Legality of using a pressure sensor on the high pressure circuit?

[feverittm]

Our team was intending on including a pressure sensor on our robot this year. To be most effective it should be on the high pressure side of the main regulator (120psi).

However rule R82 implies that this would be illegal.

I know this is not the Q&A area, however I was looking for some thoughts from the CD community.

Any ideas?

[MrForbes]

Mount a video camera so it can see the pressure gauge? I don't think there's a rule prohibiting you from mounting the high side pressure gauge wherever you want, so long as it's visible to the inspectors.

[Joe Ross]

That same rule has been in the rules since at least 2009, so it doesn't seem likely that a pressure transducer was mistakenly left out of the rule, even though one is legal through R78-D.

However, it also appears that no one has asked about a pressure transducer in Q/A since at least 2009, so maybe a mistake could have propagated that long.

Worst Q/A can do is say that the rule stands as written.

A long time ago (probably sometime between 2002-2004), a pressure transducer was included in the kit, but I don't remember anyone using it.

[Kevin Selavko]

There is a pressure sensor included in the First Choice Kit of parts

Also

Pressure Switch
We have included a pressure switch manufactured by Nason. This switch is normally
closed. The switches will open at approximately 115 psi and will not close again until the
pressure drops to approximately 95 psi. This will allow you to turn off the compressor once
you are up to 115psi, saving power in the battery. It must be wired directly to a digital
input and ground port on the Digital Sidecar. No specific GPIO port is designated for the
pressure switch. The cRIO must be programmed to react to the GPIO port that is connected to the
pressure switch. The cRIO will activate the designated Spike Relay to turn the compressor “on” and
“off”. There is no default program in the cRIO to control the compressor power. Do not put the pressure
switch in series with the power supply to the compressor.

-http://www.usfirst.org/sites/default/files/uploadedFiles/Robotics_Programs/FRC/Game_and_Season__Info/2013/2013FRCPneumaticsInfo_RevC.pdf

The only pneumatic system items permitted on 2013 FRC ROBOTS include the items listed below.
...
F. Pressure transducers, pressure gauges, and connecting fittings,

-R78 F

[Mark McLeod]

We've used pressure transducers before, including that TI one that came in the kit a decade ago.
We used one last year, but we used it on the working pressure side as feedback for dynamically adjusting our throwing pressure.

So don't know about the high pressure legality.

[dtengineering]

Wow! You're right... R82 does exclude pressure transducers from the high pressure side of the robot. You're also right that the high pressure side is the place where it makes the most sense to place them!

I know we've used transducers on the the high pressure side in the past... I'll echo the suggestion to submit a Q&A... it seems silly to outlaw a useful instrument such as this.

Good catch... even if the rule doesn't say what I, personally, think it should say!

Jason

[Tristan Lall]

Originally Posted by dtengineering

I know we've used transducers on the the high pressure side in the past...

In some earlier games, this was permitted. (See the diagram on page 26 of the 2005 robot rules.)

Originally Posted by dtengineering

I'll echo the suggestion to submit a Q&A... it seems silly to outlaw a useful instrument such as this.

I completely agree that transducers should be allowed on the high-pressure side. In fact, I'd go further and say they should be allowed in place of the Nason switch.

There's no huge difference between reading a digital input for the Nason switch, and reading an analogue one for a conventional pressure transducer. The internal mechanical logic of the Nason can be accurately represented with a transducer and a snippet of built-in code.

[Mark McLeod]

Not so easy to bypass a pressure transducer to test and set the pressure relief valve. I'd keep the simple pressure switch.

Cheaper too.

[DonRotolo]

Originally Posted by Tristan Lall

In fact, I'd go further and say they should be allowed in place of the Nason switch.

Complicates inspection, so I'd vote no.

[theawesome1730]

Originally Posted by Kevin Selavko

There is a pressure sensor included in the First Choice Kit of parts

The switch you mentioned there is the Nason switch which is required on the high pressure side, so it is not a transducer that is optional.

[Racer26]

Yeah, I'm not sure it should be allowed to replace the Nason switch (though I agree it COULD be used that way safely), but it should certainly be allowed on the high-pressure side.

[Tristan Lall]

You could always pull the transducer cable and jumper the analogue pins to allow an unrestricted fill. That's a little more difficult than just shorting the Nason switch, but it's not that bad.

(I just thought of one surmountable complication: if the transducer is disconnected, the system should shut the compressor off. Therefore the transducer needs to either have a scale that doesn't intersect 0 V, or needs to scale so that 0 V represents some off-scale high pressure.)

[apalrd]

I would be a fan of the pressure transducer, because the Nason one is so heavy for it's function (well, all of the brass fittings are...), if you wanted pressure.

Any reasonable input diagnostics would prevent simple shorting to turn on the compressor, with a positive voltage-pressure curve. If the sensors limits do not include the extremes (0v-0.5v, 4.5v-5v) then the input diagnostics should prevent operation in any case.

If the slope of the pressure->voltage curve is positive, then shorting to 5v would cause the pump to turn off anyway. Shorting to ground should produce a fault which would shut off the pump, so you would need a middle value to force it to come on.

If the slope of the pressure->voltage curve is negative, then 0v would be full and would naturally turn the pump off. 5v would be naturally low pressure, and turn the pump on. This would not be failsafe in a 5v short, but would be better than the other option. The current solution is not failsafe to a ground short, and it's probably easier to short to ground than 5v, so I would consider it acceptable for FRC.

[Mark McLeod]

Originally Posted by Tristan Lall

You could always pull the transducer cable and jumper the analogue pins to allow an unrestricted fill. That's a little more difficult than just shorting the Nason switch, but it's not that bad.

I think pulling and rewiring sensors temporarily to pass inspection is of questionable utility. At the least it means going over the pneumatics cycling an extra time.
The less intrusive inspection is, the better.

And you've seen how buried in the robot some of these connections are and what a mess some of the wiring jobs are.

Not that I wouldn't love always having a pressure transducer on-board...

[funstuff]

Is there is anything specifically requiring the Nason switch?

Do the restrictions put forward by R78A, the FIRST choice selection, and R82 confine the switch used to be only the Nason one? The pressure vent plug is clearly specified by a brand and part number in the rules, which is not consistent with the rules regarding the switch?

If the transducer fulfills the duties of the switch, and meets all other rules, could it be on the high pressure side as the switch as per R82?

Has someone submitted a Q&A on this topic?