Smart Absolute Pressure Transmitter with HART Protocol and 0.05% FS Accuracy

Process engineers lose hours every month chasing readings that drift with the weather. When a storm front moves in, atmospheric pressure drops and gauge-referenced instruments report a shift that never happened in the process itself. The QWY-320 smart absolute pressure transmitter eliminates this variable completely by referencing a sealed vacuum, so your distillation column, evaporation loop or vacuum furnace holds its set point no matter what the barometer says. With 0.05% FS accuracy, HART remote configuration and a backlit LCD, it is built for engineers who need trustworthy absolute pressure data they can act on without a second check.

Why Do You Need Absolute Pressure Measurement?

Think about the processes where the physical condition of the medium is defined by absolute pressure, not by the difference to the local atmosphere. Boiling point control is the clearest example: water boils at a lower temperature on a mountain than at sea level, and the same is true inside your reactor. If your instrument references the atmosphere, the reading changes with the weather, with plant altitude and with ventilation drafts, and your control loop compensates for errors that are not there. Vacuum furnaces, vapor recovery units, evaporators, freeze dryers and sealed-tank blanketing systems all share this problem. An absolute pressure transmitter gives every one of these applications a fixed reference point - a sealed vacuum - so the measurement means the same thing on Monday, in winter, and in a plant built at 2,000 meters altitude. When the process physics depend on true absolute pressure, or when stable readings regardless of weather are essential, absolute pressure measurement is not an option; it is the only correct basis for control.

Working Principle: A Sealed Vacuum Reference with Digital Intelligence

The QWY-320 measures pressure against a sealed vacuum reference inside a diffused silicon sensing element. Process pressure deflects the diaphragm on one side, while the other side is permanently exposed to the internal vacuum, so the output represents true absolute pressure. A precision ASIC linearizes and temperature-compensates the raw signal over the full operating range, then a 4-20 mA HART loop carries the value to your DCS or PLC. Because the reference is mechanical and sealed, there is no atmospheric vent to clog, no capillary to the outside world, and no barometric correction factor to calculate. The HART protocol lets you read the process variable, reconfigure range, and run diagnostics from the control room or a handheld communicator without opening the enclosure - which matters when the transmitter is mounted on a distillation column three stories up.

Structural Advantages of the QWY-320 Smart Absolute Pressure Transmitter

• Diffused silicon sensing cell with a laser-welded sealed vacuum reference chamber, free of mechanical wear
• Full 316L stainless steel wetted parts and housing, suitable for corrosive and humid process environments
• Onboard ASIC digital linearization and compensation from -40 to 125°C media temperature
• Backlit 5-digit LCD with local zero, span and damping adjustment for fast commissioning
• HART 4-20 mA output for remote re-ranging, loop diagnostics and multi-variable trending
• IP67 enclosure with cable gland and M12 connector options for outdoor and washdown duty
• Overload protection up to 3x rated range without calibration shift
• Compact 316L body with G1/2, 1/2 NPT and M20 x 1.5 process connections for retrofit flexibility

Pain Point Analysis: 4 Working Conditions Where Absolute Reference Wins

Application Case 1: Distillation Column Boiling Point Control

Application Case 2: Vacuum Furnace Process Monitoring

Eight Product Advantages of the QWY-320

1. 0.05% FS accuracy class for precision process control and custody-quality measurement
2. True sealed vacuum reference - no atmospheric vent, no barometric correction, no drift with weather
3. HART bidirectional communication for remote configuration, diagnostics and trending
4. Backlit LCD with local buttons for fast commissioning and maintenance without a communicator
5. ASIC digital temperature compensation across -40 to 125°C media temperature
6. 3x overload protection and high shock resistance for demanding process environments
7. IP67 sealed enclosure with M12 or cable gland options for outdoor and washdown duty
8. 24-month warranty with factory calibration certificate traceable to national standards

Technical Parameters

Why Choose Our Absolute Pressure Transmitter?

