MAINTENANCE | ENGINEERING |What is Sensor Drift?

DEFINITION OF DRIFT:

Sensor drift is a gradual deviation in the output signal of a transducer from the true pressure value, even though the actual process pressure remains constant

Example:

If a transducer is calibrated so that 0 psi = 4 mA, over time it might read 4.2 mA at 0 psi (indicating false pressure). That small shift can lead to hundreds of psi error at higher pressures.

Causes of Sensor Drift in Melt Pressure Applications:

1. High Temperature Effects

   • Continuous exposure to 300–400 °C (typical melt extrusion) can cause strain gauge material fatigue or changes in electrical resistance.

   • Improper cooling (in food lines or coextrusion setups) accelerates this.

2. Thermal Cycling

   • Frequent heating and cooling of the barrel causes mechanical stress on the diaphragm and internal sensing element.

3. Overpressure or Pressure Spikes

   • Short bursts above rated capacity can cause permanent deformation of the diaphragm → false baseline shift.

4. Material Build-up / Residue

   • Residual polymer or food material can harden around the diaphragm, causing false pressure readings as the sensor is effectively “preloaded.”

5. Electrical Factors

   • Cable degradation, EMI/RFI noise, or poor grounding can mimic drift.

6. Aging of Sensor Components

   • Long-term use causes changes in strain gauge bonding, insulation resistance, or electronic circuitry.

How to Avoid or Minimize Sensor Drift

1. Correct Installation

   • Mount sensors in clean, properly machined ports.

   • Use recommended torque (too loose = leak, too tight = damage).

2. Temperature Management

   • Use flexible capillary or cooling jackets to isolate electronics from heat.

   • Avoid cold-start calibration (always calibrate at operating temperature).

3. Regular Calibration Checks

   • Zero check daily/weekly (especially after cleaning).

   • Full calibration quarterly or semi-annual to correct for gradual drift.

4. Avoid Overpressure

   • Use rupture disks / pressure limit alarms to protect against spikes.

5. Cleaning Practices

   • Never use sharp metal tools to clean mounting holes.

   • Use brass or copper cleaning tools that won’t deform the diaphragm.

6. Proper Sensor Selection

   • Choose sensors rated for higher continuous temperature and pressure than your normal operation.

   • For food → use models with flush diaphragms to reduce build-up.

7. Electrical Maintenance

   • Use shielded cables, proper grounding, and inspect connectors routinely.

TAKEAWAYS: Sensor drift is essentially the “creep” of the pressure baseline due to heat, stress, material build-up, or aging. You can’t eliminate drift completely, but with correct installation, preventive calibration, temperature isolation, and proper cleaning, drift can be minimized and controlled.

NNS Team Use : Think.... #Cleaning Tools #Correct Sensor Selection #Protective Diaphragms #Routine Sensor Checks #Planned Sensor Replacement Scheduling

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