Calibrate Pressure Switch?
 

Is it possible to calibrate the pressure switch? Ours seems to shut off closer to 105 psi. I would like to be able to carry the maximum capacity of air on board!

Re: Calibrate Pressure Switch?
 

Sadly the pressure switches are factory set...there's nothing you can adjust. Some will be low, some high.

Last year we tested 5 and used the one with the highest pressure. They are factory set. Best you can do is order a few more test them and cross your fingers.

Re: Calibrate Pressure Switch?
 

You might try putting the pressure switch far away from the compressor, so it is less likely to see momentary peak pressures that are above the steady-state pressure. For example, it might help to put it on the other side of the storage tanks from the compressor, if you can do so...

Re: Calibrate Pressure Switch?
 

You can adjust them. Not to be done lightly, but your robot inspector will check it during inspection. PM me for directions if you need them.

Re: Calibrate Pressure Switch?
 

Frank, would you mind sharing how to adjust the switch? We've tried 4 switches and they are all shutting off around 106 PSI.

Re: Calibrate Pressure Switch?
 

Pressure switches cannot be calibrated. They come as they are and not all are alike. Big Al posted somewhere that if it is cutting off early like that then it could be an old one that is starting to fail. Try moving farther from the compressor (still on 120PSI side) or a new switch.

Frank I believe that you are thinking of the pressure relief valve.

Re: Calibrate Pressure Switch?
 

That's what I thought too - as far as I knew the pressure switch is a sealed unit that doesn't take kindly to being disassembled.

Re: Calibrate Pressure Switch?
 

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

Re: Calibrate Pressure Switch?
 

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.

Re: Calibrate Pressure Switch?
 

Does the steps to calibrate the pressure switch fall within R76? It doesn't seem to so I'd be careful about actually doing this.

Re: Calibrate Pressure Switch?
 

The precedent might be that you can adjust the emergency relief valve (and often must) despite it not being an exemption in R76. Then again, the relief valve is governed by R87, which includes a blue box text that explicitly allows for adjusting it. R88, which governs the switch, does not have any similar language. It's sort of a grey area.

My gut would say it's not a alteration of the pneumatic part per se, but a calibration of one using a method designed for that purpose. So long as it turns off the compressor at or below 120 and does so consistently I don't see a rules compliance issue. This hinges on whether the GDC/Inspectors interpret it as a alteration or not.

It's probably worth a Q&A.

Re: Calibrate Pressure Switch?
 

I did a quick look and nothing states that you have to use the Nason pressure switch either (correct me if I'm wrong). Apparently the nason pressure switch may be ordered in a 120PSI variety as well.

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

Re: Calibrate Pressure Switch?
 

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

Re: Calibrate Pressure Switch?
 

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.

Re: Calibrate Pressure Switch?
 

You may not modify pneumatic parts.

Re: Calibrate Pressure Switch?
 

Is calibrating really modifying?

As you are well aware the inspection checklist explicitly requires this switch to be checked that it shuts off the compressor at the appropriate pressure. I see no harm in allowing teams to adjust these rather than forcing them to purchase new ones when a small adjustment will fix the issue. It seems wasteful.

Re: Calibrate Pressure Switch?
 

I think that depends on the switch. As pointed out before, the old Nason pressure switch is not meant to be user set.

Re: Calibrate Pressure Switch?
 

The gap in my spark plugs isn't meant to be user set either. They are a certified technician only job. But I adjust them every time I install new plugs and my car keeps running.

If you are saying I can't adjust a set screw that is designed to be turned with a screw driver because it is modifying a pneumatic component, then we all have to stop using NPT fittings because they deform when threaded together. And push to connect fittings as well because the o-ring and barbs change shape every time a piece of hose passes through them.

Re: Calibrate Pressure Switch?
 

No, you're putting words in my mouth. I was only referring to the Nason pressure switch that had been previously provided in the KOP. This switch was not designed to have the set screw to be adjusted which is why the setscrew was sealed with silicone. Additionally it is ordered with a specific set pressure at which it opens so adjusting the set screw is definitely a illegal modification.

Re: Calibrate Pressure Switch?
 

You could just order a CJ-2C3-70J/HM directly from Nason and be done with it. No problem about modification because it is adjustable.

