Causes of system interference

In the industrial production process to achieve monitoring and control need to use a variety of automation instruments, control systems and actuators, the signal transmission between them both weak to millivolt level, microampere level of small signals, but also tens of volts, even thousands of volts, hundreds of amps of large signals; Both low frequency DC signals, but also 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, resulting in system instability and even misoperation. In addition to the performance reasons of each instrument and equipment itself, such as anti-electromagnetic interference, there is also a very important factor that is due to the potential difference between the signal reference points between the instrument and equipment, thus forming a "ground loop" resulting in distortion during signal transmission. Therefore, in order to ensure the stable and reliable operation of the system, the problem of "ground loop" must be solved in the process of system signal processing.

Solution to the "ground loop"

Based on theoretical and practical analysis, there are three solutions:

The first option: All field equipment is not grounded, so that all process loops have only one ground point, can not form a loop, this method seems simple, but it is often difficult to achieve in practical applications, because some equipment must be grounded to ensure measurement accuracy or ensure personal safety, some equipment may be due to long-term corrosion and wear or climate impact and form a new ground point.

The second scheme: the electric potential of the two ground points is the same, but because the resistance of the ground point is affected by many factors such as geological conditions and climate change, this scheme can not be fully achieved in practice.

The third solution: the signal isolation method is used in each process loop to disconnect the process loop without affecting the normal transmission of the process signal, so as to completely solve the grounding loop problem.