Qinwei Instruments is a Chinese manufacturer with over a decade of experience in industrial automation instruments, serving customers in more than 30 countries. Every QWY-320 leaves the factory with a 5-point calibration record traced to national standards, a helium leak check on the vacuum reference chamber, and a 48-hour burn-in under simulated process conditions. Our engineers support HART integration projects directly, from loop checklists to troubleshooting guides, and we keep spare sensors in stock for fast replacement. When you buy an absolute pressure transmitter from us, you are not buying a black box; you are buying a documented, tested instrument backed by a factory that answers the phone.

SEO FAQ

If your process condition is defined by true absolute pressure - such as boiling point control, vacuum monitoring, vapor pressure measurement or sealed tank blanketing - a gauge transmitter will show shifts whenever atmospheric pressure changes. On a distillation column, a passing storm front can look like a process upset, and your control loop will compensate for an error that does not exist. An absolute pressure transmitter references a sealed vacuum instead of the atmosphere, so the reading is identical in a coastal plant, a mountain plant, or during a thunderstorm. If you only need the difference between two pressures, gauge or differential instruments are fine. But if the physics of your process depend on absolute pressure, the absolute reference is not a luxury; it is the only measurement that means the same thing every day.

FS stands for full scale, so 0.05% FS on a 100 kPa absolute range means the maximum error is 0.05 kPa (50 Pa) across the calibrated span, including linearity, hysteresis and repeatability contributions. For a distillation column operating at 80 kPa absolute, that is enough resolution to hold boiling point within a fraction of a degree, which directly protects product purity and energy consumption. Compare this with typical gauge transmitters at 0.25-0.5% FS, and the difference explains why precision columns, research reactors and quality-critical vacuum processes specify high-accuracy absolute instruments. The QWY-320 achieves this with digital linearization and temperature compensation, and each unit ships with its own calibration certificate so you can verify the performance on arrival.

Yes. The QWY-320 supports the HART protocol over the same two wires that carry the 4-20 mA signal. From a HART handheld communicator, a USB modem, or a DCS with HART interface, you can read the live process variable, change the upper and lower range values, adjust damping, and run sensor diagnostics without opening the enclosure. This is a major advantage on tall columns, remote skids and hazardous-area installations where local access is difficult or requires a work permit. Remote re-ranging also means one spare transmitter can cover several ranges in your plant - you simply reconfigure it for the duty it is replacing, which reduces spare-parts inventory.

The vacuum reference chamber is laser-welded and helium leak tested before shipment, and the long-term stability specification is ±0.1% FS per year. In practice, the sealed reference in a diffused silicon cell holds its vacuum for the life of the instrument because there is no mechanical pump, valve or vent involved - nothing to wear, leak or clog. The dominant aging effect is the slow drift of the sensing diaphragm, which is why we specify annual re-calibration as good practice, exactly as you would for any precision pressure instrument. If a unit ever fails its annual check, the modular sensor design allows factory repair or replacement instead of scrapping the whole transmitter.

The QWY-320 is offered with G1/2, 1/2 NPT and M20 x 1.5 process threads as standard, with flange and custom adapters available for special installations. For electrical termination, choose between a cable gland with IP67 sealing, an M12 connector for quick disconnect, or a terminal block version for conduit wiring. The housing is 316L stainless steel with a sealed display window, so the instrument can be hosed down in washdown areas without concern. If you are retrofitting an existing installation, send us the current thread size and mounting arrangement, and we will confirm the correct configuration before you order.

Each transmitter is calibrated on a dead-weight tester and pressure comparator traceable to national standards, across five points in both ascending and descending directions. The calibration record, along with the helium leak test report and a 48-hour burn-in log, is included in the shipment documentation. We also provide a recommended re-calibration interval of 12 months and can supply NIST-traceable certificates on request for regulated industries. For OEM customers we support custom range marking, special tags and customer-specific calibration points, so the documentation matches your own quality system requirements.