Precision Relative Pressure Transmitter with 4-20mA Output for Accurate Process Control

Control loops are only as good as the pressure signal feeding them. A slow or noisy transmitter forces the controller to act on stale, unreliable data, which means off-spec product and wasted energy. The QWY-306 relative pressure transmitter answers with a sub-10 ms response, IP67 ruggedness and a clean, isolated 4-20 mA signal for precision control applications.

Why Do You Need a Precision Relative Pressure Transmitter?

Most industrial processes are controlled against gauge pressure, the pressure relative to the local atmosphere, because what matters for safety and product quality is the difference between the process and its surroundings. In fast-moving systems such as pneumatic actuators, hydraulic test rigs and pump discharge control, the pressure changes in milliseconds, and a transmitter that responds slowly makes the control loop oscillate or lag. Electrical noise from motors and drives can corrupt an unshielded signal, causing false trips. And in washdown areas, moisture kills poorly protected instruments. Engineers need a transmitter that is fast, electrically robust and environmentally sealed, so the control system always acts on a true, clean and timely pressure value.

Working Principle: Measuring Pressure Relative to Atmosphere

The QWY-306 measures relative pressure by comparing the process pressure with the ambient atmospheric pressure through a vented reference inside the transmitter. The process pressure acts on a sensing diaphragm, while the reference side is open to atmosphere, so the output represents the true gauge pressure of the system. The sensing element converts the diaphragm deflection into an electrical signal, which is amplified and conditioned into a standard 4-20 mA two-wire output. With a response time of under 10 milliseconds, the transmitter tracks rapid pressure changes with minimal lag, giving the control loop a real-time picture of the process. Optional 1500 VAC galvanic isolation protects the signal from ground loops and electrical interference.

Structural Advantages of the QWY-306

• Sub-10 ms response time: fast enough for demanding closed-loop control.
• IP67 enclosure protection: dust-tight and protected against temporary immersion, ideal for washdown areas.
• Optional 1500 VAC galvanic isolation: breaks ground loops and rejects electrical noise.
• Linearity superior to 0.5%FS: dependable signal across the full span.
• Wide storage temperature -40 to +125 °C: survives harsh plant environments when not in service.
• Silicone oil fill fluid: stable, proven pressure transmission medium.
• Versatile process connections: 1/4" NPT or 1/8" NPT male threads.
• Compact, lightweight body: mounts directly on process lines without extra support.

Pain Point Analysis: 4 Challenging Working Conditions

Application Cases

Product Advantages

• Response time under 10 ms for real-time control
• IP67 protection for washdown and outdoor use
• Optional 1500 VAC galvanic isolation
• Linearity superior to 0.5%FS
• Standard 4-20 mA two-wire output
• Storage temperature range -40 to +125 °C
• 1/4" NPT and 1/8" NPT process connections
• Silicone oil fill fluid for stable transmission
• Compact design for direct line mounting
• OEM/ODM customization and rapid delivery

Technical Parameters

SEO FAQ

Q1: What is a relative pressure transmitter?

A relative pressure transmitter, also called a gauge pressure transmitter, measures the pressure of a process relative to the ambient atmospheric pressure. Its sensing element has one side exposed to the process and the reference side vented to atmosphere, so the output represents the gauge pressure, which is what most industrial systems care about. For example, a tank at 2 bar gauge is at 2 bar above atmospheric pressure. This is different from an absolute pressure transmitter, which measures pressure against a sealed vacuum reference. Relative pressure measurement is the standard for vessels, pipes and systems open to the atmosphere, because it directly reflects the pressure difference that drives flow and affects safety.

Q2: Why is response time important for pressure control?

Response time determines how quickly the transmitter's output reflects an actual pressure change. In a closed control loop, the controller compares the measured pressure with the set point and adjusts the actuator accordingly. If the transmitter is slow, the controller receives outdated information and the loop either oscillates or responds sluggishly, wasting energy and risking off-spec conditions. The QWY-306 achieves a response time of under 10 milliseconds, which is fast enough for pneumatic systems, hydraulic test rigs and variable-speed pump control. Fast response also improves safety in applications where pressure must be corrected quickly, such as surge protection and relief monitoring.

Q3: What does IP67 protection mean for this transmitter?

IP67 is an ingress protection rating defined by the international standard IEC 60529. The first digit, 6, means the enclosure is completely dust-tight, protecting the electronics from sand, dust and other particulates. The second digit, 7, means the enclosure withstands temporary immersion in water to a depth of 1 meter for up to 30 minutes. For a pressure transmitter, this rating is valuable in washdown environments such as food plants, pump rooms, marine installations and outdoor skids where the instrument may be sprayed with water or briefly submerged. The QWY-306 is therefore suitable for installations where ordinary IP65 instruments would eventually suffer moisture ingress.

