Building a lever machine.... from scratch - Page 18

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Paolo
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Postby Paolo » May 12, 2017, 6:10 pm

Absolutely amazing work, Thomas!

pizzaman383
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Postby pizzaman383 » May 13, 2017, 3:17 pm

If you want to stick with the simplicity of the PID for steady state control you could use a thermostat and a relay to handle the initial heating.
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bidoowee
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Postby bidoowee » May 16, 2017, 11:48 am

Thanks to all for the comments. I really do appreciate it.

I've spent the last couple of days getting my head into code and hooking sensors to arduinos.
This is a setup that controls a reflow oven lent to me - along with the code - by a friend.

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I'll report back when I have something to show...

In the meanwhile, I had a go at some proper LRFs (little rubber feet).
I've come to the conclusion that plastic is, well, too plastic. Good coffee is a luxury that merits the use of premium materials.
In that spirit, I broke out the king of woods, the champion of the rainforest: mahogany.
I generally try to avoid working too much wood in the shop because of the mess. So much dust...
For the same reason, I have not purchased a jointer or planer. So, a ripping blade in the table saw will have to do.

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After a change the blade to do the cross cuts.

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A 1/8" round-over in the router to finish 8 of the 12 edges.

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Then it is into the milling machine with a vacuum cleaner running to keep the dust from getting anywhere it shouldn't.

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Flip the block and drill a blind hole. For now, as this wood is hard enough to hold a bolt intended for metal, that is what I will use.
Ultimately, I will likely anchor some threaded rod in with epoxy and use a nut.

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Cut and glue on some rubber pads to provide the necessary friction.

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Then. having previously sanded them to take off the burn marks from the table saw and router the blocks can be finished with some tung oil.

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...damn. Forgot to take a picture of them installed. Watch this space.

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Chert
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Postby Chert » May 16, 2017, 2:01 pm

bidoowee wrote:
...damn. Forgot to take a picture of them installed. Watch this space.


"Same bat-time, same bat-channel", right?

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bidoowee
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Postby bidoowee » May 16, 2017, 2:06 pm


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bidoowee
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Postby bidoowee » May 16, 2017, 4:53 pm

Meanwhile...
Here is something else to contemplate: a state machine diagram for the operation of the controller.

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Key -

PWM - pulse width modulation (for the solid state relay that drives the heating element)
AF - autofill
OT - overtemperature

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bidoowee
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Postby bidoowee » May 19, 2017, 11:28 am

FYI, I have an old Urania and wanted to know if the PID actually helps with managing the water temperature or if the benefit is really to give you an accurate reading of the temperature so you can manually adjust by running water through the group, waiting a bit longer, etc.?


Someone asked me this question by PM, and I thought it was interesting enough to warrant discussion.

There is an awful lot out there on PIDing your [insert machine name here] as I would guess that it is possibly the biggest bang for the buck upgrade that can be done. I am sure that there are many people who might be able to chime in who have more experience actually doing this. My answer to this specific question is that it depends...

Firstly, it depends on what the PID is setup to control. In my case, I am starting by replacing the old Sirai pressurestat which regulates the boiler pressure with a thermocouple and PID algorithm. The Sirai is not what one might call a precision instrument. The "deadband" - i.e. the zone between the low and high pressure levels that trigger the device to change state - is around 0.2bar when the diaphragm inside the switch is new (roughly 20% of the operating pressure!).

When the device gets older, this deadband gets even larger. Translated into temperature, the deadband (when new) is about 7 Celsius - which, if you are trying to maintain the brew temperature within a degree, is quite large. This relatively large variation in boiler temperature is dampened (smoothed out) by the thermal mass of the group. In this case, a well-tuned PID will maintain boiler temperature to within a degree while the machine is at idle. This represents nearly an order of magnitude of improvement. In the case of the Aurora, the boiler temperature is the only variable that can be controlled and the thermocouple measures only that temperature - i.e. it tells you nothing about what is going on at the group. One could, however, also measure the temperature of the brew reservoir and the group itself and supply a more complicated algorithm with additional information.

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arcus
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Postby arcus » May 19, 2017, 4:19 pm

I'd be interested to know how often the element turns on/off when the PID is maintaining the boiler temperature vs. the pstat. Ideally, I'd like to increase the time between heating cycles.

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bidoowee
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Postby bidoowee » May 19, 2017, 8:10 pm

As it isn't possible to adjust the temperature of the element - it's either on or off - PWM (pulse width modulation) is used to simulate an analog response from the digital (on/off) system. Switching the element on for half the time and off for the other half is, as far as a boiler this size is concerned, almost exactly the same thing as having an element that could be regulated to "half-power" as long as the switching is done fairly quickly. The faster the on-off cycle frequency, the closer the approximation becomes. So in actual fact, you want to have the boiler "cycling" as quickly as possible to maintain a given "power" setting. In practice, a regular solid state relay is limited to a cycle time of 1Hz, or once per second - but this is more than adequate for the task it is required to perform here.

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arcus
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Postby arcus » May 19, 2017, 10:19 pm

Thanks for the interesting info. Is there any noticeable change in power consumption or noise with the boiler cycling as quickly as possible?

 
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