Archie
Member
This is a bit of an academic exercise and I wanted to check if anyone has already developed a formula before I start diving into some integral calculus.
I am experimenting with precision heat control using a phase control SSR that uses a 4-20mA signal. A phase control relay controls AC voltage output by switching on at a certain point in cycle then back off at zero crossing. At 50% it will switch on at the peak of each sine wave cycle, therefore giving an RMS output of 50% of the source (e.g 60Vrms from a 120Vrms source).
When the signal goes on either side of the 50% mark, it is not linear. For example at 75% (16mA control) you may expect to get 90Vrms, but you will get higher, let's say roughly 110Vrms.
What I want to do is to pass my control signal through a linearizing function so if I call for 75%, it will switch on at the correct angle in the sine wave to give 90Vrms. This would be formula to calculate the area under sine wave based on the angle.
I have attached an image I got from Wikipedia to give a visual of a phase control relay output.
I am experimenting with precision heat control using a phase control SSR that uses a 4-20mA signal. A phase control relay controls AC voltage output by switching on at a certain point in cycle then back off at zero crossing. At 50% it will switch on at the peak of each sine wave cycle, therefore giving an RMS output of 50% of the source (e.g 60Vrms from a 120Vrms source).
When the signal goes on either side of the 50% mark, it is not linear. For example at 75% (16mA control) you may expect to get 90Vrms, but you will get higher, let's say roughly 110Vrms.
What I want to do is to pass my control signal through a linearizing function so if I call for 75%, it will switch on at the correct angle in the sine wave to give 90Vrms. This would be formula to calculate the area under sine wave based on the angle.
I have attached an image I got from Wikipedia to give a visual of a phase control relay output.