Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 12 Page 41 of 265
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The Siemens ST900 ELV Controller is a mains-powered ELV Traffic Controller
which drives and monitors 48V LED signals and meets the requirements of
Protective Extra-Low Voltage (PELV). The system is optimised for safety, reduced
cabling costs, reduced operating and maintenance costs and extreme reliability in
operation.
The ST900 ELV Controller is designed so that there are no on-street voltages that
exceed the nominal ELV limit of 50V. This offers increased electrical safety for
engineers working on and around the intersection and improved lamp monitoring of
very low power LED traffic and pedestrian signals. Another major benefit is
simplified cabling in the controller. The standard option offers a 20A maximum lamp
load; a high current 40A version is available.
A range of equipment compatible with the ST900 ELV Controller has also been
produced; such as Helios ELV signals (traffic and far-side pedestrian signals), ELV
LED Regulatory Signs and an ELV Solar Cell. The near-side pedestrian signals
(including Wait and Demand Accepted Indicators) have been modified to function
with the ST900 ELV Controller and are clearly marked “ELV”.
The 48V supply allows semiconductor switches to be used, reducing unnecessary
heat in the controller, improving reliability and reducing power consumption.
There is an active short circuit protection system on all lamp outputs, ensuring that
the outputs are protected from damage even under direct short circuit conditions.
3.1 System Overview
The Siemens ST900 ELV Controller can be supplied in a single-door outer case with
a 6U logic accommodating the CPU and power supplies, with space for up to 16 x 4
channel detector cards, or 12 x 4 channel detector cards and a semi-integral OMU,
UTMC OTU or MOVA unit.
ELV Lamp Switch cards (LSLS) are located within the cabinet. Very large
intersections may have additional Lamp Switch, I/O and Intelligent Detector
Backplane cards located in an adjacent cabinet for ease of installation and
maintenance.
The ST900 ELV Controller is also available as a free-standing logic rack housing
the power supply, CPU and Lamp Switch cards.
The essential differences between the ST800 Controller and the new ST900 ELV
Controller are:
 The Mains-powered 8-phase / 24-output Lamp Switch cards have been
replaced with 32-output ELV lamp switch cards (LSLS cards) that drive the
48V LED aspects. The LSLS cards are mounted on the sides of the cabinet