Highly Stable Absolute Pressure Transmitter for Vacuum-Referenced Process Measurement

Some processes do not care what the weather is doing. Absolute pressure measurement references a perfect vacuum instead of the local atmosphere, so barometric changes, altitude and ventilation effects never distort the reading. The QWY-305 delivers this stability with ±0.1%FS accuracy and rugged 316L construction for the processes that demand it.

Why Do You Need Absolute Pressure Measurement?

Gauge pressure readings change with the weather: when a storm front moves in, atmospheric pressure drops, and a gauge pressure transmitter shows a shift even though the process has not changed. For most applications this is acceptable, but for others it is not. Vapor pressure measurement, boiling point control in distillation and evaporation, vacuum furnace monitoring, and processes where the absolute pressure defines the physical condition of the medium all require a reference that never moves. Absolute pressure transmitters reference a sealed vacuum, so the reading is identical in a mountain plant, a coastal plant or a storm. When the process physics depend on true absolute pressure, or when stable readings regardless of weather are essential, an absolute pressure transmitter is the correct instrument.

Working Principle: A Sealed Vacuum Reference

The QWY-305 measures pressure relative to a sealed vacuum reference inside the sensing element, rather than relative to the atmosphere. Process pressure acts on one side of the sensing diaphragm while the other side is exposed to the internal vacuum, so the output represents the true absolute pressure of the process. This design makes the measurement completely independent of atmospheric pressure changes, altitude and ventilation. The sensing element delivers ±0.1%FS accuracy with high stability over time, and the signal is conditioned for standard 24 V DC loop power with consumption below 0.5 W. The medium temperature capability of -50 to +120 °C and the IP65-protected housing make it suitable for demanding industrial environments.

Structural Advantages of the QWY-305

• Sealed vacuum reference: readings unaffected by barometric pressure or altitude.
• ±0.1%FS accuracy: precise absolute pressure values for critical processes.
• High stability: dependable readings over long service intervals.
• Medium temperature -50 to +120 °C: handles hot and cold process media.
• 316L stainless steel construction: corrosion-resistant wetted parts.
• IP65 protection: dust-tight and water-jet protected enclosure.
• Low power consumption below 0.5 W: economical loop-powered operation.
• 24-month warranty: long-term reliability commitment.

Pain Point Analysis: 4 Challenging Working Conditions

Application Cases

Product Advantages

• Sealed vacuum reference for weather-independent readings
• ±0.1%FS high accuracy
• High long-term stability
• Medium temperature range -50 to +120 °C
• 316L stainless steel wetted parts
• IP65 dust-tight, water-jet protected enclosure
• Low power consumption below 0.5 W at 24 V DC
• 1/4" NPT and 1/8" NPT process connections
• Gauge, absolute and differential type options
• 24-month warranty with manufacturer support

Technical Parameters

SEO FAQ

Q1: What is the difference between absolute and gauge pressure?

Absolute pressure is measured relative to a perfect vacuum, while gauge pressure is measured relative to the local atmospheric pressure. A gauge pressure transmitter has a vented reference open to the atmosphere, so its reading changes when barometric pressure changes, even if the process is unchanged. An absolute pressure transmitter has a sealed vacuum reference, so its reading is independent of atmospheric pressure, altitude and weather. Absolute pressure is the physically meaningful value for processes such as vapor pressure, boiling point and vacuum control. The QWY-305 uses a sealed vacuum reference to deliver stable, weather-independent absolute pressure readings.

Q2: Why does barometric pressure affect gauge readings but not absolute readings?

A gauge transmitter measures the difference between the process pressure and the atmosphere, so any change in atmospheric pressure appears directly in the reading. When a weather front passes and the barometer drops by 30 mbar, a gauge transmitter will show a 30 mbar shift for an unchanged process. An absolute transmitter measures against a sealed vacuum, which never changes, so atmospheric variations have no effect on the reading. This makes absolute measurement essential where stability matters: vapor pressure monitoring, distillation control, vacuum processes and any application where readings must be comparable across different days, seasons, altitudes and locations.

Q3: What is the accuracy of the QWY-305?

The QWY-305 offers an accuracy of ±0.1%FS, meaning the measured value deviates from the true absolute pressure by no more than 0.1% of the calibrated span. This high accuracy, combined with the stability of the sealed vacuum reference, makes the transmitter suitable for demanding applications such as distillation control, vacuum furnace monitoring and vapor pressure measurement, where small errors affect product quality or process efficiency. Each unit is factory-calibrated at multiple points across the absolute pressure range, and calibration data can be supplied on request. For critical applications, the high accuracy provides a dependable foundation for control and documentation.

