Posted by Ed Sparks at 2/13/2001 5:41 PM EST
Engineer on team #34, The Rockets, from Bob Jones High / New Century High and DaimlerChrysler.
In Reply to: compressor and light question...
Posted by Anton Abaya on 2/13/2001 3:34 PM EST:
Ok, if you do this you will discover a feature about your compressor you may not have noticed. It has a thermal cutoff
and if you run it constantly at 120 psi head pressure, you WILL experience it.
Actually, this is a good thing because the alternative is to buy a replacement pump at $177 ea (I bought a spare).
I ran into this cutoff problem with my initial version of our compressor control software but using a couple of tricks I solved our problem as follows:
rc_sw1 is where my pressure switch is wired
relay7_fwd is where my compressor is wired
I defined compressor_delay as variable VAR byte
I initialized compressor_delay with a value of 0
I defined delay_setpoint as a constant CON 120
bbox_compressorswitch is a switch on the operator panel
My MAIN LOOP calls the following SUBROUTINE
COMPRESSOR_CONTROL:
if bbox_compressorswitch=OFF then compressor_stop:
if rc_sw1=OFF then delay_compressor_stop:
compressor_delay=0
goto compressor_start:
delay_compressor_stop:
if compressor_delay > delay_setpoint then compressor_stop:
compressor_delay=compressor_delay + 1 + delta_t
goto compressor_start:
compressor_start:
relay7_fwd=ON
return
compressor_stop:
relay7_fwd=OFF
return
The plan is to keep pumping air into the volume tanks past the pressure switch trip setting (about 110 psi) until you reach the point where the pressure relief valve starts to open (about 120 psi). I do this by counting the number of program cycles plus delta_t from the point where the pressure switch opens. In my case a value of 120 (about 3 seconds) for delay_setpoint works good. When the air is consumed and the pressure drops below the pressure switch trip setting, the whole thing starts over.
It works fine for us and keeps the compressor from short cycling (not good) when there is no demand for air .
Hope this helps!