Varec TankGate Interface 8315 Series - Manual (Page 55)

8315 TGI
Varec, Inc. 45
5.1.2 Application
The LJ1000 point provides an interface to L&J MCG1000 Direct Digital Gauges. L&J Model 1000
Tank gauge transmitters are connected directly to a Model 8215 Tank Gauge Interface Module.
The Model 8215 is automatically detected at sta8130 RTUp, and an LJSCAN point is
automatically created to manage the scanning task. The Module parameter determines which
Model 8215 will be used. The ID must match the unit address of the MCG 1000.
Scanning
Scanning begins when the Module is assigned. The DevType must match the configuration of
the transmitter. Conversion from English to Metric can be performed by setting the LevelConvert
and the TempConvert parameters in the LJSCAN point associated with the LJ1000 point.
Filtering
Filtering is performed using the LevelFilter and TempFilter parameters of the associated LJSCAN
point. If a change in level greater than the LevelFilter is read from the gauge, the Level parameter
is not updated until it has stabilized. A reading is considered stable if it does not change more
than the LevelFilter value for the number of readings determined by the Filter parameter. Thus,
small changes (less than the LevelFilter) result in the Level being updated immediately. Large
changes must pass through the filter and will not be seen until the reading stabilizes. The same
strategy is applied to the Temp parameter value using the TempFilter parameter. Since the
LevelFilter and TempFilter are associated with the LJSCAN point, it applies to all LJ1000 and
LJ1500 points. The number of readings used in the filter algorithm can be set on an individual
basis. If no filtering is desired, set the Filter parameter to 0.
Time-outs
A separate time-out mechanism is employed to assure that the filter does not prevent a reading
from taking place. The LJSCAN parameter ScanTimeout is used to set an alarm bit in the
PntStatus parameter if a good reading does not take place in a specified period of time. If there
is no response from the gauge, or if there are constant parity errors, or if the level is constantly
changing by a value greater than the LevelFilter, then the 0x02 bit of the PntStatus will be set
after the ScanTimeout period elapses. The ScanTime parameter in the LJ1000 point is updated
each time a good reading takes place. If the ScanTime differs from the Elapse parameter by more
than the ScanTimeout, the 0x02 bit is set in the PntStatus.