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Question On Adjusting Thermoprobe Input Reading
cpacileo
Hi all,

First time poster here. I have a question that I haven't been able to troubleshoot through my own research that I'm hoping some here may be able help with regards to thermocouple readings.

Long story short, I rehabbed an older model U.S Roaster Corp Drum Roaster which I've been roasting on for the past couple months. After re-wiring and doing a ton of work to the electronics and control system for this thing, I noticed that the original owner had set a manual adjustment to the thermo probe reader of +30 degrees Fahrenheit. I noticed it was reading a little high at ambient / room temp. so while playing with it I re-set the control to factory setting. I also split the thermocouple feed to a Phidget so I can run Artisan roast logging on my computer to better dial in roast profiles.

After numerous roasts I have noticed that the thermocouple readings seem to be a little off for where my readings are coming in. I have been hitting FC around 358-365 degrees Fahrenheit acording to my probe (Which seems about -20-30 degrees off). I replaced with a new J type thermocouple and have been getting the same results. As far as placement goes, this may be a problem but the probe only goes in to the drum about 1- 1-1/4 inches. I'm wondering if this may be the culprit. Problem is with the design of where the probe was placed on this thing, I can't put the probe in any deeper as it will start hitting the drum blades inside the drum, unless I seriously reshaped the probe which would be a bitch and I'm thinking may compromise the integrity of the probe.

My question is what should I do to get a more accurate reading given my circumstances? I know enough roasting wise to work around this, but it will seriously make my life much easier if I know I am getting a much closer reading to what I should be getting. This thing is already like operating a stick shift car (everything is manual from gas adjustments and airflow, etc.) , anything to help make the roasting process easier and get more accurate results so I know what adjustments to make in my profiling would be of serious help. Thank you all for reading this and hopefully I can get this issue resolved.
 
MaKoMo
Never splice probes!! You will get very wrong readings. One probe should only be connected to one meter input.
 
cpacileo
I did the splice fine with enough spacing that I am not getting any electronic impedance b/w the two instruments. I am not getting feedback or any crazy jumps in the readings, both devices are measuring the same readings. I was getting these same readings pre-splice, so I didn't really rule that as part of the issue. I can certainly order another probe, and just drill another hole into the drum to get separate readings I suppose, but feel I will still be running into the same problem.
Edited by cpacileo on 01/25/2020 5:00 PM
 
renatoa
Me too, no issues to share the same TC between TC4 and MS6514, or an industrial PID.

Probe placement or sheath choice can introduce much bigger off-readings than feeding two TC amplifiers, if done right.

Maybe is a TC type issue... I mean J versus K, or viceversa.
If type is set to K on the device, and a J probe is connected instead, 200C will be read as 265C
Edited by renatoa on 01/26/2020 6:15 AM
 
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