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for the probe readings. Both use a common subroutine, “Get M.A.”, which
calls “Get ND”. Control and handshaking between the converter and the com-
puter is performed by this latter subroutine. Data is fetched in 2 bytes, first
the low order 8 bits, then the high order 4 bits, the sign and over range bits.
“Get M.A.” uses the converter reading to either cram or update, as directed
by a counter within the computer.
The program then enters “Compensate”. The factor derived from “Gaincheck”
is added to or subtracted from the latest reading.
“Range” then examines the compensated answers to see if we are on the cor-
rect scale. The unit always comes in the low range and remains there unless
there is an over range indication which causes the range to be changed to
high. If a negative reading exceeds that which would be lower than -300
degrees, the routine branches to give an over range display indication, If the
unit is in the high range, and over range is indicated (above 1500°F), the over
range condition is displayed (-OL-). If the reading is lower than about 370
degrees, the unit downranges. Any of these conditions cause the program to
return to get a new probe reading with instructions that the moving average
be crammed with new data. Additionally, if over range is displayed indicating
on open probe lead or removed probe, conditions are set for the next entry
into “Gaincheck” to cause the compensation reading to be crammed; and also
that rapid updates to it are to be made on following passes. This is done to
accommodate changes in probes by the user, so that the display will repre-
sent the actual probe readings as soon as possible.
If no change to the current range is indicated, a fall-through occurs to “Get
Temp”. This routine essentially looks up the Fahrenheit temperature from
tables. There are separate tables for each range.
The “Display” routine updates the display on every other trip through to limit
possible rapid changes when the probe moving average is being updated in
the fast mode. The answer to be displayed is converted to decimal, and then
transmitted to the display driver in the order of most significant digit first.
Leading zeros are suppressed up to the unit’s digit. The decimal point is sup-
pressed if the routine is called for the purpose of displaying “over range” or
“Help”.
The program is now complete and a jump to “Gaincheck” completes the loop.
Figure 9.1. Flow Chart
Power On
Initialize
Evaluate Compensation
Circuits
Get Probe Reading
Compensate As Required
Range Check
Lookup Temperature
Display Temperature
°F/°C
Monitor/Peak
Main Program Platinum Heat Prober 392M
Changed
