Tempature probe DIY

[wolves63]

I have a K Type sensor I am hooking up to my PID through an XLR 3 pin on the outside of my electrical box. The k type has 2 wires and I have 3 possible hookups with the XLR 3 pin. Have I made a horrible mistake and need to order new temp probes or is there a way to connect the k type up to the XLR and if so please let me know how.

 

[wolves63]

Please some help. Or am I screwed and need to buy new temp probes?!?

 

[day_trippr]

Confused - you own both sides of the connector interface and can pick whichever pair of pins through the mini-XLR connectors for your two-wire sensor, yes?

So what's the problem?

Cheers!

 

[wolves63]

I wasn't sure if I was missing the 3rd connector like the rtd ones are. With two I will just hook up to 4 and 5 slot on pid. Finally, which wire will be positive from the thermocoupler?

 

[day_trippr]

You could take a look around for K type thermocouple polarity markings.
Here's one site http://www.hotkilns.com/tc-polarity and there are many others...

Cheers!

 

[Just-a-sip]

although im not certain i will point out that i don't believe you can use the XLR connection like an RTD can. Type K sensors are made of dissimilar metals that react, creating the temp reading. i also l know that when changing connections of RTDs you can use several types of metals and connectors unlike the thermocouple. i think if you use the Connectors you have there will be an extreme discrepancy in your read out.

 

[Just-a-sip]

unfortunately i was right this article explains why using the wrong metal at a connection point wont work.

http://www.marttechservices.com/pdf...rmocouple_&_Temperature_Controller_Wiring.pdf

 

[rekoob]

unfortunately i was right this article explains why using the wrong metal at a connection point wont work.

http://www.marttechservices.com/pdf...rmocouple_&_Temperature_Controller_Wiring.pdf

I'm not sure I agree... or at least not 100%
If your using the same "type" of wire thats used for the probe then you are right that you have to keep like wires together.
However, he isn't using a connector with those materials so the connection shouldn't be "seen" as another probe.
He is basically connecting to the PID, regardless if he uses standard wire to move that conection to the mini XLR connection, electrically it's going to the pins on the PID.

 

[ryane]

using the XLR shouldnt matter, the problem with thermocouples is anytime you make a junction you need a reference temperature for the junction because it will affect the readout

without compensating for this junction your readings will be skewed

http://www.maximintegrated.com/en/app-notes/index.mvp/id/4026

RTD's or IC probes dont suffer from this problem which is why they are used in everything where I work

 

[Minbari]

^^^ if that were the case then the PID board traces, connectors and solder would have to made of the same metals too and they are certainly not.

From what i gather on this bulletin, is for wiring up thier sensor with more than one thermocouple.

I know plenty of people that use the very common type K with xlr connectors and they have good temp readouts.

 

[MagooBrew]

Any type connection will work as it will not affect precision but it will affect accuracy. Precision related to how many decimal points of resolution you can achieve on a repetitive basis. Accuracy is how close to an actual temperature you can achieve. If you are aware that you are off by a few degrees because of a cold junction point that is fine as long as it is repeating it for each use. Most better temp controllers will have an offset for compensation.

 

[mattd2]

^^^ if that were the case then the PID board traces, connectors and solder would have to made of the same metals too and they are certainly not.

From what i gather on this bulletin, is for wiring up thier sensor with more than one thermocouple.

I know plenty of people that use the very common type K with xlr connectors and they have good temp readouts.

Either that or the temperature they are at measured and used to offset the reading - Have a look at the Thermocouple Wikipedia page which shows a thermistor sensor on a fluke meter to do just this.

The point would be that the temperature inside the PID case is probably close enough to that at an external XLR connection so that the same reference temperature can be used to offset the XLR connection.

 

[Minbari]

Either that or the temperature they are at measured and used to offset the reading - Have a look at the Thermocouple Wikipedia page which shows a thermistor sensor on a fluke meter to do just this.

The point would be that the temperature inside the PID case is probably close enough to that at an external XLR connection so that the same reference temperature can be used to offset the XLR connection.

Was kinda my point as well. One more connection isnt going to upset the apple cart

 

[crane]

^^^ if that were the case then the PID board traces, connectors and solder would have to made of the same metals too and they are certainly not.

No, If you look at a well designed PID there will be a surface mount thermistor located very close to the terminals for the thermocouple to measure the cold junction temp. This is used to compensate for the voltage created across this junction.

I know plenty of people that use the very common type K with xlr connectors and they have good temp readouts.

Good temp readouts doesn't mean much. Sure it will be close to what you expect and in some cases where XLR temp and PID pub temp are the same then it will be accurate, but any difference in XLR temp and PID pcb temp will introduce an equal difference between actual temp and measured temp. I would not expect to see a 10 degree difference between XLR and PID, but I would not be surprised to see a 1-3 degree difference and when it comes to mashing I don't want to introduce the possibility of extra inaccuracies just because I chose to buy the wrong type of connector. The entire reason we add temp controllers to our systems is to have better control so why go a route that introduces uncertainty of the accuracy of the measured temp you are trying to control.