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Silvia PID - high steam temp


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Hello

Fitted Auber PID to my Silvia this week, it's only the "brew" PID, no additional functionality for steam temp control.

Prior to fitting the PID, I had fitted a K-Type thermocouple underneath the bracket for the brew thermostat, in order to try to get a repeatable brew temperature.
From having this thermocouple installed, I am now quite in tune with the temperatures seen at the top of the boiler (within reason of the accuracy of my thermocouple and reader).

For example, when brewing, typically I would see heating from 85C, up to 95C and then overshoot up to 105C. 
When using steam, typically heater shut off around 135C.

Since installing PID brew temperature looks reasonable, I can set PID to 105C and it holds steady.
However, when using steam I am now seeing heating up to 155C on the PID readout, significantly higher than before and I've not touched the steam side thermostat.
I checked the part number (Campini Ty60) and as I read it, it should shut off at 140C +/- 5C.

I checked the difference between the RTD (replaces brew thermostat) and my thermocouple on brew temperature and see a difference around 3C. 
I've not checked steam yet but will do so within the next few days.

Has anyone had similar before? Could it be my steam thermostat has failed?

Edited by Miniwill
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What temperature does the element light cut out at, as those shows when it stops heating. I have a similar setup and the power cuts off at ~135 C, but the heat continues to climb towards 150C, so I don’t think what you’re seeing is unusual.

RTD probes respond quicker than k type thermocouples, so perhaps you didn’t wait as long before, or you started steaming earlier, which will obviously cause it to cut out. 

If the steam thermostat had failed and the safety was cutting power then it would stopping heating completely, as you have to press the button to reset the safety.

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I just checked on mine and the orange light (and audible click) of the steam thermostat cut power to the element at 139C. The temp readout on pid maxed out at 155.8C. This was with a cold machine.

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31 minutes ago, BenH said:

I just checked on mine and the orange light (and audible click) of the steam thermostat cut power to the element at 139C. The temp readout on pid maxed out at 155.8C. This was with a cold machine.

Thanks for checking. The way I described it in my post, temperature is when the light goes out. 

When testing today, my machine has been pre warmed for probably an hour, so that might make some difference. Other times I've tested this evening the machine has started at circa 50C, so again, probably some difference. 

I'll see where I am with it tomorrow from ambient but I'm confident the audible click was around 155C for me today, climbing to 162 at its highest. (150 shown here from thermocouple, clearly some drift between RTD and thermocouple at higher temperature) 

IMG_20210223_165328.jpg

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That does seem a bit high then. Like you said, cutout should be around 140C.

If i remember correctly the thermostats work by a piece of metal expanding and breaking the connection, so there isn’t much that could cause it to drift. It should either work, or not.

The only other idea I can think of is that the thermal conductivity between the boiler and thermostat isn’t great. Did you use plenty of thermal paste? If you didn’t then that might explain it. Not having perfect thermal conduction between the boiler and thermostat would mean the boiler had to be a bit hotter before the thermostat reached 140C. It might also explain why you get a bit of drift, as expansion and contraction might affect it slightly.

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33 minutes ago, BenH said:

That does seem a bit high then. Like you said, cutout should be around 140C.

If i remember correctly the thermostats work by a piece of metal expanding and breaking the connection, so there isn’t much that could cause it to drift. It should either work, or not.

The only other idea I can think of is that the thermal conductivity between the boiler and thermostat isn’t great. Did you use plenty of thermal paste? If you didn’t then that might explain it. Not having perfect thermal conduction between the boiler and thermostat would mean the boiler had to be a bit hotter before the thermostat reached 140C. It might also explain why you get a bit of drift, as expansion and contraction might affect it slightly.

Plenty of thermal paste on the RTD. Not touched the steam side which makes it all the more puzzling!

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1 minute ago, Miniwill said:

Plenty of thermal paste on the RTD. Not touched the steam side which makes it all the more puzzling!

Might be worth repasting the steam thermostat anyway. The brackets share the same screw, and as the paste gets squeezed out there probably isn’t much left. I guess you could also try another thermostat, or just start steaming earlier. I can’t help be a little suspicious of the accuracy of the reading. If it was genuinely switching off at 162C I would have expected you to have tripped the safety thermostat by now, as that’s specified at 165C.

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14 minutes ago, BenH said:

Might be worth repasting the steam thermostat anyway. The brackets share the same screw, and as the paste gets squeezed out there probably isn’t much left. I guess you could also try another thermostat, or just start steaming earlier. I can’t help be a little suspicious of the accuracy of the reading. If it was genuinely switching off at 162C I would have expected you to have tripped the safety thermostat by now, as that’s specified at 165C.

Yep, me too! Makes me think the RTD and PID calibration is way off. 

Edited by Miniwill
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I tested some more this morning. From cold there's around a 20C delta between the thermocouple and the RTD, the delta is reduced as the machine warms up.

There is a difference in response time between thermcouple and RTD but I don't believe it to be significant enough to take this long for thermocouples to "catch up".

I also ran steam again with thermocouple attached. The thermostat is shutting off heating for steam at 130C read on thermocouple, 155C read on PID.
I think my PID is out of calibration with the RTD or there's something else going on. I've emailed Auber and I'm going to remove the PID for now.

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