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La Marzocco - Linea - PID Question

Postby Euology101 on Thu Sep 01, 2011 10:42 pm

Linea 2AV, with the Fuji PID on the brew boiler.

I started off with the PID, following instructions from Espresso Parts, did the Autotuning, and then I changed the values P.I.D to match Greg Scace's values.

Here is where I am at: SV = 205F
Water temp measured (crudely Using double insulated Styrofoam cup and Digital thermo) at head after a 6-8oz flush, is barely reaching 195F.

Machine on 3 hours: Idle for about 25 minutes, I pulled 2oz, looked at the reading on the thermometer barely 185F, 2oz more, rising, 190f, 2oz more 192f, etc. I seem to plateau at 195, and can't seem to get above that. Not sure if it makes any difference, but I also notice when I do the same to both group heads, the left head is almost always higher values, the right group seems to plateau at around 192F max. Obviously this is not enough for good espresso.

I put the SV up around 210 (EDIT: typo), and seem to plateau around 198. SV at max, 215, lucky to hit 200f.

What gives? I know Greg is running his SV around 205, and it's around a 5degree drop at the head, so it's hitting the puck around 200F, if I read his posts correctly.

Any thoughts?

Thanks,
Justin
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Postby mitch236 on Fri Sep 02, 2011 10:03 am

A couple of thoughts. First, what type of probe and meter are you using? Is the meter set to the correct probe? Maybe the styrofoam setup is to blame? I know someone on CG rents a Scace device with Fluke meter, maybe rent that and try again? Is the Fuji setup correctly to use the thermocouple?

Do you have the Linea AV? If so, and I'm not sure how much this can affect the temps, the flowmeter uses the brew temp water and there is some cooling of the water as it flows along this path. Maybe that's causing some cooling?
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Postby HB on Fri Sep 02, 2011 10:08 am

mitch236 wrote:I know someone on CG rents a Scace device with Fluke meter, maybe rent that and try again?

See For rent: Scace thermofilter and Fluke 54-II thermometer.
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Postby Arpi on Fri Sep 02, 2011 10:17 am

Your pid is probably doing an excellent job. What happens is that the pid sensor is connected to the boiler not the brew head. There is a difference in temperature between those two. You can adjust the offset by setting a variable called "PV offset". You need to download the manual of the pid and look at the instructions on how to change it.

Cheers
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Postby mitch236 on Fri Sep 02, 2011 11:17 am

Arpi wrote:Your pid is probably doing an excellent job. What happens is that the pid sensor is connected to the boiler not the brew head. There is a difference in temperature between those two. You can adjust the offset by setting a variable called "SV offset". You need to download the manual of the pid and look at the instructions on how to change it.

Cheers


Maybe so but I think a 15 degree offset is a little high. If I remember correctly, mine is about 8 degrees.
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Postby Euology101 on Fri Sep 02, 2011 11:24 am

mitch236 wrote:A couple of thoughts. First, what type of probe and meter are you using? Is the meter set to the correct probe? Maybe the styrofoam setup is to blame? I know someone on CG rents a Scace device with Fluke meter, maybe rent that and try again? Is the Fuji setup correctly to use the thermocouple?

Do you have the Linea AV? If so, and I'm not sure how much this can affect the temps, the flowmeter uses the brew temp water and there is some cooling of the water as it flows along this path. Maybe that's causing some cooling?


I have the EP kit, set up on a 2AV. At first thought I figured it was just my styrofoam setup, but I did a similar test on my Anita, and it turned up results or close results based on my cooling flush technique. I admit this is not the best way to test, but it should get in the general range, not 10 degrees different. Fuji is set up as per EP's instructions, and the massive amounts of reading on here, so I'm fairly certain It's correct.

I know the 2av thing will give me a much greater offset, but Greg Scace has his set at around 205, and gives him about 200 at the group. (same machine as him)


Thanks Dan, this is on my list of things to try, I just want to see if I can get it in "range" before I spend the $$ on this, which I'm sure I will to fine tune it.

Arpi wrote:Your pid is probably doing an excellent job. What happens is that the pid sensor is connected to the boiler not the brew head. There is a difference in temperature between those two. You can adjust the offset by setting a variable called "SV offset". You need to download the manual of the pid and look at the instructions on how to change it.

Cheers


I agree with this, but I also think that it is a very large offset. I have the SV-H set up at 215, and even with the SV at 215, the group is barely 198.
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Postby cannonfodder on Fri Sep 02, 2011 12:31 pm

Is your AC on? That will lower it, ceiling fan on, that will lower it, blower on the HVAC on, that will lower it, sitting beside a refrigerator, that will lower it... There are many, many different environmental variables that will affect the temperature at the group vs temp at boiler and that offset will change as the seasons change. The placement of the probe in the boiler also has a lot to do with the offset, then there are all the error possibilities of your measurement technique. I would not worry much about it until you can get your hands on a scace to check your temps.
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Postby Arpi on Fri Sep 02, 2011 12:35 pm

Well, it could be many things. You best bet would be to cover the basics. Make sure that if the pid says 200F then you go and measure the same spot to be 200F. Offsets can be in C or F, which could cause confusion if omitting this when spreading information. But a 5F offset sounds really low even in the summer. The PXG allows a factory reset but I don't think the PXR allows that. A little setting somewhere could cause problems.

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Postby Euology101 on Fri Sep 02, 2011 12:46 pm

cannonfodder wrote:Is your AC on? That will lower it, ceiling fan on, that will lower it, blower on the HVAC on, that will lower it, sitting beside a refrigerator, that will lower it... There are many, many different environmental variables that will affect the temperature at the group vs temp at boiler and that offset will change as the seasons change. The placement of the probe in the boiler also has a lot to do with the offset, then there are all the error possibilities of your measurement technique. I would not worry much about it until you can get your hands on a scace to check your temps.


Current ambient temp is around 73F I have a ceiling fan on in the room, but that is all, no AC.

Arpi wrote:Well, it could be many things. You best bet would be to cover the basics. Make sure that if the pid says 200F then you go and measure the same spot to be 200F. Offsets can be in C or F, which could cause confusion if omitting this when spreading information. But a 5F offset sounds really low even in the summer. The PXG allows a factory reset but I don't think the PXR allows that. A little setting somewhere could cause problems.
Cheers


Any chance you can explain what the "SV Offset" does? I think I understand, but I want to make sure. Currently the SV Offset is set to 0.0

Appreciate the responses.
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Postby Arpi on Fri Sep 02, 2011 1:15 pm

Oops. I think it is the "PV offset" the one you want to change (not the SV offset). All it does is to tell the pid to read higher or lower by so many degrees. For example, if you set it to -5F, then the temperature at the boiler will be +5F than the temperature displayed. If you match this value to the temperature difference between the boiler and the head, then the pid will display the temperature of the water reaching the head.

Keep raising the pid temperature till you get 200F at the head (water running-shot), then the pid display value minus 200 is the offset value you would put in the "PV offset" variable so that the temperature of the head and the pid display match.

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