Calibrate Pressure Switch?

[Mark Sheridan]

Originally Posted by lonnie lascelle

Calibrating the pressure switch is possible. There is a setscrew on the side which is allen head, the manufacturer has originally set them and put silicone around the threads where the plastic meets metal base. That is what the set screw is for. Take a utility knife score the silicone and peal it out. Loosen setscrew pressurize system, adjust pressure switch by threading the top and bottom half in or out (A little adjustment goes a long way). Adjust to the proper cut in/out pressure, tighten setscrew, reverify pressures, re-silicone – done.

I do this too for the Nason SM model but apparently the SM model is not marketed as field adjustable. Only the CJ model is marketed as field adjustable.
http://www.nasonptc.com/pdfs/Switches_Catalog.pdf

I could not find a source indicating the SM model is ok for field adjustments. As far as I can tell, the manufacture never intended for the SM model to be adjusted by the user.

So would this be an illegal modification to a pneumatic component? Luckily I have a pair of factory set SM models as replacements.

[Tom Line]

Originally Posted by IndySam

Have you tried a different gage? If 4 switches are reading the same I would suspect the gage is bad.

Yep, we tried multiple different pressure gages and they are read similarly (within a psi or two).

[Jaxom]

We are specifically allowed to use other switches; see Q258. Also see http://www.chiefdelphi.com/forums/sh...74&postcount=9

[Nirvash]

Originally Posted by Steve W

The inspector was actually Big Al and Frank was also in on the decision I believe.

What rule was cited in the decision?

[Al Skierkiewicz]

The pressure switch that is being discussed was resettable in seconds, without tools, to a max of 145 psi. For those reasons and others that I discussed with the team, it neither meets the rules, the Q&A nor the intent.

Frank, the calculation I was looking for is the pressure volume conversion. So with two Clippard 41 cu. in. tanks, the conversion to 60 psi results in 157 cu in. @115 psi and 164 cu. in. @ 120 psi. About 4% increase in volume at 60 psi.

Sorry I didn't answer sooner, I was at the Minnesota State HS Champs this weekend.

[ArtemusMaximus]

Originally Posted by Al Skierkiewicz

The pressure switch that is being discussed was resettable in seconds, without tools, to a max of 145 psi. For those reasons and others that I discussed with the team, it neither meets the rules, the Q&A nor the intent.

It seems to me that inspectors have to interpret rules rather than rules being clear enough so they don't need to be interpreted. It puts inspectors and teams in hard position: inspectors to interpret rules and teams to comply with interpretations of the rules rather than comply with clear rules themselves.

If we are going to include "ill-intent" in the considerations, then there are few more ways that things can be reset after passing inspection (i.e. Pressure release valve, or even code itself). What makes pressure switch to be under more scrutiny? After all, for it to work (for pressure above 120 PSI), pressure release valve has to be reset as well.

I suppose asking simple questions on Q&A and getting clear answers would help this situation.

[Al Skierkiewicz]

Art,
We are not saying that the team intended to increase pressure, nor are we saying that they would recalibrate the relief valve. Inspectors do need to make interpretations all the time. This is only one of a hundred + that I made this season. A few were... Are tywraps suitable fasteners for springs? Can a team use barbells for ballast? Is a 16 pound mallet legal for a ball shooter? Can I use a leg lamp from the Christmas Story as a kicker? Can I bring in my protobot and my alternate drive base in addition to my bagged robot? Can I use a ratchet wrench as a mechanism for my shooter release device? Can I use an electro magnet that we rewound for use at 12 volts? When I replace the nylon stockings on my leg lamp that are damaged during a match, is that a repair or modification? Can I put this "mini=sun" on my robot to help my vision system? Can I make a 300 volt power supply to power the neon lights our sponsor would like to see on the robot? Can I write my own protocol software, I don't like that which is provided? These are in addition to the questions asked on the Q&A.

[Jon Stratis]

Al, you missed a classic one at the State Champs over the weekend... Our bumper fell off in the last match, can I attach it to the robot with Duct Tape for the next match?

[ArtemusMaximus]

Originally Posted by Al Skierkiewicz

Art,
We are not saying that the team intended to increase pressure, nor are we saying that they would recalibrate the relief valve. Inspectors do need to make interpretations all the time. This is only one of a hundred + that I made this season. A few were... Are tywraps suitable fasteners for springs? Can a team use barbells for ballast? Is a 16 pound mallet legal for a ball shooter? Can I use a leg lamp from the Christmas Story as a kicker? Can I bring in my protobot and my alternate drive base in addition to my bagged robot? Can I use a ratchet wrench as a mechanism for my shooter release device? Can I use an electro magnet that we rewound for use at 12 volts? When I replace the nylon stockings on my leg lamp that are damaged during a match, is that a repair or modification? Can I put this "mini=sun" on my robot to help my vision system? Can I make a 300 volt power supply to power the neon lights our sponsor would like to see on the robot? Can I write my own protocol software, I don't like that which is provided? These are in addition to the questions asked on the Q&A.

