The zero-point drift of a pressure transmitter means that under the specified test conditions, when the input pressure is zero, the output value jumps positively, negatively or up or down over time over the specified index. In order to prevent moisture, rain, and harmful gas erosion, the circuit board of the pressure transmitter is designed and manufactured according to a sealed structure. If the watch case is not tightened and the hexagonal lock nut is tightened, the normal working conditions of the electronic circuit will be destroyed, and the intrusion of moisture, rain, and harmful gases will cause the insulation performance to decline or the electronic components to be corroded, causing pressure transmission. The drift of the output value of the converter. The output value of the pressure transmitter is unstable, which will directly affect the work of the measurement and control system.
But some zero point changes are allowed. For example, the zero point output value change caused by the difference between the installation position of the pressure transmitter and the position during adjustment; the measurement diaphragm is perpendicular to the ground during calibration, but the measurement diaphragm is parallel to the ground or inclined to the ground when installed on site. The zero point change caused by the deviation of the measuring diaphragm from the center position caused by the weight of the diaphragm is a normal phenomenon. The smaller the measuring range of the pressure transmitter, the greater the change value. Simply adjust the changed zero output value back to zero by adjusting the zero position.
The change in the output value caused by the change in the ambient temperature of the pressure transmitter is called the additional temperature error of the pressure transmitter. Any change value that meets the technical indicators is a normal change. The temperature index given in the manual of the pressure transmitter refers to the high range. When calculating the temperature index of the adjusted range, you need to multiply this index by the range ratio (the ratio of the highest range to the adjusted range), and the model of the pressure transmitter , Different specifications, temperature indicators are also different. In the use site, the early, mid, and late output value changes within the index range should be a normal zero point and regular change. This change is especially obvious on the pressure transmitter with a large temperature difference and a lower range, as long as there is no It is normal to exceed the target.
The output change that meets the technical index caused by static pressure is also a normal change. Especially for pressure transmitters with a small range, due to their large conversion magnification, the output value changes caused by static pressure are also large. The key is to see if the technical indicators are exceeded.
Causes and solutions of zero drift of pressure transmitter
The zero drift of pressure/differential pressure transmitter means that under the specified test conditions, when the input pressure is zero, the output value jumps positively, negatively or up and down over time over the specified index.
1. The output signal is zero
When the pressure of the pressure transmitter is zero, it can be dealt with from the following aspects: first check whether there is pressure in the pipeline, whether the instrument is normally powered, then check whether there is a phenomenon of reverse polarity of the power supply, and finally check the electronics Circuit board, pressure sensitive film head, transmitter power supply voltage, etc.
2. No response to reading
If there is no response when pressure is applied, check whether the valve of the pressure pipe is normal, whether the transmitter protection function jumper switch is normal, whether the pressure pipe is blocked, check the zero point and range of the white feeder, and replace the sensor film head.
3. Pressure drift reading deviation
When the pressure reading of the pressure transmitter is obviously high or low, first check whether there is leakage in the pressure taking pipe, then check the valve on the pressure taking pipe, and fine-tune the sensor. If there is still a problem, replace with a new one. Sensing film head.
4. The pressure variable reading is unstable
This problem can be checked by isolating external interference sources, checking whether the pressure guiding tube is leaking, whether there is debris in the pipeline, clothing or deformation when checking the isolation diaphragm, and checking the pressure-sensitive membrane head.
However, some zero point changes are allowed, such as the change in the zero point output value caused by the pressure transmitter installation position and the position during adjustment. The measuring diaphragm is perpendicular to the ground during calibration, but the measuring diaphragm is parallel to the ground during on-site installation. Or inclined to the ground, this kind of zero point change caused by the deviation of the measuring diaphragm from the center position caused by the weight of the diaphragm is a normal phenomenon. The smaller the measuring range of the pressure transmitter, the greater the change value. Simply adjust the changed zero output value back to zero by adjusting the zero position.