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A cause of error in a pressure transmitter during pressure transmission

Post: 2020-02-29

What is the difference between pressure transmitter and pressure gauge?First working principle is not the same, stability, reliability is not the same;The standard current signal transmitted by the pressure transmitter has good interchangeability, while the pressure gauge transmits the resistance signal, and the resistance signal is not a standard signal, with poor interchangeability.Transmitters are used where measurement accuracy is required, while pressure gauges are used where measurement accuracy is not required.

Talk about the requirements of selecting pressure transmitter:

First, liquid material

What we need to consider is the medium measured by the pressure transmitter. The general material of the contact part of the pressure transmitter is 316 stainless steel. If your medium is not corrosive to 316 stainless steel, then basically all pressure transmitters are suitable for you to measure the pressure of the medium.

Second, accuracy grade

Each kind of electronic measuring meter will have accuracy error, but because each country mark the accuracy level is different, for example, China and the United States and other countries mark the accuracy is the sensor in the linearity part, that is, we usually say the measurement range of 10%~90% accuracy;The accuracy of European standard is the part with poor linearity, that is, the accuracy between 0~10% and 90%~100% of the inverse measurement as we usually say. If the accuracy of European standard is 1%, the accuracy of Chinese standard is 0.5%.

Third, range range

The measuring range of the sensor is generally 70% of the full range of the sensor. Yes, that is to say, to measure the pressure of 70bar, we should choose the measuring range of the pressure transmitter to be 100bar.

Fourth, output signal

At present because of the various acquisition, now in the market there are many kinds of pressure transmitter output signal, the main 4 ~ 20 ma, 0 to 20 ma, 0 ~ 10 v, 0 ~ 5 v, etc., which are frequently used but is 4 ~ 20 ma and 0 ~ 10 v, in my above for the output signal, only 4 ~ 20 ma for two wire (what we call the output for some wire system does not contain grounded or shielded wire), other are all three wire system.

Fifth, medium temperature

Because of the pressure transmitter signal is through the electronic circuit part of the transformation, so in general, the measurement of pressure transmitter medium temperature was minus 30 ~ + 100 degrees, if the temperature is too high, we usually use is condensing cooling medium, to such relative manufacturers have come to make sure your production a high temperature resistant pressure transmitter would reduce the cost a lot.

Sixth, measuring medium

Generally we measure relatively clean fluid, we can directly use the standard pressure transmitter can be, if you measure the medium is easy to crystallize or viscous, we generally use external diaphragm or with the chemical seal, which will effectively prevent the medium from blocking the pressure measuring hole.

Vii. Miscellaneous

After we determine the above five parameters, we need to confirm the process connection interface of your pressure transmitter and the supply voltage of the pressure transmitter.If used in special occasions also consider the explosion protection and protection level.

Application process of pressure transmitter:

1. The output indicator index is zero

Check whether the power electrode is connected reversely, whether the power supply voltage is 24VDC, and replace the damaged diode in the circuit board or wiring block in time

2. Transmitter cannot communicate

To ensure the pressure transmitter in 24 VDC power supply voltage, load resistance value is 250 Ω, inspection unit address is correct

3. There is pressure change, and the output is not responsive

Check if the transmitter is set correctly, check and reset, and replace the sensor module in time if it is damaged

4, the transmitter meter reading is not accurate

If the standard meter is accurate in the process of calibrating the transmitter, the standard meter with higher accuracy can be replaced to ensure that the pressure tube of the meter is unobsated and the transmitter is properly set

5. The meter reading is unstable

Measure whether the pressure is stable, contact with the process in time if it is unstable, increase damping, eliminate the influence of interference source.

During the pressure transmission process of the pressure transmitter, the possible causes of errors are as follows:

1. Disclosure;

2, wear loss (especially suitable for cleaning agent);

3. There is gas in the liquid pipeline (resulting in head error);

4. There is liquid in the gas pipeline (resulting in head error);

5. The density between the pressure guide tubes on both sides is different due to the temperature difference (resulting in the head error).

The error reduction method of pressure transmitter is as follows:

1, guide pipe as short as possible;

2. When measuring the liquid or steam, the pressure guide pipe shall flow upward and connect to the process pipe, and its slope shall be no less than 1/12;

3. For gas measurement, the pressure guide pipe shall be connected downward to the process pipe, and its slope shall be no less than 1/12;

4. The liquid pressure guide pipe shall be arranged to avoid the middle high point, and the gas pressure guide pipe shall be arranged to avoid the middle low point;

5. Keep the same temperature between the two pressure tubes;

6. To avoid the impact of friction, the diameter of the pressure guide pipe should be large enough;

7. There should be no gas in the pressure pipe full of liquid;

8, when using the isolation fluid, both sides of the pressure tube of the liquid should be the same;

9. When using the cleanser, the cleanser connection should be close to the pressure mouth of the process pipeline, and the length and diameter of the pipeline through which the cleanser passes should be the same, so as to avoid the cleanser passing through the transmitter.

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