Al,
I hear what you saying and NEVER implied that inspectors purpose was to make teams life harder. I also recognize that it is not an easy job to do the inspections considering so many variables on each robot and decisions have to made quick. But now that we are discussing it without added pressure of the competition event, reasoning you provided did not seem fully align with the rules and that's why I was questioning it.
I wasn't hoping for FRC to include all the variety of weird questions in the rule book. What I was hoping is the rules that already exist to be more clear. In the instance of Pressure Switch something like these would be a lot more definitive:

• Only pressure switch that can be used is Nason fc14-006 (part #SM-2B-115R/443)
  or
• Any COTS pressure switch can be used that switches at 120PSI or less
  or
• Any COTS pressure switch can be used that switches at 120PSI or less. However, no adjustable switches allowed.

This is probably an idealist speaks in me, but I cannot see a reason why rules cannot be clearer.

[Al Skierkiewicz]

Might be more like:

R78
If pneumatic COMPONENTS are used, the following items are required as part of the pneumatic circuit and must be
used in accordance with this section, as illustrated in Figure 4-15.
A. Compressor
B. Pressure Relief Valve, calibrated for release at 125 psi.
C. Pressure Switch, Nason #SM-2B-115R/443 or identical specification (115-120 psi), non-adjustable, equivalent.
D. Pressure Vent Plug
E. “Stored” Pressure Gauge (upstream from Primary Regulator)
F. “Working” Pressure Gauge (downstream from Primary Regulator)
G. “Working” Pressure Regulator

For everyone, the part number shown above is the device sold by AndyMark and the part number refers to a set point of 115 psi. The data sheet specifies the set point at +/- 1 psi with a differential (hysteresis) of 8-16%. That translates to turn compressor back on when the pressure falls below 97-107 psi.
While it is hard to see due to the formatting of the pdf, remember...
R81
“Stored” air pressure on the ROBOT must be no greater than 120 psi.

[ArtemusMaximus]

Originally Posted by Al Skierkiewicz

Might be more like:

R78
If pneumatic COMPONENTS are used, the following items are required as part of the pneumatic circuit and must be
used in accordance with this section, as illustrated in Figure 4-15.
A. Compressor
B. Pressure Relief Valve, calibrated for release at 125 psi.
C. Pressure Switch, Nason #SM-2B-115R/443 or identical specification (115-120 psi), non-adjustable, equivalent.
D. Pressure Vent Plug
E. “Stored” Pressure Gauge (upstream from Primary Regulator)
F. “Working” Pressure Gauge (downstream from Primary Regulator)
G. “Working” Pressure Regulator

For everyone, the part number shown above is the device sold by AndyMark and the part number refers to a set point of 115 psi. The data sheet specifies the set point at +/- 1 psi with a differential (hysteresis) of 8-16%. That translates to turn compressor back on when the pressure falls below 97-107 psi.
While it is hard to see due to the formatting of the pdf, remember...
R81
“Stored” air pressure on the ROBOT must be no greater than 120 psi.

Yeah, something like that. Clearly specifying "non-adjustable" or "adjustable" definitely helps to determine if ability to adjust is allowed or not.

[Tristan Lall]

Do we have confirmation on how the pneumatics control module (PCM) works on the 2015 control system? It has two dedicated Weidmüller terminals for a pressure switch. If there's a microprocessor on the PCM (almost certainly, since there's CAN to decode), can it handle enabling and disabling the pneumatics without influence from the user code and firmware of the RoboRIO (other than a state flag over CAN)?

If it's the case that the user code has no effect on pneumatic cutoff, then that's a big improvement. Perhaps even a big enough improvement to justify leaving out the ability to read an analogue transducer in place of a traditional pressure switch.¹ Right now, the prohibition on using a transducer instead of a pressure switch for sensing the 120 lb/in² limit is pointless, because the team has ultimate control over the compressor relay.

¹ If it's software-controlled in the user code, there's not much added overhead to run a transducer instead. If it's firmware-controlled on the PCM, it might be simplest to avoid providing a method to calibrate an analogue transducer, even though electrically it's equivalently simple.

[adciv]

The PCM works based on the Pressure Switch and the enable flag from the robot. The RIO is not directly in the loop for this.