I have now received the Seeed Studio current sensors I ordered a couple of weeks ago. They worked a treat and I get a good voltage level out of them when I use a 60W element @ 240VAC. I am now modifying my existing design to utilise these to detect that the heating elements are drawing current. Thanks to all that contributed from the list. R/- Grant On Thu, Nov 17, 2011 at 1:10 PM, Grant Tudor wrote: > Thanks for all the great information. I have ordered a couple of the Seee= d > Studio current sensors and I will get back to the list when I have had a > chance to try them out. > > Regards, > > Grant > > > On Tue, Nov 15, 2011 at 12:12 PM, Joe Wronski wrote: > >> Yes, I believe so, but others here know more, from what I've read. I >> recall using commercial current probes from tektronix. >> < >> http://www.tek.com/products/accessories/current.html?WT.srch=3D1&WT.mc_i= d=3Dppc,covtekggl91000000014973s >> < >> http://www.tek.com/products/accessories/current.html?WT.srch=3D1&WT.mc_i= d=3Dppc,covtekggl91000000014973s >> >> >> for low current, high speed measurements. >> With the SCT-013 I've observed nice waveforms of 60 Hz current at about >> 1 amp in the primary. I imagine it would be high frequency you'd be >> concerned with in a triac circuit. >> Joe W >> >> >> On 11/14/2011 3:43 PM, KPL wrote: >> > wil CT's provide output signal more or less same form as the current? >> > I mean, are they usable to use as current pickups for scope, when >> > testing triac-regulated circuits? I'm just not sure how ferrite works >> > with these low frequencies. >> > I do not need to measure amplitudes, just to see the angle when triac >> > is switched on. >> > That would be much easier than using big isolation transformer before >> > whole circuit. >> > >> > On Mon, Nov 14, 2011 at 17:42, Joe Wronski >> wrote: >> >> Not much technical info here, but there are some sources of CTs and >> >> examples of biasing, etc. >> >> >> >> I bought CTs with and without internal burden resistors from >> >> seeedstudio. I use the unburdened one to simply detect lower current= s, >> >> but might need an op amp for any accuracy with a burden R. Using a >> >> freebie ferrite core is tempting, but I like the clamp on method the >> >> SCT-013 units use. I've seen how-to's of making your own calmp on >> using >> >> a ferrite core and a big alligator clip. >> >> >> >> Joe W >> >> >> >> >> >> >> >> >> >> On 11/14/2011 5:56 AM, Isaac Marino Bavaresco wrote: >> >>> Em 14/11/2011 03:12, Grant Tudor escreveu: >> >>>> Issac, >> >>>> >> >>>> There is a low temperature alarm hence the desire to have a battery >> back up >> >>>> so that the unit can sense when there is a mains failure. This work= s >> well >> >>>> if both elements have failed or the door is left ajat etc as you >> mentioned. >> >>>> >> >>>> The idea of the current drawn indication is to show that elements a= re >> >>>> working (or not). The incubator has two heating elements for >> redundancy. >> >>>> Either is sufficient to heat the incubator to the required >> temperature. The >> >>>> problem is that it may be possible for one element to sop working >> and you >> >>>> would not notice it because there is no indication that it is >> working or >> >>>> not. The second element would then take over the heating of the >> incubator >> >>>> but the redundancy is no longer there. If the second element stops >> working >> >>>> then there is a potential catastrophe. If there is still power, the >> low >> >>>> temperature alarm will sound but if may be a while before anyone is >> around >> >>>> to hear it. If I had an indication that one of the element had >> stopped >> >>>> working then the element could be replaced and redundancy restored. >> >>>> >> >>>> I like the ferrite core concept as it is simple, easy to retrofit a= nd >> >>>> provides a level of isolation between the LV circuit and the 240VAC= .. >> I just >> >>>> need to get the voltage up to a sufficiently high level to be >> workable. I >> >>>> could then either monitor the voltage using the PIC directly, or us= e >> the >> >>>> voltage to light a LED to provide a visual indication that the >> element is >> >>>> working. >> >>>> >> >>>> R/- >> >>>> >> >>>> Grant >> >>> You could amplify the signal with an Op-Amp as I suggested in my >> >>> previous post or you could offset the signal to VCC/2 and measure th= e >> >>> sinusoid directly with the A/D converter of the PIC. >> >>> >> >>> You told that you got an 100mV signal. That is 200mVpp. If you offse= t >> >>> the signal to 2.5V then you would get 2.4V in the negative semi-cycl= e >> >>> and 2.6 V in the positive semi-cycle. That would give a differentia= l >> >>> reading in the ADC of 40 counts, this may be enough to detect that t= he >> >>> heater is consuming power and even how many heater elements are >> working. >> >>> >> >>> >> >>> Best regards, >> >>> >> >>> Isaac >> >>> >> >> -- >> >> http://www.piclist.com PIC/SX FAQ& list archive >> >> View/change your membership options at >> >> http://mailman.mit.edu/mailman/listinfo/piclist >> >> >> > >> > >> >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .