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New EPD Format and Implementation (continued)

CMS Pulse Height Analysis (PHA) Data

The CMS rate channels are used to group measured events into categories, such as "low energy protons." This categorization approach is necessary because there is insufficient telemetry, even in the Version 2 software mode, to send down detailed data on each event. While the rate channel data is sufficient for most of our science, detailed data from a few of the measured events must be sent down to help us check the rate channel data and look more closely at selected aspects of the measurements.  The PHA data provides this window into the individual particle measurements.

Sectored PHA Event Collection Scheme:

In the Version 3 software, four events will normally be collected in each motor position, one per spin sector. In the calibration position (motor position=0), however, PHA data will be read only in one sector (A). Based on normal EPD motor scanning between motor positions 0 and 6, the PHA collection sequence will be as follows:

0A, 1A, 1B, 1C, 1D, 2A, 2B, 2C, 2D, 3A, 3B, 3C, 3D, 4A, 4B, 4C, 4D, 5A, 5B, 5C, 5D, 6A, 6B, 6C, 6D, 5A, 5B, 5C, 5D, 4A, 4B, 4C, 4D, 3A, 3B, 3C, 3D, 2A, 2B, 2C, 2D, 1A, 1B, 1C ,1D, 0A, 1A, 1B, 1C, 1D...

The PHA events will be stored in a buffer within the EPD memory.  There will be either 12 or 24 events transmitted in a science record (depending on which telemetry mode the EPD is in). The buffer size (12 or 24) will be determined based upon a variable loaded from the CDS during telemetry mode changes. The PHA events will be loaded into this buffer by the EPD software on a rotating basis.

We wish to maximuze the number of events that are sent down via the PHA, even when event rates are very low. Empty slots will be filled with events from other spatial sectors and tagged with a rate channel ID of "F." 

TABLE 29. Rate Channel Assignments for EPD LEMMS Sensor; Channel Map 1

TABLE 30. Rate Channel Assignments for EPD CMS Sensor; Channel Map 1

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Updated 7/27/04, T. Hunt-Ward
tizby@ftecs.com