ESAB PCM-875, Instruction Manual

Page: 21 / 48

SECTION 4 MAINTENANCE
20
4.4 FLOW SWITCH (FIGURE 4-2)
When excessive contamination is found in the air, the
flow switch (FS-4) should be disassembled and cleaned
as follows:
A. Ensure the system is shut down and there is no
trapped air under pressure in the piping.
B. Remove the piston plug.
C. Remove the spring. Use care when handling spring
to prevent distortion.
D. Remove the piston.
E. Clean all parts with cleaning agent.
NOTE
Ensure cleaning agent does not contain solvents
which can degrade polysulfone. Warm water and
detergent is recommended for cleaning. Allow all
parts to dry thoroughly before reassembly.
Reassemble the flow switch in reverse order.
PISTON PLUG
PISTON
SPRING
FLOW SWITCH
Figure 4-2. Disassembly / Assembly of Flow Switch
• Use grounded work station with grounded floors and
grounded wrist straps when handling devices.
• Use a 100 Ω resistor in series with the gate when
performing curve tracer tests.
• Never install devices into systems with power con-
nected to the system.
• Use soldering irons with grounded tips when solder-
ing to gate terminals.
When mounting IGBT modules on a heatsink, certain
precautions should be taken to prevent any damage
against a sudden torque. If a sudden torque (“one-sided
tightening”) is applied at only one mounting terminal the
ceramic insulation plate or silicon chip inside the module
may get damaged.
The mounting screws are to be fastened in the order
shown in Figure 4-3. Also, care must be taken to achieve
maximum contact (i.e. minimum contact thermal resis-
tance) for the best heat dissipation.
Application of a thermal pad on the contact surface
improves it thermal conductivity. See Replacement Parts
section for the required pad.
A torque wrench should be used. Tighten mounting
screws to 28 in-lbs; wire connecting screws to 19 in-lbs.
If torque is too heavy, the device can damage like the
above “one-sided tightening”.
4.5 IGBT Handling & Replacement
Since IGBT gates are insulated from any other conduct-
ing region, care should be taken to prevent static build
up, which could possibly damage gate oxides. All IGBT
modules are shipped from the factory with conductive
foam contacting the gate and emmiter sense pins.
Always ground parts touching gate pins during installa-
tion. In general, standard ESD precautlions application
to FETs should be followed.
Other handling precautions that should also be ob-
served are as follows:
Figure 4-3. Screw Fastening Order
Two-Point Mounting Type
Temporary tightening  
è
‚
Final tightening  ‚
è

Four-Point Mounting Type
Temporary tightening  
è
‚
è
ƒ
è
„
Final tightening  „
è
ƒ
è
‚
è



‚
‚
ƒ
„