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Symptom: The equipment is operating normally, and the DC current indication is too high. If the current is set to the rated value, the voltage is too low, and the indicated value of the power meter does not match the DC voltage DC current, which was consistent with the previous one.
Fault Analysis and Processing: The cause of this fault is because the indication of the DC ammeter is inaccurate, causing an illusion that the current is large.
The cause of this failure is more subtle and difficult to find. If you analyze it carefully, you can find that the indicated value of power does not match the product of voltage and current, indicating that the displayed value of the meter may be incorrect. The voltage value can be proofed by the multimeter's DC voltage block. The current value can be corrected by measuring the incoming current with a clamp-type ammeter and dividing by 0.816. If it does not match, the ammeter indication is not accurate.
The value of the DC ammeter is taken from the 75mY voltage signal generated by the shunt. Under the condition of long service life and harsh operating environment, there is dirt or oxidation between the wiring and the shunt on the shunt, and the contact resistance increases. , so that the voltage generated on the shunt is increased, greater than 75mY, causing the indication of the DC ammeter to be too large.
The treatment is to treat the dirt and oxide layer between the shunt and its wiring.
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