4-20 mA Signal Helper - Linear Scaling With Review Prompts

How It Works

1. Enter Configured Range

   Input the lower range value (LRV), upper range value (URV), and engineering unit from the live transmitter, DCS/PLC, or loop documentation. The app does not verify that the entered range matches the field device.

2. Select Action

   Choose direct action when 4 mA maps to LRV and 20 mA maps to URV. Choose reverse action only when the actual configuration maps 4 mA to URV and 20 mA to LRV.

3. Enter One Known Value

   Enter either a measured mA value to screen the process value, or a process value to screen the mA value. Values outside the configured span are shown as extrapolated local prompts.

4. Review Status Prompts

   Use the loop-status band as a review prompt. NE43-style thresholds, transmitter fail direction, input-card alarms, filtering, and diagnostics must be confirmed from source data.

5. Carry Source Gaps Forward

   Before calibration, adjustment, repair, proof test, or process action, reconcile device configuration, loop power, barriers, calibrated references, procedure, permits, bypass state, and qualified review.

Built For

• Instrument technicians screening linear 4-20 mA math before opening the device manual or procedure
• Controls engineers checking draft PLC or DCS scaling values against a local arithmetic prompt
• Maintenance techs documenting which configuration, loop-power, alarm, and measurement gaps still need source review
• Operators converting a known mA value to a process-value prompt without treating it as a field diagnosis
• Commissioning teams building a preliminary five-point scaling table before formal loop checks
• Reliability engineers preserving NE43 and input-card alarm settings as explicit source gaps
• Apprentice instrument techs learning linear live-zero math with calibration boundaries visible

Features & Capabilities

Bidirectional Linear Conversion

Convert from process value to mA or from mA to process value for a user-entered linear range. Reverse action is handled as a source-visible setting.

Scaling Tables

Build five-point and 5% linear scaling tables for the entered LRV, URV, unit, and action.

NE43-Style Review Prompts

Surface local bands around 3.6/3.8 mA and 20.5/21.0 mA while warning that actual alarm interpretation belongs to transmitter and input-card source data.

Source Warnings

Keep configuration, square-root extraction, HART mapping, loop power, barriers, measurement uncertainty, LOTO, permits, and qualified-review gaps visible.

Exportable Report

Export the entered range, local result, scaling table, warnings, assumptions, source pointers, and residual gaps for review records.

Assumptions

• User-entered LRV and URV match the active transmitter, input-card, or controller scaling configuration.
• The screen uses linear 4.0-20.0 mA arithmetic only.
• Reverse action is user-selected and not verified against live configuration.
• NE43-style bands are review prompts, not final alarm approval.
• Loop-power, HART, barriers, grounding, intrinsic safety, and calibrated-reference details are outside the local arithmetic.

Limitations

• Does not validate transmitter configuration, range, trim, damping, fail direction, or alarm settings.
• Does not support square-root extraction, flow cutoff, segmented-linear, or polynomial characterization.
• Does not calculate HART digital overlay data or verify communication margin.
• Does not diagnose wiring faults, ground loops, shielding, barriers, burden, or electromagnetic interference.
• Does not approve calibration, loop checkout, SIS proof testing, hazardous-location work, LOTO, bypassing, or process operation.

References

• IEC 60381-1 - Analogue Signals for Process Control Systems, Part 1: Direct Current Signals.
• ANSI/ISA-50.00.01 - Compatibility of Analog Signals for Electronic Industrial Process Instruments.
• NAMUR NE 43 - Standardization of the Signal Level for the Failure Information of Digital Transmitters.
• ISA-51.1 - Process Instrumentation Terminology.

Frequently Asked Questions