PID autotuning - not working for heating application
in [Embedded]
|
Prev: Artesyn BAJA PPC 750
Next: FPGA Soft Core CPUs
From: pnachtwey on 10 Nov 2009 18:51 On Nov 10, 2:59 pm, Tim Wescott <t...(a)seemywebsite.com> wrote: > Speaking of overkill, why not just use an on-off thermostat with some > hysteresis? Good idea, then there are no gains to tweak so coffee can be made right away and the coffee drinking can begin. How accurate must the temperature control be on a coffee maker and who would be able to tell the difference between 85 and 86 degrees C? 85-86 degrees seems to be a few degrees too low unless Frank W knows something the rest of the world doesn't. Peter Nachtwey
From: Frank W. on 11 Nov 2009 03:54 pnachtwey" <pnachtwey(a)gmail.com> wrote: > unless Frank W knows something the rest of the world doesn't Don't speak for the rest of the world if you are an ignoramus. - With a thermostat, temperature swings are far more pronounced than you claim. It's not just two degrees: The PID has reduced temperature swings of ~15 degree Celsius with the original thermostat to nearly nothing. Such variations had a noticeable influence on taste (cold = sour). Here's a PID-vs-thermostat temperature plot for a different, slightly higher-end 500$ home coffee machine which has even bigger 23.9C swings: http://www.espressoparts.com/espressoparts/content/graphics/pagebuilder/pidsd3c_silvia_tempplot.jpg - An equally important benefit is that with a PID instead of a thermostat, the PV is adjustable. Different beans/roasts call for different brew temperature - roughly between 85 and 99 degree Celsius.
From: RockyG on 11 Nov 2009 04:51 > Here's a >PID-vs-thermostat temperature plot for a different, slightly higher-end 500$ >home coffee machine which has even bigger 23.9C swings: >http://www.espressoparts.com/espressoparts/content/graphics/pagebuilder/pidsd3c_silvia_tempplot.jpg >- An equally important benefit is that with a PID instead of a thermostat, >the PV is adjustable. Different beans/roasts call for different brew >temperature - roughly between 85 and 99 degree Celsius > Just for interest, is the boiler pressurised? I saw that the graph show temepratures higher than 100 deg C. and wondered how they were achieved. --------------------------------------- This message was sent using the comp.arch.embedded web interface on http://www.EmbeddedRelated.com
From: pnachtwey on 11 Nov 2009 10:33 On Nov 11, 12:54 am, "Frank W." <frankw_use...(a)mailinator.com> wrote: > pnachtwey" <pnacht...(a)gmail.com> wrote: > > unless Frank W knows something the rest of the world doesn't > > Don't speak for the rest of the world if you are an ignoramus. You have pissed me off. I searched the internet, the rest of the world, to find the correct brewing temperature and normal limits which apparently you don't know and know one else has bothered to do. DON'T YOU THINK THAT IS IMPORTANT???? I see have wasted my time. Peter Nachtwey
From: Tim Wescott on 11 Nov 2009 11:35
On Wed, 11 Nov 2009 09:54:22 +0100, Frank W. wrote: > pnachtwey" <pnachtwey(a)gmail.com> wrote: > >> unless Frank W knows something the rest of the world doesn't > > Don't speak for the rest of the world if you are an ignoramus. Actually Peter is one of those "control experts" that you were looking for. If anything he can claim more pertinent experience at this stuff than me -- and if a potential customer came to me with a problem that seemed to be in his bailiwick I wouldn't hesitate* to send them his way. Control problems seem to attract overly complicated solutions; so one of the things a responsible control engineer always needs to do is to ask "is there some bone-head simple way to do this that will be adequate". > - With a thermostat, temperature swings are far more pronounced than you > claim. It's not just two degrees: The PID has reduced temperature swings > of ~15 degree Celsius with the original thermostat to nearly nothing. > Such variations had a noticeable influence on taste (cold = sour). > Here's a PID-vs-thermostat temperature plot for a different, slightly > higher-end 500$ home coffee machine which has even bigger 23.9C swings: > http://www.espressoparts.com/espressoparts/content/graphics/pagebuilder/ pidsd3c_silvia_tempplot.jpg > - An equally important benefit is that with a PID instead of a > thermostat, the PV is adjustable. Different beans/roasts call for > different brew temperature - roughly between 85 and 99 degree Celsius. Not to say that you aren't right in the end, but there are thermostats and there are thermostats. Design your software for relay control, keep the hysteresis low and the setpoint adjustable, and you may find that a swing of a degree or two is quite achievable. I don't know if it would be adequate, but you can do a heck of a lot better than a $0.1 snap- action bit of bimetal and a switch. Of course, if "PID control" has become a sales point, then you'd better have it in there. * I may do so wistfully if work were slow, but I'd still do it. -- www.wescottdesign.com |