High Accuracy Negative Pressure Transmitter for Reliable Vacuum Measurement

Vacuum processes fail silently. A small leak, a clogged line or a drifting sensor can shift the process vacuum by a few millibar, and the result is wet product, failed seals or wasted energy. The QWY-302 negative pressure transmitter brings high accuracy, 0.01%FS resolution and rugged 316L construction to vacuum measurement, so your system always knows exactly what its vacuum really is.

Why Do You Need High Accuracy Negative Pressure Measurement?

Negative pressure, or vacuum, is a controlled working condition in countless industrial processes: vacuum drying removes moisture at low temperature, vacuum packaging extends shelf life, degassing eliminates air from liquids, distillation separates components under reduced pressure, and medical suction systems rely on precise vacuum levels. In every case, the process result depends on holding the vacuum within a narrow band. If the vacuum is too weak, drying takes longer and packaging seals poorly; if it is too strong, delicate products are damaged. Operators therefore need a transmitter that measures vacuum accurately and repeatably, responds to small changes, and survives the overpressure events and temperature swings that are common in real plants.

Working Principle: Measuring Pressure Below Atmosphere

The QWY-302 measures negative pressure by sensing the difference between the process vacuum and the ambient atmospheric pressure. A 316L stainless steel diaphragm is exposed to the vacuum on the process side, while the reference side is vented to atmosphere, so the output represents the true gauge vacuum. The diaphragm deflection is converted into an electrical signal and conditioned into a standard 4-20 mA two-wire output, factory-mapped across your chosen range such as 0 to -100 kPa or 0-1000 psi equivalent. With an output resolution of 0.01%FS, the transmitter resolves small vacuum changes that matter for process repeatability, and the 150%FS proof pressure rating protects it when the vacuum is accidentally broken by positive pressure.

Structural Advantages of the QWY-302

• High accuracy sensing: 0.01%FS output resolution for fine vacuum control.
• 316L stainless steel wetted parts: corrosion resistance for aggressive vapors and chemicals.
• Wide operating temperature -40 to +85 °C: reliable in cold climates and hot process areas.
• 150%FS proof pressure: survives vacuum-break and overpressure events.
• Standard 4-20 mA two-wire output: direct connection to PLC, DCS and displays.
• Multiple ranges: from 0-1 bar up to 0-1000 psi equivalents, including vacuum scales.
• Factory calibration options: custom zero and span settings for your process.
• OEM/ODM/OBM support: private-label and custom-configuration programs.

Pain Point Analysis: 4 Challenging Working Conditions

Application Cases

Product Advantages

• 0.01%FS output resolution for precise vacuum control
• 316L stainless steel wetted parts for corrosion resistance
• Standard 4-20 mA two-wire output
• 150%FS proof pressure for overpressure safety
• Operating temperature range -40 to +85 °C
• Ranges from 0-1 bar to 0-1000 psi equivalents
• Factory-calibrated zero and span, custom settings available
• Compact, rugged design for industrial service
• OEM, ODM and OBM programs available
• Fast delivery and direct manufacturer support

Technical Parameters

SEO FAQ

Q1: What is a negative pressure transmitter?

A negative pressure transmitter measures pressure below atmospheric pressure, which is commonly called vacuum. Its sensing element is exposed to the process vacuum on one side and to atmospheric pressure on the reference side, and the output signal represents the difference between the two. For example, a reading of -60 kPa means the process is 60 kPa below atmospheric pressure. Negative pressure transmitters are used wherever processes operate under vacuum, such as vacuum drying, packaging, distillation, degassing and medical suction systems. They are essentially gauge pressure transmitters calibrated for the vacuum portion of the pressure scale, and they must be selected with the correct range and materials for the application.

Q2: How accurate is the QWY-302 for vacuum measurement?

The QWY-302 offers an output resolution of 0.01%FS, which means it can resolve changes as small as one hundredth of one percent of its full-scale range. On a 100 kPa vacuum range, this corresponds to roughly 10 Pa, allowing the control system to detect very small vacuum fluctuations. This high resolution is combined with factory calibration at multiple points to ensure linearity across the entire vacuum span. The result is a transmitter that not only measures the absolute vacuum level accurately, but also reveals small changes and slow leaks that lower-resolution instruments would miss, making it ideal for quality-critical vacuum processes.

Q3: Can the transmitter survive an accidental overpressure or vacuum break?

Yes. The QWY-302 is rated for a proof pressure of 150%FS, meaning it can withstand pressures up to 1.5 times its full-scale rating without permanent damage to the sensing element. In vacuum service, the most common overpressure event is a vacuum break, where the system is suddenly vented to atmosphere or pressurized by a backflow of process gas. The 150%FS proof rating absorbs these transients, and the transmitter returns to normal operation once the pressure is restored. For applications with frequent or severe overpressure events, we recommend adding a pressure snubber or protection valve and discussing the duty cycle with our engineers to select the most robust configuration.

