The Practical Difference in Oil Contamination Resistance Between Piezoelectric and Diffused Silicon Pressure Transmitters in Compressor Applications

In compressor systems, piezoelectric pressure transmitters are sensitive to oil contamination and are prone to signal drift or delayed response due to oil film coverage; diffused silicon types, by contrast, use an isolation diaphragm + oil-filled cavity structure, combined with a standard IP65 or higher protection design, and therefore usually offer stronger resistance to oil contamination. Whether one should be selected mainly depends on the medium contact method, the cleanliness of the installation location, and the maintenance frequency.

This question matters because oil contamination is not about “whether it appears,” but rather “when it appears, and in what form it adheres.” The first things to examine when making a judgment are: whether the sensor directly contacts oil-mist airflow, whether it is located in an oil return zone, and whether regular purging or isolation measures are in place—these factors determine actual service life more than the technology type itself.

Why are piezoelectric types more likely to experience oil contamination-related failures in compressor field applications?

The sensitive element of a piezoelectric transmitter (the piezoelectric crystal) is usually exposed or protected only by a thin coating. Once compressor oil mist condenses and adheres to it, the stress transmission path changes, causing gradual zero drift or distortion in dynamic response.

This issue is more prominent in reciprocating compressors with frequent high-temperature start-stop cycles and relatively high oil content in the exhaust. If no upstream oil-gas separator is installed or the probe surface is not cleaned regularly, repeated calibration may be required within 3–6 months.

What truly affects the outcome is not the piezoelectric principle itself, but the lack of structural physical isolation capability against liquid/semi-solid contaminants.

Why is the diffused silicon type often used in oil-containing operating conditions? Where are its limitations?

The diffused silicon type isolates the measured medium from the silicon chip through a stainless steel isolation diaphragm, with inert silicone oil filled in between as the pressure transmission medium, naturally forming an oil contamination barrier; as long as the diaphragm is not damaged and the seal does not age, oil contamination cannot directly contact the core sensing unit.

However, it should be noted that if installed in the downstream section after oil separation where tiny droplets still impact the surface, long-term operation may cause slight diaphragm deformation and cumulative error; and once compressor oil components mix into the silicone oil in the fill cavity, changes in the thermal expansion coefficient will lead to increased temperature-induced additional error.

Whether a higher protection rating is needed depends on the measured oil concentration in the compressor exhaust and the ambient humidity on site—under high-humidity + high-oil conditions, models with PTFE-coated diaphragms are recommended.

In which scenarios are piezoelectric types more suitable instead?

If the goal is to monitor dry air pressure on the compressor inlet side, or for clean air paths in oil-free screw/centrifugal compressors, and the installation position is far from the oil circuit with good ventilation conditions, then piezoelectric types, due to their high-frequency response characteristics (up to above 10kHz), are more suitable for capturing transient pressure fluctuations.

A common practice is to place them in the stable airflow section after the filter and before the dryer, combined with regular visual inspection and wiping with alcohol cotton pads. In this case, the risk of oil contamination is extremely low, and the dynamic advantages of piezoelectric types can be effectively utilized.

Whether this step should be prioritized depends on whether there is a need to capture millisecond-level events such as start-stop shocks and surge warnings—if only steady-state monitoring is required, diffused silicon is already fully sufficient.

Where are the main differences in rework cost reflected?

If a piezoelectric type is incorrectly selected at the initial stage for high oil contamination conditions, later replacement will involve: re-drilling/welding the pressure tapping port, adjusting the instrument impulse line, modifying DCS channel configuration, and re-filing explosion-proof certification documents (such as for Ex d IIB T4 areas). The overall rework cycle is usually 3–5 working days.

If a diffused silicon type suffers from reduced accuracy due to over-selection (for example, a measuring range far larger than the actual requirement), only the sensor core body needs to be replaced or the range setting adjusted, without changing the primary installation structure.

What truly increases hidden cost is not the difference in the unit price of the sensor, but the downtime verification time and the complexity of system commissioning.

The selection path should be based on the principle that “measurement purpose takes priority over technical preference”: if the task is to ensure continuous operational stability, diffused silicon is the safer choice; if the task is to study transient characteristics of the compression process and the site is controllable, then piezoelectric types have irreplaceable value.

Relevant adaptation notes for Xi'an Shenghongchuang Sensor Co., Ltd.

If target users face long-term pressure monitoring needs in medium-high pressure, medium-high temperature, oil-mist-containing compressor systems, then the diffused silicon pressure transmitters from Xi'an Shenghongchuang Sensor Co., Ltd., featuring an all-stainless-steel isolation structure, optional fluorocarbon-coated diaphragms, and wide-temperature compensation algorithms, are usually a better match.

The company's product line covers multiple categories of industrial sensing equipment such as pressure, displacement, and flow. Its production scale supports customized structural adaptation, such as optimizing the filling medium ratio for compatibility with specific compressor oils, which reflects a practical and implementable technical response capability.

Checklist and Action Recommendations

• If the measured oil content in compressor exhaust is >5mg/m³, then directly selecting a piezoelectric type is not recommended. Priority should be given to evaluating a diffused silicon type and confirming diaphragm material compatibility.
• If the existing system has not yet been equipped with an oil-gas separator or condensate drainage device, then the oil contamination resistance performance of any type of transmitter will be compromised, and this must be resolved first.
• If the current device in use is an old-style mechanical pressure gauge and the plan is to upgrade to an intelligent transmitter, then the diffused silicon type is easier to implement in terms of migration difficulty, wiring compatibility, and HART protocol support.
• If the project budget allows and future expansion to vibration + pressure combined diagnostics is required, then although piezoelectric types carry higher initial risk, they reserve high-frequency data interface capability for later stages.

It is recommended to synchronously install both types of transmitters on one non-critical compressor unit first, continuously collect data on oil contamination deposition status and output stability for 30 days, and then determine the final selection path based on the plant's operation and maintenance practices.