AMETEK 888 — Trend & Response Time Guide
Understanding analyzer dynamics helps differentiate real SRU process upsets from sample-system or analyzer issues. Use this as a technician quick reference.
Typical Response Characteristics
- Initial response: 30–60 seconds
- 90% response time (T90): 2–5 minutes
- Full stabilization: 5–10 minutes
Slower response usually indicates sample line fouling, sulfur condensation,
restrictions, or heater performance issues.
Normal Trend Behavior
- Smooth trend following SRU load changes
- No oscillation during steady operation
- Stable baseline after calibration
- Repeatable step response during verification gas checks
Quick check: If process is steady, the analyzer should also be steady.
Persistent drift in steady operation usually means contamination or temperature instability.
Abnormal Trend Patterns (What They Usually Mean)
- Flat line → sample blockage, probe plugging, flow loss, or signal hold
- Slow ramp → sulfur deposition, cold spot, restricted filter/line
- Noisy signal → grounding/shielding issue, unstable pressure/flow, detector contamination
- Sudden step change → likely real process upset (confirm with other plant tags)
- Saw-tooth / hunting → pressure hunting, regulator instability, switching valve issue
Field Checks When Response Is Slow
Temperature
Verify heat trace end-to-end. Check for cold fittings and exposed metal junctions.
Flow / Restrictions
Confirm stable sample flow. Inspect filters, probe, line restrictions, and DP increase.
Leaks / Dilution
Leak check sample system. Leaks can cause dilution and unstable readings.
Calibration Gas Test
Apply span gas and watch response speed. Slow response on span = sample system problem.