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Unread 01-27-2004, 11:57 AM
ErichKeane ErichKeane is offline
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Question Pressure Sensor Readings

Didnt want to cross post, so if a mod believes this would be better in Programming/elsewhere, please let me know, or move it.

I have coded in my pressure sensor for everything as ordered, and technically, it should all work. The sensor returns a 1 to turn off, a 0 to turn on, and all works perfectly in that respect (ie, turns on when it reaches a certian pressure etc).

My problem is this, the sensor turns off the pump at 80PSI, and turns it back on at 30PSI! I could have sworn it was supposed to be either 65/55 or 125/115, yet it does not!

Is this a defective piece, or do i have something hooked up incorrectly?

Thank you all,
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Unread 01-27-2004, 12:08 PM
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Re: Pressure Sensor Readings

which sensor did you use? the one with 2 scews to hold the wires, or the new analog one (I think the wires are molded into it) ?
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Unread 01-27-2004, 12:54 PM
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Re: Pressure Sensor Readings

Well, if your using the same one that was suplied last year (which you must if its returning 1's and 0's) It must be faulty. Its very difficult to program wrong because it IS a digital input.

Another posibiliy could maybe be where it is plumbed though. It might get all crazy if its plumbed past a regulator. My thoughts are still with faulty part though
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Unread 01-27-2004, 01:10 PM
KenWittlief KenWittlief is offline
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Re: Pressure Sensor Readings

wait, there is one possibllity

if you have the pressure sensor right next to the compressor - the pressure in the line tends to pulse, and it might cause the sensor to trip at the wrong times

make sure you have the sensor on the opposite side of the storage tank from the compressor.
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Unread 01-27-2004, 01:17 PM
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Re: Pressure Sensor Readings

Also a very good point. But it seems like that would make it erratic, is it would cycle on and off quite quickly, instead of just changing compressor activity at wrong times. We put it about 3 inches from out compressor last year and had no problems. I don't think the pulse is large enough to make a differenace
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Unread 01-27-2004, 01:17 PM
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Re: Pressure Sensor Readings

The sensor is this year's sensor, which i did not realize was analog, i have had it plugged into the digital in. Does anyone have the spec sheet on this year's pressure sensor, and possibly an example on how it would be coded as an analog in?

Ken, that does describe exactly the problem we were having previously.

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Unread 01-27-2004, 01:20 PM
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Re: Pressure Sensor Readings

The KIP came with both an anolog and digital sensor, you probably better off just using the one that is the same as last years.

As for the spec sheet, TI's website does not have the paticular part number, which leads me to believe they have given the wrong part number to us. they have one with a very similar part number, so just search for it on TI's website.
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Unread 01-27-2004, 01:26 PM
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Re: Pressure Sensor Readings

As far as i know, we only got the one with the molded 3 wires, Power, Ground, and sig wires.

We do have left over ones from last year that are digital, but i assumed they changed the pressure ratings this year, from 60psi to 120psi.

Now, does anyone know that the analog sensor returns based on? because when used as a digital sensor, it works perfectly with the exception of off at 80, on at 30.
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Unread 01-27-2004, 01:28 PM
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Re: Pressure Sensor Readings

I am *almost* positive that this years digital switch is the same as last years. I do know that you should have got one of both.
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Unread 01-27-2004, 01:32 PM
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Re: Pressure Sensor Readings

And a side note, here is a mini ascii diagram of the setup:

S is the sensor:
(ZZZZ) are the tanks:
G is another mini guage:
* is a place holder(empty space)

S-(ZZZZ)-|--(release valve)
********|---(to compressor)
G-(ZZZZ)-|

ETA: Ascii art doesnt work with spaces!

Does anyone know how the analog sensor would be used? i have seen no documents at all on the topic. I do have the sensor from last year with the 2 screws, which i can use if worse comes to worst.

Last edited by ErichKeane : 01-27-2004 at 01:37 PM.
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Unread 01-27-2004, 02:32 PM
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Re: Pressure Sensor Readings

the analog sensor gives you an output based on the pressure, I dont know the specs off the top of my head, but it would have a linear range from say, 0 to 60 psi or 0 to 120 psi

to be honest, I havent thought of an application for it (since the regulator holds the working line pressure at 60psi

unless you wanted to get fancy with your high pressure side, and use the analog sensor to choose your compressor on and off points, instead of using the digital sensor with its fixed trigger points.

its amazing that the analog sensor sort of worked connected to a digital input - I guess when the pressure got high enough the analog signal was such that the digital input changed states.
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Unread 01-27-2004, 02:56 PM
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Re: Pressure Sensor Readings

I also find that odd, especially because it works as intended other than the individual on/off points.
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Unread 01-27-2004, 04:47 PM
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Re: Pressure Sensor Readings

Quote:
Originally Posted by ErichKeane
I also find that odd, especially because it works as intended other than the individual on/off points.
That would be the nature of using an analog sensor on a digital input, less than the trip point typicaly 1 volt is off more than 2 or 3 is on. The only uses I could see for the Analog sensor would be to rush the on point of the system say when pressure drops to 110 get the compressor running and use the other switch on to cut off at 120, or to sense the "load" in a lower pressure part of the system to cut off the air supply to a piston when the "grip" reaches some point this eats more valves but gives you a measure of back force for the controler.
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Unread 01-27-2004, 05:20 PM
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Re: Pressure Sensor Readings

Ah, makes a lot of sense biff, thank you very much. if we have school tom. ill definately try it.
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Unread 01-27-2004, 10:43 PM
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Re: Pressure Sensor Readings

Quote:
Originally Posted by KenWittlief
the analog sensor gives you an output based on the pressure, I dont know the specs off the top of my head, but it would have a linear range from say, 0 to 60 psi or 0 to 120 psi
We tested our analog pressure sensor today. We ran the analog signal to analog input 1. Our programmer had the RC read the input as a 10 bit variable, then used the code shown in the programming reference guide to strip off the two Least Significant Bits (LSB) to get it down to an 8 bit number which he then sent back to the OI and the dashboard over user byte 6.

As we ran the pressure up we watched the count climb on the dashboard. It went from a count of 25 for 0 psi up to a count of 225 for 125 psi. Our programmer will probably do a linear scaling of the input so that the dashboard will show the pressure directly in psi.

We're not sure exactly what we're going to do with the info, but it seems cool to have it. I suppose we could also use it to control the compressor relay out rather than the digital pressure switch.
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