Re: Calibrate Pressure Switch?
 

Not putting words in your mouth, I said if...

Also, if the manufacturer didn't want it adjusted, they would manufacture it in such a way that it couldn't be adjusted. I would venture to say the set screw is sealed with silicone to prevent it from loosening under vibration commonly associated with compressors, not to keep me from adjusting it. That being said, we never have and probably never will adjust ours. 112-115 psi has worked for two years so far. I think the 114 we have right now will do just fine.

Re: Calibrate Pressure Switch?
 

The product catalog seems to disagree with that assertion as it seems to have purposely left out the set screw in the drawing for the SM switch but not the CJ/CM model. It also includes a adjustment knob and instructions.

Re: Calibrate Pressure Switch?
 

I emailed Nason and got a straight answer on the SM calibration switch. It can be adjusted but only a couple PSI. Unlike the CJ the SM only as 0.030" of contact with the switch so there is a risk of of over turning causing the sensor to always stay on or completely turn off. They said this roughly translate one turn of the sensor relative to the brass hex.

I did not want to copy their email without their permission, but if you PM me I can forward it to you.


Lastly, I already made preparations for my un-adjusted SM sensor. I don't really want go back to the adjusted one which has a unknown number of turns. It could be right at the edge where the sensor does not work and I want to avoid having that potential risk.

So far the level of adjustment that teams are suggesting they need, they are way outside the +/-2PSI of adjustment Nason is recommending. While i think adjusting this sensor is legal, for me personally, +/-2 PSI is too much work for me to care for. The risk of disabling your sensor by going beyond 1 turn of rotation, I would not recommend the adjustment to any team. it would be far simpler to order a SJ sensor, and not worry about that risk.

thoughts?

Re: Calibrate Pressure Switch?
 

To quote Big Al "You may not modify pneumatic parts."

Re: Calibrate Pressure Switch?
 

If you seal your pneumatic system and calibrate your pressure release valve correctly then you can always jump your pressure switch to 120 psi before the match starts. Yes, you would not get 120 the whole match but you would get an extra 20 psi in storage at the start.

Re: Calibrate Pressure Switch?
 

Is it modification if it is a manufacture allowed change? According to Mark, the email from the manufacture states it can be calibrated, while it is only a slight change.

Re: Calibrate Pressure Switch?
 

Ask the question from FIRST in the Q&A and see what they say.

Re: Calibrate Pressure Switch?
 

Mark showed me the response from Nasson and it appears to be more of a calibration of the switch actuator than actual pressure calibration. If you move to far in one direction the switch will turn off and too far in the other direction and it will never turn on. The effect is the pressure on the actuator caused by the spring in the switch I am guessing. The manufacturer states that this is only 2 psi. If you want your switch to operate reliably, I would not recommend any adjustment in addition to my previous statements.
Thanks to Mark for this in depth research.

Re: Calibrate Pressure Switch?
 

Thank you for your response, I am gonna throw away that modified sensor, I have no idea if its set right anymore. Its not worth the risk.

Re: Calibrate Pressure Switch?
 

Before you throw it away, see if you can cut it open and post a photograph. That might be useful for future reference.

Re: Calibrate Pressure Switch?
 

Or send it to me please. I love to break things to see how they work.

Re: Calibrate Pressure Switch?
 

Sure. I will see if I can post it after my team's regional.

Edit: Or I can send it to AL

Re: Calibrate Pressure Switch?
 

I contacted Nason today and spoke with their technical support for the SM switch. They did indicate that it comes precalibrated/preset from the factory. They did indicate that if it is out of calibration you could contact them and they would be happy to repace it or recalibrate it by giving you an RMA. The technical support rep said that if the end user wants to "tweak" the pressure, that they will not warranty it. They said to field calibrate it, but only in a small band ~5-10psi, this is what they do at the factory if the proper base was assembled. The factory uses different bases that have different height diaphram pins for different PSI ranges. I asked that if the switch setscrew is loosened and silicone is removed is this a safety issue, and they indicated that the entire plastic top (limit switch) is removable without a safety problem. We did take one appart at our shop and it is a limit swith screwed onto a blind threded hub with a small diaphram pin that extends out of the ~. 0625 hole to push on the limit swith metal lever. They did indicate that if you desire an on the fly fully adjustabe switch that the CJ switch is the way to go http://www.nasonptc.com/pdfs/Switches_Catalog.pdf page 13.
I could post images of a disassembled switch possibly tuesday when we have our next meeting.

