Data Sheet

Diagnosing VSD failure
Using a DMM
• Check the input line voltage (figure 1)
– A typical multimeter will display either average
or rms voltage values
– Depending on the type of distortion, the rms or
peak value may not reveal if a problem exists
• Check the VSD dc bus voltage
– The dc bus voltage is directly proportional to the
peak of the input line voltage
– Any distortion or error in peak amplitude of the
line voltage can cause an over- or under-
voltage error
• The drive dc bus voltage in figure 2
shows around 20 % under the nominal
value of 160 V
Figure 1. Measuring the line voltage at
the input to a Pulse Width Modulated
drive, appears to be normal
Figure 2. Checking the dc bus voltage
level is less than nominal revealing a
potential problem
Do you replace the drive
controller and/or motor?