The effect of static pressure on the performance of differential pressure transmitters

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The performance of differential pressure transmitters under different static pressures was studied. Experimental investigations were conducted using differential piston manometers to examine the characteristic curves of various differential pressure transmitters at different static pressures, and the results showed that static pressure has a significant impact on the performance of differential pressure transmitters. As the static pressure increases, the characteristic curve of the differential pressure transmitter bends significantly in the negative direction; relevant research provides important references for the production, testing, and application of differential pressure transmitters. Differential pressure transmitters are widely used in industries such as power, chemicals, and pharmaceuticals. These instruments are often involved in aspects such as industrial safety and trade settlement; therefore, it is very important to evaluate their performance objectively and scientifically to ensure the accuracy and reliability of their measurement capabilities. Due to various factors such as the limitations of the standard instruments, the measurement of differential pressure transmitters is still carried out in terms of gauge pressure; that is, pressure is applied at the high-pressure side (H side), while the low-pressure side (L side) is exposed to atmospheric pressure, which is used as the reference static pressure for measurement ； In some cases, negative pressure measurement is simulated by applying positive pressure from the low-pressure side (with the high-pressure side connected to atmospheric pressure). In actual operation, different pressure values are applied to both the high-pressure side and the low-pressure side, resulting in a differential pressure at various static pressures. Since the traditional gauge pressure measurement method cannot reflect the actual operating conditions of a differential pressure transmitter, it is also unable to reflect its true performance. Therefore, Changhui Instruments used the DH.B249T high-static-pressure differential piston pressure gauge to conduct a series of tests on the differential pressure transmitters manufactured by the three selected companies, in order to analyze the changes in the output characteristic curves of these transmitters under different static pressure conditions. Study on the Influence of Static Pressure on the Performance of Differential Pressure Transmitters yunrun.com.cn/tech/2229.html 1. Stability tests of differential pressure transmitters The information regarding the differential pressure transmitters used in these tests is shown in Table 1. To determine the impact of the stability of the differential pressure transmitter itself on the test results, tests were conducted on the long-term stability of the zero point of the selected differential pressure transmitter, as well as on its zero-point stability under different static pressures. The test data were all obtained by directly reading the pressure value from the transmitter’s display, in order to minimize the influence of the standard device on the transmitter’s output. Table 1: Information on differential pressure transmitters Code Differential pressure transmitter model Differential pressure range/kPa Maximum operating pressure/MPa Accuracy class A Changhui YR-ER101 0–50 16 0.075 grade B Fuji FKCS36V5 0–500 16 0.065 grade C Domestic JK3351 0–250 10 0.5 grade ① Long-term zero stability: Zero stability tests were conducted on the single-crystal silicon differential pressure transmitter A and the silicon microcapacitive differential pressure transmitter B under atmospheric conditions for over 1 week; the test results are shown in Figure 1. http://yunrun.com.cn/upload/201810/29/201810291812081776.png Figure 1: Long-term stability of the zero points of differential pressure transmitters A and B. The results show that transmitter A, which is made of monocrystalline silicon, has a differential pressure measurement range of 0–50 kPa, with a zero-point drift of less than 0.008% FS ； The silicon microcapacitive transmitter B has a differential pressure measurement range of 0–500 kPa, with a zero drift of less than 0.01% FS; both parameters meet the test requirements. ②Zero-point stability of differential pressure transmitters under different static pressures: Zero-point tests were conducted on the samples at static pressures of 0, 3, 6, 9, and 12 MPa. Each group undergoes 2 pressure-raising tests and 2 pressure-lowering tests, with measurements taken continuously. The test results of the single-crystal silicon differential pressure transmitter A and the silicon microcapacitive differential pressure transmitter B are shown in Figures 2 and 3 respectively. Figure 2: Zero-point stability of single-crystal silicon differential pressure transmitter A under different static