21.3 THEORY OF OPERATION
The RFL 93 Alarm I/O Alarm I/O Module provides connections for DTT input, 89B disconnect switch input, re-
close block output, and alarm relay outputs.
21.3.1 JUMPERS
The 104775-5 93 Alarm I/O replaces four previous versions of the module. The 93 Alarm I/O contains jumpers
that allow programming for the different station voltages that could be present at the DTT and 89B inputs. The
jumpers select resistors, which set input thresholds. If J1 and J3 are inserted with the other jumpers removed,
the module will operate with a 48V station battery. If J2 and J4 are inserted with the other jumpers removed, the
module will operate with a 125V station battery. If jumpers J1, J2, J3 and J4 are removed, the module will oper-
ate with a 250V station battery. The module inputs will not turn the module on at 50% of the station voltage, and
the module will be on at 80% of the station voltage. When the input voltage is greater than 80% of the station
battery U3 or U4 will turn on. This creates a low signal out of U1 on pin 5 or 7.
Additional jumpers are located at the input terminals, J5 and J6. Some end users want to wet the contacts of
circuits that activate the module inputs. These jumpers should not be inserted with station battery voltages in
excess of 125 Volts.
21.3.2 RECLOSE BLOCK OUTPUT
The reclose block output is closed when /reclose on P9 A2 goes low. This biases Q3 on which turns on the opti-
cal FET switch U2. Pins 6 and 4 are shorted to pin 5 of U2 when pin 2 is low. The optical isolated FET U2 then
in turn biases Q4 on and the reclose block output presents a low impedance. Q4 requires current from the ex-
ternal load to fully turn on. If the load is very small, the primary current path will be through R18, U2 and the
base to emitter junction of Q4. As the load increases and more current flows through the circuit, Q4 is biased
on. The maximum voltage between TB9 1 and 2 while the circuit is active should be 1.5 volts or less. The circuit
can work with up to 1 ampere of load current when turned on and can block an external voltage of 350 volts
when turned off. This allows one module to work with a 48, 125 or 250 Volt station battery. No jumper changes
are required.
21.3.3 ALARM RELAY OUTPUT
Two alarm relays are also present in the 93 Alarm I/O. If the local alarm or the com alarm connections at P9 A5
or A4 go low, Q5 or Q6 is biased on. This turns on Q1 or Q2 which actives the alarm relay.
RFL 9300 RFL Electronics Inc.
May 5, 2002 21 - 4 (973) 334-3100
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