How 4–20 mA Scaling Works
該当する場合
Use this guide when loops read correctly at the transmitter but HMI numbers disagree because span and zero were never written down.
使うツール
Browser-based preliminary check for Four Twenty MA Converter — fast estimates, not code or stamped design output.
Four Twenty MA Converter を開く →手順
- 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.
例
- Tank level 4 mA empty, 20 mA full.
- Pressure transmitter with elevated zero.
避けること
- 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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よくある質問
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.