Q4: When should I choose the galvanic isolation option?

Choose the optional 1500 VAC galvanic isolation when the transmitter is installed in an environment with electrical noise or when ground loops are a concern. Ground loops occur when multiple instruments share grounding paths at different potentials, causing unwanted currents that corrupt the 4-20 mA signal. Large motors, variable frequency drives and high-power switching equipment also inject electrical interference into nearby wiring. Galvanic isolation electrically separates the sensor circuit from the output circuit, so noise and ground potential differences cannot distort the signal. If your plant has a history of noisy analog signals, or the transmitter is mounted near heavy electrical equipment, the isolation option is a wise investment.

Q5: What process connections are available?

The QWY-306 is available with 1/4" NPT male or 1/8" NPT male process connections, covering the most common industrial pressure tap standards. NPT (National Pipe Thread) is a tapered thread that seals by thread deformation, and it is widely used for pressure instruments across industries. The 1/4" NPT connection is the most common size for industrial transmitters and offers good flow capacity, while the 1/8" NPT is compact and often used in smaller manifolds and test equipment. Both options allow direct mounting on pipe tees, manifolds or block-and-bleed valves. If you require a different connection, such as G1/4 or a flush diaphragm, please contact us to discuss options.

Q6: Can the QWY-306 be used outdoors?

Yes. With its IP67 enclosure rating, the QWY-306 is well suited for outdoor installations where it may be exposed to rain, dust and humidity. The sealed housing protects the electronics and the vented atmospheric reference from moisture ingress, which is a common failure mode in outdoor pressure instruments. The wide storage temperature range of -40 to +125 °C also ensures the transmitter survives winter storage and summer heat. For outdoor service, we recommend installing the transmitter with the electrical connector pointing downward or using a weatherproof conduit seal to prevent water from running into the cable entry, and protecting the atmospheric vent from blockage by ice or debris.

Q7: How accurate is the QWY-306 relative pressure transmitter?

The QWY-306 provides linearity superior to 0.5%FS, meaning the output deviates from an ideal straight line by less than 0.5% of the full-scale range across the calibrated span. This accuracy level is appropriate for the vast majority of industrial control applications, including pump control, HVAC, gas distribution and machine monitoring. Each unit is factory-calibrated at multiple points to verify linearity, and the calibration data can be supplied on request. For applications requiring higher accuracy, we offer other transmitter models in our range with accuracy up to ±0.1%FS; contact us and we will help you select the right instrument for your accuracy requirement.

Q8: How should the transmitter be installed for best performance?

Install the QWY-306 close to the pressure tap with a short, straight connection to minimize response lag and avoid liquid traps in gas service. Mount it with the diaphragm in a vertical plane where practical, so that sediment cannot settle on the diaphragm and liquids drain away in gas lines. Use an isolation valve and, where the process is dirty, a chemical seal or purge ring to protect the diaphragm. In steam service, install a siphon or condensate pot to keep the sensing element at a safe temperature. Tighten the NPT thread with proper sealing tape and torque, and route the cable with a drip loop below the connector to keep water away from the electrical termination.

Q9: What maintenance does the transmitter require?

The QWY-306 is designed for maintenance-free operation in normal service, but a few simple checks extend its life and preserve accuracy. Periodically inspect the process connection for leakage and the cable gland for tightness. Verify the zero point by isolating the transmitter and venting it to atmosphere; the output should read 4 mA, and the zero adjustment can correct small deviations. Check that the atmospheric vent is not blocked by paint, dirt or ice. In dirty processes, flush or clean the diaphragm port during scheduled maintenance. For critical loops, perform an annual calibration check against a reference gauge. These basic practices keep the transmitter performing to specification for many years.

Q10: What support and delivery options do you offer?

We are the manufacturer of the QWY-306, so you receive direct engineering support, competitive factory pricing and flexible customization. Standard orders are delivered within 5-8 working days, with a monthly supply capacity of 100 pieces. We support OEM and ODM projects including custom ranges, connection types, output options and branding. Every unit is factory-calibrated and tested before shipment, and we provide application advice on installation, wiring and troubleshooting. If you are planning a new control system or replacing an existing transmitter, send us your specifications and we will respond with a detailed recommendation and quotation.

Why Choose Our Relative Pressure Transmitter?

The QWY-306 is engineered for the engineer who refuses to compromise on control performance. Its sub-10 ms response keeps fast loops stable, the IP67 housing survives the harshest plant environments, and the optional galvanic isolation delivers a clean signal even in electrically noisy plants. As a manufacturer, we combine this performance with direct pricing, fast delivery and genuine application support. When your process control depends on pressure data you can trust, the QWY-306 is the precise, rugged and economical choice.