Normal temp probe fluctuations?

[NovaBiele]

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I am currently setting up my BCS-460 and I'm just curious if this amount of temperature fluctuation is normal? looks like my worst case is +-.75 degrees or so. Sample interval is 1 second.

I'm using the brewer's hardware temperature probes with 4.0 Beta 2 with the default coefficients.
All probes are currently located in plumbing or in the pot.
All readings are in air, no liqiud just yet.

-chris

[JonW]

Do you have a ground jumper in place between one of the BCS negative terminals and an earth ground (AC ground terminal)?

Really hard to say if the amount of variance is abnormal since you are measuring air. If you put the probes in some water, that in itself would smooth it out a bit.

[oakbarn]

Mine seem to do the same in the Datalog, but the Main Control Panel that are NOT changing at all or very little. I have never put it down to a couple of degrees on the X Axis. Mine are grounded well.

[BREWMASON]

There is a post in here already about this and it just resolved my same issue. Find an earth ground and connect it to one of the grounds on the BCS. Mine stabilized immediately.

Plus u might want to plug these in: http://forum.embeddedcc.com/viewtopic.php?f=10&t=2629

[NovaBiele]

just an update:

I recalibrated all 5 sensors in liquid at 0, 40, 70 degrees C. I couldn't figure out how to get the resistance values off the 4.0 firmware & ended up just using this url: http://[bcs ip address]/api/temp/0. I also currently have the earth ground jumpered to the BCS ground.

The graph is significantly improved [same time/amplitude scale & also in air]:

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I still have a major issue--when any of my heating elements are active, the probes jump in temperature a few degrees F! as soon as the elements are powered down the probes drop in temperature a few degrees. I am still tracking down the problem...but looks like an EMI issue to me. I think it may have to do with my unconventional setup & wiring. i'll post some details when I learn some more, but if anyone has any suggestions here i'm very grateful for any help!

[NovaBiele]

Anyone curious about my unconventional setup, I have a high voltage 'brew box' with relays, contactors, SSRs for heating elements, pumps and other perhipherals.

There is also a 'control panel' that houses the BCS & lower dc-only voltages. The two enclosures are located about 10' from each other. all the temperature probes connect to the 'brew box' using XLR connectors & are jumpered to a DB25 connector. The shielded 25-conductor cable is 25' long (much of it just coiled up) and connects to the control panel. It relays the temperature data to the BCS in the control panel & the control data from the BCS to the 'brew box'.

picture worth a thousand words:

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the temperature signals are non-shielded at two points: 1) 8"of wire inside the control panel from the DB25 to the BCS & 2) 4" of wire inside the 'brew box' where the back of the XLR connectors for the temp probes jumper over to the back of the DB25 recepticle. I'm starting to thing that putting the temperature probes in/near the high voltage box was a bad idea.

[oakbarn]

Have You tried moving one of the temps out of the brew box to see if it is the box? Any compressors near? Is there a drain on the shield?

[pngaudioguy]

Is your shielded DB25 grounded at both ends? If so, try floating one end (I would float the end further from the BCS.) That would be what we call a "ground loop" in pro audio land. Causes tons of noise in audio circuits, and I imagine in these low voltage control circuits as well. The two different ground paths between your enclosures, being of different lengths and paths are able to have a voltage difference instead of being equal. If neither end of the DB25 shield is connected to a ground, try connecting the end closest to the BCS to the ground. This would be the typical way of wiring up a balanced audio send with shield to prevent ground loops, worth trying here as well to see if it helps.

Also if you've got a high voltage line running near your coiled up excess DB25, even if grounded and shielded properly, you've got a transformer. The 60Hz switching from the line voltage will generate some small signal in that coil, which will affect the readings, I'm sure.

Edit: I'm curious to follow and see if you get the issue resolved, because I was looking into building my rig exactly as you've described yours in the image. Also, looking at the graph again it seems the fluctuations on each sensor are within about .25 degrees from their respective baseline. I'm not sure if that's abnormal or not, but I wouldn't expect all the sensors to read exactly the same anyway.

[NovaBiele]

Thanks for all the suggestions. I think the ground loop theory is a good one, but haven't had time to work on anything the past few days. I've got a new baby at home and been a bit under the weather. I'll be sure to post an update with my findings.

[NovaBiele]

I've done a bit of troubleshooting and have two very useful data points that I think are pointing towards my problem. first of all---i tried all kinds of differnet grounding configurations. i.e. grounding only one end, both ends, grouding everywhere i could, dozens of configurations---there were no discernable changes. here is where i did have some luck....I put all my temp probes in a single pot (5 total), 4 wired as described earlier in the thread (through the 'brew box' with the high voltage elements and then through 25' in-wall shielded DB25 cable) and 1 single probe that i bypassed the 'brew box' and the 25' in-wall cable. (1) the temp probe directly wired to the control panel (bcs) did not exhibit any offset error when the elements were turned on. (2) Additionally, The temp probes that did exhibit the offset error did so when their mechanical relays were activated independent of the state of their SSRs! So basically it isnt the elements firing that's the problem, but siomply the mechanical relays closing that is the issue. a third data point is (3) I took the in-wall cable out of the equation, connecting a 1m cable between the 'brew box' and control panel with absolutely no change in behavior.

I believe this narrows the probelm down to my 'brew box'. this is where i have a relatively short (~6") length of the temp probe conductors unshielded, but also within the viscinity of my main mechanical relays for the heating elements. my main mechanical relays use 120VAC coils to throw the contacts. I believe there is an EMI generated from the control coils of the heating element relays that is coupling onto the short, but unshielded length of conductor that is the temperature sensor signal.

i think my design flaws are as follows:
-using 120VAC coils for main heating element relays instead of 24VDC coils
-poor planning of shielded cable terminations
-bringing my millivolt thermistor conductors into the 'brew box'
-not shielding these very short lengths of conductors of millivolt thermistor signals from the relay coils.

I'd really like to keep my setup as-is, so i am going to attempt some sort of acceptable shielding, but if unsuccessful I think i may just wire my temp probes directly into the control panel.


here is a screenshot showing (1). the pink trace was directly wired while the others were wired through the 'brew box':

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