Subject: A68 Alarm...
This is Terminal 37 Safe Stop input on the drive. It is wired to the HPC switch. It can open in two scenarios, (1) HPC opens (changes state) during normal power, or (2) power loss to the drive.
An explanation for the second scenario:
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Safe Stop on the AFD needs 24Vdc at terminal 37 for normal operation
- If 24Vdc is not present, it kills power to the output of the AFD, and will internally log A68, and issue an AFD fault
- We run the AFD Safe Stop circuit through the NO contacts on 1K14
- 1K14 closes when power is applied to the chiller and the HPC is within limits (no High Pressure condition exists)
- If power is removed, 1K14 coil de-energizes and opens the NO contacts
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The AFD will stay powered ~ 40second after power is removed due to internal DC capacitance
- During that time if the AFD thinks it is seeing a HPC event because of de-energized 1K14, it logs A68
- After power is returned, 1K14 will close again
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The drive sees 24Vdc on Terminal 37 and will clear its AFD Fault in 10 seconds
- This is fast enough for the UC800 to not see the AFD Fault, this was confirmed in the lab
- If the event is long enough, the Danfoss TR200 and the UC800 will detect the fault A68
Original HUB Document: DOC-116907
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