Temp probe fluctuations - all in sync with each other

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JonW
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Temp probe fluctuations - all in sync with each other

Post by JonW »

I recently noticed that when my fermentor was plugged in that I was hearing it cycle on and off very frequently. I didn't have time to check things out, so I just increased the hysteresis on the output to try and help minimize the cycling. I always figured that I was getting some kind of interference on my probe wiring since I had extended the probe about 30 feet so my fermentor could be on the opposite side of the garage from my BCS system.

So today, I figured I'd start taking a look at things. Both of my kegerators (identical Kenmore ones) and my fermentor (a True kegerator) all run off the same "Refrigeration" process. To prevent any unnecessary fluctuations during the log, I stopped the "Refrigeration" process. I then pulled up the BCS data log screen and logged four of my probes for a bit. As you can see from the screen shot, all 3 refrigeration probes fluctuate up and down in sync with each other. Additionally, the fermentor fluctuates to an even larger extent, but always at the same up/down point as the kegerators. Interestingly, the ambient air probe does not appear to fluctuate.

Here's some info on the probes:
- All probes are 6" ones from ECC
- All 3 refrigeration probes are inside a bottle of water within each kegerator to keep fluctuations minimized.
- Ambient air probe wiring is stock length and located inside my BCS wiring cabinet.
- Serving Fridge 1 wiring has been extended approximately 8 feet.
- Serving Fridge 2 wiring has been extended approximately 8 feet.
- Fermentor Fridge wiring has been extended approximately 30 feet.

Any thoughts on what could be causing this? The wire I used to extend the probes was a 22g alarm wire. I'll be switching this to cat-5 to see if using twisted pair will help.

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Baron Ken
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Re: Temp probe fluctuations - all in sync with each other

Post by Baron Ken »

First off, you have your serving fridges at 37F?? Brrr. ;)

Did the fluctuations start after you put in the extensions? I'm guessing the 22g alarm wire is not shielded? What about grounded (see your post here about shielding/grounding)?

Since the fermenter fluctuates over a greater range, but still in sync with the kegerators, and since they all have the alarm wire (with the fermenter having a longer section of it), I think your idea of trying the cat-5 might be beneficial, especially since the ambient probe (which has no alarm wire, correct?) doesn't fluctuate appreciably.
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ECC
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Re: Temp probe fluctuations - all in sync with each other

Post by ECC »

Very interesting that the fluctuations get noticeably worse as a function of wire length. Ambient has none, the 8 foot probes are worse (and identical), and the 30' length is the worst.

I've seen plots like this before, and it has always been fixed by either using better wire (bigger, twisted, or shielded), or some grounding issue. So I'm very interested in how the Cat5 will perform. Cat6 would be even better, it has improved insulation and shielding.
JonW
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Re: Temp probe fluctuations - all in sync with each other

Post by JonW »

Baron Ken wrote:First off, you have your serving fridges at 37F?? Brrr. ;)
Actual beer temp is a few degrees higher. My probes are stuck down in a bottle of water that is right next to the chill plate inside the kegerators.
Baron Ken wrote: Did the fluctuations start after you put in the extensions? I'm guessing the 22g alarm wire is not shielded? What about grounded (see your post here about shielding/grounding)?
I never logged it before to see if it fluctuated before extending the cables. My serving fridges have always been extended (8 ft), but because their fluctuations are relatively small, I never noticed them cycling on/off frequently. I knew when I used the alarm wire on the fermentor that I could have some issues, but I didn't have any other wire handy so I did it anyways.
Baron Ken wrote: Since the fermenter fluctuates over a greater range, but still in sync with the kegerators, and since they all have the alarm wire (with the fermenter having a longer section of it), I think your idea of trying the cat-5 might be beneficial, especially since the ambient probe (which has no alarm wire, correct?) doesn't fluctuate appreciably.
I already figured the wiring was the issue and no doubt changing the wire will probably fix this or at least make the fluctuations so minimal that the it doesn't affect the cycling on and off.

My question of what is causing this was more directed to why the probes flucuate in sync with each other. The probes exit my enclosure from opposite sides of the box and do not route near each other and I was careful to not route them near any high voltage. I can't see an external stimulus that could cause the fluctuations, so I'm wondering if it could actually be something in the temperature circuit of the BCS and is only noticeable when the wiring is extended.
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Baron Ken
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Re: Temp probe fluctuations - all in sync with each other

Post by Baron Ken »

Do you have your GND pin of the BCS connected to earth ground? Wondering if that might help as well.

from the wiki:
Grounding the BCS

The BCS-460 and BCS-462 are powered by a two-prong transformer, which creates a DC operating environment that is not referenced to earth ground. If spurious sensor readings are observed due to ground loops, the GND pin of the BCS should be connected to the system ground.
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Re: Temp probe fluctuations - all in sync with each other

Post by bruin_ale »

I debugged something similar today.. it was weird because when I wired everything up it wasn't fluctuating, but then I was doing some work in the garage and realized my keezer was cycling on and off every minute or two. Anyhow, my data log looked very similar - it was about a 10 degree swing, not good. Plugging earth ground into the bus that I had my BCS gnd and all temp probe gnds seems to have fixed the problem.
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Re: Temp probe fluctuations - all in sync with each other

Post by JonW »

After seeing your post, I went and did the same thing. A quick jumper between the AC and DC grounds fixed it.
I was logging it while I connected the ground.
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