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(Another) Poppery PID controller project
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JKalpin
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JKalpin
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Posted Thu May 21, 2009, 8:49am
Subject: Re: (Another) Poppery PID controller project
 

These PID Roaster Conversions, like Dana's, sure activate my brain-cells (whatever of them I have left).  I wonder if anyone has tried to do this with a FreshRoast 8 +.  Mine has 115 roasts on it and one day (?) it will quit and I will have to buy a new bottom for it and then I will have a broken one to take apart and maybe alter.  Hmmmm.

So, could someone explain a few things about these low-cost PID controllers?

  1.  I suppose the output is to an SSR, where there is on-off switching, no doubt at waveform zero.  Typically, how fast, that is ...once a minute or 10 times a second?

  2.  All the descriptions are light on the programming, as if it's no big deal.  How indeed would you enter an instruction to go from (say) 440F to 470F over 3 minutes?

 
Jerry
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JGG
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Espresso: PID Silvia; PID Alexia
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Posted Thu May 21, 2009, 4:24pm
Subject: Re: (Another) Poppery PID controller project
 

JKalpin Said:

I suppose the output is to an SSR, where there is on-off switching, no doubt at waveform zero.  Typically, how fast, that is ...once a minute or 10 times a second?

Posted May 21, 2009 link

Easiest and cheapest is to use a DC control SSR which switches at the zero-cross of the AC power source, just as you surmised.  Minimum cycle time is dependent on the PID model.  For an air popper, with a very low mass / high power heater, you will want to use the fastest cycle time the PID will allow.  For a popper, I would try and use nothing slower than 1 second, and would use 0.1 second if supported by your controller.

JKalpin Said:

All the descriptions are light on the programming, as if it's no big deal.  How indeed would you enter an instruction to go from (say) 440F to 470F over 3 minutes?

Posted May 21, 2009 link

Typically, the profile is input as (time, temperature) pairs.  The controller will linearly ramp the setpoint between the (time, temperature) points along the profile.  The time variable at each point is usually the duration of the step.  Tedious, but not rocket science.

Jim
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dana_leighton
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Posted Thu May 21, 2009, 6:35pm
Subject: Re: (Another) Poppery PID controller project
 

Yes, the programming looks pretty trivial. The art & science will come into play when tuning the PID, translating bean mass temperatures to MET temperatures at the heater inflow.

I decided to go with the Delta DTB4824VV controller that Jim suggested. It has the RS485 interface and software for monitoring the temperatures and programming the PID. I expect it will make it a lot easier. Jim used USB, but I opted for a cheaper RS232 interface. Had to get a converter to go from RS485 to RS232 (DB9 connector), which will then be connected via a cable to the serial port of a cheap Windoze laptop I bought. The laptop will run the software for the controller.

I also ordered a cheap temperature monitor from eBay, which will display the temperature for whichever thermocouple it's hooked up to. I plan to use that to monitor bean mass temperature and let the controller run off the heater thermocouple.

As soon as I get the temperature monitor and RS485 to RS232 converter, I'll have all the parts, and ready to start wiring it together and putting it in a box. The back of the box should have a cord for AC, a master power switch (or I may put that on the front), a 15A fuse on the incoming AC (or can be installed inside I suppose), and the DB9 port. The front should have the PID, the temperature meter, and possibly a count-up timer. although those do not come cheap.

 
Dana Leighton - Espresso hack and CoffeeGeek moderator
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JGG
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Posted Thu May 21, 2009, 6:59pm
Subject: Re: (Another) Poppery PID controller project
 

Great to see your project is coming together!

Here is some food for thought:  I added a cheap SPST switch on the front my controller enclosure, and ran the DC voltage output from the PID through this switch.  This allowed me to quickly kill power to the heater at any time.  Handy for testing, emergencies, manual control, etc.

A little more food for thought:  the second output on your PID can be set up as a process alarm.  The Delta has lots of configurations for this alarm, including a config that you can use to illuminate an LED whenever the actual temperature is within "x" degrees of the current setpoint.  Just add a current limiting resistor in series with a small LED and connect directly to output 2 on the PID.  If you mount the LED on the front panel, you'll have an immediate visual as to whether the PID is tuned well and maintaining setpoint.

