Bad Temp Readings

[ShortSnoutBrewing]

During yesterdays brew session I had something interesting happen and was hoping someone could help out.

I have a direct fired mash tun where I have a "T" coming off, bulkhead on one outlet and a temp probe in the other to monitor the temp of the wort coming out. I'm using this:

with this probe from Thermoworks:

When recirculating the probe would not read above 75º, and the mash was sitting at about 156º so I know that wasn't right. After the mash was done and the boil started I removed the probe from the compression fitting base and dipped it in the wort. 212º just as you'd suspect. So what am I doing wrong?

 

[lschiavo]

This is a new probe? Or has it worked properly before? I assume you have the PID set for the proper probe type. Not famililiar with this probe type but it looks like it has a max temp at the junction. Could this be a problem?

 

[Catt22]

Did you have the meter set to Fahrenheit? If that wasn't the problem, then it's likely a problem with the probe. There's not much to the probe as it's just a pair of wires joined together inside of the tip. Not much to go wrong unless the junction is defective or the wires are shorting out somewhere in the lead. I'm assuming this is a thermocouple and not a thermistor set up. I'd try a different probe if you have one available. The problem seems to be intermittent as you got a good reading on the boiling wort. That leads me to think that there is a short or bad connection somewhere in the probe.

 

[ShortSnoutBrewing]

New probe. It's a Type K probe. Like I said it worked fine out of the compression fitting, but when in the fitting it's getting skewed results. Wondering if the contact with the fitting is throwing the results. Maybe replace the metal ferrule with a plastic?

 

[Catt22]

It might be shorting out when you tighten down the ferrule. I have a similar arrangement and instead of a ferrule, I used a small O-ring to make the seal. Just a little more than finger tight makes it leak proof. I also put a dab of keg lube on the O-ring and probe to help with the seal and reduce wear and tear on the probe.

 

[lschiavo]

That sounds like a good possiblity. I would try to isolate it with plastic. I'm sure it would take a while to bring the fittings up to wort temp but it seems like it should equalize after a while with circulation. Maybe its just a bad probe?

 

[Catt22]

When I suggested that the probe may be shorting out or otherwise being affected by the squeeze of the ferrule, I meant internally. I don't think it would be affected on the outside and insulating it probably won't solve the problem. Yes, the probe certainly could be defective. I have one probe that occasionally gives me wild readings. When it's working right, it's dead on, but once in awhile it will go bonkers. The cure is usually just wiggling the lead a little, so I'm pretty sure that there's a connection problem internally with that one. Fortunately, the probes are relatively cheap, so I have multiple backups for such occasions. Let us know if you get it figured out.

 

[ShortSnoutBrewing]

How easy is it to replace just the probe portion on these things? You say they are cheap, but this guy was $25. I see that the probes by themselves are much more affordable in the $6 - $7 range.

I'll test some more taking the ferrule off and just using the o-rings.

 

[Catt22]

Not sure what type of meter you have, but mine uses the yellow mini-plug connectors, so it's just a matter of removing the old probe and plugging in a new one. The probe prices vary widely with the source and the style. I recently bought a set of 5 of the cheap plain wire type for under $15 including shipping. Got them on Ebay and they work just fine for me. It pays to shop around for the probes.

 

[ShortSnoutBrewing]

K type probe with this plug:

http://thermoworks.com/products/probe/tc_imm_gen.html

 

[Catt22]

Any probe with that type of plug will work.