Installation guide

11
Terminal 1 is a switched-negative output. Whenever the panel piezo-sounder is beeping, a quad
Darlington-transistor integrated circuit (ULN 2004) switches to negative any load (remote
buzzer, lamp, relay, etc.) connected to these terminals. To prevent the failure of this transistor
switch, a 27-ohm, 2-watt current-limiting resistor is connected in series with this terminal.
Should a short circuit occur in the load connected to terminal 1, all of the supply voltage is
developed across this resistor, protecting the transistor switch. As a result, the useful amount of
current available to operate the buzzer, lamp, relay, etc., is limited to approximately 100 ma.
Terminal 2 is a convenient, fused, 12-volt DC source that can be used to provide positive power
for the buzzer, lamp, relay, etc.
Terminals 3, 4, 5, and 6 are not used.
Terminals 7 through 15 are standard Form C contact relays with a 2-amp, 24-volt DC resistive
load rating.
Terminals 16 and 17 can be used, only if necessary, to connect a normally open back tamper
switch to detect removal of the panel from the wall. This input, when operated, affects the
keyboard! Do not extend wiring leads from the panel!
Terminal 18 is not used.
Terminals 19, 21, 22, and 24 are switched-positive outputs. Similar to the action of terminal 1
above, a type 54563 Darlington-transistor integrated circuit will switch +12 VDC, therefore
sourcing power to a load. As above, in series with each of these terminal screws there are 27-
ohm 2-watt resistors to limit the current to approximately 100 ma. If the load requires more
current, the output voltage will drop below 10 volts. Note that in the older MKII printed circuit
board, a “pull-up” resistor is connect from 5-VDC to each output terminal screw. In the ‘off-
state’ of the 54563 switch, the output voltage will ‘float’ at 5 VDC. If the load has low resistance
(e.g., an incandescent lamp or a relay coil) the load will ‘pull down’ this floating voltage close to
0 volts. If the load has a moderate to high resistance, (e.g., a dialler module input or a LED),
then, in the off state of a switch, the outputs will again ‘float’ around 5 VDC. This can cause the
dialler to false trip or the LED to glow. To reduce the floating voltage, install a 360-ohm “pull-
down” resistor between the appropriate output terminals and a convenient negative terminal.
These “pull-up” resistors are not used on the MK3 and MK4 PBS and therefore the “pull-down”
resistors are not necessary.
Terminal 25 is the LMTC (LEM-line) ground (-ve) and must not be used as a ground (-ve)
return for any other applications. An excessive voltage drop (millivolts) could result, thereby
causing the LEM data to be incorrectly decoded.
Terminal 26 is the LMTC (LEM-line) clock line providing a continuous train of nominally 9-volt
NOTES CONCERNING THE TERMINAL CONNECTIONS cont.
square waves for use by the LEMs.