Edit- I see I posted this before seeing that Mark
contacted them too, the only discrepancy is the psi vs 5 to 10 PSI.

Re: Calibrate Pressure Switch?
 

For those lurking here, until directed by the Q&A, an inspector finding a pressure switch that has obviously broken the factory seal will be considered to be a modified pneumatic part. Fair enough?

Re: Calibrate Pressure Switch?
 

Attached is a print out from the Nason switch catalog showing a cut away of the pressure switch. The SM commonly used is the diaphragm type. This is pretty much how most mechanical pressure switch work.

Re: Calibrate Pressure Switch?
 

Thanks Al.

Re: Calibrate Pressure Switch?
 

+1 for clarity! Thank you.

Re: Calibrate Pressure Switch?
 

I felt like you turned and stared at me while you said that... I thought these bushes I was hiding behind were keeping me well out of sight.

Re: Calibrate Pressure Switch?
 

Agreed - consider pneumatic components sacred! Thou shall not touch thy pneumatics in a manner that changes their core use or function as intended by its creator. :D

Re: Calibrate Pressure Switch?
 

If you have an on board compressor you really don't want the compressor to shut off at a higher pressure, in fact you will be better off selecting a switch that turns the compressor on and off at lower pressures, assuming you have selected the proper stored volume.

Take a look at the compressor's specs and you'll see that the higher the pressure it is working against the lower the CFM output.

Some examples

80psi .45cfm
90psi .43cfm
100psi .39cfm
110psi .36cfm
120psi .34cfm

Note those numbers are based on a supply voltage of 13.8 v something that a FRC robot does not have the luxury of, and with a working voltage in the 11-12v range I would expect a steeper drop off of performance.

Personally if I were to select a switch I'd choose one that turns on at ~80 psi and off by ~100 psi to minimize the refill time, the heat build up and general stress on the compressor. If you've sized your storage system properly there should never be a case where the stored pressure drops below 60 psi with a 80/100 switch.

Now if you have an off board compressor there could be an advantage to selecting a switch that shuts off at 120psi but that would be minimal compared to the commonly used 115psi switch.

Either way a switch that has its calibration screw fixed in one way or another by the mfg should not be adjusted, doing so would be considered tampering with or modifying a pneumatic component and make it illegal.

Re: Calibrate Pressure Switch?
 

Sorry for the delay. Here is pictures of the broken pressure switch I have. The silcone seal was very easy to break. The following shows the switch and the housing for the diaphragm. You can see that diaphragm is the piece that is loaded at the factory for the pressure setting and its only factory settable. As I try to pack this up for Al, I can't put this back together, the set screw used to hold the two halves together deformed the threads on the plastic piece and I can't get the treads to engage. So its really really only factory settable. I can see by breaking the seal, the top half can easily disengage (I did this all by hand) and thus keeping the sensor closed and unable to detect full pressure.

Re: Calibrate Pressure Switch?
 

Mark et al,
It is pretty obvious now that you have posted the pictures. The switch is using a standard snap action microswitch. These are not precision devices (the switch) and one must position the switch at a point where the lever will move enough to change the switch state. The hysteresis naturally occurs in the snap action mechanism of the switch. As the catalog page shows, the plunger moves when a specific pressure is reached or exceeded. It does not move a distance that is proportional for pressure. Mark, you can verify this action by applying pressure to the now open switch. I bet when it reaches ~120 psi, the plunger will suddenly move out.

Re: Calibrate Pressure Switch?
 

Can pressure switch be replaced with this pressure sensor and then calibrate within the code?
http://www.digikey.com/product-searc...ds=734-1003-ND

Re: Calibrate Pressure Switch?
 

Sorry but no.

Re: Calibrate Pressure Switch?
 

Now that you mentioned it I looked at the rules. I should've looked at it first.
R78

So, it seems simplest method to workaround for inconsistent pressure switch is to add more air tanks on High-Pressure side, thus even at 100 PSI it will have more volume to be able to fill "Working" pressure side at 60 PSI.

