[Fews] OCT9_09.pdf

[Steve Christo]

Hey Will,
Here's the PDF printout of the Concept, PLC control program (attached) 
that is currently downloaded to the the PLC controller. Searching for 
"trouble" yields results in the "Announce_Alarms", "Fire_Wire", 
"Sniffer_Valves" and "Vesda" sections. When we were looking at the 
program sections yesterday, we only saw the "Announce_Alarms" section. 
The others were not displayed so it was not not clear until now how the 
PLC handled the nitrogen filling faults.  The following code in the 
"Sniffer_Valves" section is most likely generating the problem that we 
were seeing.
--------------
IF adc4[5] < 2000 THEN
IF liquid_nitrogen_is_filling = 0 THEN
trouble_lamp := 1; (* this shouldn't ever happen unless the filling 
failed and timed out, maybe not even then *)
END_IF ;
liquid_nitrogen_level_problem := 1;
plc_ready := 0 ;
(* stop cycling valves if we run out of LN2 in small dewer *)
(* this avoids making false alarms due to detector warming up *)
ELSIF liquid_nitrogen_level_problem = 1 THEN
(* Here we have transitioned from having an LN2 problem to not having a 
problem *)
(* Now reset the sniffer so the spectrometer background isn't stale *)
initialize_SNIFFER := 1 ;
wait_for_pc := 0 ;
liquid_nitrogen_level_problem := 0 ;
ELSE
liquid_nitrogen_level_problem := 0 ;
END_IF ;
--------------
The new level control is giving the fill signal to the PLC but channel 1 
of the old controller is being used to measure the liquid level in the 
large Dewar. Ch. 1 was formerly used to measure the level of the 
Detector Dewar before we installed the new level controller (the old 
controller wouldn't let us use Ch. 2 to monitor the large Dewar level 
without an input to Ch. 1). When there was a problem with the connection 
on the level probe to Ch. 1 of the old controller, it gave the PLC a 
"failed to fill" signal and caused our problem. I don't remember how I 
left the controller tied into the system but it's obviously affecting 
it. I'll try to find a way to remove the old LN2 level controller from 
the system without harm and let you know. Thanks again.
Steve

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