Pressure Sensors

[gthakore]

This year we only have one pressure sensor for the pneumatics. last year we had two one for high and one for low. how do we use this years pressure sensor or is there another one that we are getting at a later date? Thanks

[Harrison]

From team update 2, the following pnumatic parts will be in the late shipment:

SMC pneumatic parts:
• Double Solenoid Base Ported Valve
• Flow Control
• Fitting, Straight ¼” Tube
• Fitting, 90 Elbow ¼” Tube
• Fitting, Tee Union ¼” Tube
• Fitting, Male Run T 1/8 NPT ~ ¼” Tube
• ¼” OD Tubing

Does Flow Control=Pressure Sensor?

[Joe Ross]

The reason that we had two pressure sensors last year was to do a "hysteresis". You would turn off the pump when the pressure got to whatever the high sensor was set at (say 115 PSI) and only turn on again when the pressure got below the low sensor (say 100 PSI). This kept the pump from cycling on and off rapidly.

If you read the Pneumatics Manual from this year, you will see that the provided switch provides hysteresis. All you need to do is something like:

if pump_switch is 1, turn on pump, else turn off pump

This is much easier then last year :-)

[Ian W.]

use one sensor, much easier, and on top of that, you save a whole .1 lbs!!!

[Bruce C.]

We plan to put the compressor spike on RLY 7 output and wire the pressure switch to rc_sw1 (pins 1 & 3) of the RC digital input. Then we just use the following code:

relay7_fwd = rc_sw1
relay7_rev = 0

in place of the current relay 7 code. This will have the compressor relay state follow the state of the pressure switch. (Low pressure = closed, high pressure = open). You could use this same scheme with any of the relay outputs and switch inputs.

It works OK with the emulator. Hopefully today or Monday we'll check it against the hardware (I never really trust that software stuff. My favorite programming language is solder.)

Bruce C.

[FotoPlasma]

Originally posted by Bruce C.
We plan to put the compressor spike on RLY 7 output and wire the pressure switch to rc_sw1 (pins 1 & 3) of the RC digital input. Then we just use the following code:

relay7_fwd = rc_sw1
relay7_rev = 0

in place of the current relay 7 code. This will have the compressor relay state follow the state of the pressure switch. (Low pressure = closed, high pressure = open). You could use this same scheme with any of the relay outputs and switch inputs.

Bruce C.

If you want to put it on a Victor (say, PWM8), you can write...

PWM8 = rc_sw1 * 254

That was the first bit of code I actually wrote, early in the build period, in 2002.

[Ian W.]

just remember, if you do your code like that, it will cycle. you're better off if you can do some cheesy timer that will keep the compressor off for x number of seconds, so it doesn't cycle. something to consider, if you have variable space.

[Bruce C.]

Why do you say it will cycle? This year's pressure switch has about 20 psi of hysteresis. That's the whole point of the new switch, so it won't cycle.

[Ian W.]

oh, nevermind then. i haven't played with the new switch. heck, i saw it for a whole two seconds . i assumed it was like the other ones. ok, this makes it even easier to program now.

[Antonio]

does anyone have a program written up for this year's pressure switch yet?

[Bduggan04]

Originally posted by Harrison
From team update 2, the following pnumatic parts will be in the late shipment:

SMC pneumatic parts:
• Double Solenoid Base Ported Valve
• Flow Control
• Fitting, Straight ¼” Tube
• Fitting, 90 Elbow ¼” Tube
• Fitting, Tee Union ¼” Tube
• Fitting, Male Run T 1/8 NPT ~ ¼” Tube
• ¼” OD Tubing

Does Flow Control=Pressure Sensor?

No, I'm almost positive that flow controls are the elbow shaped fittings with screw on top to adjust the rate of flow into the cylinder.

[Chubtoad]

The "flow control" is the elbowed fitting that reduces air flow to slow down say the extension of a piston.

Last year we just used one sensor and built hysteresis into the program. We hooked up the sensor today, in the program simply, if 1 then turn comp on, if 0 turn comp off, (or whatever the numbers and code is) i thnk the limits are 115 and 95. It works very nicely though. Even when it shuts off at 115, the pressure goes a little above 120.

[Moshingkow]

Originally posted by Chubtoad
The "flow control" is the elbowed fitting that reduces air flow to slow down say the extension of a piston.

The flow controls are those elbow things on the ends of the cylinders, but it doesnt control flow, it controls exhaust.

[rbayer]

Originally posted by Antonio
does anyone have a program written up for this year's pressure switch yet?

Look above. All you need is:

relayX_fwd=rc_swY
relayX_rev=0

where X is the relay your pump is connected to and Y is the switch your pressure sensor is wired to.

The flow controls are those elbow things on the ends of the cylinders, but it doesnt control flow, it controls exhaust.

It controls both. If you tighten the screws, air will not be able to enter the cylinder as quickly, thus making it extend slower. Likewise, air will not be able to exhaust out the other side so you will have pressure pushing back the other way for a longer period.

[Jeff Waegelin]

Originally posted by rbayer
Look above. All you need is:

relayX_fwd=rc_swY
relayX_rev=0

where X is the relay your pump is connected to and Y is the switch your pressure sensor is wired to.

It's that simple, then? Does the switch have an upper and lower limit, or is it fixed at 120 psi?

EDIT: I went back and checked the other posts, and I found my answer. Thanks.