Re: Calibrate Pressure Switch?
 

In our setup we normally have two tanks on high pressure side and one or two on the low pressure side (after the regulator). For our practical purpose it works great. On related topic, last year one of the inspector wanted to test pressure relief valve by shorting the pressure switch. Unfortunately the pressure switch was not easily accessible, he was not very pleased. We believed pressure relief valve was factory set and this year we made sure that pressure relief valve was explicitly tested before mounting on the robot. Had the pressure switch next to the gauges and behold, we had the same inspector but this time he did not want to test it. Anyways SAFETY should be top priority, a lesson learned (no, we did not blow any tanks, just the discussion with inspector) and enforced by our team.

Re: Calibrate Pressure Switch?
 

Hard to say what will be legal in 2015, but by the 2014 Q& A, this would be legal. Or you could send the first choice pressure switch back to Nason & asked that it be re calibrated so that it actually switches at 115 psi rising. Or order one from Nason with a 118 psi rising SP. That would keep you keep you below the about 120 PSI stated in the rules.

The instructions from Nason for recalibrating the SM series pressure switch calls for rotating the barrel 1/2-3/4 turn. Not dissembling the switch. I have done this on our tee shirt cannon & it has been working fine with a consistent set point (120psi) for the last year or so. Per the 2014 Q&A you cannot do this on your comp bot whether or not it works is a mute point for FRC. As in all things, you should always thoroughly test your adjustment to be sure they have the result you intended.

Re: Calibrate Pressure Switch?
 

Adjusting or attempting to adjust the switch to a higher pressure is a huge wast of time. If anything you want a switch that shuts of and turns back on at a lower pressure. The compressor will thank you with building up less heat over time and getting it back up to pressure quicker. Take a look at the rated outputs of compressors the lower the pressure it is working against the higher the cfm. Or take a look at your gauge when you fill the system from empty you'll find the rate of increase in stored pressure decreases dramatically as the stored pressure rises.

Re: Calibrate Pressure Switch?
 

This discussion got started because the OPs switch was turning off at 105 psi. I am not sure where the point of diminishing returns on your system is, but I would say generally speaking I expect it is more than 105 psi. Our comp bot was good at 110 psi. I think our compressor was on for most of the match so the HP cutoff wasn't that important. If you are running a off robot compressor, there is a big difference between 105 & 120 psi in terms of storage. Compressor efficiency is less of an issue if you are running an off board compressor.

Re: Calibrate Pressure Switch?
 

Yes if you are running an off board compressor that is a different story but with an on-board compressor having it shut off at 105 is perfectly fine and I would say desirable.

Re: Calibrate Pressure Switch?
 

Has anyone actually done the math? How much more storage volume conversion at 60 psi do you get with 110 psi stored in two tanks as opposed to 120 psi? Assume that the regulator is the same efficiency at both pressures, and that the compressor efficiency doesn't matter.

Re: Calibrate Pressure Switch?
 

In terms of air storage, it is a linear calculation. Essentially ideal gas law, PV=nRT. So saying 60 psi is the minimum useful pressure. 110 PSI gives a delta P of 50. 120 PSI gives a delta P of 60. A 20% difference. That is in the physics lab with no friction, a perfect vacuum & ignoring entropy. All of this will effect how useful the extra air will be.

Life is always more complicated than that. In our case, the minimum useful pressure was 100 psi because that is what it took to consistently shoot the ball. What was important for us was that the compressor turned on before then. 120 psi would have been useful for precharging before the match, but 110 was good for during the match. We also went with minimal on board air storage to keep the recharge time low. So I largely agree with Mr V about what is a good set pressure.

Re: Calibrate Pressure Switch?
 

Frank, I would suggest that the Q&A does not allow that part. The Q&A states that the part being substituted must be the same or equivilant to the Nason pressure switch. The fact that it is ajustable means that it is not the same or equivilant.

Re: Calibrate Pressure Switch?
 

Q258 Allows any pressure switch that meets the pneumatic rules.

Q459 Allows switches to be callibrated per manufacturer-provided instructions. It does not allow the end user to adjust a switch that the manufacturer did not intend to be adjustable.

R88 calls out the requirements for the pressure switch. The adjust-ability of the switch is not specified.

