Temperature Probes still not accurate

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ScotPrice
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Temperature Probes still not accurate

Post by ScotPrice »

Hello,

I am still trying to get the temperature probes to provide an accurate reading. I followed the instructions from this thread, http://forum.embeddedcc.com/viewtopic.php?f=6&t=10, and Im still getting wild readings. I put ice in my HLT in order to get it to 32 degrees, at which point I took my calibrated thermometer reading, and the Ohms reading from the BCS. I then heated the water to 104 degrees, and followed the same procedure. Finally I heated the water to 158 degrees, and again followed the same procedure. I performed these steps twice, once yesterday, and once today, and ended up getting wildly different ohms readings at the 104 degree, and 158 degree marks.

What could be wrong here? I am starting to believe they are bad probes.
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bbrally
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Re: Temperature Probes still not accurate

Post by bbrally »

It's normal for the resistance to float around a bit, so as long as it isn't moving to much, it's best to take a number of readings and average the values out. If your values are jumping around alot, I'd check to make sure you have your BCS grounded properly and that your probe wires are routed as best as possible away from any 120 volt sources.

If you mean that the resistance readings vary between different probes, that can be normal depending on the precision of the probes, but I've used BH probes in the past, and haven't had any differences to great.

Perhaps you could paste a copy from the data log page here to see what type of swings you are referring to.
ScotPrice
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Re: Temperature Probes still not accurate

Post by ScotPrice »

The swings I am referring to are from two separate readings I have taken (three now). I went all the down to 32 degrees, verified the temperature with a calibrated thermometer, then took the resistance reading from the bcs460 sensor. I did this for 104 degrees, and 158 degrees as well. Every time I have done this test, the resistance numbers from the probe varies from test to test. Its not a small variance either, it was rather large.

I thought I had worked it all out, and got the probes to within 2 degrees of calibrated, but yesterday during brew day they were about 30 degrees off again.
clearwaterbrewer
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Re: Temperature Probes still not accurate

Post by clearwaterbrewer »

if you tie several probes together, then hang in the middle of your HLT (with pump recirculating), do they all read the same resistance? are they stable? if not, does one move more, or do they all 'jump' together?

that behavior should give you a direction to troubleshoot...
chappyman7
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Re: Temperature Probes still not accurate

Post by chappyman7 »

I'm having a similar problem hope its okay that I piggyback on this thread. Checked ground wires, I have one ground going from GND0 on the BCS to the A/C ground and one going from the SSR Ground jumper to AC ground. AC power is about 8 inches away from my probe wires in the box. Readings are looking like this: these are from 2 separate "runs" one at 32 degrees and one in 62.6 degree water verified by a calibrated thermo. The behavior seems the same. Any other ideas, gentlemen?

32 Degree ice bath:
Screen shot 2013-10-21 at 7.13.05 PM.png
Screen shot 2013-10-21 at 7.13.05 PM.png (23.82 KiB) Viewed 4105 times
62.6 degree water:
Screen shot 2013-10-21 at 7.51.52 PM.png
Screen shot 2013-10-21 at 7.51.52 PM.png (62.82 KiB) Viewed 4105 times
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