Jim
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dana_leighton
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dana_leighton
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Posted Thu May 21, 2009, 7:14pm
Subject: Re: (Another) Poppery PID controller project
 

Thanks Jim. I like the LED idea and the kill switch both.

One question: I am not all that handy with electrical, but is there any advantages or disadvantages to running the AC power in series versus in parallel?

If I wire it in series, it would go something like: cord -> fuse -> temperature meter -> PID -> relay ->heater

Oh I think I just answered my own question - At least the power to the relay/heater needs to be parallel to everything else because otherwise the on/off of the relay would be propagated back through everything else? (rusty basic electricity might be a dangerous thing...)

 
Dana Leighton - Espresso hack and CoffeeGeek moderator
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JGG
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Posted Thu May 21, 2009, 7:34pm
Subject: Re: (Another) Poppery PID controller project
 

dana_leighton Said:

One question: I am not all that handy with electrical, but is there any advantages or disadvantages to running the AC power in series versus in parallel?

If I wire it in series, it would go something like: cord -> fuse -> temperature meter -> PID -> relay ->heater

Oh I think I just answered my own question - At least the power to the relay/heater needs to be parallel to everything else because otherwise the on/off of the relay would be propagated back through everything else? (rusty basic electricity might be a dangerous thing...)

Posted May 21, 2009 link

Mine is wired like this (except I don't have the panel thermometer).

Jim

JGG: img023.jpg
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dana_leighton
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Roaster: Poppery I w/PID controller
Posted Thu May 21, 2009, 7:47pm
Subject: Re: (Another) Poppery PID controller project
 

Thanks Jim. You're a prince!

Dana.

 
Dana Leighton - Espresso hack and CoffeeGeek moderator
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dana_leighton
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Roaster: Poppery I w/PID controller
Posted Fri May 22, 2009, 1:47am
Subject: Re: (Another) Poppery PID controller project
 

OK -- Jim's circuit diagram inspired me. I added a couple things to the circuit:
1) dimmer switch and step up transformer to boost the fan motor voltage (Thanks for the idea, Ron)
2) a circuit to bypass the PID/SSR controlling the heater, so that I can use manual heater control if I want.
3) a volt meter for both the fan and heater circuits so that I can more accurately control/monitor those parameters.

Did I miswire something? Do you think there's anything else to add or to eiiminate?

dana_leighton: popper-circuit.png
(Click for larger image)

 
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rama
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rama
Joined: 4 Jan 2006
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Posted Fri May 22, 2009, 8:58pm
Subject: Re: (Another) Poppery PID controller project
 

farmroast Said:

I really like manual control,  a BT and MET TC, a variac with a kill a watt meter and count-up timer. The beans act and I can react. I datalog some roasts and record the voltage readings. I can adjust to the temp.  the bean is handling the best as the roast progresses.

Posted May 18, 2009 link

Out of curiosity, how are you reading the outputs of the two TCs? Two separate multimeters?
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JGG
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Espresso: PID Silvia; PID Alexia
Grinder: Mazzer SJ
Roaster: Hottop D w/HTC+TC4C
Posted Fri May 22, 2009, 10:18pm
Subject: Re: (Another) Poppery PID controller project
 

dana_leighton Said:

OK -- Jim's circuit diagram inspired me. I added a couple things to the circuit:
1) dimmer switch and step up transformer to boost the fan motor voltage (Thanks for the idea, Ron)
2) a circuit to bypass the PID/SSR controlling the heater, so that I can use manual heater control if I want.
3) a volt meter for both the fan and heater circuits so that I can more accurately control/monitor those parameters.

Did I miswire something? Do you think there's anything else to add or to eiiminate?

Posted May 22, 2009 link

Nice design.  

I'm not well versed on transformers, so I don't fully understand how that's going to work.  I guess it steps the voltage up by ~15%?  That would be very handy while the beans are still green and heavy, as long as the fan motor can handle a little higher voltage.  Later, when the bean density lessens, I assume you'd use the dimmer to dial back the fan.  Sounds like a good plan to me.

Jim
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