Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 64)

64 Rockwell Automation Publication 750-RM002B-EN-P - September 2013
Chapter 1 Drive Configuration
Hand-Off-Auto Many legacy drive installations included a circuit (such as a Hand-Off-Auto
switch) that provided 3-wire start and stop signals simultaneously to the drive.
PowerFlex 750-Series drives do not start unless there is a full input cycle between
the stop and start signals. P176 [DI HOA Start] adds a delay to the start signal,
allowing the required time interval between the start and stop signals. This
enables the use of a single 3-wire control circuit to start and stop the drive.
Hand-Off-Auto Start
If P161 [DI Start] and P176 [DI HOA Start] are both configured, a “DigIn Cfg
B” alarm results. You cannot use both Digital Input Start and Digital Input
Hand-Off-Auto Start at the same time.
Hand-Off-Auto Example
A Motor Control Cabinet has an Hand-Off-Auto switch wired as shown in the
figure below.
When the switch is turned to Off, the switch is open between the source and
Stop (DI:0) and between Stop and Start (DI:1). This causes the drive to be in an
asserted stop. When the switch is turned to Auto, the control signal reaches the
Stop input but not the Start. The drive can be stopped and started by another
location. When the switch is turned to Hand, both the Stop and Start ports are
energized.
In order for the drive to start, the Stop signal must be received prior to the Start.
With the wiring above, the signals are nearly simultaneous, too fast to be sure that
the drive is ready to start. This causes the switch to either be unreliable or not
work at all. This can be remedied by adding a time delay to the start signal. By
changing Digital Input 1 from DI Start to DI Hand-Off-Auto Start, the drive
+24V
H A
O
XOO
XOO
OOX
DI 0: Stop
DI 1: Start