Explosion-Protected Pressure Sensors
for Oil and Gas Applications

Reliable pressure measurement is essential in oil and gas production, chemical injection, pipeline operation, fluid storage and remote process control. In hazardous areas, however, pressure range and accuracy are only part of the selection process. Engineers must also consider the explosion-protection concept, hazardous-area classification, wetted materials, pressure reference, process connection, electrical output and operating temperature.

PRIGNITZ Mikrosystemtechnik provides intrinsically safe Ex i pressure transducers, flameproof Ex d pressure transducers and submersible Ex i level probes for different oil and gas measurement tasks. The appropriate product must always be selected according to the complete application conditions and the certification of the specific sensor configuration.

Why Pressure Measurement Matters in Hazardous Oil and Gas Areas

Pressure data can be used by a PLC (programmable logic controller), process controller, alarm system or safety system to monitor pumps, chemical injection lines, pipelines, storage systems and process equipment.

A pressure transducer does not independently prevent overpressure, leakage or dosing errors. It converts the measured pressure into an electrical signal that the control system can evaluate and use for alarms, control actions or shutdown logic.

Depending on the system design, pressure measurement can support:

· Detection of abnormal pressure conditions

· Monitoring of injection pump operation

· Identification of blocked or leaking process lines

· Monitoring of pipeline operating pressure

· Hydrostatic measurement of liquid levels

· Remote monitoring of oilfield process equipment

The pressure sensor must be selected for the expected normal pressure, possible pressure peaks, process medium, environmental conditions and required hazardous-area approval.

Intrinsically Safe Ex i and Flameproof Ex d Pressure Sensors

The term explosion-protected covers several protection concepts. Intrinsically safe Ex i and flameproof Ex d pressure transducers are not technically identical and should not be described as interchangeable.

Intrinsically Safe Ex i Pressure Transducers

Intrinsic safety limits the electrical energy available in the measurement circuit. The sensor must be operated as part of a correctly designed intrinsically safe circuit with the required associated equipment.

The intrinsically safe portfolio from PRIGNITZ Mikrosystemtechnik includes:

· PMP-S111-Exi and PMP-C111-Exi

· PMP-S122-Exi and PMP-C122-Exi

· PMP-S131-Exi and PMP-C131-Exi

These models cover low-pressure, medium-pressure and high-pressure applications. Depending on the selected electrical connection and certification, configurations are available for ATEX (EU equipment requirements for explosive atmospheres) and CSA (Canadian Standards Association) hazardous-area requirements.

View the complete range of intrinsically safe pressure transducers for hazardous areas.

Flameproof Ex d Pressure Transducers

A flameproof Ex d enclosure is designed so that an ignition inside the enclosure does not propagate into the surrounding hazardous atmosphere.

PRIGNITZ Mikrosystemtechnik offers the following flameproof pressure transducers:

· PMP-S122.04-ExD

· PMP-C122.04-ExD

The CSA-certified Ex d models are intended for high-pressure applications. The current certificate lists nominal pressure ranges from 10 to 900 bar, with maximum working pressure up to 1,000 bar depending on the pressure cell and product configuration. Wetted parts are stainless steel 316L.

The PMP-S122.04-ExD has an accuracy of approximately ±0.5% BFSL (best-fit straight line). The configurable PMP-C122.04-ExD provides accuracy better than 0.25% FS (full scale) and supports signal downscaling, zero adjustment and signal filtering through dedicated PC software.

Pressure Sensors for Chemical Injection Systems

Chemical injection systems introduce corrosion inhibitors, scale inhibitors and other treatment chemicals into oilfield and pipeline processes. These systems may operate with low flow rates but relatively high line pressures.

Pressure measurement can provide the control system with information about injection pump operation and pressure conditions in the dosing line. It can support the detection of abnormal pressure, a blocked line or loss of pressure, but the sensor does not regulate chemical flow by itself.

For applications between 4 and 1,000 bar, the PMP-S122-Exi and PMP-C122-Exi intrinsically safe pressure transducers can be considered.

