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Related Products: |
EGMA-401, EGSA-310, EGSA-320, EGSK-404, EGSK-405, EXMC-001, EXMC-002 |
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Related Documents: |
EZDP-2080 |
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Type: |
Troubleshooting |
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Keywords/Labels: |
ground current, shaft voltage, wear indicator, rope fault |
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Summary: |
This document describes how to monitor and troubleshoot test points. |
The test points in the monitoring system connect directly to the following sensor locations:
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“Shaft Voltage” is connected directly to the SGA’s meter rope on the shaft.
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“Exciter Shaft Voltage” is connected directly to the SCA’s meter rope on the shaft (if SCA is installed).
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“Signal Ground” is connected to the unit case grounding location and is the ground reference for both the shaft voltage and Wear Indicator test points.
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Each Wear Indicator test point is connected to a resistance-based wear indicator circuit. A 5V DC reading at the test point indicates a rope in good condition, whereas a voltage close to 0V DC indicates a worn rope in need of replacement.
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Ground Current + and - are connected to the output of the ground current sensor on the grounding wire.
Note
Monitoring must be powered on for ground current to be measurable at the test points. All voltage readings are direct connections and can be taken regardless of whether the monitoring system is powered on or off.
Please note, the ground current test points are connected to the output of the current sensor located at the grounding location so the monitoring system must be powered on to take measurements at the ground current test points.
To measure current flowing to ground from the shaft, place the positive and negative probes of a scope or hand-held meter on the “Current +” and “Current –“ test points, respectively. Refer to the following table to convert the resulting voltage reading to the associated ground current value.
|
Meter Reading (V) |
Shaft-to-Ground Current (A) (100mV/Amp scale) |
|---|---|
|
4.65 |
-30 |
|
3.65 |
-20 |
|
2.65 |
-10 |
|
1.65 |
0 |
|
0.65 |
10 |
|
-0.35 |
20 |
|
-1.35 |
30 |
To read the shaft voltage, place the positive probe of the hand-held device on the Shaft Voltage or Exciter Shaft Voltage test point, and place the negative probe on the Signal Ground test point. The resulting voltage or waveform read at this point represents the shaft voltage at the associated metering rope location. The Shaft Voltage test points do not require power, so valid measurements can be taken even if the monitoring system is powered off.
Cutsforth Shaft Grounding Assembly ropes come equipped with an insulated conductor threaded into the center of the grounding and metering ropes. If the rope has not worn out to its center point, the conductor insulation will be intact and there will be no electrical contact between the wear indicator conductor and the outer portion of the ground rope. When the conductor insulation has worn through, the resistance may vary, but a value less than 500 Ohms, as measured per the technique described in Rope Fault Troubleshooting Recommendations, indicates that a breach of the insulation has taken place. If you observe a value below 500 Ohms, inspect the rope. It is likely that rope replacement is required.
Using a voltmeter set to measure resistance, measure between the wear indicator contact and the outer rope contact on the underside of the rope grip to confirm whether or not the rope needs replacement. See the image below:
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If 500 Ohms or greater resistance is measured, the rope does not require replacement.
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If less than 500 Ohms is measured, the rope requires replacement, even if it may not look like it.
If the above recommendation does not resolve the issue, contact Cutsforth Support.