Theory Of Operation - Electrical; Push/Pull Switch - Nfpa Installations; Figure 3-2 Photo Interrupter And Flag - Will Burt Night Scan Chief Installation, Operation & Maintenance Manual

3.2 THEORY OF OPERATION – ELECTRICAL
The Chief control is based on a distributed intelligence control structure. Each main section of the Chief
has a circuit board with an embedded micro controller. These sections are: the Base, the RCP, and the
Remote Control(s). These boards "talk" to each other over a multi-drop RS-485 serial communications
link.
Another key component of the control is an initialization circuit. In an NFPA compliant installation, a
completely stowed Night Scan Chief draws zero current and cannot be extended or operated until the
initiate circuit is engaged. Included in this initialization circuit is an input for a safety interlock. This can be
used for an emergency stop, or other interlock function such as a "Park/Neutral" switch from the vehicle
transmission. Relay contacts inserted in the violet wire coming from pin J4-6 of the base circuit board
function to inhibit operation of the Chief (See schematics in section 4.4)
Additionally, a bi-stable (latching) contact closure is provided that indicates that the mast is properly
stowed. It will close when the mast is properly stowed. If the mast is not stowed, the contact will be open.
Even if the emergency stop feature is used prior to the mast completely stowing, the contact will still
remain open. If the Night Scan has been stopped using the emergency stop button or by some other
interruption of power, the initiate circuit will need to be activated again in order to continue operation.
When stowing the mast to horizontal position, the control monitors the current of the actuator. When the
mast lowers, trips the Mast Nested limit switch, and comes up against the mechanical resistance of the
saddle; it senses it, considers itself stowed, and shuts itself down. This ensures a certain amount of pre-
load on the RCP saddle.
If at any time during the operation of the mast an unexpected control situation occurs, the mast will stop
any movement and a fault message will be displayed on the Remote Control(s) display. Clearing the fault
is accomplished by pushing the Push/Pull switch or momentarily interrupting power in some other way.
Then the control may be re-initiated and operated again.
3.3 PUSH/PULL SWITCH – NFPA INSTALLATIONS
All operation of a completely stowed mast must be preceded by proper initialization. The initiate switch must
be momentarily closed to power-up the Night Scan. When the Will-Burt Accessory Kit is used, the Push/Pull
switch is located on the junction box. It is used to perform two functions. First, it can be used to "initiate" the
Revision 1
PHOTO
INTERUPTER
Figure 3-2 Photo Interrupter and Flag
Night Scan Chief
FLAG
3-3