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\rIII.
THERMOCOT]PLES
,
A.
Troubleshooting
Control Circuit
a) an open
thermocouple
will inhibit
the conirol
from operating
b) a shorted
thermocouple
will
cause
the control
to
run
away
since it defaults
to
room tempemture
c) a reversed
wired
thermocouple
will
cause
the
confiol to read
backwards
and runaway
Shorting the thermocouple
is
a
good
way
to
see if
the control
quickly
responds
by coming
on
during
troubleshooting.
Since
shorting
the thermocouple
is the
same as
bridging
the circuit,
it will
default
to room
temperature
and
naturally
call for
heat
if the
potentiometer
is
set at a higher
temperature.
When
perform-
ing this very
brief
TEST,
be
sure to
remove
ttrre
short from the circuit
before
placing
the
griddle
back into
service.
The
followingchartlists
the
Type
Kthermocouple
millivoltreadingfrom200"F(93"C)
to
500"F(26trC).
Griddle
Temperature
Junction
Temp
200eF
(93rC)
300eF
(149sC)
400eF
204ec)
500eF
(260ec)
90eF(32rC)
2.s2
4.80
7.02
9.27
85eF(29e
2.U
4.91
7.13
o?a
SorF(zFC)
2.75
5.02
725
9.49
7seF(24eC)
2.86
5.14 7.36
9.60
70eF(24eC)
2.98
5.25
7.47
9.72
65e(18eC)
3.09
5.36 t.c6
9.83
60eF(16eC)
3.2A
5.47 7.69
9.94
Example:
The
thermocouple
millivolt
reading
at
300'F( 149"C) with
a
junction
temperature
of 85.F(29.C)
should
be 4.91
mV.
At room
temperature
a
good
thermocouple
will
read
between 5-8
ohms.
Cold resistance
reading:
6.5
OHMS
average.
t2