Thread Content
With the advancement of instrumentation technology, differential pressure transmitters are evolving toward higher precision and greater intelligence. However, technological advancements have led designers into a misconception: when choosing transmitters, people tend to focus on their precision alone, while ignoring other factors that affect measurement accuracy. In fact, what users really need is a measurement accuracy that accurately reflects the true value of the quantity being measured, rather than the accuracy of the transmitter itself. There are many factors that affect the measurement accuracy of differential pressure transmitters, and some of these factors are related to environmental conditions and installation methods. Therefore, during design, the precision of the product itself does not guarantee the actual measurement results. Designers must take into account the impact of the actual environment on the product’s precision when making selections, and they should also strive to minimize the impact on the transmitter’s precision during installation. So, what factors can affect differential pressure transmitters? 1. Influence of range ratio: The range ratio of a differential pressure transmitter refers to the ratio of the maximum value to the minimum value that can be measured by the transmitter while still meeting the accuracy requirements. Generally, the larger the range ratio, the lower the measurement accuracy. A high range ratio in pressure transmitters has many advantages, as it allows such instruments to be used in various different applications after being calibrated. However, in practice, if the range ratio is set too high, it will cause many problems related to measurement stability. Most differential pressure transmitters maintain their reference accuracy within a range ratio of 10:1, and this accuracy is not affected by the range ratio. However, there is still a considerable number of differential pressure transmitters whose range ratio ensuring reference accuracy is less than 10:1; this figure is even as low as 3:1 and 2:1 ； Furthermore, for different range codes of the same model of product, the range ratio that ensures the reference accuracy can also vary significantly; these are all aspects that users need to pay close attention to when calculating the accuracy affected by the range ratio. 2. Effect of temperature: In process applications, the process temperature and ambient temperature can vary significantly, and these will certainly differ from the conditions under which the transmitter was tested. This means that its performance will also differ from the reference accuracy specified. The effect of temperature on differential pressure transmitters is minimal when the range is large (i.e., a low range ratio), but it becomes significant when the range is small (i.e., a high range ratio), sometimes even beyond our expectations. 3. The effect of static pressure: Similar to the effects of temperature and range, static pressure also has a significant impact on the accuracy of the transmitter’s zero point and range. In the case of capacitive differential pressure transmitters, such transmitters are almost always affected by static pressure during the operation of production process systems. When the static pressure under operating conditions exceeds a certain value, the error caused by this static pressure can exceed the precision of the transmitter itself. When calculating the precision of the measurement channel, if the error resulting from static pressure is taken into account, it may not be possible to meet the required precision standards. Therefore, it is necessary to correct for the effect of static pressure when calibrating capacitive differential pressure transmitters. 4. Influence of installation inclination angle on the transmitter The installation inclination angle refers to the angle between the transmitter’s central axis and the vertical line after the transmitter is installed in the field. During differential pressure measurement, the sensing element detects the pressure difference between the two sides by measuring the deformation displacement of the central diaphragm. Since the central measurement chamber is filled with silicone oil, when the differential pressure transmitter is tilted perpendicular to the plane of the measuring diaphragm, the silicone oil itself exerts pressure on the diaphragm, causing it to deform and resulting in changes in the output value. When the differential pressure transmitter is tilted in a direction parallel to the plane of the measuring diaphragm, the filled silicone oil will not press on the measuring diaphragm, so there is no effect. Transmitters with different measurement ranges are affected by inclination to varying degrees; the smaller the range, the greater the impact ； When the differential pressure transmitter is tilted forward or backward, there is no significant change in its output linearity or output value, which does not affect its normal operation ； When the differential pressure transmitter tilts to the left or right, its output value will drift in one direction depending on the degree of tilt; the greater the angle, the greater the impact, but the linearity will not change significantly. 5. Impact of the height difference between the measurement point and the installation point: Due to the overall design requirements of industrial sites, differential pressure transmitters often cannot be installed near the measurement point where the readings are taken; instead, pressure is transferred to a centralized location through pressure transfer pipes, to facilitate maintenance and management. This results in a height difference between the measurement point and the installation point, and the pressure medium in the pipes experiences additional pressure due to this height difference, thereby causing effects and introducing additional errors. In process industry applications, since the density of the medium is often high, even a small height difference results in significant additional errors.