How to Select a Pressure (Differential Pressure) Transmitter

Pressure transmitter sensor is a direct contact with the measured medium on-site instrumentation, often at high temperatures, low temperatures, corrosion, vibration, shock and other environments, so the pressure transmitter selection, in addition to consider the measurement range and accuracy of the general instrumentation needs to be considered, the working environment and the measured medium is also one of the important indicators. Overall, pressure transmitter sensor selection, the main basis for:

Measuring range

General pressure (differential pressure) Transmitter has a certain range of adjustable range, it is best to rely on the technical documents, so that the common measurement value falls in the high-precision range, for the micro-differential pressure transmitter is even more important. To determine the maximum value of the measured pressure in a system, it is generally necessary to select a transmitter with a pressure range that is about 1.5 times larger than the maximum value. This is mainly due to the fact that in many systems, especially water pressure measurement and processing, there are peaks and continuous irregular up and down fluctuations, and such momentary peaks can destroy the pressure sensor. So a snubber can be used to reduce the pressure burr, but this reduces the response speed of the sensor. So in the selection of transmitters to fully consider the pressure range, accuracy and its stability.

Accuracy level

At present, the majority of pressure (differential pressure) Transmitter's accuracy index for 0.1% or 0.075%, high precision index for 0.05% or 0.025%. However, the accuracy mentioned above is only provided by the pressure differential pressure transmitter manufacturer's indicators, in the actual application of the user's production site, if the overall performance error to express words, only a very small portion of the actual application of the field of the overall performance error may reach the indicators provided by the manufacturer, the majority of cases the two are far from each other. Practical application of the factors affecting the accuracy of the main range ratio, the impact of temperature on the zero point, the impact of temperature on the range, the impact of static pressure on the zero point, the impact of static pressure on the range, of which the pressure transmitter only need to consider the temperature and range ratio of the impact of the differential pressure transmitter need to consider all the impact.

In addition, the factors affecting the accuracy also include the influence of power supply, vibration, installation position, etc., but these factors are relatively small, and need to be considered according to the actual needs.

Measuring medium

If the measurement is relatively clean fluid, it can directly use the standard pressure transmitter sensor. If the measured medium is high viscosity and easy to crystallize strong corrosion occasions, you must choose the isolation type transmitter. In the selection of the medium to consider the corrosion of the liquid part of the docking, be sure to select the material of the liquid part of the material, otherwise the diaphragm will be corroded after a short period of time after the use of bad process connections will also be corroded resulting in bad equipment and personal accidents. The diaphragm material of the pressure product can be selected from stainless steel 316L, Hastelloy C, Tantalum and so on according to the working conditions on site.

Liquid material

General pressure transmitter sensor contact media part of the material used is 316 stainless steel, if the measurement medium on the 316 stainless steel corrosive, then basically all the pressure transmitter sensor is suitable for the medium pressure measurement.

If the measurement medium is corrosive to 316 stainless steel, then we should use chemical sealing, so that not only can play a role in measuring the pressure of the medium, but also can effectively prevent the medium and the pressure transmitter contact liquid part of the contact, so as to protect the pressure transmitter sensor, to extend the life of the pressure transmitter.

Medium temperature

Because the signal of pressure transmitter sensor is converted by electricity to the line part, so in general, the temperature of the measurement medium of pressure transmitter is -40~+85℃, if the temperature is too high, it is generally recommended to use condensation bend to cool the medium.

Output signal

At present, due to a variety of collection needs, now on the market pressure transmitter sensor output signal has a variety of. The main 4 ~ 20mA, 4 ~ 20mA + HART, Modbus RS485, 0 ~ 20mA, 0 ~ 10V, 0 ~ 5V and so on. But the more commonly used are 4～20mA, 4～20mA+HART and Modbus RS485.

Other

Some applications in practice (level measurement) require migration of the measuring range of the transmitter, which is calculated based on the field installation location and the amount of migration for migration. At present, intelligent transmitters have become quite popular, characterized by high accuracy, adjustable range, and very easy to adjust, good stability. In addition, it is necessary to determine the process connection interface of the pressure (differential pressure) Transmitter, as well as the supply voltage of the pressure transmitter sensor, and, if used in special situations, to consider the explosion-proof as well as the level of protection.

What can the pressure (differential pressure) Transmitter do?

1、Level

The pressure (differential pressure) Transmitter measures pressure and differential pressure (the difference between two pressures) by its name alone, but it can indirectly measure many quantities. In addition to measuring pressure, but also can measure the level of the equipment. When measuring the liquid level in an atmospheric pressure vessel, a pressure transmitter is required. When measuring the level of pressurized containers, consider using two pressure (differential pressure) Transmitter, i.e., measuring the lower limit of a, measuring the upper limit of a, their output signals for subtraction operation, you can measure the liquid level.

2、Density

In the container level and pressure values remain unchanged it can also be used to measure the density of the medium.

3、Flow

Pressure transmitter sensor's measuring range can be made very wide, from the absolute pressure 0 can be more than one hundred megapascals (general). Differential pressure transmitter in addition to measuring the difference between the two measured pressure value, it can also be used with a variety of throttling elements to measure the flow of media fluids.