PRESSURE SWITCH

[Mr. Steve]

Quoted from the FIRST Pneumatics Manual:

We have included a pressure switch manufactured by The Nason Company. These switches are normally closed. The switches will open at approximately 115psi and will not close again until the pressure drops to approximately 95psi. This will allow you to turn off the compressor once you are up to 115psi, saving power in the battery. It should be wired directly to the robot controller digital input bank with PWM type cable. No specific Digital Input Port is designated for the pressure switch. The Robot Controller must be programmed to react to the Input Port that is connected to the pressure switch The Robot Controller will activate the designated Spike Relay to turn the Compressor “on” and “off”. There is no default program in the Robot Controller to control the Compressor power. Do not put the pressure switch in series with the power supply to the compressor.

Maybe I am missing something, but how is this of any use to us. The highest we can run our pneumatic system is at 60psi, so how is a sensor that measures 95/115 psi be of any use?

Am I just way off track?

[cabbagekid2]

Originally Posted by Mr. Steve

Quoted from the FIRST Pneumatics Manual:


Maybe I am missing something, but how is this of any use to us. The highest we can run our pneumatic system is at 60psi, so how is a sensor that measures 95/115 psi be of any use?

Am I just way off track?

The highest you can run the pneumatic system is 60psi (to solenoids, pistons, etc) but you can store up to 115 psi in the two pneumatic tanks that are connected before the main 60 psi regulator. I guess this is so you can charge up the tanks to 115 psi and run the pistons numerous times before charging the tank up again (since charging the air tanks takes longer than using the air in them).

[Mr. Steve]

Originally Posted by cabbagekid2

you can store up to 115 psi in the two pneumatic tanks that are connected before the main 60 psi regulator.

Thanks for the reply, is there a rule number for this? I couldn't find anything regarding 115psi in pneumatic part of section 5 in the manual.

[Kyle]

I thought it was 120 psi in the system not 115?

[BoyWithCape195]

It is 120...

[Mr. Steve]

Rule R02, finally found it. Thanks

[Sscamatt]

120 psi and 115psi are both correct....in a way:

The maximum allowed by the rules is 120psi. Your robot will be limited to 115 psi because the Nason Pressure Switch shuts off at 115psi.

"The switches will open at approximately 115psi and will not close again until the pressure drops to approximately 95psi."

from page 3 of : http://www2.usfirst.org/2005comp/Man...ticsManual.pdf

[Al Skierkiewicz]

Originally Posted by Mr. Steve

Thanks for the reply, is there a rule number for this? I couldn't find anything regarding 115psi in pneumatic part of section 5 in the manual.

When your robot is inspected, you will need to demonstrate that the compressor turns of via software at a high side pressure of no more than 120 PSI. For that reason it is recommended you follow the system diagram at the bottom of page 20 of the robot manual and include a presuure guage at both the high side (120 PSI) and working pressure (60 PSI) side of the regulator.

"<R88> The Nason Co. pressure switch must be connected to the output end of one of the Clippard tanks to sense the tank’s pressure. The two wires from the pressure switch must be connected directly to a digital input and ground terminals on the Robot Controller, and the controller must be programmed to sense the state of the switch to operate the relay that powers the compressor."

[Dave Flowerday]

Originally Posted by Al Skierkiewicz

When your robot is inspected, you will need to demonstrate that the compressor turns of via software at a high side pressure of no more than 120 PSI.

FIRST has indicated that it is legal to run the pump all the time and ignore the pressure switch:

Originally Posted by FIRST Q&A

ID: 1350 Section: 5.3.10 Status: Answered Date Answered: 1/28/2005
Q: R88 indicates that the Nason pressure sw. is required if we use the pump, but it's not mentioned as a 'minimum' in R86. May we use the analog sensor instead? May we run the pump all the time and not install either sensor?
A: Part 1: You must use the pressure switch. You cannot use the analog sensor. Part 2: You may run the pump all the time; you can ignore the sensor BUT you MUST use the sensor. It is unwise to run your pump all the time as it uses power from your battery.

[Mr. Lim]

Good info on this thread!

To follow-up:

I'm sure teams are going to want to push the limit and get exactly 120 psi into their Clippards. 115 wont cut it - whether it be for practical reasons, or just out of principle =).

I see two options here:

1) use only the Nason pressure switch, and code a timer that causes the compressor to run just long enough after the 115 psi cut-off to get roughly 120 psi.

2) connect both the Nason pressure switch AND the analog pressure sensor. Ignore the output from the pressure SWITCH, and use only the reading from the pressure sensor to dictate compressor shutoff at exactly 120 psi.

Seems a littleweird to me, but are there other options here to get 120psi legally?

-SlimBoJones...

[Steve W]

Originally Posted by SlimBoJones

2) connect both the Nason pressure switch AND the analog pressure sensor. Ignore the output from the pressure SWITCH, and use only the reading from the pressure sensor to dictate compressor shutoff at exactly 120 psi.
-SlimBoJones...

Unfortunately this year there is also a rule (or in Q&A) that states that you cannot use the pressure sensor to shut off the compressor .

[phillutz]

Originally Posted by Steve W

Unfortunately this year there is also a rule (or in Q&A) that states that you cannot use the pressure sensor to shut off the compressor .

Can we use the Pressure Sensor to turn ON the compressor?
We don't like the idea that we need to run the compressor at 95psi when only 60 is passed beyond the next gauge.
If we code the "Start compressor with the Analog, we can run down the pressure to 60-65 and use the battery less... I think

[ttedrow]

Originally Posted by phillutz

Can we use the Pressure Sensor to turn ON the compressor?
We don't like the idea that we need to run the compressor at 95psi when only 60 is passed beyond the next gauge.
If we code the "Start compressor with the Analog, we can run down the pressure to 60-65 and use the battery less... I think

Running the high side at about 115 psi gives your system more air volume to work with. If you run the high side at 65 psi your compressor may not be able to keep up with the cycles or speed that are need during competition.

[phillutz]

Originally Posted by ttedrow

Running the high side at about 115 psi gives your system more air volume to work with. If you run the high side at 65 psi your compressor may not be able to keep up with the cycles or speed that are need during competition.

Looking toward using the Nason as the high side (115psi) and the Analog as the low side so that we can detect when the pressure drops to say 60-65 psi.

[Paul Copioli]

Remember, you must connect the pressure relief valve when using the pump. This valve relieves pressure at around 120psi, no matter what! This is why it is legal to run your pump continuously.

Why pump up to 120 psi when you only use 60psi? That is a matter of "pressure volume". Let's say I have a cylinder that uses the exact volume of air that is in the tanks. If the pressure of the tank is only 60psi, then when I fire the cylinder once I expel all of the air in the tanks. If the pressure in the tanks is 120psi, then I have double the available air to use at 60psi. Air is compressible, which means as you increase the pressure the volume the same mass of air takes up gets smaller. Since the air tanks are a constant volume, when you increase the pressure then the amount of usable air increases. For this reason, you should try to maximize the pressure you have in the tanks.