
VIU STEPUP
_________________________________________________________________________________________________________
4-4
SIG-00-07-11 SEPTEMBER 2012 (REVISED OCTOBER 2019)
Version No.: B.2
4.3
HOW SIGNALS AND SWITCHES ARE MAPPED TO VITAL INPUTS
The number of VIUs required to monitor the wayside signals and switches at a location is
dependent on the number of signal lamps, switches, and hazard detectors.
Figure 4-3 Example 1 Vital Input Wiring for Signal Lamp & Switch Monitoring
Each lamp in a signal head requires one input; each switch requires two inputs (one for normal,
one for reverse) and each hazard detector requires one input.
Point
Detection
Terminals
SWITCH
Green +
Green -
Yellow -
Red +
Red -
Red +
Red -
Head A
Head B
Signal 1
Red +
Red -
Green +
Green -
Yellow -
Red +
Red -
Red +
Red -
Head B
Head C
Signal 2
Head A
R
Reverse -
Normal -