Classification and Handling of Common Faults in Differential Pressure Transmitters
Taking the cost-effective E+H model PMD55B as an example, this article introduces common faults of differential pressure transmitters and their handling methods. Mastering these fault types helps quickly troubleshoot problems on site and reduce downtime.
Wiring Faults
When a wiring fault occurs, the instrument usually shows abnormal display, such as the screen not lighting up. At this time, the transmitter housing can be opened to check whether there is a short circuit or open circuit in the wiring.
- Check whether the power supply is normal
- Check whether the signal wires are reversed or loose
- Check whether the terminal blocks have water ingress or oxidation
Variable-Frequency Interference
During wiring, mutual interference among multiple signal lines and the influence of variable-frequency drives can cause abnormal data transmission. When subjected to variable-frequency signal interference, measurement accuracy and stability will decrease.
- Avoid routing signal cables parallel to power cables during installation and wiring
- Wiring should not be too densely packed; maintain sufficient spacing
- Use shielded cables with single-end grounding when necessary
Impulse Piping Faults
Impulse piping faults are generally divided into three types: blockage, leakage, and liquid accumulation, and they are a high-incidence link in on-site faults of differential pressure transmitters.
| Fault Type | Main Cause | Impact |
|---|---|---|
| Impulse piping blockage | Failure to drain in time; medium is dirty and viscous | Distorted differential pressure transmission and large measurement deviation |
| Impulse piping leakage | Too many accessories such as joints and shut-off valves, resulting in many leakage points | Pressure loss and zero drift |
| Liquid accumulation in impulse piping | Unreasonable gas pressure tapping method or incorrect installation | Contact with liquid affects accuracy and causes inaccurate measurement |
Typical Applications of Differential Pressure Transmitters
Differential pressure transmitters are widely used in industrial sites, mainly for flow measurement and level measurement. A correct understanding of their principles helps with selection and commissioning.
Flow Measurement
Differential pressure transmitters can be used for flow measurement and metering, and they are simple and reliable. Their principle is to install a throttling device in the pipeline through which the fluid passes. When the fluid flows through, a differential pressure is generated, and the magnitude of the differential pressure is related to the flow rate.
- Commonly used throttling devices: orifice plates and Venturi tubes
- Combined with differential pressure flowmeters to achieve flow measurement
- Suitable for various media such as gas, liquid, and steam
Level Measurement
Differential pressure transmitters can also be used for level detection. For example, the PMD78B can perform level measurement by measuring the static pressure at the bottom and converting it into liquid level height.
Installation Requirements for Differential Pressure Transmitters
Installation quality directly affects measurement accuracy and long-term stability. The impulse piping on the high-pressure side of the sensor is led to the three-valve manifold and connected to the high-pressure chamber of the differential pressure transmitter, while the low-pressure side is connected to the low-pressure chamber. The installation position is related to the measured medium, and the following requirements should be comprehensively considered.
- Prevent the transmitter from direct contact with corrosive or overheated media.
- Prevent sediment from depositing and blocking the impulse piping.
- The lengths on both sides of the impulse piping and the liquid column heads should be kept consistent.
Following the above installation requirements can effectively reduce impulse piping faults and measurement errors and extend the service life of the transmitter.