First, the product introduction
The pressure transmitter measures the negative pressure, pressure, and absolute pressure of steam, gas, and liquid, and then converts it into a 4-20 mA DC signal output.
The pressure transmitter is divided into AP type (absolute pressure) and GP type (table pressure). The combination of the intelligent amplifier board and the GP and AP models is an intelligent pressure transmitter that can communicate with each other through the handheld communicator (in accordance with the HART protocol) to set and monitor.
The chamber of the GP type pressure transmitter has one side connected to the atmospheric pressure and the other side receives the measured pressure signal, so it can be used to measure the gauge pressure or negative pressure.
The AP type absolute pressure transmitter's chamber is closed to the high vacuum reference chamber on one side and the absolute pressure signal is measured on the other side to measure the absolute pressure of the crystallizer, exhaust system, evaporator and distillation column. .
Second, the working principle
Capacitive pressure and differential pressure transmitters are mainly composed of chamber-sensitive components that implement pressure/capacitance conversion and convert the capacitor into a two-wire 4-20 mA DC electronic circuit board. (See the figure below)
When the process pressure is applied to the isolating diaphragm from both sides (or one side) of the measuring chamber, the silicone oil filling liquid is transferred to the central diaphragm of the & chamber, and the central diaphragm is an edge-tensioned diaphragm. Under the action of pressure, displacement (up to about 0.1mm) will occur, which can form differential capacitance change. After adjustment, vibration and amplification of the electronic circuit board, it will be converted into two-wire 4-20mA·DC signal output, output current and The process pressure is proportional to the magnitude of the process.
Fourth, technical parameters and performance
1, the output signal: 4-20mA · DC two-wire system;
2, power supply; 12-45V · DC;
3, power supply impact: <0.05%>0.05%>
4, load impact: when the power supply voltage is stable, no load impact;
5. Migration characteristics: the maximum positive migration amount is 500%, and the minimum negative migration amount is 600%;
● The absolute value of the negative migration is not more than one engineering atmospheric pressure;
● The absolute values of the upper and lower limits after migration should not exceed the upper limit of the maximum measurement range;
● Migration of differential pressure flow transmitter will destroy the square root characteristics, so migration cannot be performed;
● Absolute pressure transmitters cannot perform negative migration;
6, damping: usually adjustable between 0.2 ~ 1.67 seconds, when filling the inert liquid or with a remote transmission device, the time constant will increase;
7, start-up time: <2 seconds,="" no="" need="" to="">2>
8, explosion-proof type: explosion-proof ExdIIBT4-6 intrinsically safe type ExiaII CT5;
9, indicator table (%); ammeter, scale length 44.5mm, accuracy ± 2%, liquid crystal display, accuracy ± 0.2%;
10. Vibration effect: ±0.005%/g when vibrating in 200HZ in any direction;
11, installation position: the diaphragm is not installed vertically, can produce less than 0.24KPa;
12, temperature effect: ± 0.2%;
13. Static pressure effect: ±0.5%;
14. Accuracy: 0.25%, 0.5%, 1.0%
15, weight: 5.4Kg (excluding accessories);
16. Overpressure effect: ±0.25%;
1. The effects of temperature and overpressure should be measured at the maximum range of the transmitter.
2. Under other ranges, the zero point change caused by overpressure can be restored to normal work through zero adjustment;
3. The working pressure of the GP type pressure transmitter in conformity with the technical indicators is:
When filling with silicone oil: ≥3.5KPa.abs
When filling with fluorine oil: above atmospheric pressure
Five, capacitive pressure transmitter selection