Strange BCS behavior-board by board temp variation

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fallingsky
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Strange BCS behavior-board by board temp variation

Post by fallingsky »

Hi Folks,

So I have been scratching my head for about an hour over this one. Firstly, I see lots of talk on here about temp probe calibration being a part of bcs 4.0 utilities, but I don't see it when I go to the page. Do you have to be currently connected to the BCS to see it? Right now as I test things I just have my 3 BCS boards linked to a RaspberryPi via a router that is not connected to the internet. I have wifi on the Raspberry Pi and there is a wifi network elsewhere in the house, but it doesn't work when the ethernet cable is plugged in it would appear. Anyway, I digress. Here is the real issue.

As I mentioned, I have 3 BCS boards. I have 8 temp probes that I attached to the green terminal blocks that came with the BCS from Brewer's Hardware. I made my own sensors with the thermistors from there as well. The temp probes all read within about a degree of one another in a ice bath, but I am getting a 2-3 degree difference between ALL the temp probes when I plug the whole terminal block with the 8 probes wired up into the 3 different boards:

BCS.1- 31.0-32.1
BCS.2- 33.9-34.7
BCS.3- 32.8-33.3

These boards are brand new and I haven't changed any coefficients (or anything else) yet. This is the first time I have fired them up. Any idea what could be causing this and how to rectify it? I'm aware that I could fudge things to get the right answer as long as the same probe is always associated with the same BCS board, but I was hoping for a more "real" and permanent fix. Thanks!

Jason
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JonW
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Re: Strange BCS behavior-board by board temp variation

Post by JonW »

fallingsky wrote:Firstly, I see lots of talk on here about temp probe calibration being a part of bcs 4.0 utilities, but I don't see it when I go to the page. Do you have to be currently connected to the BCS to see it?
There's a great calibration utility that was created by one of the forum members here: http://bbrally.from-ca.com/
fallingsky wrote:The temp probes all read within about a degree of one another in a ice bath, but I am getting a 2-3 degree difference between ALL the temp probes when I plug the whole terminal block with the 8 probes wired up into the 3 different boards:
I've kicked this question over to the hardware guys at ECC, but from my understanding of the 10K thermistors, the resistance output generated by the probes is in direct response to the input signal used to excite them. Thus, the power supply and associated circuitry could have an influence on the output. The fact that all probes move as a group when changed between BCS's makes me believe that would be the issue. When tuning the probes, the power circuitry would also be accounted for, but that tuning is only going to be good for the current BCS/probe combination.
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bbrally
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Re: Strange BCS behavior-board by board temp variation

Post by bbrally »

.....but I don't see it when I go to the page. Do you have to be currently connected to the BCS to see it?

If you are refering to the page at http://bbrally.from-ca.com/ or http://calculator.from-ca.com/, then yes, the first thing the page does when loaded is look for a bcs. Once found, the rest of the page becomes available.
fallingsky
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Re: Strange BCS behavior-board by board temp variation

Post by fallingsky »

Thanks for your response Jon. That makes some sense. Since you say the following:
Thus, the power supply and associated circuitry could have an influence on the output.
would that mean that I not only need to make sure that the probes are always associated with the same BCS board once I do the calibration, but also with the same exact power supply?

And yes, I managed to find those tools that are hosted on different web pages after I had posted. They look super helpful. Thanks!

Cheers,
Jason
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