Nordson 303 779B, Customer Product Manual

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Profile Verification with Thermocouples
C 5-1
E
1998 Nordson Corporation
All rights reserved
303 779B
Issued 11/98
Manual 12-44
Section C 5
Profile Verification with Thermocouples
Periodically, it may be necessary to observe the temperature of the circuit
board surface as it moves through the Select Cure IR oven. This can be
done by mounting thermocouples on the board surface. Accurate
temperature readings can be made with thermocouples if they are used
properly. However, every variable must be considered, and control
checks must be made to ensure every aspect.
Use a small gage wire to reduce the thermal mass of the thermocouple
junction. Also, the stiffness of thicker wires tends to push or pull on the
board while it is moving through the process cavity. Use a 30 gage or
smaller wire for testing the oven’s profiles.
A commonly used and inexpensive type of thermocouple is the J type
thermocouple. The positive element of the J type thermocouple is
commercially pure iron, while the negative element is a copper- nickel
alloy known as constant. This type of wire is suitable for use between 0
°
and 750
°
C (32–1382
_
F). However, it is more subject to oxidizing at a
high temperature.
The usable temperature range on a thermocouple also depends on the
type of insulation on the wire. Several types of insulation are available
for thermocouple wires. Some have good heat resistance properties,
others have good flexibility, and some are highly abrasion resistant. An
ideal insulation will have all of these properties, but unfortunately, there is
no such material. A Teflon insulation has fairly good abrasion resistance
and is also quite flexible. Since it can withstand temperatures up to
260
°
C (500
_
F).
Use Teflon insulation for profile tests.
1. Introduction
2. Thermocouple Wire