Precision Control Systems 1025 - Manual (Page 11)

MODEL 1022 & 1025 8 05/10/2007
MODEL NUMBER IDENTIFICATION
102X-VV-AA [-SCXXX] [-MOXX]
X = 2 for 1022,
5 for 1025
1022 (0/5Vdc, 0/10Vdc or POT control)
1025 (4/20mA input)
VV = Rated voltage:
12 = 120Vac
24 = 240Vac
48 = 480Vac
57 = 570Vac
AA = Rated amps:
10, 20, 30, 40, or 70 amps
Note:
The addition of "-SCXXX" implies that the controller has been modified to have a different input command. For example,
a "-SC1/5Vdc" implies the controller has been modified to operate with a 1/5Vdc control signal.
The addition of "-MOXX" implies a special mounting or assembly of the controller.
THEORY OF OPERATION
The model 1022 and 1025 are phase-angle controllers, therefore, the load voltage is controlled by turning the appropriate
SCR on for a portion of each electrical half cycle as shown in Figure 6. The waveform shown as E
L
represents the “ON”
time of the SCRs in each half cycle and therefore represents the voltage waveform applied to the load. As the load
voltage is increased the SCRs are turned ON earlier in the cycle. As the load voltage is decreased the SCRs are turned
on later in cycle. The load voltage can be varied with infinite resolution from 0 to 100 percent of the line voltage. Circuit
tolerances may limit the maximum load voltage to about 97% of the supply voltage.
Is I
E Es
L
L
L
O
A
D
Figure 6. Phase angle control at 50% power.