Building RIMS Control Panel, RTD sensors reading way off

[jdub1782]

I am building a RIMS control panel with two MyPIN TA4-SNR PIDs and I am in the process of testing the components before I start to assemble the panel

I ordered two PT100 RTD temperature probes from Amazon and the probes are reading 12 and 14 degrees F too high. Is it normal that they would be that far off and require using the temperature offset in the PID?

I've tried wiring the PID both with and without the jumper from pins 7 - 10, as I was not clear whether this was required, but I get the same results both ways.

Is this normal?, am I doing something wrong, or did I just get bad sensors?

pics of PID's and wiring attached

thanks for any suggestions

 

[Punx Clever]

It's fine. Just set the offset in your controller.

But:

Are you sure your other thermometer is correct? Use an ice/water mix to check them at 32* (freezing) and boiling water to check at 212 (boiling).

 

[jdub1782]

thanks for the suggestion

the digital thermometer matches my lab thermometer which is correct. I tried an ice bath last night and I was getting about 33 degrees on the lab thermometer and 47 on the RTD.

if this is normal, I'll calibrate the RTD's at about 152 and determine the required offset at that temperature range -- I just didn't want to start cutting wires if the RTD's are defective

 

[BlkWater_brewer]

Were you testing the sensors in liquid or just air temp? But it is always necessary to set the offset.

 

[jdub1782]

Mostly just in air, but I also tried an ice bath and was still off 14 degrees.

Is it normal for the offset to be 12-14 degrees, I was expecting maybe 1 or 2?

 

[LandoLincoln]

I had a similar problem with my PIDs giving me bad readings. I couldn't figure it out until I had the things plugged in and I wiggled the wires around near the connection to the PIDs and the numbers started jumping around. The crimp spade terminals were giving me problems. So I clipped the spade terminals off and wired the wires direct to the screws on the PID connections and bam - no more problems. Hopefully this is your problem as well and you don't have to replace anything.

 

[Punx Clever]

Any number of things could be causing the offset to be 14 degrees. Could be the construction of your RTD's, could be the resistors in the PID. Either way, you always have to set an offset.

Set the offset at freezing, then check to see if they are linear by checking at boiling. If you get 212 at boiling after setting offset at 32, then don't worry about it any more.