Selecting an E+H pressure transmitter requires consideration of the measurement medium, pressure range, process connection, and other conditions. This article outlines the key points to consider to help technical personnel reduce selection risks.

1. First, define the measurement target and medium properties

The first step in selection is not to look up a model, but to confirm what the instrument needs to measure: gauge or absolute pressure in a pipe or vessel, or differential pressure used to calculate level or flow. Different reference points mean that even readings that appear similar are not directly interchangeable.

Gauge pressure is referenced to the local atmospheric pressure and is commonly used in applications such as water supply networks and compressed air systems. Absolute pressure is referenced to a perfect vacuum and is suitable for conditions where the effects of changes in atmospheric pressure need to be excluded. If the liquid level in a sealed vessel is affected by the pressure of the gas phase above it, a differential pressure measurement solution should generally be assessed in light of the actual process.

Assess the effects of the medium on wetted parts

Record the medium’s name, concentration, and temperature, as well as whether it contains particles, grease, or corrosive substances. For mixed media, also consider changes in composition during cleaning, disinfection, and process fluctuations; do not make a selection based solely on a single medium at room temperature.

316L stainless steel is suitable for many standard operating conditions, but this does not mean it can withstand all acids, alkalis, or chlorine-containing media. When selecting materials, check the compatibility of the diaphragm, process connection, and seals with the medium individually. If corrosion is a concern, provide the supplier with complete information about the medium.

For highly viscous, crystallizing, or solid-laden media, also consider the risk of impulse passage blockage and diaphragm wear. Depending on the operating conditions, assess flush diaphragm designs, diaphragm seals, or flushing solutions, and confirm that the cleaning method will not damage sensitive components.

2. Determine the range and measurement performance based on operating conditions

The range should cover the normal operating range while also accounting for possible peak pressures during startup and shutdown, valve switching, water hammer, and abnormal operating conditions. Normal pressure is only one selection factor; allowable overpressure and the equipment’s allowable working pressure must also be checked separately.

For example, a pipeline has a normal pressure of 0.6 MPa, may reach 0.8 MPa during operation, and is subject to startup and shutdown surges. In this case, the instrument should not be selected based only on 0.6 MPa. The range and overpressure capability should be determined based on measured peak pressure, process design pressure, and the specific product specifications.

An excessively wide range may result in inadequate measurement performance in the low-pressure region, while a range that is too narrow may shorten service life due to frequent overpressure. For systems with significant fluctuations, damping settings, pulsation dampeners, or other protective measures can be assessed, but accessories cannot replace selecting the correct pressure rating.

Distinguish accuracy specifications from field errors

When comparing accuracy, check whether the specification is given relative to full scale, calibrated span, or reading, and whether it includes nonlinearity, hysteresis, and repeatability. Specification formats vary between products, so figures such as “0.1%” or “0.5%” should not be compared on their own.

Field errors may also result from temperature changes, installation location, diaphragm seals, and long-term drift. When selecting an instrument, it is advisable to provide the allowable error, calibration interval, and actual operating range together, rather than focusing only on an individual laboratory specification.

3. Check temperature, environmental, and electrical conditions

Provide the process temperature and ambient temperature separately. The medium in the pipe may be hot, while the instrument housing is exposed to sunlight or low temperatures. When selecting an instrument, check the allowable temperature ranges for the process connection, sensor, and electronic components individually.

For steam or high-temperature media, assess siphon tubes, heat-dissipation accessories, or diaphragm seals based on the operating conditions. When using a diaphragm seal, also consider the temperature suitability of the fill fluid, response speed, and the effect of installation height on measurement.

For outdoor, humid, dusty, or washdown environments, check the ingress protection rating and inspect the cable entries, connections, and installation orientation. The stated protection rating depends on correct installation; if the terminal connections are not properly sealed, the housing rating alone cannot ensure protection in the field.

Hazardous areas and control system interfaces

For flammable or explosive environments, check the explosion-protection certification of the selected configuration against the area classification, gas or dust group, temperature class, and installation method at the site. Do not assume that a product is suitable for every hazardous location simply because its name includes the words “explosion-proof.”

The electrical interface must be compatible with the existing control system, including supply voltage, output signal, communication protocol, and load capacity. For a common 4～20 mA loop, also calculate voltage drops across the power supply, cable, and input module. If remote configuration is required, check the relevant communication functions as well.

4. Match the process connection to the installation conditions

A process connection involves more than whether it can be screwed into place; thread standards, sealing method, pressure rating, and installation space must also be considered. Before ordering, confirm whether the interface is threaded, flanged, or sanitary, and check its size, material, and applicable standard.

For threaded connections, distinguish between straight and tapered threads, and determine whether sealing occurs at the threads or at the sealing face. Interfaces that look similar must not be forcibly assembled. For flanged connections, check the nominal size, pressure rating, facing, and gasket material.

Space should also be reserved on site for wiring, removal and installation, and calibration. If the pressure tapping point is prone to liquid or gas accumulation or solids settling, select the installation location based on the state of the medium and pipe layout, and install isolation valves or discharge devices as required by the process.

Reference for selecting common connection types

For level applications, also confirm the installation method

If the requirement is to measure the level in a pond, reservoir, or wastewater tank, first distinguish between open and closed vessels, then select a measurement solution based on the liquid density, level height, and installation location. Hydrostatic level measurement is affected by changes in liquid density, so not all media can simply be converted using a water-column calculation.

For example, the domestic AOB-136 liquid level transmitter, LCD display, explosion-proof level sensor can be assessed as one domestic solution for level measurement applications. Its specifications list a range from 0～0.5 m to 200 m water column, as well as output options such as 4～20 mA. It is not the same brand as an E+H pressure transmitter, nor is it inherently interchangeable with one. Confirm the specific configuration, medium compatibility, and explosion-protection certification before ordering.

Xi'an Shenghongchuang Instrumentation Co., Ltd. can provide products and technical services to meet pressure, level, and other measurement and control requirements. Before finalizing a solution, it is recommended to compile the medium composition, normal and peak pressures, temperature, power supply and signal requirements, hazardous area classification, and interface drawings. Submit these to technical personnel for a detailed review, then confirm the specific model and configuration.