- ３-
If there is no normal boot self-calibration, instrument will show "Er" symbol, said boot error. need to
check the cause and reboot (Figure 3).
Correct boot, the meter shows "OLΩ", and the user can test it with a random test ring as shown on the
right. The display value should be consistent with the nominal value on the test ring (5.1Ω). It is
normal that there is a little difference between the display value and the nominal value. For example,
when the nominal value of the test ring is 5.1Ω, it is normal to indicate that 5 or 5.2 is normal. Users
can use it safely.
Please refer to the instruction manual for the specific operation of the tester.
5. Application of MEWOI3000+ in various grounding Systems。
Generally, we divide the grounding system into three kinds: Multipoint grounding system, limited
point grounding system and single point grounding system. The following describes the application of
MEWOI3000+ in these three grounding systems
1）Multi-Point Grounding System
Multi-point grounding system (such as electricity transmission tower grounding system,
grounding cable communications systems, certain buildings, etc.) Connect through the ground wire
(cable shielding layer) to form a grounding system. As below, when measuring, the equivalent circuit is
as follows:
Note : R1 is the target grounding resistance.
R0 is the equivalent resistance of the other entire tower grounding resistances paralleled.
Although strictly on the theoretical grounding, because of the existence of so-called "mutual resistance”,
R0 is not the usual parallel value in the sense of electrical engineering (slightly higher than its IEC
parallel output value). But because a tower-grounding hemisphere was much smaller than the distance
between the towers, and with a great number of locations after all, R0 is much smaller than R1.
Therefore, it can be justified to assume R0=0 from an engineering perspective. In this way, the
resistance we measured should be R1.
Times of comparing tests in different environments and different occasions with the traditional method
proved that the above assumption is entirely reasonable.
2) Limited point grounding system
Some tower grounding systems are connected by several towers through overhead ground wires,
and the grounding of some buildings is not an independent grounding network, but several grounding
bodies are connected with each other through wires. This 3 or more than 10 ground system is called a
limited point grounding system.
This situation is common. In this case, if the R0 is taken as 0, the measurement results will have
big error. The resistance can be calculated by a set of nonlinear equations, but it is very difficult to
solve the problem manually. To solve this problem, our company provides a "limited point grounding
system calculation program" software, users can solve the problem through the PC.
