Accuracy is the lifeline of industrial flow and pressure measurement. If your readings are "walking," it is likely due to one of these two culprits:
A response to environmental or process temperature fluctuations.
Mechanism: Expansion or contraction of internal fill fluids and electronic components.
Behavior: Temporary. Accuracy usually returns once the temperature stabilizes.
Mechanical degradation caused by repeated stress cycles.
Mechanism: The metal sensing diaphragm loses its elasticity due to overpressure or constant pulsing.
Behavior: Permanent offset. This is a physical failure of the hardware.
| Feature | Thermal Drift | Diaphragm Fatigue |
| Primary Cause | Temp fluctuations | Pressure spikes / Constant cycling |
| Impact | Fluctuating readings | Consistent offset |
| Reversibility | Reversible | Permanent |
| Fix | Heat siphons / Compensation | Replacement / Better material selection |
The frequency of a "Zero-trim" depends on the criticality of your process:
High-Precision Processes: Every 3 to 6 months.
Standard Applications: Annually during routine maintenance.
Mandatory Events: 24 hours after initial installation, after a significant overpressure event, or during major seasonal temperature shifts.
Q: Does Zero-trim affect the Span of the transmitter?
A: No. It shifts the entire curve up or down without altering the sensitivity (slope).
Q: Why is my new transmitter showing a non-zero value at atmospheric pressure?
A: This is often "Mounting Position Effect." Gravity acting on the internal oil can cause a small offset that requires a Zero-trim upon installation.
