The various sub system components are as follows:
i. Variable Message Sign Display (VMS)
i. RS-485 To UTP Converter or RS 232 to GSM modem/ pstn line or Ethernet socket
ii. Comm. To Central Control Server
iii. Central Control Console With Graphical User Interface
Figure 1 below shows the general layout of the VMS system.
3. SYSTEM FUNCTIONAL ARCHITECTURE
The VMS uses High Bright LED’s for the message display. The message to be displayed can be communicated in three manners:
i. Sent from the Central Control Room via a digital communication medium
ii. A local PC can be connected directly to the system
iii. The message can be keyed in through the LCD / key pad attached to the system.
The VMS consists of the following sub systems:
3.1.1 Cluster Controller:
The cluster controller is the heart of the system, controlling the entire operation of the VMS display. This consists of a CPU, RTC and memory. The cluster controller determines the message to be displayed on the VMS based on a predefined schedule or as defined and input manually. The message to be displayed is transmitted to the individual display modules on a serial communications link. The cluster controller manages other operations such as the manual input unit interfaces, storage of messages and the scheduler. It also provides a communication link to the VMS network on a standard RS-485.
The cluster controller can store up to 10 frames for local display storage.
3.1.2 Display Drivers
The display drivers consist of power transistors and control circuitry required to manage the transmission of data to individual pixels. In order to ensure trouble-free maintenance, the driver card is configured to a resolution of 16 x 16 pixels consisting of two LED’s of different colour (viz. red and amber).
3.1.3 LED Module
The LED module is the most visible part of the circuitry. The LED module consists of 5mm LED’s placed together to form a pixel. the pixels are used to create alphanumeric or graphic patterns. Each pixel consists of two LED’s (red and amber). The pixel pitch is maintained as 25 mm. Nine such LED modules form a single VMS Matrix module capable of displaying 48 x 48 pixels. Three such VMS matrix modules will be joined together to form the complete VMS display comprising of 48 rows and 144 columns. The module is designed to ensure visibility within a range of 300 meters.
3.1.4 Manual Input Unit
The Manual Input Unit (MIU) provides a direct user interface to the VMS display. This will normally be utilised by the maintenance engineers for testing and maintenance purposed. The MIU consists of a 16 character x 2 lines LCD display and a 4x4 matrix keyboard. The MIU can be used to manualy override the message to be displayed on the VMS, or for system RTC and data settings.
3.1.5 VMS Display Dimming
The VMS display is provided with an automatic dimming facility, depending on ambient light intensity or time of day as configured.
ISO 9001:2000, Quality Management System Cert. No. 2718
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