Unstable Temp Reading

[DaveFla]

Using JLD612 and PT100 probe.

For the first minutes of operation after being plugged in, the actual temp is unstable by +/5 degrees F. After a period of time the temp converges as if it is filtered.

I do not think it is a noise issue as described by previous posts.

Is this normal?

[glassguy213]

Dave-
Do you have the unit set for Pt10.0? This will show temp in .1 degree increments. It the fluctuation full degrees +-5 or tenths of degree? That much fluctuation in tenths is not so much.

[richiem]

It also depends on what is being sensed -- in my hot tub, from a warm restart, the measured temp will vary a lot while the temp of the water forced over the sensor is stabilizing, so some initial wobble is not unusual in my application.I do use the Pt10.0 setting...

[DaveFla]

The fluctuation is +/-5F not +/-0.5F
Also I notice if I wiggle the shielded cable the fluctuation is +/-5F.
Is this normal?
Thanks for the tip on Pt10.0
I wondered what that was.

[Mike]

mythopoeic.org/sous-vide-cooking had a similar problem with the temperature readings jumping around.
Coupling the PT100 shield to one of the return wires seemed to fix it.

[DaveFla]

Did you solder directly to the shield?

Excellent sous vide implementation.

Did you think about making a homemade stir plate to stir the water instead of water bubbles?

[Mike]

It's not my setup, but I've gotten a few good tips from it

For now, I'm just using an alligator clip to connect to the shield.

[DaveFla]

I followed Mike's tip and connected the blue leads of the Pt100 temp sensor to the shield using an alligator clip and the stability improved dramatically. I also tried connecting the shield to AC ground and there was poor stability. I wonder if there is any advantage in connecting AC ground to the shield and to the blue leads.

[richiem]

Dave, I wouldn't connect AC ground to anything associated with the controller. I think it needs to float. Maybe Marco will have something to say about this.