Compare the same quantity
The display may show mass flow while an output is assigned to volume, density or temperature. Review existing configuration records for variable, units, direction and instantaneous versus totalised quantity. kg/h and kg/min, or actual and standard volume, are not directly comparable. Time-stamp screenshots from both ends.
Review analog limits and scaling
For a 4–20 mA signal, check the transmitter's lower and upper limits and the PLC channel range. For example, if 4 mA represents 0 kg/h and 20 mA represents 1000 kg/h, 12 mA represents 500 kg/h. This illustrates linear scaling, not the site's configuration. Never assume 4 mA always means zero.
Review digital data definitions
For communications, use the correct model and firmware manual to check addresses, data types, byte/word order, units, multipliers and status bits. Do not copy register numbers from another model. Review analog fault output, communication loss and invalid-measurement status rather than treating an alarm value as normal flow.
- Compare sample timing, refresh rate and damping at both ends.
- Keep configuration, raw data and alarm records for an engineer.
Leave tests to authorised personnel
This page supports screen and document checks only. Loop tests, forced outputs, calibration, wiring changes and PLC program changes can affect control and interlocks; an engineer must follow site procedures. Cover opening, energised or pressurised work and hazardous-area tasks also require the applicable procedures. Do not change factors simply to make the values match.
