(i) Firing Angle(): Firing angle is defined as the angle between the instant the SCR would conduct if it would be a diode and the instant it is triggered or fired. Firing angle or delay angle can be defined as the angle measured from the angle that gives maximum average output voltage to the angle when the SCR is actually triggered or fired by gate pulse.
(ii) Conduction Angle (β): Conduction angle is defined as the angle between the instant the SCR is triggered or turned on and the instant at which the SCR is turned off. Assuming that the SCR is turned off naturally at the end of positive half cycle, the relation between the firing or delay angle (α) and conduction angle (β) can be expressed as:
α + β = π radian or 180o