Monday, December 27, 2010
【 Weak current College 】 electromagnetic interference on precision instrument and equipment of 】
Electromagnetic interference is defined by electric, magnetic and radio frequency, etc. produced by the radiation source. For its part, is normal and is a regular, but on other instruments, equipment, particularly high precision instrument and equipment are concerned, their impact is very harmful. Electronic technology, communication technology and the rapid development of computer technology and widely implemented, making precision instrument and equipment areas of application, particularly as they have weak signal detection capacity increasingly upgrade, EMI's influence and effect to the extent absolutely necessary. If the aircraft's navigation system, a antijamming has taken various measures and restrictions, such as all over the world every corner of the computer control center, the negative effects of electromagnetic interference; and another undeniable as increasing concern over the recent years the medical inspection system, it is becoming more and more dependent on various medical equipment inspection measurement results. Its high degree of precision and more. Various electromagnetic interference can cause these devices run an exception, their assay data for accurate work on medical direct impact and damage. With precision instruments continue to promote and apply, for its work environment offers a new, specific requirements. A comprehensive understanding of electromagnetic interference sources and routes of transmission, take effective preventive measures to improve the precision instrument and equipment operating environment, make it a prerequisite for stable work.
Effect of human body static electricity countermeasures
According to the principles of physics, two objects between friction produces static electricity. When because of the precision instrument and equipment of the environment humidity is too low, the air is too dry, wear insulated shoes walk on the chemical fiber rug, chemical fiber clothes are worn down, near high-voltage electric field, in the human body produces static, maximum up to ten thousand volts. Due to the
Energy storage effect, when in contact with metal will discharge, arcing, and once on your computer and embedded instruments discharge, will cause a run-time error, instrument light will cause the test data, heavy will panic, cause damage to components. Its consequences and risks cannot be ignored.
On such interference should take the following measures: precision instrument and equipment of the shell must be accurate and reliable grounding and single. Grounding resistance ≤ 4 Ω; precision instrument and equipment in place workplace environment relative humidity at 50%; workplace desktop, ground for strict anti-static treatment; precision instruments before proceeding contact discharge; equipment for maintenance, ground maintenance to wear bracelets; storage related circuit board, MOS devices you want to use an antistatic film.
Alternating electric field effects of countermeasures
In our environment in a significant number of AC, the body is among the alternating electro-acoustic will charge for induction alternating, although their energy level is low, but because of the precision instruments tested by the information source of energy at a lower level, such as on human bioelectricity? ECG, EEG measurement, the measured signal weak in μ V level or even lower, so in this environment does not take anti-jamming measure, interference will detect the signal, was unable to conclude that the correct submerged.
Such interference can take the following measures: the impact of electrical category weak signal measurement of major impact comes from the low-frequency electric field, so the first thing to keep away from sources of interference; to reduce the power and the body of the loop area, this can reduce the electric field flux thus reducing disturbance signals; to precision instruments detect weak biological signals such as EEG, ECG, etc., should be carried out in shieldingroom; attention should be paid to the reasonable shielding room, shielding room available metal mesh production and reliable grounding shield blanket also has certain tamperproof, conditional departments should be equipped with the precision instrument and equipment; built-in filtering method is also an effective way to eliminate interference, but choose to use this method, it will decay is the heartbeat of the active ingredient, distortion, effect measurement accuracy. To ECG machine, for example, General machine there is a filter on the open key, when the communication interference, press this button to get smooth ECG waveform, and non-interference, no filtering of graphics, will find filter bottom waveform voltage; after QRS time extension, get a worse result, if the patient is unable to spread the bed and grounding shield blanket, you can exclude Exchange interference.
Strong magnetic field of countermeasures
Due to the special diagnostic needs, this reservoir such as magnetic resonance, and other medical equipment distribution around a strong magnetic field, it will make the picture tube, x-ray image intensifier display image distortion-distortion; Accelerator Ray offset; computer disks, magnetic card record data destruction; respiratory machine work out; there are likely pacemakers work fail and endanger life. So in some can produce strong or weak field of precision instrument and equipment of the Labs site design of the above factors must be taken into account.
On the strong magnetic field the following measures should be taken, in a de facto field strength regional cordon, signs, according to the field strength distribution and equipment on the sensitivity and the magnetic field of magnets to keep a certain distance: magnet or interference with equipment related parts using magnetic shielding to reduce the influence of magnetic leakage.
The impact of high frequency radiation countermeasures
In our living room is full of electromagnetic radiation. If the radio emission of electromagnetic waves, mobile phone, EDM, high-frequency equipment, fluorescent lamps, controllable circuits, electrical, automotive, lighting, solar activity, and so on, are the exception will have high-frequency electromagnetic pollution, some also string into the power grid, interference with equipment, precision instrument and equipment installation wiring unreasonable and would produce undesirable coupling. These harmful electromagnetic radiation will produce noise to the image, the computer operation chaos, control failure; strong high-frequency interference or even cause damage to electronic circuits. Some precision instrument and equipment itself also has high-frequency source, if protection is improper, on the operation and maintenance personnel.
High-frequency electromagnetic interference countermeasures are: the elimination and prevention of the use of electrical interference, can produce metal shielding. Its basic principle is: the metal surface will be part of the electromagnetic wave reflection off through the surface of metal parts in metal internal whirlpool transformed into thermal energy consumed, which absorb electromagnetic interference, thereby significantly attenuated. In order to be effective shielding effect, shield metal thickness should be close to the electromagnetic wavelength λ = 2 π-d, d a penetration depth using metal net also has good effect, when the shield of voids to be 50%, if each wavelength6 of the above network cable, you can get substantially the same as with the metal plate. Due to the more grounded generates multiple current loop, effects, masking layer should be grounded. If necessary, between the ground and covered with insulating layer shielding guarantee reliable grounding point. In the use, maintenance attention shielding net enclosures, cabinets door seal, so as to minimize all avoid radiation. In addition, the choice of the power line to use with screen; using purification power supplyfiltering out all kinds of Burr and installation of high frequency components, precision instruments, power lines and signal lines to separate laying; mutual with high power cable twisting of the way to offset their own produce electromagnetic interference; Earth grounding resistors achieve technical requirements, etc., can play a role in the prevention of interference.
On precision instruments cause electromagnetic interference factors there are many, it will give precision instruments caused strange, it is difficult to judge the strange fault. Therefore, in the sector of precision instrument settings? as control center, hospitals, etc. in the planning, design, layout, equipment maintenance, anti-jamming, and electromagnetic pollution should not be ignored, only fully understand and master the knowledge and strategies, take effective preventive means for the accurate measurement precision instruments, better service to mankind.