WTC MedWeld 3005, Operator'S Manual

Page: 36 / 206

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The SCIB consists of
• An analog integrator,
• A voltage-to-frequency (V/F) converter,
• A microprocessor and
• Switching circuitry.
The air-wound (Rowgowski) current-sensing coil induces a
signal which represents the first derivative of current. The
integrator integrates this signal to determine current. The result
then goes to a V/F converter. The microprocessor controls the
integrator and switching circuitry. In response to commands from
the weld timer, the microprocessor switches the source for the
C
CNT
and V
CNT
V/F pulses fed to the weld timer into several
different configurations.
At power-up, the SCIB routes the V/F converter pulses from the
firing board. The pulses represent primary current and voltage to
the C
CNT
and V
CNT
inputs of the weld timer. If the SCIB is
installed in a system which does not have the software installed
in the weld timer to control it, the SCIB does not interfere with
the operation of the system at all. It will act as if it is not there.
If commanded by the weld timer, the SCIB will disconnect the
C
CNT
input of the weld timer from the firing board and re-
connect it to the V/F converter on the SCIB board. In this
configuration, the weld timer will read the secondary current, not
the primary current.
Normally, the integrator is controlled by the microprocessor to
achieve the most accurate measurement of AC secondary current.
In response to a command from the weld timer, the
microprocessor will control the integrator in a different way to
achieve the most accurate measurement of DC secondary current.
In response to another command from the weld timer, the C
CNT
signal from the firing board will be re-routed to the V
CNT
input of
the weld timer. In this mode, the weld timer can read both
secondary and primary current simultaneously (but it cannot
read primary voltage).
A command from the weld timer activates a self-calibration
feature. In self-calibrate, the SCIB places a known accurate signal
into the integrator. The weld timer reads the output of the V/F
converter (representing secondary current). The actual readings
are compared with “standard” values to derive correction factors.