Application

ScenariosA grain-export terminal running a Zone 21 flour-dust elevator had three VFD cubicles (ABB ACS880) inside a non-Ex-rated enclosure, protected by Ex p purging. The original PCU-02 boards were 12 years old, and the grain dust seasonal humidity swings (30% → 88% RH) were causing the pressure-transmitter 4–20 mA signal to drift at the terminal block — the PCU-02​ had no input-filtering, so every humidity spike threw a “Low Pressure / Purge Fail” and tripped the VFD cubicle mid-shipment, costing ~€8 K/hour in demurrage. The retrofit swapped to ABB PCU-03​ boards: the -03’s input-stage added a 20 ms moving-average filter on the 4–20 mA pressure channel, and the leakage-rate algorithm was tightened (the -02 tended to over-sensitive — a 0.5 mbar/min transient from a forklift door-slam would trip it; the -03 uses a 3-sample median + leak-integral, so the same transient is ignored). Post-cutover, purge-fail trips dropped from 4 per month to zero across harvest season, and the terminal standardized PCU-03​ across all seven grain-elevator cubicles. The E&I lead noted the PCU-03‘s front LED array (PURGE ACTIVE / LOW PRESS / LEAK / READY) made “which cubicle lost purge?” a 30-second walk instead of a DriveWindow session.

 

Parameter

Main Parameters	Value/Description
Product Model	ABB PCU-03​
Manufacturer	ABB
Product Category	Purging Control Board (Ex p / Ex px)
Target Enclosure	Analyzer house, VFD cubicle, paint-booth control panel, grain-elevator MCC
Supply Voltage	24 V DC (typical), some batches 100–240 V AC/DC dual-range — verify label
Pressure Input	4–20 mA (2-wire transmitter), typical range 0–100 mbar (scalable in config)
Pressure Setpoints	Low (alarm + trip), High (alarm), Purge-established threshold — all software/configurable
Purge Timer	Adjustable 0–999 min (based on enclosure volume ÷ purge flow per EN 60079-2)
Leakage Rate Monitor	Yes — calculates dP/dt post-purge; trip if > threshold (configurable)
Relay Outputs	4 × relay (typical config): Purge Active, Ready (power permit), Alarm, Trip (cut cubicle power) — ratings ~5 A @ 250 V AC
Digital Inputs	2–4 DI (door switch, flow-switch confirm, emergency override) — batch-dependent
Communication	Optional Modbus RTU (RS-485) on later batches; base version = relay-only + LED
Mounting	35 mm DIN rail (inside purged enclosure’s non-Ex compartment, or in separate safe-area panel)
Operating Temperature	-20 °C to +60 °C
Protection	IP20 (board itself); system rating depends on enclosure + purge design
Certifications	ATEX / IECEx (Ex p / Ex px, depending on system design cert — verify with ABB cert pack per project)
Dimensions (L×W×H)	Approx. 100 × 90 × 58 mm (standard DIN-rail width 6–8 TE)
Weight	Approx. 0.15–0.2 kg

 

 

Technical Principles and Innovative Values

• Innovation Point 1: EN 60079-2 Compliant Purge Timer + Leakage-Rate dP/dt.​ The PCU-03​ doesn’t just “watch pressure > setpoint” — it enforces the full Ex p sequence: (1) pre-purge (blow out accumulated gas/dust with high flow for N minutes), (2) establish pressure > P_est, (3) run-time monitor with leakage-rate integral. If dP/dt exceeds the configured threshold (e.g., 1 mbar/min), it assumes a cabinet breach or door-seal leak and trips the “Power Permit” relay — cutting non-Ex loads before the internal O₂/fuel mix hits ignition. The -03 refined the dP/dt algorithm vs. PCU-02 (median filter + integral window) to kill false trips from door-slam transients.
• Innovation Point 2: 4 Relay Outputs Covering the Full Safety Chain.​ The PCU-03​ typically spreads: Relay 1 = “Purge Active” (pilot lamp outside the cubicle), Relay 2 = “Ready / Power Permit” (holds the cubicle’s main contactor coil — ABB AF series — closed during valid purge), Relay 3 = “Alarm” (annunciator / BMS), Relay 4 = “Trip” (hard-cut cubicle 24 V / 120 V feed via a shunt-trip or contactor). This 4-relay spread means one PCU-03​ can supervise a small VFD cubicle withoutan external safety relay — the AF contactor + PCU-03​ is a self-contained Ex p node.
• Innovation Point 3: Drop-In Successor to PCU-02 with Input Filtering.​ The PCU-03​ keeps the same DIN-rail footprint, 24 V DC supply, 4–20 mA pressure-input pinout, and 4-relay spread as the PCU-02 — so a retrofit is “unrack old, rack new, carry forward the pressure-transmitter wiring and relay landing.” The gain is the input-stage filtering + leakage algorithm — no re-certification of the enclosure (the Ex p system cert is at the cabinetlevel, not the PCB level, provided the swap is PCU-02 → PCU-03 documented in the vendor’s migration note).

 

Application Cases and Industry ValueA petrochemical analyzer house (Zone 1, H2S + hydrocarbon vapor) running three process-gas chromatographs in a non-Ex cabinet protected by Ex p purge had chronic “false purge-fail” during Texas summer afternoons — the 4–20 mA pressure transducer (mounted in the cabinet sun-ward wall, 58 °C ambient) would drift the zero by ~0.8 mbar, and the old PCU-02’s fixed low-setpoint (5 mbar) would trip. The retrofit to ABB PCU-03​ did two things: (a) the -03’s input filter killed the 0.8 mbar zero-drift wander, and (b) the low-setpoint was re-configurable via the DIP/switch block (PCU-03批次 allows 2–10 mbar range, PCU-02 was fixed 5 mbar on some batches). They set low = 3.5 mbar, established = 8 mbar, leak-rate = 1.2 mbar/min. Post-cutover, zero purge-fail across a 110°F / 43 °C August. The plant E&I noted the PCU-03‘s “READY” relay (Relay 2) had cleaner drop-out timing — the GC autosampler no longer re-booted mid-run when a forklift door-slam caused a 0.5 mbar blip.