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Focus On Level Measurement
What factors will affect the differential pressure transmitter?
The working principle of the differential pressure transmitter: the pressure difference from the pressure pipes on both sides directly acts on the isolation membrane on both sides of the transmitter sensor, and is transmitted to the measuring element through the sealing liquid in the membrane, and the measuring element will measure the differential pressure signal It is converted into a corresponding electrical signal and passed to the converter, and then amplified into a standard electrical signal output. There are many factors that affect the measurement accuracy of the transmitter, and some factors are also related to environmental conditions and installation methods. Therefore, when designing, the accuracy of the product itself cannot guarantee the actual measurement effect. The designer must not only consider the impact of the actual environment on the accuracy of the product, but also pay attention to minimize the impact on the accuracy of the transmitter during installation. So, what factors will affect the differential pressure transmitter?
Impact of range ratio
The range ratio of a differential pressure transmitter refers to the ratio of the large value and the small value that the transmitter can measure when the accuracy requirements are met. Generally speaking, the larger the range ratio, the lower the measurement accuracy, and the larger the range ratio of the pressure transmitter, which has many advantages. After such an instrument is adjusted, it can be used in many different occasions. However, in fact, the range ratio is too high will bring a lot of measurement stability problems.
The influence of temperature
In the process application of the differential pressure transmitter, the process temperature and the ambient temperature will change greatly, which will definitely be different from the reference conditions during the test, which also means that the performance will be different from the reference accuracy introduced. When it is close to a large range (ie, a small range ratio), the temperature has little effect on the differential pressure transmitter, but it is very large when it is close to a small range (ie, a large range ratio), and sometimes even beyond our imagination.
The effect of static pressure
Similar to the influence of temperature and range, static pressure also has a substantial influence on the accuracy of the transmitter's zero point and range. For example, capacitive differential pressure transmitters are almost always affected by static pressure during the production process. When the static pressure of the operating condition exceeds a certain value, the static pressure influence error will exceed the accuracy of the transmitter itself. When calculating the channel accuracy of the measurement channel, if the static pressure influence error is added, the channel accuracy requirement may not be met. Therefore, the static pressure influence must be corrected when checking the capacitive differential pressure transmitter.
The influence of the inclination angle of the transmitter installation
The installation tilt angle refers to the angle between the axis and the plumb line after the transmitter is installed on the site.
When the pressure difference is measured, the detection element measures the deformation displacement of the diaphragm through the detection center to sense the pressure difference on both sides. Because the central measurement chamber is filled with silicone oil, when the differential pressure transmitter is perpendicular to the plane of the measuring diaphragm, the silicone oil itself will generate pressure on the measuring diaphragm, which will cause the diaphragm to deform and cause the output value to change. When the differential pressure transmitter is tilted in a direction parallel to the measuring diaphragm, the silicone oil infusion will not compress the measuring diaphragm, so it has no effect. Transmitters with different measurement ranges are affected by tilt to different degrees. The smaller the measurement range, the greater the impact; when the differential pressure transmitter tilts back and forth, the output linearity and output value change is not obvious, which will not affect its normal use; When the difference transmitter is tilted left and right, the output value will drift unidirectionally according to the tilt angle. The greater the angle, the greater the impact, but the linearity will not change significantly.
Influence of height difference between measuring point and installation point
Due to the needs of the overall design of the industrial site, the differential pressure transmitter cannot often be installed near the measuring point at the use site, but the pressure is led to a relatively concentrated place through the pressure pipe for maintenance and management, which will lead to the measuring point The height difference with the installation point, the pressure transmission medium in the pressure pipe will generate additional pressure due to the height difference, which will cause influence and additional errors. In industrial applications, because the density of the medium is often large, even if the height difference is small, the additional error introduced is also large.