的分类与选择 Classification and selection of pressure transmitters
1. Gauge pressure transmitter: Gauge pressure transmitter is a pressure transmitter with local atmospheric pressure as the reference zero. 2. Absolute pressure transmitter: Absolute pressure transmitter is a pressure transmitter with vacuum as the reference zero. During use, the reference zero point of the sensor can be adjusted automatically with the change of location and area without correction. 2. The appearance is the same as the gauge pressure transmitter. Differential pressure transmitter: The differential pressure transmitter is a pressure transmitter that measures the pressure difference between the two pressure chambers. The differential pressure transmitter has two pressure chambers, "+" and "-". It accepts two pressures as comparison values, and usually uses the larger end as the "+" pressure cavity. When ordering a differential pressure sensor, please pay attention to a parameter unique to the differential pressure transmitter ----withstand static pressure. For example, when using the differential pressure transmitter we applied, the pressure on the "+" pressure end is 10MPa, and the pressure on the "-" pressure end is 10.5MPa, then the differential pressure measured by the transmitter is: 10.5 -10 = 0.5MPa. The transmitter is subjected to a static pressure of 10 MPa. In the application process, the use of high static pressure and low differential pressure is common at the scene. The static pressure of the differential pressure transmitter ordered should not exceed the withstand static pressure value of the differential pressure transmitter, otherwise it will be easily damaged. 4． Input / plug-in liquid level transmitter: There are two types of liquid level transmitters: input type and plug-in type. The two forms are the same, and both convert the pressure to the liquid depth. When the water depth is 1m, the pressure on the transmitter is 10KPa. When ordering such sensors, pay attention to: 1. The measured liquid density shall be notified to the production unit. 2. The production unit shall be notified when the measuring medium is corrosive. 3． When the temperature of the measuring medium exceeds -10 ° C and 60 ° C, the production unit will be informed. 5. Medium and high temperature pressure transmitters: For the measurement site environment temperature is too high or the measuring medium temperature is too high, you must use a medium and high temperature pressure transmitter. The transmitter has a good zero temperature coefficient and sensitivity temperature coefficient, which can ensure measurement accuracy in a high temperature environment. When ordering this type of transmitter, you must inform the temperature of the measurement medium and the ambient temperature in order to facilitate the producer to respond reasonably.
选型步骤：1. 产品型号：如果是压力变送器，可以选择HHGP（电容式传感器），和HH308(扩散硅传感器）2. 量程：订购的压力变送器需要测量的压力（压强）上限，通常情况下，为了应对意外出现的过载现象而使变器免于损坏，订购的压力变送器量程通常大于现场测量最大压力约1/3。 Pressure transmitter selection steps: 1. Product model: If it is a pressure transmitter, you can choose HHGP (capacitive sensor) and HH308 (diffused silicon sensor) 2. Range: The pressure to be measured by the ordered pressure transmitter (Pressure) upper limit, under normal circumstances, in order to cope with the accidental overload phenomenon and prevent the transformer from being damaged, the range of the pressure transmitter ordered is usually larger than the maximum pressure measured on site by about 1/3. For example: the maximum range of on-site measurement is about 2MPa, and the customer is better to order a pressure transmitter with a range of 3MPa when ordering. 3. Output signal of pressure transmitter: Usually the output signal of pressure transmitter is voltage (0-5V, 0-10V, etc.) and current (0-20mA, 4-20mA, etc.) signals, which are suitable for different needs, current The output signal transmitter has strong anti-interference ability and good remote transmission ability. The electric pressure output sensor is suitable for short-distance computer acquisition and high-frequency response requirements. 4. Power supply: The proper operation of the pressure transmitter requires a suitable excitation power source. Under normal circumstances, the pressure transmitter with a current output signal is powered by 24VDC, and the pressure transmitter with a voltage output signal is powered by 15VDC, 24VDC, and ± 15VDC. Customers can also negotiate and order based on the power and supply units that they can provide on site. 5. Product measurement accuracy level: This parameter is the level that the pressure transmitter is divided according to the accuracy (precise) accuracy level. An important parameter to measure the measurement level of a pressure transmitter. 0.1% 0.25% 0.5% is more common. Customers must first figure out what level of measurement and control they need to achieve when ordering. Although the higher the measurement accuracy level of the transmitter, the better, but the price is often proportional to the accuracy level, which is enough. 6. Pressure interface: During the measurement process, the pressure transmitter needs to communicate with the measured quantity. The usual way of hooking is a thread form. The more common ones are M20X1.5 and M12X1. When the measurement pressure is small, there is also a pagoda-shaped skin cannula with a diameter of 8mm. The specific requirements depend on the measurement pressure and the site conditions. The customer can also propose other requirements and negotiate with the supply unit to resolve them. 7. Package outlet: The working environment of the pressure transmitter is more complicated. If the transmitter does not take corresponding protective measures under the harsh working environment, it will greatly affect the service life of the transmitter. For example, long-term work in outdoor wind, sun, rain, etc., must be relatively protective during production. 8. Lead length: The working and control locations of the transmitter often have a long or short distance. If the distance is short, the supply unit should be reminded when ordering to bring a long enough lead to avoid intermediate wiring. Be sure to choose a shielded signal line to avoid signal loss during transmission. 9. 如果工作的环境温度和测量介质温度如果过高的话就要对供应单位进行说明，上限通常以60℃为限。 Transmitter working environment temperature and measuring medium temperature: If the working environment temperature and measuring medium temperature of the pressure transmitter are too high, the supply unit should be explained. The upper limit is usually limited to 60 ° C. The lower limit is usually limited to -10 ° C. 10． Special medium: When the following problems exist in the measurement medium, it is necessary to communicate with the supplier. The measuring medium is corrosive. 2. The measurement medium has a strong permeability. 3． The measurement medium has a large change in temperature difference