Printed Circuit Board Functions | Lincoln Electric SVM127-A

E-5

THEORY OF OPERATION

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PRINTED CIRCUIT BOARD

FUNCTIONS

POWER BOARD

The input power (115VAC) is applied to the power board, and from that the power board develops the DC field voltage for the wire drive motor. The SCR circuit- ry, used to control the motor armature voltage, is also contained on the power board.

The relay used to activate motor armature voltage, field voltage, auxiliary output on terminals 32A-7, and power source output (#2 and #4) is housed on the power board.

The rectified and regulated power supplies, used for the LN-9 control circuitry, are incorporated in the power board.

The shut down, start response and trigger interlock cir- cuitry, in addition to the rectified and regulated power supplies used for the LN-9 control circuitry, is included in the power board design.

CONTROL BOARD

The control board provides a reference voltage to the wire speed control and voltage control potentiometers, allowing SET signals to be produced.

The control board also powers and processes the feed- back signals from the tachometer board. It compares the actual speed information to the SET speed com- mand signal and develops firing pulses that drive the motor armature SCR circuitry, located on the power board.

Initial acceleration rates for wire feed speed are con- trolled by the control board as well as the SET speed and actual speed signals for the digital meter circuitry.

VOLTAGE BOARD

The voltage board compares the SET voltage values to the actual voltage values and makes any necessary correction by sending the appropriate signal to the Lincoln CV power source. If for any reason the arc voltage cannot be controlled to the SET voltage, the voltage board interrupts the LN-9 trigger path, and the unit shuts down. The response (Fast or Slow) to changes in arc voltage is also controlled by the voltage board, as well as the SET and actual arc voltage sig- nals for the digital meter circuitry.

TRIGGER BOARD

The trigger transformer supplies 24VAC to the trigger board where it is rectified and regulated to 20VDC. This DC voltage is used in the gun trigger circuit to ini- tiate the welding operation.

TACHOMETER BOARD

A square wave frequency signal, proportional to motor speed, is generated by the tachometer board and sent to the control board.

METER BOARD

The meter board contains signal scaling and power supply circuitry for the digital meter.