I'd like to clarify and confirm the relationship between scan intervals for sensor factory sensors and the underlying sensors on which they are based? I provide some examples below but the broader questions are:

- Is whether the sensor factory sensors intelligently sample the underlying sensors or do they act independently and "sample the samples" from the underlying sensors? - If they are just sampling the samples, will this not effect the accuracy of the sensor factory graphs (because they are sampling differently than the underlying sensors)?

For example, if I have a device traffic sensor at a 10 second interval and I include that in a sensor factory sensor, what happens when:

1. The sensor factory interval is also 10 seconds? Does the sensor factory sensor sample the EXACT SAME data points as the underlying sensor (because they share the same interval), or does it take it's own sample which may be at slightly different time points (a sample of a sample)?

2. The sensor factory interval is 60 seconds (higher)? Is the sensor factory sensor just going to sample the current data point each 60 seconds and ignore all others in-between? That could produce a very inaccurate graph.

3. The sensor factory interval is 2 seconds (lower)? Will this just result in five points at the same level (e.g., 5 x 2 second samples by the sensor factory, when the underlying data point only changes every 10 seconds)?

Thanks!

Article Comments

This depends if the sensor is a absolut sensor (e.g. Diskspace) or a difference sensor (e.g. Traffic).

1. Absolut Sensors Every time the factory sensor is scanned the last value of the underlying sensors is used. If the time between the last value and "now" is bigger than the scan interval no value is returned. This happens if the scaninterval of the factory is faster than the underlying sensor. If the scaninterval of the factory is longer than the underlying sensor only a sample of the sample is displayed.

2. Difference Sensors These are more complicated since they record a volume over time. To calculate the factory value all samples of the underlying sensor coverying the interval of the factory are added. The part intervals at the beginning and end of the factory interval are calculated as percentage of the time covered.

A factory interval less than the underlying sensors is not recommended here.


May, 2012 - Permalink