RFL Electronics RFL 9300 - Theory of Operation; Table 15-1. Replaceable Parts, RFL 93 LC I;O Line Coupler I;O Module

RFL 9300 RFL Electronics Inc.
May 1, 1998 15 - 2 (973) 334-3100
15.3 THEORY OF OPERATION
Isolation transformers T1 and T2 are specified for a high isolation voltage, so they block any common-mode volt-
ages from reaching the inside of the RFL 9300. (Common-mode voltages are those where both inputs are high
relative to ground.) If the potential applied to the inputs is differential, the voltage may appear on the secondary of
the transformers and is limited by diodes CR1 through CR4. When a voltage with a fast rise-time is applied to the
transformer inputs, the inter-winding capacitance will allow the voltage to appear on the secondary; capacitors C1
through C4 form a "capacitive divider" network which attenuates this voltage on the secondary. Resistor R1 and a
resistor of equal value on the RFL 93B MO Modem Module combine to yield an impedance of 600 ohms. The resis-
tance is split between the RFL 93 LC I/O and RFL 93B MO modules to provide some termination impedance even
if the modem module is removed from the chassis.
In a field application, high voltages and currents could be induced or coupled onto the wires coming into the RFL
93 LC I/O. To reduce this possibility, the connection between the RFL 93 LC I/O and the telephone interface should
be made with twisted pairs which are shielded within the cable. The shield ground must be connected to ground at
the RFL 9300
and the telephone interface. A solid ground bus connection must be independently provided be-
tween the RFL 93 LC I/O card and the telephone interface, or the ground shield could melt from the high currents
that could be induced during a fault.
Table 15-1. Replaceable parts, RFL 93 LC I/O Line Coupler I/O Module
(Assembly No. 103835)
Circuit Symbol
(Figs. 15-3 & 15-4)
Description Part Number
C1-4
CR1-4
R1
T1,2
Capacitor,ceramic disc,0.005μF,20%,3kV,Centralab DD30-502 or equiv.
Transient suppressor,5-volt reverse standoff,5W,axial case,
General Semiconductor 1N5908 or equiv.
Resistor,metal film,604Ω,1%,1/4W, Type RN1/4
Transformer,audio coupling,600Ω impedance,Microtran TH5117 or equiv.
1007 1264
49091
0410 1267
99440