The ROC PlusDemo.sde file includes a Scanners group.
The Scanners group contains the ROC Plus Scanner objects that connect the Point objects to the Channel objects.
A ROC Plus Scanner’s configuration contains the unit and group addresses for the ROC with which it is to communicate. As such, at least one ROC Plus Scanner object is required per physical ROC device.
As a ROC Plus Scanner can only have one sampling interval and one offset, the example configuration includes multiple scanners, each with their own polling rate. They are set up as follows:
- Daily history points, which can be polled at a slow rate, are attached to the ScannerDaily scanner. This scanner also polls for new events and alarms and reads and sets the clock, since none of those tasks require a fast poll rate.
- Hourly history points are connected to the ScannerHourly scanner. In the example configuration, this scanner is configured to poll twice per hour. However, because the driver will back fill data, you could configure the scanner to poll as slowly as once or twice per day.
- Minute history points and current value points are connected to the ScannerMinute scanner. In the example configuration, this scanner is configured to poll once per minute. However, because the driver will back fill data, you could configure the scanner to poll as slowly as once or twice per hour.
- Configuration points are connected to the ScannerConfig scanner. In the example configuration, this scanner is configured to poll once per day. However, you could configure the scanner with a polling rate of 0, so that it would not poll automatically; instead you could poll the points manually, so that they are updated on demand only. This should be sufficient as there is no point in continuously reading the gas composition, or firmware version, when those values might not change for months at a time.
Using a single scanner on a ROC would be acceptable, providing that only one sampling interval and offset were required.