curves for each type
of
sensor. There can be a calibrated curve for Sensor
A,
B and ten different switch positions generated by the
SW-10A.
The program
determines the type of sensor input and what curve to use for that sensor.
Once the curve is determined, the proper Voltage-Temperature Break Point
is determined. The program finds the correct break point for temperature
determination by checking each break point voltage to see if
it
is lower than
the input voltage.
As
the break point is found, the temperature is calculated
using the following equation:
TBP
T
=
(VBp
-
V
)
*
dT
+
AD
dV
where
:
T
is temperature in
K
VBP
is break point voltage
is input voltage
VAD
dT is slope between successive break points
dV
TBP
is break point temperature
After the correct temperature has been calculated, the program looks
to see if the instrument is in the scale expand mode. In this mode, the front
panel display converts to a resolution of
.01K
from
.1K
when below
100
K.
If there is no
LO
1
error condition
(in
the case of the platinum
sensor) the temperature is output in a bit-parallel, digit-serial form and is
latched into the display board.
Once the temperature has been output, the program
looks
to the set
point. The program determines if there is an option present and if there
will
be a set point input from that option. If
no
option is present, the
program reads the front panel thumbwheel switches. If an option is present,
the front panel switches are ignored and the set point is read from the remote
source.
The program then determines whether the
LO
2,
HI
1,
or HI
2
errors have
occurred. If
so,
the program continues and outputs the appropriate error to
the display and loops back to input another set point until the error is cor-
rected. The program then calculates the break point voltage in much the same
way
it
calculates the temperature. The program determines which is the con-
trol sensor and its appropriate curve.
It
then calculates the set point volt-
age using the following equation:
BP
Vsp
=
(Tsp
-
Tsp)
*
dV
+
V
dT
-42-
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