Analysis of Several Faults of Pressure Sensors and Transmitters

With the continuous maturity and development of contemporary sensing technology, it is also widely used in the field of computer automation control. Industrial equipment primarily controlled by automated control systems has played an important role in promoting various industries. The automatic control of liquid level sensor structure is applied to weighing seasoning and pipeline pressure testing. Therefore, work efficiency has greatly improved. Sensors are the central system of modern science and one of the main ways and means to obtain information in the natural field. It refers to the general term for components or devices that have experience and verification effects on a certain determined information of the tested object, and convert it into corresponding outputtable signals according to certain rules.

1、 What is a sensor?

With the continuous progress and development of science and technology, the meaning of many technical terms has changed, leading to frequent misunderstandings. Sensors are a great example. The sensor consists of two parts: a conversion element and a sensing element. The conversion element refers to the part of the sensor that converts the experience or response of the sensitive element into an electrical signal suitable for transmission or detection; Sensitive components refer to the parts of a sensor that can be directly sensed or responded to for measurement. Due to the fact that the sensor output is usually a very weak signal, it is necessary to deploy and amplify it. However, with the continuous development of science and technology, this part of the circuit and power supply are also installed in sensors. In this way, the sensor can export usable signals that are easy to process and transmit. But in the past, when technology was relatively backward, the so-called sensor referred to sensitive components, while the transmitter was a conversion component.

How to distinguish between transmitters and sensors?

Sensors are generally composed of sensitive components and conversion components, and are devices or equipment that can inspect and convert specified measurements according to certain rules into usable output signals. When a sensor is exported as a specified standard signal, it is a transmitter. The device that converts physical signals into electrical signals is called a sensor, and the device that converts non-standard electrical signals into standard electrical signals is called a transmitter. Primary instrument refers to on-site detection instrument or base control instrument, while secondary instrument refers to the use of primary instrument signals to complete other functions.

The transmitter and sensor together constitute the detection signal source for automatic control. Different sensors and corresponding transmitters can meet the needs of different physical quantities. The weak electrical signal collected by the sensor is amplified by the transmitter for easy transmission or activation of control components. Sensors convert non electrical physical quantities into electrical signals and transmit these signals directly to the transmitter. Another type of transmitter is a remote instrument that sends the condensate water from the lower part of the water level sensor and the upper part of the steam to both sides of the transmitter's corrugated pipe based on the instrument pipe. The differential pressure on both sides of the corrugated pipe is used to push the mechanical amplification equipment to mark the water level with a pointer. In addition, there are also some that can be called transmitters, which convert electrical analog quantities into digital quantities.

3、 Liquid level sensors and transmitters are prone to malfunctions

The liquid level sensor and transmitter are prone to the following faults: firstly, the pressure rises, and the transmission of the transmitter cannot be improved. In this case, the pressure interface should be checked first for leaks or blockages. If not, check the wiring method and power supply. If the power supply is normal, simply charge it to see if the output has changed or check if the sensor zero position has been exported. If there is no change, the sensor has been damaged, which may be due to instrument damage or other issues in the entire system; The second issue is that the export of the pressure transmitter remains unchanged, and then the export of the pressure transmitter suddenly changes. The zero position of the pressure transmitter cannot be returned, which is likely due to a problem with the sealing ring of the liquid level sensor. The common reason is the specification of the sealing ring. After the sensor is tightened, the sealing ring is compressed into the sensor pressure port, blocking the sensor. Pressure substances cannot enter the pressure, but the pressure suddenly opens the sealing ring, causing the liquid level sensor to experience pressure changes. The common reason is the specification of the sealing ring. After the sensor is tightened, the sealing ring is compressed into the sensor pressure port, blocking the sensor. Pressure substances cannot enter the pressure, but the pressure suddenly opens the sealing ring, causing the liquid level sensor to experience pressure changes. The best way to clear such faults is to remove the sensor and directly check whether the parts are normal. If the parts are normal, the sealing ring can be replaced and tried again; The third type is the unstable output signal of the transmitter. This type of malfunction is definitely a problem with the pressure source. The pressure source itself is an unstable pressure, which may be due to the weak anti-interference ability of the instrument or liquid level sensor, severe vibration of the sensor itself, and sensor failure; Fourthly, there is a significant comparison error between the transmitter and the pointer pressure gauge. Deviation is a normal phenomenon that can determine the range of normal deviation; The last common fault is the impact of the installation mode of the micro differential pressure transmitter on the zero output. Due to the small detection range of the micro differential pressure transmitter, the sensing components in the transmitter can affect the output of the micro differential pressure transmitter. Place the pressure sensitive component of the transmitter radially perpendicular to the direction of gravity, and adjust the transmitter components to the standard value after installation and fixation.

4、 Precautions and maintenance when using liquid level sensors and transmitters

1. Precautions during use. The correct installation method of the transmitter on the process pipeline is related to the substance to be measured. In order to achieve the best measurement effect, several situations should be noted. The first point is to prevent the transmitter from coming into contact with corrosive or overheated media; The second point is that when measuring liquid pressure, the pressure outlet should be set on the side of the step tube to prevent slag deposition; The third point is to prevent the accumulation of residues inside the catheter; The fourth point is that when measuring gas pressure, the pressure outlet should be set at the top of the step tube, and the transmitter should also be installed at the upper end of the step tube to facilitate the accumulation of liquid and easy injection into the step tube; The fifth point is to measure steam or other high-temperature substances, and to connect coolers such as buffer tubes (coils), the working temperature of the transmitter should not exceed the limit; The sixth point is that the pressure pipe should be installed in areas with low temperature fluctuations; The seventh point is that during winter freezing, outdoor transmitters must take antifreeze measures to prevent damage to the sensor due to expansion of frozen volume; The eighth point is to tighten the sealing cap of the cable through waterproof joints or winding pipes to prevent precipitation from leaking into the transmitter casing through the cable; The ninth point is to measure the liquid pressure to avoid liquid impact and prevent damage to the sensor due to overpressure.

2. Maintenance of pressure transmitters. The pressure transmitter needs to be inspected once a week and once a month, usually to remove dust from the instrument, carefully inspect electrical components, and regularly calibrate the output current value. The internal part of the pressure transmitter is weak and must be separated from the external weak current.

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