Pressure transmitters are devices that convert pressure into pneumatic or electric signals for control and remote transmission. They can convert physical pressure parameters such as gas and liquid sensed by the pressure measuring element sensor into standard electrical signals (such as 4~20mADC, etc.) to supply secondary instruments such as indicator alarms, recorders, and regulators for measurement, indication, and process adjustment.
1. Types of pressure
The main types of pressure are gauge pressure, absolute pressure, and differential pressure. Gauge pressure refers to pressure that is less than or greater than atmospheric pressure based on the atmosphere; absolute pressure refers to pressure that is higher than absolute pressure based on the absolute pressure zero position; differential pressure refers to the difference between two pressures.
2. Pressure range
In general, the actual measured pressure is selected as 80% of the measurement range.
The maximum pressure of the system should be considered. Generally speaking, the maximum value of the pressure range of the pressure transmitter should reach 1.5 times the maximum pressure value of the system. Some water pressure and process controls have pressure spikes or continuous pulses. These spikes may reach 5 or even 10 times the "maximum" pressure, which may cause damage to the pressure transmitter. Continuous high-voltage pulses, close to or exceeding the maximum rated pressure of the transmitter, will shorten the practical life of the transmitter. However, increasing the rated pressure of the pressure transmitter will sacrifice the resolution of the transmitter. Buffers can be used in the system to weaken the peak, which will reduce the response speed of the sensor.
3. Measured medium
According to the different measuring media, it can be divided into dry gas, gas liquid, highly corrosive liquid, viscous liquid, high-temperature gas liquid, etc. Correct selection according to different media is conducive to extending the service life of the pressure transmitter.
4. Maximum overload
The maximum overload of the system should be less than the overload protection limit of the pressure transmitter, otherwise it will affect the service life of the pressure transmitter or even damage the transmitter. Usually the safe overload pressure of the pressure transmitter is twice the full scale.
5. Accuracy level
The measurement error of the pressure transmitter is divided according to the accuracy level, and different accuracies correspond to different basic error limits (expressed as a percentage of the full scale output). In practical applications, the selection is based on the control requirements of the measurement error and the principle of economic use.
6. Working temperature range
The temperature of the measuring medium should be within the working temperature range of the pressure transmitter. If it is used at overtemperature, it will cause a large measurement error and affect the service life of the transmitter; in the production process of the pressure transmitter, the temperature effect will be measured and compensated to ensure that the measurement error caused by the temperature effect is within the range required by the accuracy level.
7. Compatibility of the measuring medium and the contact material
In some measuring situations, the measuring medium is corrosive. In this case, it is necessary to select materials compatible with the measuring medium or perform special process treatment to ensure that the pressure transmitter is not damaged.