Q4: What medium temperatures can the transmitter handle?

The QWY-305 is rated for medium temperatures from -50 °C to +120 °C, covering both cold media such as refrigerants and cryogenic fluids at the low end, and hot media such as steam, hot process liquids and vapors at the high end. This wide range is achieved through careful material selection and thermal design that maintain accuracy and protect the sensing element across the temperature span. For processes with media temperatures beyond this range, a remote diaphragm seal arrangement can be considered to isolate the transmitter from extreme temperatures. Please specify your media and temperature when ordering so the correct configuration is supplied.

Q5: What is the IP65 protection rating?

IP65 is an ingress protection rating defined by IEC 60529. The digit 6 means the enclosure is completely protected against dust, and the digit 5 means it is protected against water jets from any direction. This makes the QWY-305 suitable for outdoor installations, washdown areas and dusty industrial environments where moisture and particulates would damage less-protected instruments. The sealed housing protects the electronics and the internal vacuum reference, ensuring stable operation through rain, hose-down cleaning and dusty atmospheres. For installations requiring temporary immersion protection, please discuss your requirements with our engineers, as higher-rated options may be available.

Q6: How is the transmitter installed?

Install the QWY-305 at the process point using the 1/4" NPT or 1/8" NPT process connection, with an isolation valve for maintenance access. Mount the transmitter so that the diaphragm is not exposed to sediment buildup: in liquid service, mount below the tap so bubbles rise away, and in gas or vapor service, mount above the tap so condensate drains back. Use a short impulse line to minimize lag and avoid liquid traps in vapor service. Wire the 24 V DC loop supply and output according to the terminal diagram, observing polarity, and secure the cable with a drip loop below the connection point.

Q7: What output signal does the transmitter provide?

The QWY-305 provides a standard 4-20 mA two-wire output, with the current proportional to the absolute pressure across the calibrated range. The 4 mA point represents the low end of the absolute range and 20 mA the high end, so the signal connects directly to PLC analog inputs, DCS systems, controllers and displays without converters. Two-wire loop-powered operation at 24 V DC with less than 0.5 W consumption means the same pair of wires carries both power and signal, simplifying wiring and reducing installation cost. This universal output format makes the transmitter easy to integrate into new and existing control systems.

Q8: Can the transmitter also measure gauge or differential pressure?

Yes. The QWY-305 platform supports gauge, absolute and differential pressure measurement types, and the transmitter is configured for the required type at the factory. The absolute configuration uses the sealed vacuum reference described above; the gauge configuration uses a vented atmospheric reference for conventional gauge measurement; and the differential configuration measures the difference between two process connections. This flexibility allows the same instrument family to serve different measurement tasks across a plant, simplifying spares, training and documentation. Specify your required pressure type and range when ordering.

Q9: How stable is the transmitter over time?

The QWY-305 is designed for high stability, which is essential in absolute pressure service where even small drift can affect process control. The sealed vacuum reference is inherently stable because it does not depend on external conditions, and the sensing element and electronics are engineered to minimize drift over time and temperature. In practice, the transmitter holds its calibrated accuracy for extended periods, with recalibration needed only at normal maintenance intervals. For quality-critical and safety-related applications, an annual verification against a reference standard is recommended to document performance and maintain compliance.

Q10: What warranty and support do you provide?

The QWY-305 is covered by a 24-month warranty against manufacturing defects under normal operating conditions. As the manufacturer, we provide direct technical support including application engineering, installation guidance and troubleshooting assistance. OEM and ODM services are available, such as custom absolute ranges, custom output mapping, connection options, labeling and packaging, with a monthly supply capacity of 100 pieces and delivery within 5-8 working days. Calibration certificates and test data can be provided with each order. Contact us with your absolute pressure range and process details for a quotation.

Why Choose Our Absolute Pressure Transmitter?

When the process physics depend on true absolute pressure, you need a transmitter that references a vacuum, not the weather. The QWY-305 delivers ±0.1%FS accuracy, high stability, a -50 to +120 °C medium capability and IP65 protection in a rugged 316L package, all backed by a 24-month warranty and direct manufacturer support. Whether it is a distillation column, an evaporator, a vacuum furnace or a test bench, the QWY-305 gives you absolute pressure data you can trust, in any weather, at any altitude. Choose the QWY-305 for measurement that never moves with the barometer.