15
Page 15
Mini-AT User Guide
How the Mini-AT Works
The Mini-AT is a dedicated microcomputer that uses precision sensors to measure gas pressure and
temperature and corrects metered volume. The electronic circuits are powered by the battery pack
located in the case door. The battery voltage is regulated to the various voltages required by the
remaining circuits. While in the Corrector Mode, most of the electronic circuitry is in an
‘unpowered’ (asleep) state. When the magnet disc rotates and actuates the input switches, the
electronics are energized and begins its correction cycle. The input switches not only 'wake-up' the
electronics, but are also the input for uncorrected volume. The volume that each input closure
represents is defined by Item Code 098 multiplied by the scaling value at Item Code 114.
Once the instrument 'wakes-up', the computer program in firmware instructs the CPU (microproces-
sor) to obtain analog measurements. At least five analog signals, PCor gas pressure, gas tempera-
ture, main battery voltage, memory battery voltage and case temperature, are multiplexed through
the A/D converter and sent to the microprocessor for processing.
The microprocessor converts the digitized analog signals to an equivalent numeric value and stores
this information in memory. PCor Gas Pressure is stored at Item Code 008, Gas Temperature is
stored at Item Code 026, Main Battery Voltage is stored at Item Code 048, Backup Battery Voltage
is stored at Item Code 051 and Case Temperature is stored at Item Code 031. After all measure-
ments are obtained, the microprocessor compares the measured values to the parameter limits
already in memory, i.e., PCor pressure low limit, temperature high limit, battery low limit, etc. If
any of the measured parameters are out of range, the microprocessor jumps to an alarm subroutine.
Except for battery Shutdown Voltage limit exceeded, the alarm subroutine activates the appropriate
alarm item code, turns on the alarm indicator and transmits an alarm pulse out the alarm channel.
After the alarm sequence is complete, the microprocessor returns to its normal functions.
At the time of a full 'wake-up', if the battery Shutdown Voltage low-limit (item code 50) is ex-
ceeded, the microprocessor activates the alarm indicator (all seven LCD decimal points are turned-
on), transmits an alarm pulse on the alarm channel, spells out the word "HELP" on the LCD. Under
these conditions, the "HELP" message is displayed for as long as there is enough battery voltage to
maintain the display. The Mini-AT is no longer correcting the gas volume, however, the mechani-
cal index is still functional. To restore normal instrument operation, remove the dead battery and
replace it with a fresh one.
After the alarm subroutine is complete, or if no alarm conditions are present, the microprocessor
computes new correction factors based on the new measurements and parameters already in
memory. Parameters in memory are items such as; Base Pressure, Base Temperature, Specific
Gravity, etc. The new correction factors are then applied to the uncorrected volume input to obtain
the corrected volume. The amount of corrected volume just calculated is then added to the totalized
corrected volume stored at Item Code 000. The uncorrected volume just received is also added to
the totalized uncorrected volume stored at Item Code 002.
To Next Page
Loading...
Need help?
General
