Malfunctions with Indications
2-13
Velocity Processor Faults
No.
Name
Description
Recovery
VP-10
Feedback Loss
(Selectable Soft
or Warning)
(Parameter 101
bit 0 when
Parameter
630=1)
•
The following applies when VP-10 is configured
as a soft fault:
The velocity measured from the feedback device is
less than the level programmed in parameter 732
“Tach Loss Vel” and the velocity calculated from the
CEMF of the motor is greater than the level
programmed in parameter 731 “Tach Loss CEMF”.
A coast stop will be initiated.
If parameter 106 “Velocity Fdbk” < parameter 732
“Tach Loss Vel” AND calculated CEMF from param
105 “Arm Voltage Fdbk” > param 731 “Tach Loss
CEMF” THEN fault on VP-10 Feedback Loss.
In general terms when the velocity measured from
the feedback device, either an Encoder or a DC
Tach, is less than the value programmed in
parameter 732 “Tach Loss Vel” then the first
condition of this test is met. Parameter 732 is
usually programmed to a value which represents a
velocity very close to zero speed, typically 0-5% of
base speed.The CEMF of the motor is directly
proportional to velocity below base speed, but is
not dependent on the feedback device. When the
calculated CEMF is greater than the value
programmed in parameter 731 “Tach Loss CEMF”
then the second condition of the test is met.
Parameter 731 is usually programmed to a value of
CEMF which represents a velocity significantly
above zero speed, typically 5-30% of Motor rated
CEMF. The measured value of CEMF is
represented in parameter 105” Arm Voltage Fdbk”.
Both conditions listed above must be met before
the fault is generated.
To set up the associated parameters for safe
operation use these general guidelines. The higher
the value of parameter 731 “Tach Loss CEMF”, the
greater the velocity of the motor before a Feedback
Loss is detected. If parameter 731 is too high,
excessive velocity can be reached before the drive
faults. This can be especially true in applications
requiring very fast acceleration and deceleration
rates, high current limits, and low inertias. If the
value is too low, nuisance faults may occur.
Likewise, the higher the value of parameter 732
“Tach Loss Vel” the more likely nuisance faults may
occur. If the value is too low then noise in the
velocity feedback signal could keep the fault from
occurring when indeed a feedback loss has
occurred, especially with an analog DC Tach
feedback device.
The method of recovery varies greatly depending on the
cause of the fault.
1. The feedback device (encoder or DC Tach), may have
failed and correct operation should be verified. See
page 3-9
for details. If the feedback device has
malfunctioned, then replace it and execute a Clear Fault
to continue operation.
2. Check jumpers J8, J9, J10 on Main Control Board for 5V
or 12V encoder output selection. DO NOT use channel Z,
Only A, A NOT, B, B NOT are to be used.
3. Verify that the encoder power supply has not folded back
due to a short circuit or excessive current draw. +12V (+/
-5%) must be present between TB3-14 & 13. If the
measured voltage is less than 1 volt, the supply has
folded back. Remove the power supply connections to the
encoder at those terminals and cycle power to the drive.
This will reset the encoder power supply foldback circuit. If
Voltage is now present a short circuit or malfunction of the
feedback device has occurred and must be corrected. If
the +12V is not present after cycling power, replace the
Main Control Board.
4. Verify that 621 “Fdbk Device Type” has the proper device
selected. If incorrect, select the entry that matches the
device being used and execute a Clear Fault to continue.
5. If an encoder is being used, verify that 609 “Encoder
PPR” matches the PPR (Pulses per Revolution) of the
encoder being used. Correct the entry and execute a
Clear Fault.
6. If a DC Tach is being used, verify that the Analog Input
Channel is properly configured to parameter 156 “Tach
Velocity”. Also verify the scaling and offset parameters
associated with the analog channel are correctly set-up.
Pay close attention to the polarity of the tach signal in
respect to direction of rotation. Properly scale and offset
the analog channel and execute a Clear Fault to continue
operation.
7. Verify that parameter 610 “Rated Motor Volt” matches the
nameplate rating of the motor. Also verify that parameter
739 “K Arm Volts” is properly scaled to assure that the
armature voltage being monitored is accurate. To verify
the scaling of parameter 739, rotate the motor under
armature voltage feedback and compare the measured
armature voltage, A1 to A2 with a DVM, to the reported
armature voltage as reflected in parameter 105 “Arm
Voltage Fdbk”.
Note: If using armature voltage feedback to troubleshoot the
feedback loss, the set-up procedure for armature voltage
feedback must be performed first for proper operation.
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