Um, you measure the current half cycle RMS waveform, so that you can adjust your triac firing on the following half cycles (it's called PID control). I'm not looking for "instantaneous" control, or 100% perfect control, just "reasonably" fast, accurate, and cheap. I did some experiments earlier today, and found that I need to have a "total" system reaction time of at least one second or less to make on the fly AC voltage regulation worthwhile, 1/2 second would even be better. To give you an idea, some of these little elements can heat up from ambient room temp, to 2000F, within five seconds..... -----Original Message----- From: Peter L. Peres To: PICLIST@MITVMA.MIT.EDU Date: Thursday, May 03, 2001 2:54 PM Subject: Re: [EE]: [PIC]: AC Voltage Compensation (Was RMS vs Average voltage) >I do not know what you mean to do. A triac is fired once per half period >and it is not very usefull to find out what happens with the voltage >after that until the next zero crossing because there is nothing you can >do about it (you could use a circuit to turn off the triac using a second >triac and a capacitor). > >Another way to measure power and RMS voltage is to use one of those double >resistor bridge things meant for RF RMS voltage measurement. They will >likely cost more than an AD736. The RMS readout is guaranteed to take one >full second to settle no matter what you use because of the definition of >the Watt (1J*1sec). The circuit has no way to know before that what the >RMS voltage is on an arbitrary waveform. With triac chopping you can take >a shortcut and calculate RMS volts from one half period. This will be >bogus if you change the firing angle within the following second however. > >Peter > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics > > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.