Enter A Deadband Limit For Data Collection; Save Changes; Limit Example - Merck Millipore Mobius Chrom 20 System User Manual

240

6. Enter a Deadband Limit for Data Collection

Using a deadband limit is a convenient and powerful way to compress data. During times
when process values change by insignificant amounts, the deadband limit can improve system
performance and decrease the amount of disk space used by historical data files. The deadband
limit accomplishes this by controlling how much the current value can deviate from the last
recorded value before Historical Collect records the value in the historical data file. See the next
section Limit Example for an example of data collected using a deadband limit.
Note If the limit value is 0, the system saves every sample. Tag names with a limit
value of 0 use the maximum amount of disk space available.

7. Save Changes

When completed with defining a collection group in the Group Configuration dialog box, select
the Save Changes button to save the group. The dialog box closes and the user is returned to
the Historical Assign window.

Limit Example

The following diagram illustrates how setting the Limit field reduces the amount of data
collected by Historical Collect. In this example the Limit field is set to 2.5. Of the 16 data
points shown, Historical Collect records only three. Data points within the shaded areas are not
recorded because they fall within the 2.5 deadband limit.
The first recorded value shown is 50. The next value that Historical Collect records must be
greater than or equal to 52.5 or less than or equal to 47.5.
The second value recorded is 54. The deadband limit now applies to the current value of 54.
Therefore, the third value that Historical Collect records must be greater than or equal to 56.5
or less than or equal to 51.5.
The third value recorded is 51. The deadband limit now applies to the current recorded value of
51.
User Guide