PMP-S122-Exi

· Pressure range: 4 to 1,000 bar

· Accuracy at 25 °C: 0.5% FS or better

· Wetted parts: stainless steel 316L

· Pressure types: gauge and sealed reference

· Measurement principle: P2P technology

· Certification options: CSA, ATEX and EC79, depending on the configuration

PMP-C122-Exi

· Pressure range: 4 to 1,000 bar

· Accuracy at 25 °C: 0.25% FS or better

· Wetted parts: stainless steel 316L

· Pressure types: gauge and sealed reference

· Configurable signal downscaling, zero setting and signal filtering

· Certification options: CSA, ATEX and EC79, depending on the configuration

For installations requiring flameproof enclosure protection rather than intrinsic safety, PMP-S122.04-ExD and PMP-C122.04-ExD should be evaluated. The choice between Ex i and Ex d must be based on the hazardous-area concept of the complete installation, not only on the required pressure range.

Learn more about the P2P measuring technology used in this pressure sensor series.

Pipeline and Process Pressure Monitoring

Pipeline and process installations may require low-pressure, medium-pressure or high-pressure measurement. PRIGNITZ Mikrosystemtechnik offers three main Ex i pressure sensor groups for these requirements.

PMP-S131-Exi and PMP-C131-Exi for Low Pressure

The PMP-S131-Exi covers pressure ranges from 60 mbar to 10 bar. The configurable PMP-C131-Exi starts at 20 mbar and extends to 10 bar. Both product families use PMI (piezoresistive media-isolated) technology and are available for gauge, sealed-reference and absolute pressure measurement.

Learn more about PMI technology.

PMP-S122-Exi and PMP-C122-Exi for Medium and High Pressure

The 122 series covers pressure ranges from 4 to 1,000 bar. The stainless steel 316L measuring element and P2P construction are intended for high-pressure applications where mechanical robustness and stable measurement are required.

PMP-S111-Exi and PMP-C111-Exi for High Pressure and Fast Temperature Changes

The 111 series covers pressure ranges from 3 to 2,000 bar. These models use TFT (thin-film technology) and are positioned for high-pressure applications, rapid temperature changes and demanding process media. Gauge, sealed-reference and absolute pressure versions are available.

Learn more about TFT measuring technology.

Technical distinction: A pressure transducer measures pressure rather than flow. In a flow-control system, its signal may be combined with other measurements and control components, but the pressure transducer should not be described as a direct flow sensor.

Tank Level Measurement in Hazardous Areas

Hydrostatic level measurement determines liquid level from the pressure generated by the liquid column. For a permanently submerged installation, a dedicated level probe is generally more appropriate than a conventional threaded pressure transducer.

PRIGNITZ Mikrosystemtechnik offers the following intrinsically safe submersible level probes:

· PML-S111-Exi

· PML-S131-Exi

· PML-C111-Exi

· PML-C131-Exi

The standard hydrostatic ranges extend from 1 to 30 mH2O (metres of water column). The PML-S131-Exi and PML-C131-Exi use PMI technology with stainless steel 316L. The PML-S111-Exi and PML-C111-Exi use TFT technology with 17-4PH stainless steel.

The standard PML-S models have an accuracy of 0.5% FS or better at 25 °C. The configurable PML-C models provide an accuracy of 0.25% FS or better at 25 °C. The probes have IP68 ingress protection and use a PUR cable.

View the complete range of intrinsically safe level probes for hazardous areas.

Which PRIGNITZ Mikrosystemtechnik Sensor Fits the Application?

The table provides initial product-family orientation. It does not replace verification of the pressure range, medium compatibility, overload conditions, output signal, connection, certificate and complete order code.

Technical Characteristics of the Ex i Pressure Sensor Families

The PMP-Sxxx-Exi standard pressure transducers have an accuracy of 0.5% FS or better at 25 °C. The PMP-Cxxx-Exi configurable pressure transducers provide accuracy of 0.25% FS or better at 25 °C.

According to the family datasheets, both series provide:

· Ambient and medium temperature ranges from -40 to +85 °C

· Long-term stability of ±0.1% FS per year under reference conditions

· More than 10 million pressure cycles

· Vibration resistance of 20 g on three axes

· Multiple process and electrical connection options

· Current and voltage output options, depending on certification and configuration

Wetted materials vary by sensor technology and model. The PMP-S122-Exi, PMP-C122-Exi, PMP-S131-Exi and PMP-C131-Exi use stainless steel 316L as the standard wetted material. The family datasheets list stainless steel 304 for the wetted parts of the PMP-S111-Exi and PMP-C111-Exi, while the product pages specify a 17-4PH measuring membrane. Material compatibility must therefore be checked for the actual process medium and complete sensor construction.

