Delta ASDA-A3 Series User Manual page 199

Wiring
AL501 SF1 lost / AL502 SF2 lost (signal loss or signal error): see the following diagram.
When the motor runs normally, but one of the safety signal source is low for 1 second, the "STO
signal detected by firmware" flag is on, and the servo drive becomes off, triggering AL501 or
3
AL502. The following diagram illustrates how AL501 occurs.
Note:
Contact the distributor if AL503 (STO self-diagnostic error) occurs.
1.
Refer to Section 3.10.5 for the EDM signal.
2.
3-118
SF1
H
H
SF2
L
STO signal
STO not
detected by
active
firmware
Open
EDM
DO.SRDY
ON
Alarm
No alarm
L
1s
STO active
Max. 20 ms
Open
OFF
AL501
ASDA-A3