How to Calibrate Differential Pressure Sensors in Extreme Cold

Calibrating pressure sensors at very low temperatures — especially below -20°C — is a challenge for many manufacturers. Metals contract; mechanical stresses intensify causing traditional strain-gauge sensors to drift significantly.

Validyne’s VR-based differential pressure sensors behave differently. Our variable reluctance sensors are made from metals whose coefficients of thermal expansion and contraction are matched, minimizing stress during extreme temperature changes.  But even with VR advantages, extreme cold calibration requires specialized techniques

Here’s how it works, why it’s difficult, and best practices Validyne follows

Why Cold Calibration Is Difficult for Most Sensors

1. Different Material Contraction Rates Change Sensor Behavior

All metals contract at low temperatures. In strain-gauge sensors, this affects:

• Adhesives
• Bonded foil grids
• Backing materials
• Beam structures

Temperature changes lead to unpredictable offset shifts and result in pressure measurement errors.

With VR sensors, the only moving part is a solid metal diaphragm, with a thermal coefficient matched to the sensor body material so cold effects are far less drastic and more repeatable.

2. Oil Fill Fluids Become Viscous

MEMS and strain-gauge sensors often use silicone oil or gel behind their isolation membranes. At low temperatures, silicone oil viscosity changes dramatically, slowing dynamic response and increasing hysteresis.

Validyne VR sensors have no internal oil fill, so this issue does not exist.

3. Electronics Drift at Low Temperature

Amplifiers and signal conditioners drift when very cold. This can reduce the accuracy of the pressure readings.

Validyne minimizes this with stable AC excitation, temperature compensation and matched coil design.

How Validyne Performs Calibration at Low Temperatures

Step 1: Condition the Sensor for Temperature Equilibrium

A sensor must soak at the target temperature long enough for all the parts to reach thermal equilibrium.  This includes the sensor

• Diaphragm
• Body
• Coils
• Electronics

Validyne typically uses a 30-to-90-minute soak cycle depending on sensor size and mass.

Step 2: Apply Known Calibration Pressures Slowly

Rapid application of pressure at low temperatures can shock the diaphragm or cause transient offsets. Validyne applies pressure gradually to:

• Stabilize magnetic flux changes
• Reduce mechanical overshoot
• Ensure consistent diaphragm deflection

Step 3: Capture Both Upscale and Downscale Data

Cold can affect the downscale pressures differently than the upscale path. Validyne always captures complete calibration data:

• Increasing pressure
• Decreasing pressure

to fully characterize sensor linearity and cold hysteresis.

Step 4: Analyze Zero Shift and Span Shift Errors Independently

Cold effects are often more pronounced in zero shift errors. VR sensors typically:

• Hold span well
• Shift zero modestly
• Return to normal after temperature normalization

Best Practices for Customers

1. Avoid Applying Rapid Environmental Temperature Changes

Rapid Freeze → heat → freeze cycles can induce stress.

2. Recalibrate after extreme environmental testing

If a sensor has been cold soaked, recalibrate after returning to room temperature.

Conclusion

Calibrating differential pressure sensors for extreme cold can be difficult — but VR sensors offer significant advantages. Our solid metal diaphragms and sensor materials are thermally matched, have dry interiors, and stable A/C excitation circuits. VR sensors outperform oil-filled or strain-based sensors in extremely cold environments.

Validyne’s factory calibration process ensures accuracy and stability, even in the most demanding temperature conditions.