Explosion Proof Absolute Pressure Transmitter Ex d IIC T6 for Hazardous Areas

In a plant that handles flammable gas, the instrument itself can become the ignition source. That is why the QWY-321 absolute pressure transmitter is built inside a flameproof Ex d IIC T6 enclosure: the housing contains any internal explosion and cools the flame path before it can reach the surrounding atmosphere. It gives safety engineers a vacuum-referenced absolute pressure measurement that does not drift with barometric changes, in a package certified for Zone 1 and Zone 2 hazardous areas. For offshore platforms, gas processing, chemical plants and hydrogen systems, this is the instrument that lets the control room trust the number without trusting the environment.

Why Do You Need Absolute Pressure Measurement in Hazardous Areas?

Hazardous-area processes are full of applications where absolute pressure is the physically correct measurement basis. Gas blanketing systems on storage tanks must hold a precise absolute pressure to prevent air ingress; vacuum distillation columns need true vapor pressure readings to protect both product quality and safe operation; flare and vapor recovery systems monitor absolute vacuum to avoid pulling air into a flammable stream. A gauge-referenced transmitter adds a second problem on top of the process problem: its vent to atmosphere can become blocked by ice, paint or debris, and its reading wanders with every weather front. On a remote wellhead or offshore platform, nobody wants to climb out to re-verify an instrument because the barometer moved. The QWY-321 removes the atmospheric vent entirely, giving a sealed vacuum reference that needs no maintenance and no correction, while the flameproof enclosure keeps the whole assembly safe in the classified area.

Working Principle: Flameproof Enclosure, Sealed Vacuum Reference

The QWY-321 combines two independent safety and measurement systems. Inside, a diffused silicon sensing element measures process pressure against a laser-welded sealed vacuum reference, so the 4-20 mA HART output represents true absolute pressure with no vent to the atmosphere. Around it, a die-cast aluminum alloy enclosure with an Ex d flameproof joint contains any potential ignition: flame paths are machined to certified gap and length tolerances, and the tempered glass window and cable entries are all part of the certified assembly. If an internal fault ever ignites gas inside the housing, the flame is cooled below ignition temperature before it exits, and the surrounding explosive atmosphere never ignites. The HART signal lets operators re-range and run diagnostics from the safe area, which means the enclosure rarely needs to be opened at all.

Structural Advantages of the QWY-321 Explosion Proof Absolute Pressure Transmitter

• Ex d IIC T6 flameproof certification for Zone 1 and Zone 2 gas groups IIA, IIB and IIC
• Sealed vacuum reference - no atmospheric vent to block, clog or freeze in outdoor service
• Heavy-wall die-cast aluminum enclosure with epoxy coating for offshore-grade corrosion resistance
• Certified cable entry options (3/4 NPT, M20 x 1.5) with Ex d approved glands
• 4-20 mA HART output for safe-area configuration, diagnostics and live trending
• IP68 protection against dust, rain, hose-down and temporary immersion
• 316L wetted parts with overload protection for demanding gas and chemical duty
• Removable terminal block and large wiring chamber for gloved-hand installation

Pain Point Analysis: 4 Working Conditions Where Absolute Reference Wins

Application Case 1: Nitrogen Blanketing on a Chemical Storage Farm

Application Case 2: Vacuum Column Monitoring in a Gas Plant

Eight Product Advantages of the QWY-321

1. Ex d IIC T6 flameproof certification covering gas groups IIA, IIB and IIC
2. True sealed vacuum reference with no atmospheric vent, immune to weather and blockage
3. IP68 rated enclosure for offshore, outdoor and washdown installations
4. HART protocol for safe-area configuration and diagnostics without opening the housing
5. ±0.1% FS accuracy with digital temperature compensation
6. 316L wetted parts and 3x overload protection for gas and chemical service
7. Corrosion-resistant epoxy-coated die-cast aluminum housing
8. 24-month warranty with factory calibration certificate and Ex certificate documentation

Technical Parameters

Why Choose Our Absolute Pressure Transmitter?

