Understanding Historical Trends

Historical trends show a contiguous segment of data from the past. Unlike real-time trends, historical trends are updated only by a script or an operator action.

A historical trend shows a graphical representation of data from a maximum of eight tags. You assign the data that appears in a historical trend by assigning a tag to a trend pen.

The figure below shows the three types of InTouch historical trends.

• The Average/Bar historical trend shows the average value of a data point during the time intervals in bar form.
• The Min/Max historical trend shows the changes in the percentage of engineering units scale as a vertical line over the time span. The emphasis is on time flow and rate-of-change, rather than amount of change.
• The Average/Scatter historical trend shows the average value of the data points over each trend time interval.

You can create graphical sliders called scooters to access the details of trend data based on the scooter's current position within a trend. For example, when the operator positions the scooter over an area on the trend that has visible data, the time and values at that location for all database values being trended are shown.

You can also create buttons or sliders to zoom in and out between the scooters or to data, such as the maximum to minimum value. Average and standard deviation can be shown for the complete chart or for the area between the scooters.

Historical trends can also be scrolled by any amount of time. You can create custom scales and link them to the .MinEU and .MaxEU dotfields to create a trend that shows the full range of data set by its engineering unit.