Doing a quick control-F search on the game manual, the only time the word Nason showed up was in the word Panasonic when referencing allowable batteries. When searching Q&A only 258 and 459 mention the word Nason. Where does the phrase "must be the same or equivilant to the Nason pressure switch." come from. I can't seem to find it.

I heard there was an inspector who successfully got adjustable pressure switches removed from a robot at Champs. Clearly it was not a universal interpretation amongst inspectors, as we ran with this.

Re: Calibrate Pressure Switch?
 

Can I respectfully request that references are posted to specific Q&A?

Doing Q&A search I find these related answers:

Q258

Q. Are teams required to use the Nason Pressure Switch (am-2006) or can we use another switch that stops below 120 psi?
2014-01-30 by FRC3669
A. Any pressure switch may be used, provided it meets all applicable ROBOT rules.

Q459

Q. Can the pressure switch be calibrated per the manufacture's directions? (Specifically the Nason SM-2b-115R supplied in the kit of parts)
2014-03-18 by FRC2974
A. Calibration of pneumatic components per manufacturer-provided instructions would bot be considered alteration. The specific part in question is not marketed to be field/user adjustable so any calibration would be considered an alteration and therefore illegal per R76.

From which I draw conclusion that any pressure switch can be used that meet rules requirement.
In fact I cannot even find the rule the prohibits replacement Pressure Switch with Pressure Transducer.

Re: Calibrate Pressure Switch?
 

Alpha Beta beat me to it LOL

Re: Calibrate Pressure Switch?
 

OK, to be a stickler here, the Pneumatic Rules also include the 2014 FRC Pneumatics Manual which lists the specifications for the switch as "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." In addition paragraph 4 of Section 4, "In addition, another intent of these rules is to have all energy sources and active actuation systems on the ROBOT (e.g. batteries, compressors, motors, servos, cylinders, and their controllers) drawn from a well-defined set of options. This is to ensure that all Teams have access to the same actuation resources, and to ensure that the Inspectors are able to accurately assess the legality of a given part."
For those reasons, adjustable pressure switches are deemed illegal, in particular any switch that can be set to a pressure higher than 115 psi. Throughout section 4.10 the Nason Pressure switch is shown as the pressure switch. BTW, I am betting that the OP is using a standard robot pressure gauge that may or may not be accurate. Tapping on several (hundred) over the years have caused them to change pressure displayed.

Re: Calibrate Pressure Switch?
 

Where in the rules is the pneumatic manual referenced? It seems to be more guidance than a rule. If it going to be taken as rule then it needs to be incorporated into the rules at least by reference so team know they are a rule.

R81 only says stored pressure needs the be below 120 PSI.
The Robot inspection checklist under power on checks specifies the compressor turns at about 120 PSI.
The Q&A Q459 specifically allows pressure switches to be calibrated if intended to be so by the manufacture.
All of this seems to be in conflict with pneumatic manual.

Using cheap non calibrated gauges to verify pressure settings, particularly safeties is a separate thread.

Re: Calibrate Pressure Switch?
 

I wish the rules and manual's language would be a lot clearer.
I am reading same paragraph and I do not see that it means prohibition of pressure switches other than Nason switch provided in KOP

Re: Calibrate Pressure Switch?
 

The pneumatics manual clearly says it cannot supersede the rules.

Al has hinted that there will be some rule changes for 2015. Hopefully this will get cleared up. I still can't find the leg that the inspectors are standing on when disallowing adjustable pressure switches this year. As always the LRI has the final say at the tournament, and we will continue to respect that. At the same time we hope their decisions can be fully backed up by a reasonable interpretation of the rules.

Re: Calibrate Pressure Switch?
 

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

Re: Calibrate Pressure Switch?
 

not within the current rules.

What rule was cited in the decision?

Re: Calibrate Pressure Switch?
 

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.

Re: Calibrate Pressure Switch?
 

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.

Re: Calibrate Pressure Switch?
 

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.

Re: Calibrate Pressure Switch?
 

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?

Re: Calibrate Pressure Switch?
 

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.

Re: Calibrate Pressure Switch?
 

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.

Re: Calibrate Pressure Switch?
 

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

Re: Calibrate Pressure Switch?
 

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.

Re: Calibrate Pressure Switch?
 

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.