Qinwei Instruments has supplied explosion-proof instrumentation to oil, gas and chemical projects for more than a decade, and every QWY-321 ships with its Ex d certification documents, a 5-point calibration record and a 48-hour burn-in log. Our engineers routinely support hazardous-area projects - from loop design and cable gland selection to HART integration and commissioning checklists - and we answer within one working day. Because we manufacture the sensing element, the housing and the final assembly in our own facility, we control the whole quality chain and can offer lead times that trading companies cannot match. When safety certification and measurement integrity both matter, that combination is exactly what you need.

SEO FAQ

Ex d is the flameproof enclosure protection concept: the housing is built to contain an internal explosion and cool the flame so it cannot ignite the surrounding atmosphere. IIC means the certification covers the most demanding gas groups, including hydrogen and acetylene, which automatically covers the easier groups IIA and IIB as well. T6 is the temperature class, limiting the maximum surface temperature to 85°C, which is safe for gases with auto-ignition temperatures above 85°C. In practical terms, the QWY-321 can be installed in Zone 1 and Zone 2 hazardous areas for gas groups IIA, IIB and IIC, making it suitable for most oil, gas, chemical and hydrogen applications without needing a separate instrument air purge system.

Tank blanketing keeps a flammable liquid under an inert gas blanket at a slight positive pressure to prevent air ingress. The physically correct variable is the absolute pressure inside the tank, because what matters is whether the internal pressure stays above atmospheric at all times. A gauge-referenced transmitter compares the tank to the local atmosphere, so its reading changes with the weather even when the tank is perfectly stable, and its vent to atmosphere is a potential leak path in a classified area. An absolute transmitter with a sealed vacuum reference has no vent, holds a stable reading in any weather, and directly shows whether the tank remains safely blanketed. This is why safety-conscious operators specify absolute measurement for blanketing and vapor recovery duty.

Yes. The QWY-321 supports the HART protocol, so all configuration - ranging, damping, units, tag and diagnostics - is performed digitally from the safe area through a HART communicator, a USB modem, or your DCS. You never need to remove the cover in the hazardous area for routine configuration, which reduces both safety risk and the cost of work permits. The terminal block chamber is designed for gloved-hand access on the rare occasions when wiring work is required, and the cover uses a captured flameproof thread with an anti-loosening mechanism. For plants that prefer local operation, an optional LCD display window is available within the certified assembly.

Every QWY-321 ships with a certificate of conformity for the Ex d IIC T6 design, the calibration certificate, and the inspection records for the flameproof joints and cable entries. These documents support your plant's hazardous-area equipment register and inspection file. If your project requires a specific notified body endorsement or additional documentation for a particular region, tell us before ordering and we will confirm what can be supplied. We also keep batch records for traceability, so each serial number can be traced back to its manufacturing and test data - useful for audits and for planned maintenance programs.

The QWY-321 is supplied with Ex d approved cable entry options in 3/4 NPT or M20 x 1.5, and we can pre-fit certified flameproof cable glands to match your armoured or unarmoured cable specification. The wiring chamber accepts conductors up to 2.5 mm² and includes a removable terminal block for easy installation in confined spaces. For projects with strict grounding requirements, internal and external earth terminals are provided as standard. Send us your cable specification and hazardous-area classification, and we will confirm the complete gland and termination package before shipment, so your installation team has everything on site.

Because the reference is a sealed vacuum rather than a vented chamber, there is no moisture ingress, no ice formation and no condensation risk inside the reference side of the sensor. The ambient temperature rating of -40 to 85°C covers arctic winter operation, and the epoxy-coated aluminum housing with IP68 protection shrugs off snow, ice and hose-down. The main cold-weather consideration is the process connection itself - if the media can freeze, use heat tracing on the impulse line, exactly as you would with any pressure instrument. The transmitter's own electronics are temperature compensated, so the reading stays within specification across the full ambient range without field adjustments.