Understanding Zero Drift, Span Shift & Long-Term Stability and Differential Pressure Sensors

Pressure sensor accuracy isn’t determined only at the moment of calibration. Over days, weeks, or years, every pressure sensor experiences some degree of zero drift, span shift, and long-term stability changes, and the magnitude varies significantly depending on sensing principle and construction.

Validyne’s variable reluctance (VR) technology is inherently resistant to long-term drift because it relies on a solid metal diaphragm and an inductive circuit to sense pressure, rather than bonded strain gauge elements that can degrade over time.

This article explains what drift is, why it happens, how to minimize it, and why VR sensors excel in applications that demand stable, long-term performance.

1. What Is Zero Drift?

Zero drift occurs when a sensor’s output signal changes at zero applied differential pressure — in other words, the sensor reports a pressure change when none has occurred.

Causes of Zero Drift

• Mechanical stress from temperature changes
• Mechanical creep in bonded materials
• Hysteresis in strain gauge substrates
• Vibration and shock
• Residual stress in the diaphragm

Why VR Sensors Drift Less

VR sensors use a single-piece stainless steel diaphragm as the only moving part. Across its full pressure range, the diaphragm deflects only a few thousandths of an inch, and its position is sensed inductively — no mechanical linkages required. There are no epoxies, bonding agents, or elastic substrates that can deform or age. The result is extremely low zero shift, even after extended pressure cycling or exposure to harsh conditions.

2. What Is Span Shift?

Span shift refers to a change in a sensor’s output sensitivity — its gain — over time.

Example: A strain gauge sensor that originally outputs 50 mV at full scale might later output only 48 mV.

Causes of Span Shift in Strain Gauge Sensors

• Changes in strain gauge element resistance over time
• Temperature effects on strain gauge resistance
• Electronic component aging
• Mechanical wear on sensing element linkages

Why VR Sensors Hold Span Better

Because the sensing diaphragm is the only moving part, deflection is highly repeatable, and the inductive sensing circuit remains stable over time. VR sensors tend to hold their span better than strain gauge devices, especially in:

• High-line pressure / low differential pressure applications
• High-cycle applications
• High-vibration environments

3. Long-Term Stability: The Metric That Matters Most

Long-term stability reflects the cumulative effect of mechanical, thermal, and electrical drift over the life of a sensor.

Strain gauge sensors can drift significantly over years due to:

• Epoxy aging
• Strain gauge foil fatigue
• Cracking of protective layers
• Thermal cycling stress

VR sensors avoid these failure modes entirely.

How to Minimize Drift in Any Pressure Measurement System

1. Avoid unnecessary temperature cycling. Thermal shock is one of the primary contributors to drift in any sensor technology.

2. Use a proper signal conditioner. Validyne’s CD Series conditioners provide stable AC excitation and precision carrier demodulation. Because VR sensors typically produce five times the output signal of strain gauge-based sensors, less downstream gain is required, which means less amplification of any residual noise or drift.

3. Mount the sensor securely to avoid mechanical stress. Stress on the sensor housing can cause zero shift and amplify temperature effects.

4. Verify calibration regularly in demanding applications. All pressure sensors benefit from routine calibration checks, particularly in safety-critical or high-precision systems.

Zero drift, span shift, and long-term stability degradation are common challenges in pressure measurement, but not all sensor technologies are equally vulnerable. Validyne’s variable reluctance sensors are built around solid metal diaphragms and stable inductive circuits, making them exceptionally resistant to drift over time. For aerospace, medical, and industrial applications where measurement stability is critical, VR sensors offer a measurable and lasting advantage.