Injection Pressure / Servo Pressure Sensor Drift: How Often Should It Be Calibrated?

An LSR injection molding machine can run for months producing parts that still pass visual inspection, while the pressure sensors driving the process have already started drifting out of spec. This is one of the least visible failure modes in liquid silicone production — because unlike a mechanical breakdown, sensor drift doesn't stop the machine. It just quietly shifts the process window until parts start failing in ways that look, at first, like a material or mold problem instead of an instrumentation problem.

Why Pressure Sensor Accuracy Matters More in LSR Than in Standard Injection

LSR processing is more pressure-sensitive than many thermoplastic processes, for a few reasons:

• Shot sizes are often small and precision parts have tight tolerance for shear and fill balance, so a small pressure error has a proportionally larger effect on the finished part.

• Multi-cavity molds rely on consistent injection pressure to keep cavity-to-cavity fill balanced — sensor drift can push some cavities toward flash while others underfill, without any single obvious cause.

• Servo-driven feeding and injection systems depend on the pressure signal as a real-time control input, not just a readout. If the sensor's reported value drifts from the actual pressure, the machine's own closed-loop control is now compensating based on wrong information.

What Sensor Drift Actually Looks Like on the Production Floor

Because drift is gradual, it rarely announces itself. The more common pattern is a slow accumulation of symptoms that get blamed on other causes first:

• Gradual increase in flash or short-shots on the same mold and settings that used to run clean

• Inconsistent shot weight between cycles, even with material viscosity and mold temperature stable

• Cavity-to-cavity imbalance that appears over time on a mold that was previously well-balanced

• Rework or scrap rate creeping upward over weeks without a clear root cause in material or mold inspection

If any of these issues show up gradually rather than suddenly, sensor calibration should be checked early in the investigation — not after mold and material have already been ruled out.

A Practical Calibration Interval

There's no single universal number, because it depends on sensor type, duty cycle, and operating environment, but a reasonable framework looks like this:

• Routine scheduled calibration: most manufacturers recommend checking pressure sensor accuracy on a recurring interval — commonly every few months of continuous multi-shift operation — rather than waiting for a visible problem.

• Trigger-based calibration: calibration should also be checked immediately after any event that risks physical or thermal shock to the sensor — a mold crash, an overpressure event, or after major maintenance work near the injection unit.

• Cross-check against a known reference: periodic verification against a calibrated reference gauge, rather than only trusting the machine's own displayed value, is the only way to catch drift that the control system itself won't flag as an error.

• Document the trend, not just the pass/fail. Recording actual calibration readings over time — not just a pass/fail checkmark — makes it possible to see gradual drift coming before it crosses out of tolerance, and to plan sensor replacement proactively instead of reactively.

Questions to Ask an Equipment Supplier

When evaluating a machine or planning maintenance for one already in operation, it's worth asking directly:

• What sensor type and accuracy class does this machine use for injection and clamp pressure?

• What is the manufacturer's recommended calibration interval for continuous multi-shift use?

• Is calibration verification available as part of a service contract, and can it be done on-site or does the sensor need to be removed?

• How is calibration data logged — is there a record that shows drift trends over time, or only the current reading?

The Cost of Ignoring It

Pressure sensor drift rarely causes a dramatic failure. It causes a slow erosion of yield that's easy to misattribute to material lot variation or mold wear — both of which get investigated and ruled out before anyone checks the sensor itself. Building a routine calibration interval into preventive maintenance, rather than treating it as an afterthought, is one of the lowest-cost ways to protect consistent LSR part quality over the life of the machine.