Lightobject.com Support Forum

Current temperature readings with the probe in a water bath are jumping around by 3-4 degrees in a time period of about 30 secs. I have the filtering parameter set to 3. Temperature fluctuation is worse with lower filter values.

I'm looking for ideas on how to diagnose and fix the problem. Alas I have only one probe and controller so I can't swap parts. The controller is successfully switching the SSR on and off and the SSR is connected to a 1000w bucket heater. I've routed the probe wires away from the heater wires, in hope that that would reduce any electrical noise. Though that shouldn't be a problem with a 3 wire pt100 probe set up.

Any ideas what to try?

It's P,I,D parameters setup issue. You can do two things: test and try the PID settings or use Auto tune but it may take hours to complete the tuning.

Or, see this post: viewtopic.php?f=5&t=320&p=847&hilit=ssr#p847

I do not think this is a tuning issue. But as suggested I have repeated the auto tune procedure. Little change in behavior. The displayed temperature varies by 8 to 9 degrees F over a 15 sec time period. (Video is here http://gallery.me.com/johncarnes/100041).

Note that I've just reduced the set value, which is why the water bath is much hotter that the set value. The heating element is unplugged and the water is slowly cooling. I am very sure the temperature of the water is not changing as displayed by the controller. Photos of the set up are here http://gallery.me.com/johncarnes#100042

I am still seeking ideas to diagnose or fix the problem.

I have another controller and probe on order from a different manufacturer. Once they arrive I'll have a few more options to figure out the problem. I suspect I have a bad controller or probe. It would be hard to imagine that this is normal behavior for a JLD612.

Parameters are as follows:

IntY: Pt10.0
outY: 2
HY: 000.3
PSb 000.0
rd: 0
CorF: 1

P: 00.7
I: 0012
d: 003
SouF: 0.2
ot: 2
Filt: 0

Su: 100.0
AH1: 080.0
AL1: 090.0
AH2: 080.0
AH2: 090.0

For sure there is two mistakes on your settings (so far)

1) SV value always set in between AH and AL. Why did you set the SV over the value of AH?? It doesn't make any sense. Doing so will set off the relay before water temperature reach SV (but no harm though).

2). Controller shouldn't be located next to the SSR as the SSR will generate a lot of heat during peak time. The JLD612 has a "auto sensor" built in (a small diode) that need to simulate an ambient condition. But if you put them in the same 'closed' enclosure, how could it do the job right: Auto Tune for the SSR?!

It's too early to make the claim of bad JLD612. Remember, it's PID, not a thermostate. So, you got to do fine tune it before it can works properly.

I should be able connect the probe to the controller and get a reasonably stable and accurate reading of the temperature at the probe without anything else connected to the controller, and that is what is not working.

The problem is that the temperature value displayed on the controller, measured via the PT100 probe jumps back and forth by +/-8 degrees in just a few seconds! How can any of the tuning and PID control hope to work correctly if the measured temperature is so unstable.

The problem is not with the control side of the PID controller, it's on the temperature measurement side of things.

I am not using the alarm relays to run the heater. I'm using the SSR output. So the alarm high/low settings should not matter, right?

The heat sink on the SSR is not event slightly warm to the touch, the controller is in an environment that's about 50 degrees F, my garage. The lid on the enclosure has not been closed. This is not a controller that is too hot.

More experimentation has led me to think there is interaction between my bucket heater and the PT100 probe. When I unplug the heater, the temp readings are stable. When I plug it in, the readings start to fluctuate. When the SSR switches it on, the readings fluctuate even more wildly.

Tomorrow I'll try grounding the probe to see if that helps.

Problem solved. See this post viewtopic.php?f=5&t=387