Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 216 of 265
29.8 Signal Dimming
29.8.1 Solar Cell
Signal dimming is provided to dim the signals during darkness hours under control
of a photoelectric solar cell mounted on a signal head.
29.8.2 Solar Cell – ST900 and ST900LED (230V Operation)
Section 2.5 details the specification of the solar cell input of the controller.
There are three values of dimming voltage available for the standard ST900:
120V 140V 160V
(preferred value)
The size of the dimming transformer required by a controller depends on the
average signal lamp power and the dimming voltage required. See section 2.11.3.
The ST900LED has only one dimming tap of 154V and is 500VA (0.5KVA)
Note that dimming is not available on 110V/120V mains supplies.
29.8.3 Solar Cell – ST900ELV
The ST900 ELV Controller must only be used with the STC ELV Solar Cell (part
number 506/4/97891/005) in order to maintain the integrity of the Extra Low Voltage
system on the street.
There is only one dimming voltage available: 27.5V
The size of the lamp supply transformer required by a controller depends on the
average signal lamp power. See section 3.14.5.
29.8.4 Dimming by Time of Day
The dimming facility may be operated by time of day rather than a light operated
switch (Solar Cell). To allow this facility to be implemented, the Solar Cell input of
the controller must be wired to the solar cell supply to switch the controller to ‘DIM’
permanently. This state is then ‘overridden’ by special conditioning to switch the
controller to the Bright State.
A special conditioning flag can be set from the MTCS timetable to indicate when to
switch to bright, allowing the time of dim state change to be altered by changing the
timetable using the handset.