Tachometer Input; Current Relay - ESAB MEK 4 Service Manual

BRAKING
When the motor starts, capacitor C60 charges up to 15 V, with zener diode D20
limiting the voltage across it. Braking is activated by the optocoupler IC3. When
the transistor in IC3 is turned on by the LED, 15 V from capacitor C60 is connected
to the gate of transistor Q4. Transistor Q4 turns on and short circuits the motor
through the resistors R85 and R86. The resistors limit the braking current to about
20 A.
11

Tachometer input

The tachometer G01 is fitted inside the motor casing. At a wire feed speed of 25
m/min, it produces a signal frequency of 660 Hz.
Comparator IC5;2 converts the sine wave signal from the tachogenerator to a square
wave at the same frequency.
Pins XP01;R and XP01;S are used if there is a separate display unit for showing wire
feed speed. The digital displays in the MEK 4 and the LAW power units cannot
show the wire feed speed. Connections D01 - - D02 are used only if there is an
external instrument for displaying the wire feed speed.
Wires 401, 402 and connector XS12 are not fitted from serial number 514 615 . . . .
and above.
12

Current relay

The current relay operates if the welding current exceeds 20 A. If the creep start
function has been selected, this is disengaged when the current relay operates. If the
crater filling function has been selected, it will work only when the current relay has
operated.
cmek0de1
XS12
XS12
cmek0e19
- - 19 - -
cmek0e18