SCADA data acquisition requiring ±0.1% accuracy on 0-30V and 4-20mA channels, surrounded by VFDs and motor starters generating heavy electrical noise.
The Solution
Dual-channel analog front-end with software-selectable gain stages, galvanic isolation between the analog section and digital/comms side, and TVS-based transient protection rated for IEC 61000-4-5. Gain configuration is firmware-controlled, so the same board covers multiple signal ranges without hardware changes.
Results
Deployed across the client's SCADA system. False alarm rate dropped from several per week to near-zero once the isolation eliminated ground loop issues.
How the Isolation Is Arranged
Where the isolation sits. Everything that touches the field wiring, from transient protection through the gain stage and ADC, lives on the isolated side. Only data crosses the barrier, so noise currents from the drives and motor starters have no path through the measurement ground. That is what removed the ground loops behind the false alarms.Where the false alarms came from. With the analog ground shared with the plant, every drive that starts lifts the local ground by a few hundred millivolts, which a 4-20 mA input reads as a step in the process value, often enough to cross an alarm threshold. Isolating the front end from the digital and comms side breaks that loop, so the same drive starts leave the reading inside its ±0.1% accuracy.
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