I
NTRODUCTION
S
YSTEM
OVERVIEW
AlphaXpress 8731 Sign Installation and Maintenance Manual (pn 1508610601 rev. A)
11
LED brightness control system
The VMS is equipped with a brightness control system for the LEDs. The brightness control system ensures
that the display is readable in all lighting conditions.
The photocells are enclosed in the light sensor globe to protect them from the environment. Three photocells
continually monitor the ambient light conditions. The photocell assembly is constructed in such a manner that
adverse weather conditions (such as heavy snow) should have no effect on its performance. The main
components of the brightness control system are the following:
•
IDI 1320 controller
•
Light sensor globe
General operation
The photocells are enclosed in a globe to protect them from the environment. The photocells continuously
monitor the ambient light conditions and send the information directly to the controller. The controller assembly
determines exactly how much ambient light is present through the light-sensing photocells and sends the
proper command to the display module for it to adjust duty cycle of the LED current drive, thus dimming or
brightening the LED modules according to the ambient light. (If the on time of the duty cycle is 50%, then the
brightness will be at 50%; if the on time of the duty cycle is 75%, then the brightness will be at 75%, and so on.)
The photocell assembly is constructed in such a manner that adverse weather conditions should have no
effect on its performance.
Light sensor globe mounting
Because the function of the photocells depends on ambient lighting, the light sensor globe should be mounted
in a location where it will receive maximum light exposure throughout the day. When choosing a mounting
location for the light sensor globe, make sure the globe can receive ambient light on all sides of the globe.
Environmental control system
To protect the sign components from overheating, two fans are mounted in each of the sign’s modular cases.
The operation of each fan is controlled independently by a thermostat dedicated to each fan. The fans turn on
when the internal temperature of the sign reaches 122ºF (50ºC), and turn off when the internal temperature is
below 90ºF (32ºC).
Electrical system
The electrical supply system is responsible for supplying the necessary power to operate the LED sign system.
The sign housing AC and DC electrical system consists of the following components:
•
GFCI outlet
•
DC power supply
Electrical distribution (AC)
The AC input to the sign system consists of 120VAC 30A single-phase service wired to the input AC terminal
block located on the controller plate. See “AlphaXpress 8731 models (three row models)” on page 7 or the
“Appendix” on page 51 for the number of circuits required for your sign. AC is internally wired to the DC power
supplies.
