In the supercritical extraction business, temperature control accuracy directly affects batch consistency. Temperature probe drift is one of the most troublesome faults-it doesn't trigger an alarm, and the equipment looks perfectly normal, but product quality starts to fluctuate and yields swing up and down, and you can search for a long time without finding the cause. Put simply, this is a hidden fault that has to be judged from on-site experience.
1. Look at the Symptoms First: No Error, but Batches Start to "Drift"
Probe drift won't shut down the equipment directly or pop up a fault code. It behaves "mildly": with the same set of process parameters, the oil from this batch comes out with the wrong color, the next batch has a different yield, and the aroma is inconsistent. If operators only look at the screen, it's hard to spot anything abnormal. So whenever quality fluctuates or yield swings, don't just stare at the process parameters-check the temperature probes first.
2. Judgment Method: If the Three Temperatures Don't Match, There's Basically a Problem
On normal equipment, the displayed temperature on the screen, the actual vessel temperature, and the temperature measured by an infrared thermometer should not deviate by more than 1°C. If you take an infrared thermometer reading on site and the difference from the equipment display exceeds 2°C, the probe can basically be judged as drifting. There is also a typical symptom: when the equipment is shut down and left to stand at ambient temperature, the temperature readings at multiple points are inconsistent-this is also a common sign of drift. If it can't read accurately at ambient temperature, it will be even less reliable under pressure and heat.
3. Where Drift Comes From: Mostly Worn Down by Long-Term Operating Conditions
Probe drift is rarely a sudden failure; most of the time, sensing accuracy slowly degrades under long-term high pressure and alternating hot and cold conditions. The probe surface tends to accumulate oil, scale, or material build-up, which reduces sensing sensitivity and causes the data to lag and shift. Equipment vibration and aging wiring can also make readings inaccurate. These problems build up little by little, and if you don't pay attention in normal operation, you only find out when the product has a problem.
4. Don't Just Replace the Probe Right Away
For slight drift, you can first calibrate the temperature offset in the PLC backend to compensate for the deviation. If the deviation is too large and calibration doesn't work, remove the probe and clean the oil and fouling from its surface-many times it will recover after cleaning and reinstallation. If it is still inaccurate after cleaning and reinstallation, then consider replacing the probe. Don't replace it right away; calibrate first, then clean, and replace last-this order is more reliable.
5. Prevention: Calibrate Once a Month-More Cost-Effective Than Fixing After Problems Appear
It is recommended that the workshop calibrate all temperature probes once a month. Don't wait until product quality fluctuates to check them; avoid parameter drift in advance so that every batch maintains consistent processing. Only when temperature control is stable can batch consistency have a foundation.