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| The role of signal isolators |
| 2011-6-1 15:31:25 |
The role of signal isolators
The role of signal isolators
First, the cause of the system's interference
The realization of monitoring and control in the industrial production process requires the use of a variety of automated instruments, control systems and actuators. The signal transmission between them can range from small signals to the millivolt level and milliamp level, as well as dozens of volts. Even large signals of thousands of volts and hundreds of amps; both low-frequency DC signals and high-frequency pulse signals, etc. After forming the system, it is often found that the signal transmission between the instrument and the equipment interferes with each other, causing the system to be unstable or even malfunction. In addition to the performance reasons of each instrument and equipment, such as resistance to electromagnetic interference, this situation is also very important because of the potential difference between the signal reference points between the instrument and the equipment, thus forming a "ground loop "Causes distortion during signal transmission. Therefore, it is necessary to ensure the stable and reliable operation of the system. The "ground loop" problem is a problem that must be solved during system signal processing.
Second, the method to solve the ground loop
To solve the ground loop, there are three solutions based on theoretical and practical analysis:
The first solution: all field devices are not grounded, so that all process loops have only one ground point and cannot form a loop. This method seems simple, but it is often difficult to achieve in practical applications, because some equipment requires grounding. To ensure measurement accuracy or personal safety, some equipment may form new ground points due to long-term corrosion and wear or weather.
The second scheme: make the potentials of the two ground points the same (make V1 = V2), but because the resistance of the ground points is affected by many factors such as geological conditions and climate change, this scheme cannot actually be achieved in practice.
The third solution: use the signal isolation method in each process loop to disconnect the process loop without affecting the normal transmission of the process signal, thereby completely solving the problem of the ground loop.
Third, the advantages of using signal isolators
The use of signal isolation methods in various process loops can be achieved using isolation cards such as DCS or PLC or isolated transmitters on the field (some equipment can do this), or can be implemented with signal isolators . In comparison, using signal isolators has the following advantages:
● In most cases, it is cheaper to use a signal isolator + non-isolated card than to use an isolated card.
● Signal isolators are superior to isolation cards in terms of isolation capability and anti-electromagnetic interference.
● The signal isolator is flexible in application, and it also has signal conversion and signal distribution functions, which makes it more convenient to use.
● Signal isolators usually have single channel, dual channel, and the channels are completely independent of each other, which makes the configuration and routine maintenance of the system more convenient.
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