What are the interference sources of the cablerope displacement encoder

What are the interference sources of the cable/rope displacement encoder-okplazas.com displacement sensor

What are the interference sources of the cable/rope displacement encoder

The output signal of the cable displacement encoder is an electrical signal, and the electrical signal is easy to receive environmental interference, so how to avoid this problem? Today, Xingfeng editor will take you to understand the specific interference sources of the rope displacement encoder:

1. Switching signals. All non-sinusoidal electromagnetic waves and rising and falling switching signals contain electromagnetic waves of various frequency bands, among which are high-frequency electromagnetic waves that are easier to radiate outward.

2. Metal conductors, all open non-contacting two metal conductors, or between a sharp metal tip and the earth, may form a capacitor. Longer metal wires or wire coils can also form an inductance Components. Capacitive components and inductive components will form one or several circuits with special frequency oscillations, which send or receive radiation signals, especially higher frequency electromagnetic waves that are more likely to form such radiation and reception.

3. High-frequency electromagnetic waves. The digital square wave signal device contains a lot of high-frequency electromagnetic waves. This part of the high-frequency waves is easily affected by the high-frequency electromagnetic waves of the same frequency from space and changes its form. This part of the high-frequency electromagnetic waves in the wire Transmission, because its high-frequency signal is easier to attenuate and radiate outward, and lose this part of high-frequency energy. Similarly, because this part of the high frequency part is easier to radiate outward, it also becomes the interference source of other digital square wave signals. The signals of various waveforms generated and conducted by various circuits can be decomposed into high-frequency parts in the transformation, and are interfered by the high-frequency of the same frequency from space, causing attenuation and even interference to the waveforms of other signals. .

4. Electrostatic interference. Static electricity refers to the charge or potential difference that does not flow. There are different charges or potential differences between two media. When the energy accumulates to a certain extent, or the distance is close, or there is electric field distortion at the sharp end, or there is The charge conduction breakdown of the gray layer will cause the breakdown and discharge of this static electricity. This is a sudden change in the spatial electromagnetic field layout, causing the short-term reconstruction of the electromagnetic field to release energy, the most typical being lightning. One of the most typical examples in actual industrial control automation is the closing and opening of contact switches: charge accumulation when non-metallic media is dry, more dusty charge accumulation, sharp corners and wire burrs of metal conductors, and equipment From the moment of power outage to power on, the difference in static electricity caused by the non-equal potential of various parts and so on. There is a lot of static electricity, and various micro-discharges may occur at any time. This short-term discharge will interfere with the digital signal, as small as a glitch on the waveform, and large enough to damage the output and receiving devices.

In industrial control, there are still more NPN devices in use. The common end of this type of device is at high level, and most of the equipment is at 0V low level as the common ground. These two "common ends" are Two non-equal-potential electrostatic potential differences are pre-established, which is also the possibility that electrostatic interference is more likely to occur. Avoid using NPN encoders and various switches.

Coping with electrostatic interference: equipotential connection, no metal sharp corners and burrs, no dust, isolation, antistatic treatment of non-metallic media.

5. Low-frequency and magnetic field interference. Low-frequency and magnetic field interference mainly comes from power electricity, motors, and various coils. The power used in industry is AC 50Hz three-phase or two-phase AC. In the surrounding area with large power, the surrounding electromagnetic field changes due to the transmission of AC (linear cable distribution and various wire coils), as well as electromagnetic wave reflection and beat superposition , Harmonic, the contribution of the external magnetic field due to the instantaneous three-phase imbalance when the motor is rotating, and the low frequency leakage of the switching power supply and the inverter. Low frequency interference is mainly close-range inductive coupling and direct medium conduction. Low-frequency interference destroys the energy part of the digital signal, and the entire waveform is cut down.

Responding to low-frequency interference: open the distance, magnetic ring or ferromagnetic material absorbs low-frequency energy, and metal seal isolation needs to protect the device to prevent low-frequency conduction.

6. Various other high-frequency interferences. According to the principle of Fourier change, all changing waveforms can be separated into electromagnetic waves of various frequencies. Except for the perfect sine-cosine waveform, which has only one frequency, the other various waveforms contain high-frequency parts. In addition to conducting on the surface of the conductor medium, this kind of high frequency will also radiate outward, especially the part with metal sharp corners and wire burrs. For signal generating sources, signal conducting cables, and signal receiving units, high-frequency interference will exist. It is easier to absorb external high-frequency interference in areas with metal sharp corners, open terminal sharp corners, and metal cable burrs. High-frequency interference destroys the graphic outline part of the digital signal. When the high-frequency energy is large, it will instantly heat and destroy the device.

The high-frequency radiation wave reflects the bright metal surface and absorbs energy to the thin and dense metal wire. This is the function of the cable shielding layer.

Coping with high-frequency interference: fine metal shielding and energy absorption, no metal sharp corner burrs. Change the designed capacitance value or inductance value, and change the LC frequency to prevent high-frequency self-excitation.