WTC MedWeld 3005, Operator'S Manual

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The MedWeld 3005 can switch multiple contactors with one weld
timer, a firing board and a system of relays. The Cascade Firing
Board
(CFB) implements this capability.
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The CFB controls a system of three relays. They switch the gate
lead connections between each firing board and three SCR pairs.
This "pass-through" configuration of relays prevents the
possibility of firing more than one SCR at a time (which can cause
catastrophic failure).
This is controlled by using Functions #10 and #11:
10 TURN ON CONTACTOR SELECT #nn (nn = 1-15)
11 TURN OFF CONTACTOR SELECT #nn (nn = 1-15)
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You must select a contactor BEFORE the weld function, and allow time
for relay switching before any weld current statement.
One CFB switches three SCR pairs. Two CFBs can switch six SCR
pairs, etc., depending on the firing configuration required.
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The Cascade Firing Board is the same size as a 645 firing board,
and uses the same mounting centers. The interface consists of
• Four connectors on the board to receive inputs to the SCR
gate leads,
• Three output signal connectors to the SCR gate leads and
• Three red LEDs. Each LED flashes to indicate activation (if
any) of its respective SCR.
The CFB gets its power and control inputs from the A-B output
module installed (according to the integration scheme used). The
signals may be either 24 VDC, 24 VAC or 120 VAC.
The CFB connects between one firing board and three or more
SCR pairs. The board has three relays which are controlled by the
PLC I/O.
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When the SCR signal is gated in a single-pack configuration,
power is passed to the weld transformer through connector H1.
When a given SCR is gated in a tri-pack configuration, power is
passed to the weld transformer through its respective H1, H2 or
H3 connector. (Refer to the drawings supplied with your control
for more information.)