I'm doing a power controller for an electric grill, where through PWM I allow to pass x number of cycles from the 124V @ 60 Hz source of my lab.
Here you have the diagram:
It consists on a triangle signal that joins the LM311 comparator on one pin, and in the other one the input is the LM35 signal multiplied x 7. The system has been designed to get thinner pulses from the LM311 as the temperature on the sensor gets closer to 60 °C, where pulses must disappear. The PWM signal goes directly to a MOC3011, whose job is to excite the Gate pin from the SCR TIC116. I've checked everything so far with and scope. So, so far, so good.
As you may see, the frequency of the square signal that generates the triangle one, is 0.6 Hz. This means that in a whole pulse, 100 cycles from the 60 Hz might be involved. So, when the Gate is on, the grill would be working the number of cycles that are "inside" the gate pulse according to the temperature on the sensor.
Here comes the problem: the grill keeps working even when there is not any signal at the comparator output. I haven't seen the voltage signal at the grill because I have no way to isolate the scope from ground (it is not mine so I don't want to break it). But, anyway, something is happening in between the moc and the scr.
I can't use a TRIAC, my professor banned it.
EDIT: Do you think that replacing the moc3011 with a moc3041, the one with zero-cross circuit inside, may help to solve this? What would you be so kind to suggest?