Titanium Plate,Custom Titanium Plate,Titanium Sheet 1Mm,Gr1 Titanium Coil Plate Titan Super Bond Co., Ltd , https://www.laget-ti.com
Why can't the shield of the shielded cable be grounded repeatedly?
Shield grounding is usually handled in two ways: Single-end grounding of the shield and double-end grounding of the shield
1 The single-end grounding of the shield is to ground the metal shield directly at one end of the shielded cable, and not at the other end or through protective grounding.
Single-ended grounding is to eliminate electromagnetic interference by suppressing the potential difference. This grounding method is suitable for short length lines, and the induced voltage corresponding to the cable length cannot exceed the safety voltage.
2 Double-ended grounding is to connect both ends of the shielded cable's metal shield to ground.
When the shield is grounded at both ends, the metal shield will not generate an induced voltage, but the metal shield will be shielded by the influence of the interfering magnetic flux. If the potentials of the site A and the site B are not equal, a large potential will be formed. Circulation and circulation will counteract the attenuation of the signal.
There are three methods of system grounding: floating ground, direct grounding, and capacitive grounding.
For the PLC control system, it is a high-speed low-level control device and should be directly grounded. Because of the influence of signal cable distribution capacitance and input device filtering, the signal exchange frequency between devices is generally lower than 1 MHz, so the ground wire of the PLC control system adopts one-point grounding and one-point grounding.
The centrally-arranged PLC system is suitable for parallel grounding at one point. The central ground point of the cabinet of each device is led to the grounding electrode by a separate grounding wire. If there is a large distance between the devices, use a point-to-point grounding method. Use a large-section copper busbar (or insulated cable) to connect the center ground points of the cabinets. Then connect the ground bus directly to the grounding electrode.
When the signal source is grounded, the shielding layer should be grounded on the signal side; when it is not grounded, it should be grounded on the PLC side; when there is a connector in the middle of the signal line, the shielding layer should be firmly connected and insulated, and must be grounded at multiple points. When shielded twisted pairs of multiple measuring points are connected to a multi-core twisted shielded cable, the shielding layers should be connected to each other and be insulated and grounded at a single point.
Summary: 1: There is no potential difference between the two ends of the ground, there will be a weak current potential difference, so that the shielding actually becomes a grounding line. 2: The shielded wire at both ends is grounded in the work site where the high-frequency interference is severe, and the line capacitance formed between the shield layer and the internal signal line is coupled to the signal circuit, which will seriously affect the signal misjudgment. 3: Various types of governors and PLCs specify that the signal line shield must be single-ended grounded and the ground should be on the controller side.