Maintenance of pressure sensors

1. What is a sensor

At present, the sensor that people say is composed of two parts: a conversion element and a sensitive element. Among them, the conversion element refers to the part of the sensor that converts the measurand felt or responded by the sensitive element into an electrical signal suitable for transmission or measurement; the sensitive element refers to the part of the sensor that can directly feel or respond to the measurand.

Since the output of the sensor is usually a very weak signal, it needs to be modulated and amplified. However, with the continuous development of science and technology, people have installed this part of the circuit and power supply circuits together inside the sensor. In this way, the sensor can output a usable signal for easy processing and transmission. In the case of relatively backward technology in the past, the so-called sensor refers to the sensitive element, while the transmitter is the conversion element.

2. How to identify the transmitter and sensor

Sensors are usually composed of sensitive elements and conversion elements, and are a general term for devices or devices that can detect specified measurands and convert them into usable output signals according to certain rules. When the output of the sensor is a specified standard signal, it is a transmitter. A device that converts a physical signal into an electrical signal is called a sensor, and an instrument that converts a non-standard electrical signal into a standard electrical signal is called a transmitter. The primary instrument refers to the on-site measuring instrument or the base control meter, and the secondary instrument refers to the use of the signal of the primary meter to complete other functions.

Transmitters and sensors together constitute the monitoring signal source for automatic control. Different sensors and corresponding transmitters can be combined to meet the needs of different physical quantities. The weak electrical signal collected by the sensor is amplified by the transmitter, and the signal is amplified for transmission or activation of the control element. Sensors convert non-electrical quantities into electrical signals and transmit these signals directly to transmitters. There is also a transmitter that sends the water in the lower part of the liquid level sensor and the condensed water in the upper part of the steam to both sides of the bellows of the transmitter through the instrument tube, and the differential pressure on both sides of the bellows drives the mechanical amplification device to indicate with the pointer A remote gauge of water level. In addition, there are transmitters that convert electrical analog quantities into digital quantities.

3. Failures prone to occur in pressure sensors and transmitters

The main faults that are prone to occur in pressure sensors and transmitters are as follows: The first is that the pressure goes up, and the transmitter can’t go up. In this case, first check whether the pressure port is leaking or blocked. If it is not confirmed, check the wiring method and check the power supply. If the power supply is normal, simply pressurize to see if the output changes, or check whether there is an output at the zero position of the sensor. If there is no change, the sensor is damaged, which may be caused by damage to the instrument or other problems in the entire system;

the second is that the output of the pressure transmitter does not change, and the output of the pressure transmitter changes suddenly, and the pressure release transmitter zero If the bit does not go back, it is likely to be a problem with the pressure sensor seal.

Commonly, due to the specifications of the sealing ring, after the sensor is tightened, the sealing ring is compressed into the pressure port of the sensor to block the sensor. When pressurized, the pressure medium cannot enter, but when the pressure is high, the sealing ring is suddenly opened, and the pressure sensor is under pressure. Variety. The best way to troubleshoot this kind of failure is to remove the sensor and directly check whether the zero position is normal. If the zero position is normal, replace the sealing ring and try again;

The third is that the output signal of the transmitter is unstable. This failure is likely to be a stressor issue. The pressure source itself is an unstable pressure, which is likely to be due to the weak anti-interference ability of the instrument or pressure sensor, the strong vibration of the sensor itself, and the sensor failure; the fourth is the large deviation between the transmitter and the pointer pressure gauge. Deviation is a normal phenomenon, just confirm the normal deviation range; the last kind of failure that is prone to occur is the influence of the installation position of the differential pressure transmitter on the zero output.

Due to the small measurement range of the differential pressure transmitter, the sensing element in the transmitter will affect the output of the differential pressure transmitter. When installing, the axis of the pressure sensitive part of the transmitter should be perpendicular to the direction of gravity. After installation and fixing, adjust the zero position of the transmitter to the standard value.

4. Matters needing attention and maintenance during the use of pressure sensors and transmitters

1. Matters needing attention during use.

The correct installation position of the transmitter on the process pipeline is related to the measured medium. In order to obtain the best measurement results, several points should be paid attention to. The first point is to prevent the transmitter from contacting with corrosive or overheated media; the second point is to measure the pressure of the liquid, the pressure tap should be opened on the side of the process pipeline to avoid sedimentation of slag; the third point is to prevent the slag in the conduit Internal deposition; the fourth point is that when measuring gas pressure, the pressure tap should be opened at the top of the process pipeline, and the transmitter should also be installed on the upper part of the process pipeline so that the accumulated liquid can be easily injected into the process pipeline; the fifth point is to measure steam or other high-temperature media, it is necessary to add a condenser such as a buffer tube (coil), and the operating temperature of the transmitter should not exceed the limit; the sixth point is that the pressure guiding tube should be installed in a place where the temperature fluctuation is small; the seventh point When freezing occurs in winter, the transmitter installed outdoors must take anti-freezing measures to prevent the liquid in the pressure port from expanding due to freezing and causing damage to the sensor; the eighth point is when wiring, pass the cable through the waterproof joint or Wrap the flexible tube and tighten the sealing nut to prevent rainwater from leaking into the transmitter housing through the cable; the ninth point is when measuring liquid pressure, the installation position of the transmitter should avoid the impact of liquid to avoid sensor overpressure damage .

2. Maintenance of pressure transmitter.

The pressure transmitter is required to be inspected once a week and once a month. The main purpose is to remove the dust in the instrument, carefully check the electrical components, and check the output current value frequently. The inside of the pressure transmitter is weak, so it must be Separated from external strong electricity.