Phidget Bridge 1046 quickly losing calibration

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gwilkinson
Phidgetsian
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Phidget Bridge 1046 quickly losing calibration

Postby gwilkinson » Mon Mar 12, 2012 1:26 pm

I have a phidget Bridge 1046 with 3x 5kg Load Sensors making up a weight platform I have built for measuring weight and to flag the presence of a bird on the platform. We use these in cognitive behavior research in pigeons. The flow of my program is as follows: The Bird lands on platform - a Phidgets RFID reader hits the ankle ring on the birds leg and logs his Tag # and launches the research session run by another program. (This works 100% perfect). As part of this launch procedure the program logs the birds weight when he/she lands via the load sensors. This has worked well with a margin of error +- about 20 grams. The load sensors have worked wonderfully for this for about 8-9 Months. In the recent 2 weeks the system falls grossly out of calibration by up to 200 grams +. The Program does a loop every 3500ms to check if there is at least 70 Grams on the platform to signify a bird is still present. This miscalibration happens pretty much every day now despite the fact we do a fresh re-calibration every morning. I am wondering do these load sensors wear out? If so is 8 Months a little soon to do so or is there something we can look further into. My hope was to code my program to calibrate the platform after every bird leaves and resets the system but despite using an exact 1KG weight to calibrate the sensors the Conversion equation is VERY different each time we calibrate so I cannot see how to hard code this in as a function. I have new sensors and an extra bridge ordered and my plan is to build a 2nd platform using 4 sensors instead of 3 at each corner of the platform so the balance is more stable. I currently have all 3 sensors wired to input #0 based on past support conversations with Phidgets support. Basically the 3 sensors tethered together act as one but this recent unreliability has me stumped. I am also wondering how tightly I should be securing the sensors to the base the live on. Of course to loose and I don't get a solid reading but I am weary of tightening them to much as well.

Any Ideas?

-I can provide pics of my platform and how I arrange my sensors if needed.

- My phidgets interface says my bridge is version 100, is there a newer firmware that may address this?

fraser
Engineering
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Re: Phidget Bridge 1046 quickly losing calibration

Postby fraser » Mon Mar 12, 2012 1:34 pm

Its possible that there is a bad connection on the load cell wires. Try un-screwing the terminal blocks on the 1046 and removing the loadcell wires; put the wires back in and screw the terminal blocks down again. See if this helps the problem at all, and let me know the result. I can see about throwing some more ideas your way if this doesn't work.

gwilkinson
Phidgetsian
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Joined: Thu Sep 01, 2011 5:00 pm
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Re: Phidget Bridge 1046 quickly losing calibration

Postby gwilkinson » Mon Mar 12, 2012 1:57 pm

Totally, this was actually the first thing I tried. I redid my ends and secured it back to the terminals. Now that you mention it I will try connecting my wire harness to one of the other 3 inputs to rule out a possible broken connection on interface #0

Thanks for the help a 2nd set of eyes and another brain always helps...

I also have some of the 0-780g sensors Since I have no birds heavier than 500g on average it may help to lower my margin for error by using these. Brian and Patrick at Phidgets suggested the 0-5Kg sensors because they are the best bang and can give very accurate results usually. I also am looking back through my records of conversations and I may have my sensors to far apart but I am hoping I can make this work for better balance on the platform.


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