With the continuous maturity and development of sensor technology, it has also been widely applied in the field of computer automation control. Mechanical equipment mainly controlled by automation control technology has played a great driving role in various industries. The construction of pressure sensors for automated control has been applied in weighing and batching, pipeline pressure testing, and other fields. Therefore, it greatly improves work efficiency.
Today’s society is an era of informatization, and people’s social activities mainly rely on the development, acquisition, transmission, and processing of information resources. Sensors are the central nervous 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 the ability to sense and detect certain information about the tested object, and convert it into corresponding output signals according to certain rules.
1、 What is a sensor
With the continuous development and progress of science and technology, the meanings of many technical terms have changed, often leading to misunderstandings. Among them, sensors are a good example. At present, sensors are composed of two parts: conversion elements and sensitive elements. The conversion element refers to the part of the sensor that converts the measured signal sensed or responded by the sensitive element into an electrical signal suitable for transmission or measurement; Sensitive components refer to the parts of a sensor that can directly sense or respond to the being measured. Due to the fact that the output of sensors is usually very weak signals, it is necessary to modulate and amplify them. But with the rapid development of science and technology, people have also installed this part of the circuit and power supply circuit inside the sensor. In this way, the sensor can output usable signals that are easy to process and transmit. In the past, when technology was relatively backward, sensors referred to sensitive components, while transmitters were conversion components.
2、 How to distinguish between transmitters and sensors
Sensors are usually composed of sensitive elements and conversion elements, and are a general term for devices or equipment that can detect specified measurements 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. The device that converts physical signals into electrical signals is called a sensor, while the instrument that converts non-standard electrical signals into standard electrical signals is called a transmitter. A primary instrument refers to an on-site measuring instrument or base control table, while a secondary instrument refers to the use of signals from the primary instrument to perform other functions.
The transmitter and sensor together form the monitoring signal source for automatic control. Combining 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, which amplifies the signal for transmission or activation of control components. Sensors convert non electric physical quantities into electrical signals and transmit these signals directly to the transmitter. Another type of transmitter is a remote instrument that sends the condensed water from the lower part of the liquid level sensor and the upper part of the steam through an instrument tube to both sides of the transmitter’s bellows. The differential pressure on both sides of the bellows drives the mechanical amplification device to indicate the water level with a pointer. In addition, there is also a transmitter that converts electrical analog signals into digital signals.
3、 Common malfunctions of pressure sensors and transmitters
The main faults that are prone to occur with pressure sensors and transmitters are as follows:
The first type is when the pressure goes up, the transmitter output cannot go up either. In this situation, first check whether the pressure interface is leaking or blocked. If not, check the wiring method and power supply. If the power supply is normal, perform a simple pressurization to see if the output changes, or check if the sensor zero position has output. If there is no change, the sensor is damaged, which may be due to instrument damage or other issues in the entire system;
The second type is that the output of the pressure transmitter does not change, and then the output of the pressure transmitter suddenly changes, causing the zero position of the pressure relief transmitter to not return, which is likely to be a problem with the sealing ring of the pressure sensor. It is common that due to the specifications of the sealing ring, after tightening the sensor, the sealing ring is compressed into the sensor pressure port and blocks the sensor. When pressurized, the pressure medium cannot enter, but when the pressure is high, the sealing ring suddenly opens, causing the pressure sensor to change under pressure. The best way to troubleshoot this issue is to remove the sensor and directly check if the zero position is normal. If the zero position is normal, replace the sealing ring and try again;
The third type is unstable transmitter output signal. This kind of malfunction may be a problem with the pressure source. The pressure source itself is an unstable pressure, which is likely due to weak anti-interference ability of the instrument or pressure sensor, severe vibration of the sensor itself, and sensor failure; The fourth type is that there is a large deviation between the transmitter and the pointer pressure gauge. Deviation is a normal phenomenon, and confirming the normal range of deviation is sufficient;
The last common fault is the influence of the installation position of the differential pressure transmitter on the zero position output. Due to its small measurement range, the sensing elements in the micro differential pressure transmitter can affect its output. During installation, the axial direction of the pressure sensitive part of the transmitter shall be perpendicular to the gravity direction. After installation and fixation, adjust the zero position of the transmitter to the standard value.
4、 Precautions and maintenance during the use of pressure sensors and transmitters
1. Precautions to be taken 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 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 tap should be opened on the side of the process pipeline to avoid sedimentation and slag accumulation; The third point is to prevent sediment from depositing inside the conduit; 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 at the upper part of the process pipeline, so that the accumulated liquid can be easily injected into the process pipeline; The fifth point is that when measuring steam or other high-temperature media, a condenser such as a buffer tube (coil) should be connected, and the working temperature of the transmitter should not exceed the limit; The sixth point is that the pressure pipe should be installed in a place with small temperature fluctuations; The seventh point is that when freezing occurs in winter, anti freezing measures must be taken for transmitters installed outdoors to prevent the liquid in the pressure inlet from expanding due to freezing volume and causing damage to the sensor; The eighth point is to thread the cable through the waterproof joint or flexible tube and tighten the sealing nut during wiring to prevent rainwater and other substances from leaking into the transmitter housing through the cable; The ninth point is that when measuring liquid pressure, the installation position of the transmitter should avoid the impact of the liquid to prevent damage to the sensor due to overpressure.
2. Maintenance of pressure transmitters. It is required to inspect the pressure transmitter once a week and once a month, mainly to remove dust from the instrument, carefully check the electrical components, and regularly calibrate the output current value. The pressure transmitter has weak electricity inside and must be isolated from external strong electricity.
Post time: Apr-23-2025