Chart Rollover
To prevent the loss of data, the chart output will "rollover" if a
measurement would cause the chart output to exceed the limits (± 3 V).
This feature is especially useful with strip chart recorders.
Rollover can be used to increase the resolution of the chart since smaller
values of span can be specified. As smaller values of span are used, chart
rollover will occur more frequently.
Rollover occurs when a chart limit is exceeded. The chart output voltage
rolls over to the opposite limit. The result, on a strip chart, is a step from
one limit to the opposite limit, effectively shifting the chart range and
center values. By counting the steps and noting their direction, the
actual measurement values can be deduced.
Example:
The chart output voltage is set to ± 3 V to correspond to an input
temperature range of 5° C to 45° C with the 0 V output at 25° C,
span = 6.66 and chart null = 25.
If the actual measured temperatures ranged from 20° C to 100° C, a strip
chart recorder might look like the one shown. The actual measurements
recorded could be reconstructed by cutting and pasting the chart between
the rollovers.
chart range chart range chart range chart range
5° C to 45° C 45° C to 85° C 85° C to 125° C 45° C to 85° C
chart center chart center chart center chart center
25° C 65° C 105° C 65° C
Chapter 3 Features and Functions
Chart Output (Analog Output)
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