pressures. http://yunrun.com.cn/upload/201810/29/201810291814547770.png Figure 3: Zero-point stability of silicon microcapacitive differential pressure transmitter B under different static pressures. The results show that the effect of static pressure on the zero-point output follows the same pattern: as the static pressure increases, the impact also increases, and the characteristic curve shifts gradually in the direction of negative error. This should be a typical characteristic of differential pressure transmitters. Transmitter A has a zero drift of no more than 0.015% FS at a static pressure of 12 MPa ； Transmitter B has a zero drift of no more than 0.03% FS at a static pressure of 12 MPa ； Transmitter C failed to show any significant zero drift, as its display resolution is only 0.1 kPa. 2. Characteristics of the differential pressure transmitter under different static pressures: For the selected differential pressure transmitter, the differential pressure output values were measured at static pressures of 0, 3, 6, 9, and 12 MPa respectively, in order to assess the impact of different static pressures on the accuracy of the differential pressure output values. ①Changhui YR-ER101 Monocrystalline Silicon Differential Pressure Transmitter A: Figure 4 shows the average value of 5 measurements taken for Changhui’s monocrystalline silicon differential pressure transmitter A at a static pressure of 0–12 MPa. It can be seen that at a static pressure of 6 MPa, the curve begins to bend downward; in other words, as the static pressure increases, the error gradually becomes more negative. At a static pressure of 12 MPa, the characteristic curve bends downward most significantly; at 50 kPa, the measurement values from the differential pressure transmitter already exceed the maximum allowable error. http://yunrun.com.cn/upload/201810/29/201810291817374280.png http://yunrun.com.cn/upload/201810/29/201810291828380301.png Figure 4: Output characteristics of the single-crystal silicon differential pressure transmitter A at different static pressures. ② Fuji FKCS36V5 silicon microcapacitive differential pressure transmitter B. The differential pressure measurement range for transmitter B is 0–500 kPa. As shown in Figure 5, as the static pressure increases, the characteristic curve bends significantly in the negative error direction. Only at a static pressure of 0 MPa is the measurement error within the allowable range specified by the manufacturer; at a static pressure of 12 MPa, the error exceeds 0.25% FS, which is four times the maximum allowable error. This result is caused by both the measurement standards and the transmitter characteristics. http://yunrun.com.cn/upload/201810/29/201810291818163572.png http://yunrun.com.cn/upload/201810/29/201810291825364308.png Figure 5: Output characteristics of differential pressure transmitter B at different static pressures. ③ Domestic capacitive differential pressure transmitter C: The differential pressure measurement range for this domestic capacitive differential pressure transmitter C is 0–250 kPa; the test results are shown in Figure 6. http://yunrun.com.cn/upload/201810/29/201810291819533266.png http://yunrun.com.cn/upload/201810/29/201810291834262260.png Figure 6: Output characteristics of the capacitive differential pressure transmitter C at different static pressures. The characteristic curves are similar to those of the previous sets. Among them, the measurement error at a static pressure of 9 MPa has exceeded the accuracy requirements specified by the manufacturer (Note: None of the above differential pressure transmitters have received information from the manufacturer regarding the allowable variations in their characteristic curves under high static pressure conditions; therefore, analysis is carried out solely based on the actual measurement results). The output characteristic curves of multi-type differential pressure transmitters under different static pressures were measured. The experiments showed that all differential pressure transmitters are affected by static pressure; if the zero point shifts due to this influence, then the characteristic curves also change. The effect of static pressure on the characteristic curves of differential pressure transmitters is consistent: as the static pressure increases, the output characteristic curves of these transmitters bend significantly in the negative error direction, and in some cases, the transmitters exceed their maximum allowable error at the highest static pressure levels tested. The relevant conclusions hold significant reference value for the production, testing, and application of differential pressure transmitters, and thus deserve proper attention. It is recommended that metering institutions with the necessary resources increase the use of differential pressure transmitters in tests, in order to obtain more comprehensive test data for effective analysis and to provide a reliable technical basis for the metrological standards of differential pressure transmitters.