Varec 8315 Series manual Application

8300 8315 L&J Tankway Software Description

4.17.2Application

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 8315 Tank Gauge Interface Module. The Model 8315 is automatically detected at startup, and an LJSCAN point is automatically created to manage the scanning task. The Module parameter determines which Model 8315 will be used. The ID must match the unit address of the MCG 1000.

Scanning begins when the Module is assigned. The DevType must match the configuration of the transmitter. Conversion from English to Metric can be performed be setting the LevelConvert and the TempConvert parameters in the LJSCAN point associated with the LJ1000 point.

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.

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.

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