压力变送器 的选型 1 Selection of pressure transmitter
From a physics perspective, the pressure on any object includes two parts: atmospheric pressure and the pressure of the measured medium (generally called gauge pressure). The sum of the two pressures acting on the measured object is called absolute pressure.
绝 =P 表 + 大气压 P absolute = P table + atmospheric pressure
Instruments that measure absolute pressure are called absolute pressure gauges. For ordinary industrial pressure gauges, the gauge pressure is measured, that is, the pressure difference between absolute pressure and atmospheric pressure. When the absolute pressure is greater than the atmospheric pressure value, the measured gauge pressure value is positive, which is called positive gauge pressure; when the absolute pressure is less than the atmospheric pressure value, the gauge pressure value is negative, which is called negative gauge pressure, that is, the degree of vacuum. The instrument that measures the degree of vacuum is called a vacuum gauge.
为了保证压力测量精度，最小压力测量值应高于压力表测量量程的 1/3 ； ⑴ In order to ensure the accuracy of pressure measurement, the minimum pressure measurement value should be higher than 1/3 of the measurement range of the pressure gauge ;
对需远距离测量或测量精度要求较高的场合，应选用压力传感器或压力变送器； ⑵ Where long-distance measurement or high measurement accuracy is required, a pressure sensor or pressure transmitter should be selected;
在测量精度要求不高时，可选择电阻式或电感式、霍尔效应式远传压力变送器； (3) When the measurement accuracy is not high, you can choose resistive or inductive, Hall effect remote pressure transmitter;
气动基地式压力指示调节器适宜做就地压力指示调节； ⑷Pneumatic base pressure indication regulator is suitable for local pressure indication adjustment;
⑸ 、压力开关应根据安装场所的防爆要求合理选择。 The pressure transmitter and pressure switch should be reasonably selected according to the explosion-proof requirements of the installation site.
． 2 . Selection of differential pressure transmitter
根据以下几点选型： Differential pressure transmitters are selected according to the following points:
测量范围、需要的精度及测量功能； ⑴Measurement range, required accuracy and measurement function;
测量仪表面对的环境，如石油化工的工业环境，有可热（有毒）和爆炸危险气氛的存在， 的 The environment that the measuring instrument faces, such as the industrial environment of petrochemical industry, has the presence of hot (toxic) and explosive dangerous atmosphere,
High ambient temperature, etc.
被测介质的物理化学性质和状态，如强酸、强碱、粘稠、易凝固结晶和汽化等工况； (3) Physical and chemical properties and state of the tested medium, such as working conditions such as strong acid, strong alkali, thick, easy to solidify crystallization and vaporization;
操作条件的变化，如介质温度、压力、浓度的变化。 的 Changes in operating conditions, such as changes in medium temperature, pressure, and concentration. Sometimes it is necessary to take into account
Changes in gas and liquid concentrations and densities during normal production;
被测对象容器的结构、形状、尺寸、容器内的设备附件及各种进出口料管口都要考虑，如 考虑 The structure, shape, size of the container under test, the equipment accessories in the container, and the various inlet and outlet nozzles must be considered, such as
Towers, solution tanks, reactors, boiler drums, vertical tanks, spherical tanks, etc .;
其它要求，如环保及卫生等要求； ⑹ Other requirements, such as environmental protection and sanitation requirements;
工程仪表选型要有统一的考虑，要求尽可能地减少规格品种，减少备品备件，以利管理； ⑺ Engineering instrument selection must have unified considerations, requiring that specifications and varieties be reduced as much as possible, and spare parts and components are reduced for management;
实际的工艺情况： ⑻The actual process:
考虑被测对象是属于哪一类设备。 ① Consider what kind of equipment the test object belongs to. Such as tanks and tanks, the volume of the tank is small, the measurement range is not too large, and the volume of the tank is large, the measurement range may be large
要看介质的物化性质及洁净程度，首选常规的差压变送器及浮筒式液位变送器，还要对接触介质部分的材质进行选择； ② Depending on the physical and chemical properties and cleanliness of the medium, conventional differential pressure transmitters and float-type liquid level transmitters are preferred, and the material of the contacting medium should be selected;
对有些悬浮物、泡沫等介质可用单发兰式差压变送器。 ③Some suspensions, foams and other media can be used single-blue differential pressure transmitter. Some easy-to-precipitate and easy-to-crystal double-blue differential pressure transmitters are used;
对高黏度介质的液位及高压设备的液位，由于设备无法开孔，可选用放射液位计来测量； ④ For the liquid level of high-viscosity media and the liquid level of high-pressure equipment, since the equipment cannot open holes, a radiological level gauge can be selected for measurement;
除了测量方法上和技术上问题以外，还有仪表的投资问题。 ⑤ In addition to the measurement method and technical problems, there are also investment problems with the instrument.
In summary, the selection of the transmitter must be technically feasible, economically reasonable, and convenient to manage.