Analysis of Application Issues of Pressure Transmitters in Engineering Practice

Overview

Pressure is one of the most fundamental and critical process variables in industrial production, widely involved in process control, interlock protection, and equipment safety management. With the rapid development of silicon technology, micromachining, very-large-scale integrated circuits, and new material technologies, pressure sensors have become representative products with high technological maturity and excellent stability among various types of sensors, thereby establishing the important position of pressure transmitters in the field of industrial control.

However, as field instruments that are in direct contact with the measured medium, pressure transmitters operate for long periods under complex working conditions such as high temperature, low temperature, corrosion, vibration, and impact. Their measurement accuracy and operational stability depend not only on the performance of the product itself, but also largely on whether the engineering application method is appropriate.

Starting from engineering practice and combined with common problems in actual applications, this article systematically analyzes the key technical points of pressure transmitters in field use.

Zero Adjustment Issues in Pressure Transmitter Applications

Engineering Significance of Zero Adjustment

After installation, pressure transmitters are often affected by installation height, residual pipeline pressure, and process conditions, resulting in output signal deviation under zero-pressure conditions. Therefore, zero adjustment is a step that must not be ignored before on-site commissioning.

Comparison of Common Zero Adjustment Methods

In engineering practice, two methods are commonly used for zero adjustment:

• Software zero adjustment using a handheld communicator

• Hardware zero adjustment using buttons on the transmitter body

The characteristics of the handheld communicator adjustment method are:

The adjusted zero output can remain consistent with the original setting, but the adjustment range is relatively limited, making it suitable for fine adjustment.

Hardware-based zero adjustment essentially redefines the measurement range by forcing the current measured value to be defined as the corresponding 4 mA value, while automatically adjusting the upper range limit and keeping the range span and characteristics unchanged.

Engineering Practice Recommendations

In most engineering applications, zero adjustment via a handheld communicator is safer and more controllable. It meets on-site correction requirements without significantly affecting the original range configuration.

Grounding Design Issues of Pressure Transmitters

Main Purpose of Grounding

The core function of grounding for pressure transmitters is to shield interference, improve signal stability, and enhance resistance to transient voltages. Improper grounding design is often an important cause of unstable on-site measurements.

Distinction Between Internal Grounding and External Grounding

Common pressure transmitters in engineering applications usually provide:

• Internal grounding: located on the terminal side, with the internal circuit insulated from the housing

• External grounding: used for grounding the transmitter housing; some models require specification at the time of ordering

If internal grounding is mistakenly used as housing grounding, effective grounding may not be formed; if the housing is not properly grounded, transient voltage protection capability will be weakened.

On-Site Grounding Precautions

During engineering installation, special attention should be paid to the following:

• Transient voltage protection grounding wires must never be laid in the same conduit as signal wires

• Avoid lightning strikes or surge currents coupling into signal loops through grounding wires

• Ensure that the grounding path is short, reliable, and has low impedance

  
  

Engineering Application Issues of Remote Diaphragm Pressure Transmitters

Typical Application Scenarios of Remote Diaphragms

Pressure transmitters with remote diaphragms usually consist of a transmitter body, remote diaphragm, capillary tube, and process connection components, and are mainly used in the following conditions:

• High-temperature media unsuitable for cooling via ordinary impulse lines

• Measured media that are corrosive to the transmitter diaphragm

• High-viscosity, easily solidifying, or easily crystallizing media

• Measurement of vessel level, density, or liquid/liquid interfaces

• Process requirements to reduce dead zones or avoid impulse lines

Limitations in Engineering Applications

It should be noted that the high accuracy and high stability specifications of pressure transmitters generally apply only to standalone transmitters. When capillary tubes and remote diaphragms are introduced, the overall system measurement error and dynamic response characteristics will change significantly, and clear quantitative indicators are often unavailable.

Therefore, where conditions permit, the use of remote diaphragms should be minimized.

Issues in Small-Range Pressure Measurement

In small-range pressure measurement, remote diaphragms are not suitable. Remote diaphragms with different sensing areas correspond to minimum recommended ranges. When the actual range is lower than this value, the overall instrument performance will decline significantly and may even fail to meet measurement requirements.

In applications such as level measurement, small-range pressure transmitters usually require zero shift. From an engineering perspective, higher-range instruments may be appropriately selected to improve stability while ensuring accuracy.

Impact of Capillary Tubes and Filling Oil Selection

After introducing remote diaphragms, capillary tubes and filling oil become key factors affecting measurement performance:

• Capillary length: should be minimized as much as possible while meeting operating conditions

• Capillary diameter: should be selected based on filling oil properties and dynamic response requirements

• Capillary material: selected according to ambient temperature and corrosiveness

Principles for filling oil selection include:

• Process temperature and pressure should be within the stable performance range of the filling oil

• DC200 silicone oil is widely used due to its stable overall performance

• High-temperature measurement requires higher-viscosity filling oil and thicker capillary tubes

• The potential chemical reaction between the filling oil and the measured medium must be evaluated

Pressure Transmitter Application Issues in Harsh Environments

Application Risks in Negative Pressure Environments

In negative pressure environments, pressure transmitters mainly face the following issues:

• The diaphragm remains under negative pressure for long periods and is prone to deformation

• Filling oil may vaporize or decompose under negative pressure

• Pressure transmission performance deteriorates, increasing measurement error

Engineering solutions typically include ensuring sealing through fully welded structures and selecting appropriate installation positions to reduce the impact of negative pressure on the diaphragm.

Issues in Corrosive and Abrasive Environments

In corrosive or abrasive environments, common protection methods include:

• Installing protective covers on diaphragms

• Selecting special metal materials with high hardness and corrosion resistance

It should be noted that while protective covers can reduce corrosion risk, they will affect dynamic response. In highly corrosive environments, replacing only the diaphragm material while ignoring welded parts may also lead to failure risks. Therefore, an overall corrosion-resistant material structure should be adopted.

Failure Mechanisms in High-Temperature Environments

Under high-temperature operating conditions, pressure transmitter issues are mainly concentrated in:

• Volume expansion caused by vaporization of filling oil

• Insufficient cooling measures for installation nozzles

• Diaphragms exceeding maximum temperature limits

Engineering countermeasures include selecting filling oils with wider temperature resistance ranges and reasonably designing thermal insulation and cooling structures.

Comprehensive Recommendations for Engineering Applications

In complex industrial sites, reliable operation of pressure transmitters should be ensured from a system perspective:

• Reasonable selection to avoid long-term operation under extreme conditions

• Standardized installation with emphasis on zero adjustment and grounding design

• Cautious use of remote diaphragms with full evaluation of system errors

• Material and structural optimization for harsh environments

Nexisense fully considers the complexity of engineering applications in product design, providing diversified solutions for different operating conditions.

Conclusion

Pressure transmitters are not simply “plug-and-play” instruments. Their measurement accuracy and long-term stability are highly dependent on engineering application methods. Zero adjustment, grounding design, remote diaphragm selection, and appropriate responses to negative pressure, corrosion, and high-temperature environments are all critical factors that must not be overlooked in engineering practice.

Through scientific selection, standardized installation, and systematic management, Nexisense pressure transmitters can achieve reliable and stable pressure measurement under complex operating conditions, providing solid support for industrial process control and equipment safety.