20.3.2 CURRENT SENSE BOARD
The current sense board translates logic-level signals into relay drive signals. It also routes many signal lines
between the current sense board and the relay output board, and provides other interface functions. The com-
ponents on the current sense board have circuit reference numbers between 201 and 299. Interfacing to the
relay output board is through connectors P202 and P203.
20.3.2.1 TRIP ENABLE FUNCTION
During power-up sequences and system test modes, the RFL 9300's trip outputs must be disabled. The TRIP
RELAY ENABLE signal from the oscillography board in the display module controls this function. When this line
is high, the outputs of U203 tri-state. Tripping is further inhibited during power-up by the normally-open contacts
of relay K201 that opens the 15V supply of the high-speed relays. A low enable signal, and system power, must
be present to turn on K201. The normally-closed contacts of K201 generate a confirmation signal (TRIP
DISABLE LED). Current from the 15V supply is limited by R220 and is used to activate the LED in optocoupler
U207. U207's output phototransistor pulls the line low and lights the PROTECTION DISABLED indicator on the
display controller in the display module. When TRIP RELAY ENABLE is low, the same output of U203 is en-
abled to turn on PNP transistor Q201. This supplies base current to transistor Q202, which is normally reverse-
biased. Q202 turns on conducting current from the -15-volt supply to energize K201. The normally-open relay
contacts will close, and providing a +15V supply for the coil circuits of both the TRIP and DTT relays.
20.3.2.2 TRIP AND DTT FUNCTION
With the TRIP RELAY ENABLE signal low U203 is transparent to circuit operation other than for buffering and
edge shaping. When the AUX_TRIP line goes low the signal goes through U202 where it is inverted and then
routed into U204. U204 is a darlington transistor relay driver. Two identical circuits in U204 are paralleled for
increased reliability. The output from U204 provides a return path for the relay drive current supplied through
K201. Relays K203 through 206 on the current sense board are activated, as are relays K1 and K2 on the relay
output board. The DTT output is similar with only relays K7 and K8 on the relay output board being activated.
20.3.2.3 TRIP LATCH AND DTT LATCH FUNCTION
The current flowing through TRIP COIL1 and DTT COIL 1 goes through Optoisolators U206 and U205 respec-
tively. The output of these isolators goes high when current is flowing. These signals go into AND gates inside
U202. Assuming the latch disable signals are high, the output signals of these gates are fed back to the oscil-
lography board to latch the trip or DTT signal.
20.3.2.4 TRIP LATCH AND DTT LATCH DISABLE FUNCTION
In order to terminate a trip condition, the display controller issues a 10 ms active low TRIP LATCH DISABLE or
DTT LATCH DISABLE signal. These signals force the latch signals from U202 to go high. As long as there is no
trip command, the relay is released.
20.3.2.5 CURRENT SENSE FUNCTION
The relay output board has 4 current sense relays on it. The relay coils are in series with the output contacts.
When the contact is closed and current is in the range of 150 to 250 ma, the sense relay contacts will close.
One side of all four contacts is tied to +5V. The 5V current sense signals flow to the current sense board. The
signals are filtered to remove noise and the edges are squared using U201 Schmitt trigger inverter. These
sense signals are used by the display controller to light the indicators and maintain the trip relay output until the
contact current drops below the set point.
20.3.3 RELAY OUTPUT BOARD
The RELAY OUTPUT BOARD contains 4 trip relays and 4 current sense relays. Along with 4 more trip relays on
the CURRENT SENSE BOARD, they provide for 6 form A, CCS Trip contacts and 2 form A, DTT Trip contacts.
The outputs of the relays are protected with surge withstanding capacitors. The relay board also provides a
BNC connector for IRIG-B input. Surge withstanding components allow this input to survive 8 KV ESD dis-
charges.
RFL 9300 RFL Electronics Inc.
May 5, 2002 20 - 6 (973) 334-3100
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