Q4: What wetted materials are used in the QWY-302?

The wetted parts of the QWY-302 are manufactured from 316L stainless steel, a low-carbon molybdenum-bearing austenitic steel with excellent corrosion resistance. It withstands a wide range of chemicals, including many acids, alkalis, salt solutions and organic solvents, and it is compatible with the vapors commonly found in vacuum processes such as pharmaceutical drying and chemical distillation. The 316L grade also offers good weldability and resistance to pitting and crevice corrosion. For media that attack 316L, such as strong hydrochloric acid or certain chlorides at elevated temperature, please discuss alternative wetted materials with our engineers before ordering.

Q5: What output signals and ranges are available?

The standard output is a 4-20 mA two-wire signal, the most common analog standard in industrial automation, which is directly compatible with PLCs, DCS systems, panel meters and recorders. A wide choice of measuring ranges is available, from 0-1 bar to 0-25 bar, including vacuum scales such as 0 to -100 kPa, and the 0-1000 psi equivalent range mentioned in the product name. The zero and span can be factory-set to your exact process values, for example mapping 4 mA at -100 kPa and 20 mA at 0 kPa. Custom output options can be discussed for special projects, and our engineers will help you define the correct range and mapping for your application.

Q6: How is the QWY-302 installed in a vacuum line?

Install the transmitter at a representative point in the vacuum line, preferably close to the vessel or chamber whose vacuum you need to control, using a tee or dedicated tap. Mount the transmitter with the pressure port pointing downward or sideways so that condensate cannot pool on the diaphragm. In lines carrying condensable vapors, install a condensate pot or trap between the process and the transmitter to protect the sensing element. Always provide an isolation valve so the transmitter can be removed for maintenance or calibration without breaking the process vacuum. Ensure the atmospheric vent is open and protected from blockage, and route the cable with a drip loop below the connector.

Q7: What is the operating temperature range of the transmitter?

The QWY-302 operates over an ambient temperature range of -40 °C to +85 °C, which covers cold outdoor installations, refrigerated environments and hot process areas alike. The wide temperature range is achieved through careful thermal design and compensation, minimizing zero and span drift as the ambient temperature changes. This makes the transmitter suitable for applications such as outdoor vacuum pumps in cold climates, where the instrument may be exposed to freezing temperatures during winter startup. If your installation exposes the transmitter itself to process temperatures beyond this range, a remote mounting arrangement or a longer impulse line should be considered.

Q8: Can I get the transmitter with custom calibration and branding?

Yes. As the manufacturer, we offer full OEM, ODM and OBM programs for the QWY-302. We can factory-calibrate the transmitter to your exact range and output mapping, configure special zero and span points, provide custom labels and packaging with your brand, and adapt the product documentation to your requirements. This makes the QWY-302 an excellent platform for equipment manufacturers who integrate pressure transmitters into their machines and want a consistent, branded component. We support both prototype quantities and series production, with a monthly supply capacity of 100 pieces and delivery within 5-8 working days.

Q9: How do I verify the transmitter reading in the field?

To verify the QWY-302 in the field, first isolate the transmitter from the process and vent the process port to atmosphere. With atmospheric pressure on both sides, the output should read 4 mA, which is the zero point of a vacuum-calibrated transmitter. Then apply a known vacuum using a hand vacuum pump and a reference gauge, and compare the transmitter output with the expected value at that point. If the reading deviates beyond the accuracy specification, the zero can be adjusted, and for span errors the unit should be returned for factory calibration. Regular verification with this simple procedure gives confidence in the measurement between scheduled calibrations.

Q10: What is the delivery time and supply capacity?

Standard orders of the QWY-302 are delivered within 5-8 working days, and our monthly supply capacity is 100 pieces. This allows us to support urgent replacement needs as well as planned projects and series production. Every unit is factory-calibrated and tested before shipment, and test certificates can be provided on request. Our technical team is available to advise on range selection, installation and troubleshooting, and we respond to inquiries with application-specific recommendations. Contact us with your vacuum range, process media and connection requirements, and we will provide a quotation and delivery schedule promptly.

Why Choose Our Negative Pressure Transmitter?

Vacuum measurement demands sensitivity, robustness and trust, and the QWY-302 delivers all three. Its 0.01%FS resolution reveals the small changes that define product quality, the 316L construction stands up to corrosive vapors, and the 150%FS proof rating shrugs off real-world upsets. As the manufacturer, we offer factory calibration to your exact vacuum range, flexible OEM programs and delivery in days, not weeks. When your process depends on knowing its vacuum precisely, choose the QWY-302 and measure with confidence.