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Re: [PSUBS-MAILIST] Barometers



Like Sg. Peppers, the R300 is a small boat.  In early years I to had some pesky O2 and air leaks which I eventully sorted out.  Initially I tried to control my O2 makeup valve using the measured cabin pressure with a barometer (700 to 1100 mBar).  I found this quite problematic.  I changed to controlling off the O2 concentration measurement rather than cabin pressure.  This worked a lot better for me.  When the O2 level drops below 18% the PLC opened the O2 makeup solenoid valve until the O2 concentration reaches 23% then it cuts off.  It takes about 1 minute for the O2 makeup value to cycle from closed to open to closed. In additon to the automatic O2 makeup system, I have a backup manual metering needle valve with a simple direct reading medical flow rate gage.  I added a cabin pressure gage that is 0-30 psia that I use to trigger overpressure alarms.   I had this alarm sound on one dive when a hair line crack developed in O2 regulator high pressure fitting.  The high O2 alarm also went off.  At that point I surfaced the boat.  After blowing my MBTs, I began relasing my hatch latches.  After releasing the first one, the other released poping the hatch open to releave the 5 psi overpressure in the boat.  This sudden release of cabin air was enough to unseat my hatch o-ring. I was very nervous for about a minute until I reseated this o-ring as I could not close the hatch and my freeboard is quite small.   Needles to say, my diving was over for the day and I did not dive the boat again until I found and fixed the source for the high pressure leak and installed a hull equlization valve for the hatch.  I also have a high CO2 alarm which triggers when the CO2 partical pressure exceeds 5000ppm (0.5%). This happens when the CO2 absorbent becomes saturated. Normal air has about 300 ppm of CO2.  I did quite a few 4-8 hour "garage" dives to make sure the environmental controls were working and to sort out the CO2 scrubber fan size. Acturally they are a lot of fun but a bit boring. Garage dives are a great way to debug systems.  The 15 alarms on the R300 are:
 

High Oxygen Level, > 23%

Low Oxygen Level, < 18%

High CO2 Level, > 5000ppm

Hatch Open on Dive

High Main Current, > 300 Amps

High Aux Current, >20 Amps

Low pressure in Air Tank, <750 psia

Low pressure in O2 Tank, < 550 psia

Depth Exceeds 300 ft

Low Cabin pressure , < 12 psia

High Cabin pressure , > 20 psia

Motor field winding > 248 F

Seal Barrier Fluid Outlet Temp >200 F

Low Main Battery Voltage, <110Vdc

Low Aux Battery Voltage, <22Vdc

 
Cliff