Electronic equipment grounding resistance value in addition to other provisions, generally should not be greater than 4 Ω and the use of a point of grounding. Electronic equipment grounding and lightning grounding system **** with the grounding body. But then the grounding resistance should not be greater than 1 Ω. If separated from the lightning protection grounding system, the distance between the two grounding systems should not be less than 20 m. Regardless of whether the use of *** with the grounding system or separate grounding system, should meet the provisions of the provisions of chapter 12 of this specification lightning protection.
Electronic equipment should be based on the need to decide whether to use shielding measures.
(1) DC ground (including logic and other analog signal system ground).
(2) AC operating ground.
(3) Safety protection ground.
The above three grounding resistance value of the general requirements are not greater than 4 Ω. In general, the signaling system of electronic computers, should not be used to suspend the ground.
There are many factors that affect the grounding resistance: the size of the grounding electrode (length, thickness), shape, number, depth of burial, the surrounding geographic environment (such as flat, ditch, slope is different), soil moisture, texture and so on. In order to ensure good grounding of the equipment, the use of meters to grounding resistance measurement is essential.
The measurement of grounding resistance can be divided into: voltage and current meter method, ratio meter method and bridge method. According to the specific measuring instrument and cloth pole number can be divided into: hand-operated ground resistance meter method, clamp-type ground resistance meter method, voltage and current meter method, three-pole method and four-pole method.
Extended information:
Measurement of the grounding resistance of the earth's surface. p>Measurement of grounding resistance, some factors cause grounding resistance inaccuracy:
(1) the soil around the ground network composition is not consistent, geological different, tight, dry and wet degree is not the same, with the dispersion of the ground surface stray currents, especially overhead ground, underground water pipes, cable outer skin, etc., the test is particularly large impact. Solution: take different points for measurement, take the average value.
(2) The test line direction is not right, the distance is not long enough. Solution: Find the right test direction and distance.
(3) Auxiliary grounding electrode resistance is too large. Solution: Splash water at the ground stake or use resistor to reduce the grounding resistance of the current pole.
(4) test clip and grounding measurement point contact resistance is too large. Solution: Grind the contact point with a file or sandpaper, and use the test line clamp to adequately clip the grounding contact.
(5) interference effects. Solution: adjust the release direction, try to avoid interference in the direction of the meter readings to reduce the jump.
(6) meter use problems. Battery power is insufficient, the solution: replace the battery.
(7) meter accuracy decline. Solution: Recalibrate to zero.
The accuracy of the test value of the grounding resistance is one of the important factors to determine whether the grounding is good. Once the test value is inaccurate, either a waste of manpower and resources (measured value is large), or will bring safety hazards to the grounding equipment (measured value is small).
Fixed resistors are available in a variety of types, the choice of which material and structure of the resistor, should be based on the specific requirements of the application circuit. High frequency circuits should use non-wirewound resistors with small distributed inductance and distributed capacitance. High-gain small-signal amplification circuit should be selected with low noise resistors, such as metal film resistors, carbon film resistors and wirewound resistors, rather than using noisy synthetic carbon film resistors and organic solid-state resistors.
The resistance value of the selected resistor should be close to a nominal value calculated in the application circuit, and priority should be given to the standard series of resistors. The general circuitry used in the resistor allowable error of ±5% ~ ±10%. Precision instruments and special circuits used in the resistor, should be selected precision resistors, the precision of 1% or less of the resistor, such as 0.01%, 0.1%, 0.5% of these levels of resistance should be used in the Jabil letter resistor.
The power rating of the selected resistors should be in accordance with the requirements of the application circuit on the power capacity of the resistors, and generally should not be increased or decreased arbitrarily resistor power.
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