Quick Checks (Do these first)

• Safety: confirm SRU area safety, permits, and isolation rules.
• Sample temperature: verify heater setpoint vs actual; check for cold spots.
• Sample flow: confirm flow indication; check restrictions.
• Leaks: check sample system for air ingress (especially at fittings/manifolds).
• Filters: check filter ΔP / condition; replace if fouled.
• Calibration gases: verify correct cylinder and regulator stability.

Symptom: Low / Zero Reading

• Check: sample flow low? filter clogged? probe plugged?
• Check: sample temperature low? condensation/sulfur dropout likely.
• Check: cal valve stuck in zero? manifold leakage?
• Likely cause: probe/line plugging, sulfur deposition, cold spot, valve fault.
• Fix: restore heat, clean/replace filters, verify blowback (if available), verify valves return to process.

Symptom: High Sulfur Reading / Sudden Step Change

• Check: validate with span gas (does it track expected value?).
• Check: process upset? compare SRU parameters and any redundant analyzer.
• Check: air leakage can bias reading depending on measurement method/config.
• Likely cause: real SRU upset, calibration drift, sample contamination.
• Fix: confirm calibration, inspect sample system, correlate with DCS trends.

Symptom: Unstable / Noisy Reading

• Check: sample pressure fluctuation (regulator hunting, restriction).
• Check: water/moisture ingress; confirm heater temps and drains.
• Check: grounding/shielding; inspect cable routing near VFD/motors.
• Likely cause: sample instability, moisture, electrical noise, detector contamination.
• Fix: stabilize pressure, correct heat, improve grounding/shielding, clean sample path.

Symptom: Slow Response / Sluggish Trend

• Check: long sample line, dead volume, partially plugged probe/filter.
• Check: sulfur deposition (common SRU) causing adsorption and delay.
• Likely cause: restrictions, cold spots, internal fouling.
• Fix: clean/replace probe and filters, eliminate cold spots, verify heater performance.

Symptom: Calibration Failure

• Check: correct gas cylinder + concentration? regulator stable?
• Check: cal line leaks? cal valve passing or stuck?
• Check: sample system still contaminated/sulfur dropout?
• Likely cause: wrong gas, leaking manifold, insufficient warm-up, sample contamination.
• Fix: verify cylinder, leak test manifold, restore proper temperature/flow, repeat calibration.

Symptom: Analyzer Offline / No Output

• Check: power supply, fuses, UPS, internal breaker.
• Check: I/O wiring to DCS (4–20 mA loop power, AO range, scaling).
• Check: network/Modbus settings if digital communication used.
• Likely cause: power fault, controller fault, loop wiring issue.
• Fix: restore power, verify loop, check configuration, reboot only after confirming stable utilities.

SRU Field Best Practices

Tail gas analyzers fail most often because of sample system design/maintenance. Use this guide to prevent recurring issues.