IGBT Gate Signal measured with the Signal Test Board: 2 V
per division vertical scale, 50 ms per division time scale.
Unit running at 30 Hertz.
8.
Using a voltmeter, again check these same signal
board terminals. A correct reading is 2.2–2.5 V
DC.
An incorrect reading of a gate signal indicates that the
control card is defective. Replace the control card.
If the signal is good on the signal test board but missing
on the gate drive board, the failure could be the gate
drive board, the power card, or the ribbon cable between
them. Replace the gate drive board and repeat the test.
6.4.12 Current Sensors Test
The current sensors are Hall effect devices that send a
signal proportional to the actual output current waveform
to the power card. The current scaling card, attached to
the power card, scales the signals from the current sensors
to the proper level for monitoring and processing motor
control data. A defective current sensor can cause
erroneous ground faults and overcurrent trips. In such
instances, the fault only occurs at higher loads. If the
incorrect current scaling card is installed, the current
signals are not scaled properly. Incorrect scaling could
cause erroneous overcurrent trips. If the current scaling
card is not installed, the adjustable frequency drive trips.
There are two ways to determine the status of the sensors.
If the control card parameters are set up to provide
holding torque while at zero speed, the current displayed
is greater than expected. To perform this test, disable such
parameters.
1.
Apply power to the adjustable frequency drive.
2.
Ensure that the following parameter setups are
disabled:
2a
Motor check.
2b
pre-magnetizing.
2c
DC hold.
2d
DC brake.
2e
Any others that create a holding torque
while at zero speed.
If these parameters are not diable, the current
displayed exceeds 1–2 A.
3.
Run the adjustable frequency drive with a zero
speed reference. Note the output current reading
in the display. The correct reading on the display
is approximately 1–2 A.
If the current is greater than 1–2 A and no current-
producing parameters are active, disconnect the motor
cables and repeat the test.
4.
Remove power from the adjustable frequency
drive.
5.
Remove the output motor leads from terminals U,
V, and W.
6.
Apply power to the adjustable frequency drive.
7.
Run the adjustable frequency drive with a zero
speed reference. Note the output current reading
in the display. A correct reading is less than 1 A.
If an incorrect reading was obtained from these tests,
further tests of the current feedback signals are required
using the signal test board.
To test current feedback with the signal test board.
8.
Remove power to the adjustable frequency drive.
Make sure the DC bus is fully discharged.
9.
Install the signal test board into power card
connector MK104.
10.
Using an ohmmeter, measure the resistance
between terminals 1 and 4, 2 and 4, and 3 and 4
of the signal test board. The correct resistance is
an identical readings on all three terminals.
11.
Reapply power to the adjustable frequency drive.
12.
Using a voltmeter, connect the negative (-) meter
lead to terminal 4 (common) of the signal test
board.
13.
Run the adjustable frequency drive with a zero
speed reference.
14.
Measure the AC voltage at terminals 1, 2, and 3
of the signal test board in sequence. These
terminals correspond with current sensor outputs
U, V, and W, respectively. Expect a reading near
zero volts but no greater than 15 mV.
The current sensor feedback signal in the circuit reads
approximately 400 mV at a 100% adjustable frequency
drive load. Any reading above 15 mV while the adjustable
frequency drive is at zero speed negatively affects the way
the adjustable frequency drive interprets the feedback
signal.
Test Procedures
Service Manual
86
Danfoss A/S © Rev. 2014-02-10 All rights reserved.
MG94A222
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Summary of Contents for VLT FC 103
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