Heat-Prober
®
Platinum-RTD Thermometers User Manual
26
The next routine entered, “Get Probe”, performs as described above for the compensation
readings; however a separate moving average is maintained for the probe readings. Both use a
common subroutine, “Get M.A.”, which calls “Get ND”. Control and handshaking between the
converter and the computer 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 correct 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 represent 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 fir
st. Leading zeros are suppressed up to the unit’s digit. The decimal point is
suppressed 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.
