Path: csiph.com!eternal-september.org!feeder.eternal-september.org!mx02.eternal-september.org!.POSTED!not-for-mail From: Folderol Newsgroups: comp.sys.raspberry-pi Subject: Re: controlling a mains-powered oven Date: Tue, 8 Sep 2015 19:11:45 +0100 Organization: A noiseless patient Spider Lines: 28 Message-ID: <20150908191145.551bce78@debian> References: <9d3accff54.Alan.Adams@iyonix.adamshome.org.uk> <20150908182109.45fde42d@debian> <4711030055.jim@abbeypress.net> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Injection-Info: mx02.eternal-september.org; posting-host="4c8c017bf2000d02e906f28de06f0c9d"; logging-data="14092"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19mQUr4aEkmiCHBNGWN8vP19dPJb9ZLpWY=" X-Newsreader: Claws Mail 3.11.1 (GTK+ 2.24.25; x86_64-pc-linux-gnu) Cancel-Lock: sha1:W6d65KQqB+uDyjGX7WTXmWz6wwY= Xref: csiph.com comp.sys.raspberry-pi:9581 On Tue, 08 Sep 2015 19:03:31 +0100 Jim Nagel wrote: > Folderol wrote on 8 Sep: > > > A low temp coefficient, near perfect resistor (heating element) is the > > simplest load of all to drive. Use a zero-crossing SSR and you then > > need only minimal - if any - EMI suppression. Also, pick up the mains > > itself and use it as your gate trigger source, and you will always use > > complete cycles, so no nasty DC offset being created. > > > In theory, with full PID control that gives you a 20mS response time. > > Considering the thermal inertia of the oven is in tens of seconds, > > this is way over-engineering :) > > I was imagining software that would cause the heating element to > switch on or off only when the sensor gets to, say, 10% above or below > the desired temperature. Am I being electrically simplistic? > No, not at all. For a domestic oven that's quite good enough. It only (potentially) becomes a problem with big industrial heaters where you want precise temperature control and the heating system itself has a minutes long thermal inertial, because when you reach your setpoint and switch off, the element will still be pumping out heat for some time, and vice-versa for cooling. -- W J G