Logic Error - Out of ideas

I am trying to stagger pumps from starting right after each other. I have a running TON that resets after a pump has been called, next pump can only be called when TON is done. The accumulator does get reset, but immediately goes back to 60 secs and the TON always evaluates True even when accumulator is reset... Why is this ?



--- alot stripped out, tried only leave in pertinent stuff----
In one Task:
(* Sequential Start Delay *)
SEQSTRT_TON (IN:=True, PT:=t#60s,
Q=>Sequential_Start_OK, ET=>Seqential_Start_Acc);

In another derived FB, passing accumulator to reset it to t#0s:

(* Pump Motor Start/Stop *)
IF pump_required AND NOT pump_motor_call THEN
pump_motor_call := TRUE ;
seq_start_acc := t#0s;
END_IF;
IF NOT pump_required AND pump_motor_call THEN
pump_motor_call := FALSE;
END_IF;

FYI: Using Unity Pro XL 3.0

Fixed it using a TON for each pump. Basically the TON IN needs to evaluate false to reset the accumulator. Anyone know why you can't reset the accumulator manually, this would result in more versitile code one would think.



---- code snip ----
Task: Sequential Start Bit
IF P1_Seq_Start_OK AND P2_Seq_Start_OK THEN
Sequential_Start_OK := TRUE;
ELSE
Sequential_Start_OK := FALSE;
END_IF;


---Derived function block-----
(* Pump Motor Start/Stop *)
IF pump_required AND seq_start_ok AND NOT pump_motor_call THEN
pump_motor_call := TRUE ;
pump_seq_start_rst := TRUE;
END_IF;
IF (NOT pump_required AND pump_motor_call THEN
pump_motor_call := FALSE;
END_IF;

PUMP_SEQ_TON (IN:=NOT pump_seq_start_rst, PT:=seq_start_time,
Q=>pump_seq_start_ok);

pump_seq_start_rst := FALSE;

(* pump_seq_start_ok returned as PX_Seq_Start_OK *)

For a delay start between pumps I would use a single timer looking at all of the pumps off for x time. I don't know about other plcs, but in the ABs you should be able to reset the .acc valve.

The start delay is to prevent the pumps from coming on at the same time, because the transformer cannot handle the start current for more than one pump at a time and/or things need to stabilize before determining if more pumps are needed. Thats why the counter resets after each pump is called, to delay the start of the next pump etc.