Barnstead International Thermolyne 859 Series, Service Manual

Page: 98 / 118

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Thermocouples
The NCAT utilizes two type K thermocouples. One
thermocouple is routed into the back of the chamber.
The other is routed into the top plenum (filter).
A type K thermocouple generates a millivolt signal. As
the temperature rises in the chamber and filter section,
the millivolt signal generated by the thermocouple
increases. The generated millivolt signal is utilized by
the main microprocessor to detect chamber and filter
temperature changes.
A type K thermocouple is manufactured with nickel-
chromium and nickel-aluminum wires and has definite
polarity (positive and negatively charged wires). The
negative wire has a RED insulator sleeve. The posi-
tive wire has a YELLOW insulator sleeve and a (+)
sticker. It is also marked with a black indicator mark on
the terminal end of the actual wire itself. Barnstead
International recommends replacing the chamber and
filter thermocouples every 12 months.
A) Chamber Thermocouple
Equipment needed:
- Digital ohm meter or continuity tester
- Phillips screw driver
1) Disconnect the NCAT from the power source.
2) The chamber must be at ambient tempera-
ture to properly test the thermocouple. Allow
unit to cool to ambient if necessary.
3) Remove the back panel from the NCAT.
a) 14 screws around the outer edges hold
the back panel in place (4 on each side, top
& bottom).
4) Disconnect the chamber thermocouple from
the terminal block located near the
middle/bottom of the back of the chamber.
a) The thermocouple has a yellow and red
wire that run lengthwise up the back of the
chamber wall, entering into the chamber
approximately half way up the back wall.
E
QUIPMENT
T
EST
P
ROCEDURE
A
B
C
D
E
F
G
H
I
Key Description
A Element terminal blocks
B Element terminal blocks
C Element terminal blocks
D Element terminal blocks
E Element terminal blocks
F Element terminal blocks
G Element terminal blocks
H Filter thermocoupler
I Chamber thermocoupler
1087 or 1275 series back view