Use a differential pressure transmitter, you should know these precautions

Differential pressure transmitter is one of the most widely used instruments in industrial production. There are also many physical parameters measured by it. For example, pressure, liquid level and flow rate can be obtained through it, which is important for industrial production. significance.

Differential pressure transmitters are widely used in industrial production, and the effect of measuring industrial flow is very significant. It is usually used with orifice flowmeter, V-cone flowmeter, elbow flowmeter, Verabar flowmeter, and Annubar (both beam tube) flowmeter.

As the detection and transformation part of the process control system, the differential pressure transmitter converts the process parameters such as differential pressure (pressure), flow rate and liquid level of liquid, gas or steam into a unified standard signal (such as DC 4mA to 20mA current). Displays input signals from meters, operators, and regulators for continuous inspection and automatic control of the production process.

Differential pressure transmitter wiring steps

1. Remove the electronic housing. 2. Connect the positive lead to the “PWR/COMN” terminal and the negative lead to the “-” terminal. Be careful not to connect the live signal cable to the test terminal (Test), which will damage the test diode in the test circuit. Shielded twisted pairs should be used for optimum measurement. To ensure proper communication, a 24AWG or higher cable should be used. 3. Use a conduit plug to seal the unused conduit interface on the transmitter housing. 4. Re-tighten the cover.

Installation requirements for differential pressure transmitters

The installation diagram of the differential pressure transmitter can be seen in detail: “Pressure transmitter installation diagram and description”

1. The installation position of the differential pressure transmitter on the process pipeline is related to the measured medium. In order to obtain a good installation effect, the following conditions should be considered:

Prevent the transmitter from coming into direct contact with corrosive or overheated test media;

Prevent dross from depositing and clogging in the pressure guiding tube;

The length of the pressure guiding pipe on both sides of the positive and negative pressure should be the same as possible;

The liquid column indenter in the pressure pipe on both sides of the positive and negative pressure should be balanced;

The impulse piping is installed where temperature gradients and temperature fluctuations are minimal.

2. When measuring the liquid flow, the differential pressure transmitter should be installed beside or below the pipe to be tested so that the bubble is discharged into the pipe; 3. When measuring the gas flow, the differential pressure transmitter should be installed next to the pipe to be tested. Or above, so that the accumulated liquid can easily flow into the pipeline; 4. When measuring the steam flow, the differential pressure transmitter should be installed under the pipeline to be tested so that the condensate can be filled in the pressure piping. Special care should be taken to prevent the differential pressure transmitter from contacting the medium at temperatures above the limit temperature used by the transmitter when measuring steam or other high temperature media.

Commissioning and zero check

1. Operation procedure when integrated three-valve and differential pressure transmitter are put into operation:

First, open the two drain valves on the differential pressure transmitter, then open the balancing valve, and then slowly open the two shut-off valves to remove the air or dirt in the pressure guiding tube, close the two drain valves, and then close the balancing valve. The transmitter can be put into operation.

2. Differential pressure transmitter zero point online verification operation procedure:

The zero point check can be performed on the transmitter by first opening the balancing valve and closing the two shut-off valves.

Three-valve state when zeroing

3. Differential pressure transmitter zero adjustment matters:

1 Zero adjustment screw and span adjustment screw must be mistaken. Do not adjust the range of the differential pressure transmitter at the installation site; 2 When the differential pressure transmitter is zeroed, the temperature of the positive and negative pressure chambers and the pressure tubes on both sides must be the same. If there is a temperature difference between the two sides, the adjusted zero point will occur with time. Drift; 3 If the transmitter is used to perform positive and negative migration compensation, the zero adjustment should be made in the operation and delivery state. If the amount of migration is too large, the migration compensation can no longer be performed on the differential pressure transmitter.

Precautions in daily use

1. Do not apply voltage higher than 36V to the transmitter, resulting in damage to the transmitter;

2. Do not touch the diaphragm with a hard object, resulting in damage to the isolation diaphragm;

3. The measured medium is not allowed to freeze, otherwise the sensor element isolation diaphragm will be damaged, resulting in damage to the transmitter. If necessary, the transmitter should be temperature-protected to prevent freezing;

4. When measuring steam or other high temperature medium, the temperature should not exceed the limit temperature when the transmitter is used. Above the limit temperature used by the transmitter, a heat sink must be used;

5. When measuring steam or other high temperature media, use a heat pipe to connect the transmitter to the pipe and use the pressure on the pipe to transfer it to the transformer. When the measured medium is water vapor, an appropriate amount of water should be injected into the heat pipe to prevent the superheated steam from directly contacting the transmitter and damaging the sensor;

6. During the pressure transmission process, the following points should be noted:

Do not leak air when the transmitter is connected to the heat pipe;

Before starting to use, if the valve is closed, the valve should be opened very carefully and slowly, so as to prevent the measured medium from directly impacting the sensor diaphragm and damaging the sensor diaphragm;

The pipe must be kept clear, deposits in the pipe will pop up and damage the sensor diaphragm.

to sum up

In the process of using the differential pressure transmitter, it must be installed, wired, zeroed, and adjusted in strict accordance with the requirements, and put into operation in the correct way. Only in this way can the measurement be accurate and reliable.