Knowledge of pressure transmitters

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Pressure transmitters are used in applications for measuring the pressure of various media. For flammable and explosive environments, pneumatic pressure transmitters as well as electric pressure transmitters with the appropriate explosion-proof rating should be used. Flanged pressure transmitters can be chosen for measured media that are prone to clogging, viscous, corrosive, or have a low boiling point. Intelligent transmitters are suitable for applications requiring high measurement accuracy in harsh environmental conditions. The accuracy of pressure measurement depends to a large extent on the proper installation of the transmitter, measuring tube, and pressure tapping components. In some cases, electric pressure transmitters can be installed directly on the process pipeline without the need for additional supports. The condition for installing them directly on the pipeline is that both the temperature of the process and the ambient temperature must meet the requirements for using the transmitter. When pressure tapping components are installed on horizontal and inclined process pipelines, the location of the pressure tapping points shall comply with the following regulations: 1. When measuring gas pressure, the pressure tapping points should be located in the upper half of the process pipeline. 2. When measuring liquid pressure, the pressure measurement point should be located in the lower half of the process pipeline, at an angle of 0° to 45° relative to the horizontal centerline of the process pipeline. 3. When measuring steam pressure, the pressure measurement points should be located in the upper and lower sections of the process pipeline, at angles of 0° to 45° relative to the horizontal centerline of the process pipeline. 4. The installation location of the pressure tapping component should be selected in a pipe section where the flow of the process medium is stable. 5. When the pressure sensor and the temperature sensor are located on the same pipeline, the pressure sensor should be installed on the upstream side of the temperature sensor. 6. The ends of the pressure tapping components shall not extend beyond the inner walls of the process equipment and process pipelines. 7. When measuring the pressure of turbid media such as dust, solid particles, or sediment in vertical process pipelines, the sensor element should be installed at an upward angle, with an angle greater than 30° to the horizontal line; in horizontal process pipelines, it is advisable to install it at an acute angle in the direction of flow. 8. The pressure transmitter should be installed in a location with sufficient lighting, where it is easy to operate and maintain; it should not be placed in areas subject to vibration, humidity, high temperatures, corrosive conditions, or strong magnetic field interference. 9. The pressure transmitter should be installed as close as possible to the sensing element. The installation height of the transmitter for measuring low pressure should be the same as the height of the pressure sampling point, especially when measuring liquid media and condensable gas media. 10. When measuring the pressure of gaseous media, the transmitter should be installed at a higher position than the pressure sampling point; when measuring the pressure of liquids or vapors, the transmitter should be installed at a lower position than the pressure sampling point. This is done to reduce the need for additional devices for venting gas or liquid. Apart from being installed directly on the process pipeline, pressure transmitters are usually mounted separately. Column brackets can be fabricated on-site and secured using U-bolts, or wall bracket installations can also be used. In whatever installation method is adopted, the pressure transmitter must be installed vertically, and the cable inlet of the instrument junction box should not face upward.