General comparisons of SCR power controllers
SCR Switching control type
type can not control the angle of thyristor (SCR) as below mentioned
angle control and zero-crossing,but only turns on/off thyristor (SCR)
sending control signals to SCR.This type has more efficiency and fewer
than SCR phase angle control type, and can produce low cost.
the resistance element temperature experiences very large temperature
SCR Phase angle control type
type is phase angle control base which turns on/off thyristor (SCR)
a certain angle with the controlling input of waveform 0~180 degree
load power.This type is effective to control a specific voltage and
to use the control of inductive load. This type generates
of producing wave distortion. So this type takes troubles
be surrounded electronic machines and tools, and reduces the efficiency
the transformer because of generating ineffective power during turning
SCR Zero-crossing(Zero-voltage switching) control type
type is time control base which turns on/off thyristor (SCR)
zero point of ac power sine wave, and this does not produce
distortion. Thus, this type does not generate harmonics and
power. Today, this type is better for controlling a big
and heaters surrounded with sensitive machines to noise
SCR phase angle control type. But this type cannot control
heater load. The Zero-crossing control type can use
time base zero-crossing,variable time base zero-crossing,
mixed(phase angle+variable time zero-crossing) control.
Fixed Time Base Zero-Crossing control
fixed time base means that the “cycle time” on the SCR power
set or fixed(not adjustable).
During this time period(1 second, for
the SCR power controller
will turn the SCR ON and OFF the provide the
correct percentage of power
to the heater. For example, the SCR has a
fixed time base of 1 second,
and the power supply is 60Hz. If
the process output demands a 40% power
requirement,the SCR will be turned
on for 24 cyles(40% of 60 cyles) and
turned off for 36 cyles.
Variable Time Base Zero-Crossing control
SCR power controller with a variable time base changes th time base
the power requirement, and uses the smallest possible number
of ac power
to deliver the required percentage power to the heater.
If the process
demands a 40% power requirement, the SCR will be
turned on 2 cyles out of
5 cyles.For 90% power requirement,
the SCR will be turned on 9 out of 10
SCR Mixed Control (Phase angle + Variable Zero-Crossing control)
type combines the best features of the phase angle and variable time base
firing method, and is utilized on the power control of variable
heater loads(for example, halogen , molybdenum,tungsten heater).
mixed type is under phase angle control during initial power application
then switch to variable time base zero-crossing. So, this ensures maximum
when needed, and then revert to RF interference free zero-crossing
control after process stabilization.