Hazardous-Area Certification Must Match the Configuration

It is not technically correct to state that every Ex i pressure sensor configuration is approved for every Zone 0 application. For the PMP-Sxxx-Exi and PMP-Cxxx-Exi families, the certification marking depends partly on the electrical connection.

The family datasheets distinguish between:

· Selected metallic connectors with Class I, Zone 0 AEx ia IIC T4 Ga marking

· Other plugs and cables with Class I, Zone 1 AEx ia IIC T4 Gb marking

· Class I, Division 1 configurations for specified gas groups

· ATEX flange-plug configurations with II 1G Ex ia IIC T4 Ga

· Other ATEX connections with II 1G Ex ia IIB T4 Ga or II 2G Ex ia IIC T4 Gb

The exact product marking, certificate, installation instructions and intrinsic-safety parameters must be checked for the complete order code. The same principle applies to the PML Ex i level probes and the PMP-S122.04-ExD and PMP-C122.04-ExD flameproof transducers.

How to Select a Pressure Sensor for Oil and Gas

1. Hazardous-area classification. Specify the required zone, division, gas group, equipment protection level and certification system.

2. Pressure range. Define minimum, normal and maximum operating pressure. Include pressure peaks, pulsation, possible vacuum conditions and fault pressure.

3. Type of pressure. Determine whether the application requires gauge, sealed-reference or absolute pressure measurement.

4. Process medium. Identify the liquid or gas and verify compatibility with every wetted material.

5. Temperature. Specify both ambient temperature and process-medium temperature.

6. Output signal. Define whether the control system requires 4 to 20 mA, a voltage output or a ratiometric signal.

7. Process and electrical connections. Select connections according to the installation, mechanical load, sealing method and required hazardous-area certification.

8. Required accuracy. Distinguish between accuracy at room temperature and overall accuracy across the operating temperature range.

9. Installation method. Confirm whether the sensor will be threaded into a process connection, installed with a flameproof conduit system or submerged for hydrostatic level measurement.

10. Complete certification. Verify the certification of the exact ordered version rather than relying only on the general product-family name.

How to Select a Pressure Sensor for Oil and Gas

Are intrinsically safe and explosion-proof pressure sensors the same?

No. Intrinsically safe Ex i equipment limits electrical energy in the circuit. Flameproof Ex d equipment uses an enclosure designed to contain an internal ignition. The correct concept depends on the hazardous-area design of the installation.

Which PRIGNITZ Mikrosystemtechnik pressure sensor is suitable for chemical injection?

For operating ranges from 4 to 1,000 bar, PMP-S122-Exi and PMP-C122-Exi can be evaluated for intrinsically safe circuits. PMP-S122.04-ExD and PMP-C122.04-ExD can be evaluated where flameproof Ex d protection is required.

Which model is intended for low-pressure measurement?

PMP-S131-Exi covers ranges from 60 mbar to 10 bar. PMP-C131-Exi covers configurable ranges from 20 mbar to 10 bar.

Which model covers pressures above 1,000 bar?

PMP-S111-Exi and PMP-C111-Exi cover model-specific pressure ranges up to 2,000 bar.

Which product should be used for tank level measurement?

For submerged hydrostatic measurement, use the PML-S111-Exi, PML-S131-Exi, PML-C111-Exi or PML-C131-Exi level-probe families.

Are all Ex i configurations approved for Zone 0?

No. Zone approval can depend on the electrical connection, certification and complete product configuration. The exact marking and certificate must be checked before selection.

Related PRIGNITZ Mikrosystemtechnik solutions

The correct pressure or level sensor depends on the hazardous-area classification, operating pressure, process medium, temperature, output signal and required connections.

Explore the complete range of pressure sensors for hazardous areas or contact PRIGNITZ Mikrosystemtechnik with the technical parameters of your application.

Find out more information about our pressure sensors solutions here or contact our sales team info@prignitz-mst.de or call +49 (0) 38 77 5 67 46-0

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