Rockwell Automation FlexPak 3000 Digital DC Drive Version 4.3 - Manual (Page 146)

13-14 FlexPak 3000 DC Drive Software Reference
13.4 SCR Diagnostics and Adjusting Open
SCR Sensitivity
Under normal drive operation, the load carried by each SCR is relatively equal, as
shown in figure 13.1.
If one or more SCR s fail to turn to on, a unique pattern of insufficient or missing current
pulses results, as shown in figure 13.2.
Open SCR diagnostics detects SCR s that are not conducting by analyzing the level of
current produced by each SCR pair firing. If one or more SCR consistently fails to
produce current at a level approximately equal to other SCR s that fired, the drive
concludes that an open SCR has occurred.
The open SCR diagnostic calculates the percentage deviation of current feedback for
each pair of SCR s from the average current feedback. The percent deviation must
exceed the value set for OPEN SCR SENSITIVITY (P.600) before the diagnostic proceeds
to the next part of the diagnostic.
In the next part of the diagnostic, deviations from the average current are integrated
over time to eliminate transient effects from the calculation. When the integration
reaches the value of
OPEN SCR TRIP THRESH (P.601), an open SCR fault is generated.
If you are experiencing nuisance SCR faults, you can use these parameters to increase
the tolerance to conditions that could trigger an open SCR fault.
Figure 13.1 – SCR Armature Current During Normal Operation