Pressure transmitter with elevated zero.
Vermijd dit
- Using raw mA in SCADA without engineering conversion.
- Confusing square-root relationships for orifice DP without configuring properly.
- Ignoring square-root extraction done inside the device vs in software.
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Veelgestelde vragen
HART digital values?
Digital PV may differ if secondary variables are addressed; verify which variable scales to mA.
Fault currents?
Some devices use <3.6 mA or >21 mA for fault; know your device.