What is ground loop interference? What harm does it do? For ground loops, ground loops often come and go without a trace, leaving only a trace on the oscilloscope. It popped up and then disappeared while the electronics were working properly.
Ground loop interference is a relatively common interference phenomenon that often occurs between far-flung devices connected by long cables. The intrinsic reason for its generation is the existence of ground loop current. Since the ground loop interference is caused by the ground loop current, in practice, it is sometimes found that when the safety ground wire of a device is disconnected, the interference phenomenon disappears. This is because when the ground wire is disconnected, the ground loop. This phenomenon often occurs when the interference frequency is low. When the interference frequency is high, it does not matter whether the ground wire is shorted or not.
Reason 1 for the formation of ground loop interference:
The ground potential of the two devices is different, forming a ground voltage, and driven by this, current flows between the loop formed by Device 1 – the interconnecting cable – Device 2 – ground. Due to the unbalance of the circuit, the current on each wire is different, so a differential mode voltage will be generated, which will interfere with the circuit. The voltage on the ground wire is caused by the fact that other devices with high power also use this ground wire, causing a strong current in the ground wire, and the ground wire has a large impedance.
Reason 2 for the formation of ground loop interference:
Since the interconnected equipment is in a strong electromagnetic field, the electromagnetic field induces a loop current in the loop formed by the equipment 1 – the interconnecting cable – the equipment 2 – the ground, causing interference as in the process of cause 1.
There are two basic ideas for solving ground loop interference:
One is to reduce the impedance of the ground wire, thereby reducing the interference voltage. Another is to increase the impedance of the ground loop, thereby reducing the ground loop current. When the impedance is infinite, the ground loop is actually cut off, that is, the ground loop is eliminated. For example, floating the equipment at one end, or disconnecting the circuit board from the chassis is a direct method. But for electrostatic protection or safety reasons, this direct method is often not allowed in practice. More practical methods are the isolation transformers, opto-couplings, common mode choke coils, balanced circuits and other methods described below.
The specific practices are as follows:
1, [干扰形成原因]: The “ground potential loop” applies the potential divider to both ends of the cable shielding layer, and forms a loop through the 75 ohm matching resistors at both ends of the cable, which generates an interference voltage on the load.
2. Cut off the ground loop – it is the most effective and easiest way; without any anti-interference equipment;
3. One of the anti-jamming design principles of the monitoring system is that one end of the terminal monitoring equipment is connected to the ground, and the front-end camera, BNC head shell, and cable shielding layer must be insulated from the ground (open circuit); even if the ground loop interference is suppressed by the use of anti-jamming equipment, It should also be excluded, because the “ground loop” is changing and unstable. With the increase of high-power equipment in the power grid and the change of power imbalance, the size of the ground potential difference will also change, and the equipment will be burned in severe cases. The above is some analysis of ground loop interference, I hope it can help you.