- Nov 27, 2017 -
With the advances in instrumentation technology, all kinds of brand differential pressure transmitter are toward high-precision, intelligent direction. However, advances in technology have created a misunderstanding for designers: People tend to focus on their own precision when choosing a transmitter, ignoring other factors that affect the accuracy of the measurement. In fact, what you really need is the true value of the measured value - the accuracy of the measurement, not the accuracy of the transmitter itself. There are many factors that affect the measurement accuracy of the transmitter. Some factors are also related to the environmental conditions and installation methods. Therefore, the design accuracy of the product itself can not guarantee the actual measurement results, designers should not only consider the actual environment in the selection of the accuracy of the product, but also pay attention to minimize the accuracy of the transmitter during installation Impact. So, what are the factors that will affect the differential pressure transmitter it? Xiaobian for everyone finishing the following points ~
The impact of the turndown ratio
Differential pressure transmitter range ratio is to meet the accuracy requirements of the transmitter can measure the maximum and minimum ratio. Under normal circumstances, the larger the range ratio, the lower the measurement accuracy, pressure transmitter range ratio, there are many benefits, such a meter after adjustment, can be used in many different occasions. However, the actual range than the tone is too high, will bring a lot of measurement stability issues.
Most differential pressure transmitters in the range of 10: 1 range ratio accuracy is still the reference accuracy, regardless of the span ratio. But there are still a considerable number of differential pressure transmitters to ensure that the reference accuracy of the turndown ratio of less than 10: 1, this indicator is even 3: 1 and 2: 1; and the same model of different range code to ensure reference accuracy of the turndown ratio There may also be a big difference, which is why users should pay particular attention to the accuracy of calculating the influence of the measuring range ratio.
Effect of temperature
Differential pressure transmitter In the process of application, the process temperature, the ambient temperature will have a great change, certainly with the transmitter test reference conditions are different, it also means that the performance will be different from the reference accuracy. The effect of temperature on differential pressure transmitters is small near the maximum range (ie, low range), but the effect is large near the minimum range (ie, large range) and sometimes beyond our imagination. According to some product manuals that provide the combined effect of temperature on zero accuracy and span accuracy, you can get close to 10% if you enter a maximum range ratio of 100.
Some modern smart pressure transmitter products, an increase of internal temperature sensor, used to correct the thermal effects caused by changes in ambient temperature.
Effect of static pressure
Similar to the effects of temperature and range, static pressure also has a substantial effect on the transmitter's zero and span accuracy. Such as capacitive differential pressure transmitter, the transmitter in the production process system operation, almost all will be the impact of static pressure, when the operating conditions of the static pressure exceeds a certain value, the impact of static pressure will exceed the error The accuracy of the transmitter itself, the measurement channel channel accuracy calculation, if adding static pressure error, you may not be able to meet the channel accuracy requirements, capacitance differential pressure transmitter calibration static pressure effect must be corrected.
Effect of installation tilt angle on the transmitter
The tilt angle is the angle between the transmitter axis and the plumb line after the transmitter is installed in the field.
Differential pressure measurement, the detection element is measured by the center of the diaphragm deformation displacement sensor to perceive the pressure difference between the two sides. As the center of the measuring chamber is filled with silicone oil, when the pressure transmitter tilts perpendicular to the plane of the measuring diaphragm, the filling of the silicone oil itself produces pressure on the measuring diaphragm, causing the diaphragm to deform and causing variations in the output value. When the differential pressure transmitter tilts along the direction parallel to the plane of the measuring diaphragm, the filling of the silicone oil will not pressure the measuring diaphragm and therefore has no effect. Transmitters of different ranges have different degrees of influence due to tilt. The smaller the range is, the greater the influence is. When the differential pressure transmitter is tilted forward and backward, its output linearity and output value do not change obviously, and will not affect its normal use. When the differential pressure transmitter left or right tilt, the output value will be based on the tilt angle of the unidirectional drift, the greater the angle, the greater the impact, but the linear will not be significantly changed.
Effect of measuring point and mounting point height difference
Due to the needs of the overall design of the industrial site, the differential pressure transmitter often can not be installed in the field near the measuring point, but by the pressure tube pressure to a more concentrated place for maintenance and management, which will result in measurement There is a height difference between the point and the mounting point, and the pressure transmitting medium in the pressure guiding tube will generate additional pressure due to the height difference, thereby affecting the introduction of the additional error. Process industrial applications, due to the medium density is often larger, so even a small height difference, the introduction of additional error is larger.
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