Figure 6-32. - Block diagram of constant-current regulator.

The output voltage is applied to the input of the gate pulse generator that determines the condition angle of the SCRs and changes it to bring the system to equilibrium. Transient overload protection is provided for the semiconductor element of the Hall unit. Open- circuit protection is provided when no current is drawn by the load and the brightness potentiometer output voltage is any value other than zero. Under these con- ditions, the SCRs will be prevented from conducting, and the output voltage to the load will be zero.

Remote Control

The airfield lighting systems may be operated completely by the remote control panel assembly. The only operation required at the electrical distribution vault is to ensure that all circuit breakers are engaged, the regulators are set for remote operation, and the load switches are in the ON position. The electrician must ensure that the unit is installed properly and that the different levels of light intensity desired can be achieved. Figure 6-33 is a typical view of a remote control unit that you may encounter in the installation of a contingency airfield lighting system.

The unit uses 120 volts as the control voltage with low-burden pilot relays to compensate for the voltage drop caused by the long distances usually found between the control tower and the vault. In this type of control system, the switches on the control panel actuate low-burden relays; these, in turn, actuate the power switches, contactors, and the relays controlling the regulators that supply the airfield lighting circuits.

Figure 6-33. - Typical remote control panel operating controls.