Application and Practice of High-Speed Double-Flange Differential Pressure Transmitters in Complex Level Measurement

— Analysis of Nexisense Engineering-Level Solutions

In industries such as chemical processing, pharmaceuticals, food, and fine materials, level measurement is often associated with complex operating conditions including high corrosion, high temperature, high pressure, crystallization tendency, or strict hygiene requirements. Traditional hydrostatic level transmitters are prone to measurement distortion, sensor contamination, or even failure under these conditions.

High-speed double-flange differential pressure transmitters, relying on diaphragm isolation structures and differential pressure measurement principles, have become one of the most widely used and reliable level measurement solutions in these industries. Taking the Nexisense double-flange differential pressure transmitter as an example, this article provides a systematic analysis from an engineering application perspective.

Working Principle of Double-Flange Differential Pressure Transmitters

A double-flange differential pressure transmitter is essentially a diaphragm-type differential pressure measuring instrument.

The core structure includes:

• Two flange-mounted diaphragms installed at different heights on the vessel

• Capillary tubes filled with stable filling fluid

• Differential pressure sensing element

• Signal processing and output circuitry

When the liquid level of the measured medium changes, the static pressure acting on the upper and lower diaphragms varies with the liquid column height, forming a stable differential pressure. This differential pressure is transmitted through the fluid-filled capillaries to the differential pressure sensor and is finally converted into a standard 4–20mA DC output signal.

In sealed or pressurized vessels, this measurement method effectively eliminates the influence of vapor-phase pressure inside the tank, enabling true level measurement. This is the core advantage of the double-flange structure compared with conventional hydrostatic level gauges.

Main Features of Nexisense High-Speed Double-Flange Differential Pressure Transmitters

High Structural Reliability for Long-Term Online Operation

Nexisense double-flange differential pressure transmitters adopt a fully enclosed, welded solid structure. The measuring components contain no mechanical transmission parts or moving friction components.

Internal electronic components undergo strict aging screening and utilize industrial-grade dedicated connectors, significantly improving overall reliability under vibration, temperature variation, and long-term operation.

Fast Response and High Measurement Accuracy

By eliminating traditional mechanical structures, pressure changes act directly on the sensing element, with large signal variation and a short transmission path, enabling:

• Short response time

• Excellent repeatability

• Outstanding long-term stability

This makes the transmitter especially suitable for applications with rapid level fluctuations or high process control requirements.

Adjustable Damping Design for Pulsation and Disturbance Conditions

For operating conditions involving pressure pulsation, such as agitated tanks or circulation tanks, Nexisense products feature built-in adjustable damping devices. These effectively suppress transient fluctuations, providing smoother output and preventing false alarms or control oscillations.

Wide Rangeability with Positive and Negative Zero Suppression

The transmitter supports local zero adjustment and full-scale calibration.

The rangeability is typically greater than 10:1 and supports both positive and negative zero suppression, making it suitable for non-standard installation heights or special level reference requirements.

Strong Overload Capability with Sufficient Safety Margin

The one-directional overload capacity can reach up to 10 MPa.

An internal concave-arc overload protection structure effectively protects the sensor core under abnormal pressure shocks, reducing the risk of irreversible damage.

Fully Welded Filling System to Eliminate Leakage Risks

Nexisense double-flange differential pressure transmitters use a fully welded rigid sealing and filling structure, fundamentally eliminating the filling fluid leakage issues common in traditional designs and significantly enhancing long-term operational safety.

Multiple Explosion-Proof and Display Options

• Flameproof / intrinsically safe circuit designs

• Maximum output current less than 30 mA

• Optional analog pointer, LCD, or LED digital displays

• Display modules support 360° rotation for easy on-site reading

Compact Size, Light Weight, and Flexible Installation

With fewer components and highly integrated structure, the transmitter achieves compact and lightweight design while maintaining performance, reducing installation and maintenance costs.

Typical Measurement Methods of Double-Flange Differential Pressure Transmitters

Level Measurement in Sealed Vessels

The upper and lower flanges are installed at the high and low pressure tapping points of the vessel, effectively eliminating vapor-phase pressure influence. This is a standard configuration for pharmaceutical reactors and chemical storage tanks.

Level Measurement of Corrosive or Crystallizing Media

The diaphragm completely isolates the medium from the sensor, preventing corrosion, crystallization, or blockage from directly damaging the measuring elements.

High-Temperature or Hygienic Applications

By selecting appropriate diaphragm materials and filling fluids, the transmitter can meet temperature resistance and cleanliness requirements in food and pharmaceutical industries.

Installation Considerations for Double-Flange Differential Pressure Transmitters (Engineering Practice)

• Verify model, range, flange specifications, and filling fluid type before installation

• Install the transmitter in a ventilated, dry, non-corrosive environment; outdoor use requires a protective cover

• Avoid strong vibration, impact, or dropping to prevent capillary damage

• Wire strictly according to the wiring diagram to ensure signal loop stability

• Signal cables should be protected with metal conduits or cable trays to prevent water ingress

• When cleaning pressure ports, use only alcohol or trichloroethylene; inserting hard objects is strictly prohibited

Analysis and Solutions for Typical Inaccurate Level Measurement Problems

On-Site Problem Description

In ammonium sulfate solution level measurement, the double-flange differential pressure transmitter was accurate after shutdown calibration, but measurement deviation gradually increased after startup.

The current output was normal, the flange diaphragms were not blocked, and the medium concentration exhibited certain variations.

Engineering Cause Analysis

Such issues are typically not caused by signal loop or calibration errors, but rather by:

• Long-term adhesion of the medium to the surface of the sensing element

• Chemical changes of the medium during shutdown exposure to air

• Alteration of the physical characteristics of the sensing element

These factors lead to drift in the sensor linearity curve. Calibration can only provide short-term correction and cannot fundamentally resolve the issue.

Recommended Solutions

• Replace the affected sensing element

• Re-evaluate the compatibility of diaphragm materials and filling fluid

• Add flushing or heat tracing measures for media prone to crystallization or reaction

Frequently Asked Questions (FAQ)

Do double-flange differential pressure transmitters require periodic calibration?

It is recommended to perform calibration every 6–12 months depending on operating conditions. For highly corrosive or crystallizing media, the interval should be shortened accordingly.

Does capillary length affect measurement accuracy?

Within the allowable design range, the impact is negligible. However, excessively long capillaries increase response time and should be avoided through proper selection.

Conclusion

With advantages such as reliable structure, strong adaptability, and stable measurement performance, high-speed double-flange differential pressure transmitters have become core instruments for complex level measurement applications.

Through engineered structural design, mature diaphragm and filling systems, and flexible configuration options, Nexisense provides long-term stable and highly maintainable level measurement solutions for chemical, pharmaceutical, and food industries.

In practical applications, proper selection, standardized installation, and engineering optimization tailored to medium characteristics are equally critical to ensuring long-term measurement accuracy.