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13.4.1.2 Compression Deviation (PI Only)
The OSI Soft PI Data Archive uses a “swinging door” algorithm to compress time-series data. The
algorithm stores only what is needed to provide an accurate data history. The sensitivity of the
algorithm is controlled by the Compression Deviation setting. Compression Deviation should be set at
twice the Exception Deviation value.
When the machine is in a transient condition, the SETPOINT PI Adapter can temporarily bypass PI
Compression. This allows higher resolution data to be stored and improves diagrams (Bode, Polar,
etc.) used for startup and shutdown analysis (see 13.4.1).
To learn more about Exception Deviation and Compression Deviation see the many tutorials
available on the OSI Soft YouTube channel.
13.4.1.3 High Trigger, Low Trigger (0,0) – Special Case
When Low Trigger and High Trigger are both set to zero the SETPOINT PI/XC Adapter uses an
algorithm to detect when the machine is in transient mode. The algorithm is continuously executed
(every second or faster) and performs as follows:
• Calculate max speed, min speed, and delta speed (over the last 30 seconds)
• Evaluate using current speed, and look-up table
For systems using the PI/XC Adapter 7.x or later the algorithm is shown in Table 13-10. For systems
using CMS 6.x or earlier the algorithm is shown in Table 13-11.
7,500 to 60,000 RPM
Above (max speed * 0.002) RPM
(Typically, 15 to 120 RPM)
Above 60,000
Above (max speed * 0.004) RPM
(Typically, above 240 RPM)
Table 13-10) Algorithm (CMS 7.x and later)
1,000 to 60,000 RPM
Above (max speed * 0.002) RPM
(Typically, 2 to 120 RPM)
Above 60,000
Above (max speed * 0.004) RPM
(Typically, above 240 RPM)
Table 13-11) Algorithm (CMS 6.x and earlier)
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