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Linear adjustment function for the sum of the signal

This step ends with the result for ARAW for the formula described before. This step is performed by the firmware, not the software.

In the first step, we selected integration windows for the background (the left region on the pictures above) and for the signal (the right region). What the firmware does is to integrate over the points in one window, integrate over the points in the other window and subtract them. Essentially, this corresponds to subtracting the background from the signal. I will call these two integrations as BKGND and SIGNAL. In this first and simple approach, we are just doing:

[1] ARAW = SIGNAL - BKGND

The system provides a better level of flexibility where you can define separate weights for each integration. Suppose that the Physicist selected a small region for the background and a big region for the signal. We would need to give more weight for the background in order to compensate for the smallest number of samples to integrate. So, we add the weight factors A0 and A1 to the formula:

[2] ARAW = SIGNAL*A1 - BKGND *A0

The last level of flexibility is an offset. This is for adjusting the non-normalized sum for, as an example, avoiding negative values for the sum. The final formula for the sum is:

[3] ARAW = SIGNAL*A1 - BKGND *A0 + OFFSET

This is the screen that can be used to set the parameters:

Image Added

The weight parameters A0 and A1, and Offset are the first 3 boxes on the snapshot.

The last section of this document showed how the integration windows are adjusted. An EPICS database takes care of changing A0 and A1 automatically when the windows' width is changed. So, this guarantees that if the background and signal are approximately horizontal lines, no change in the window's width will change the final result of ARAW. A deep detail about this database is described in Auto adjustment of weight factors A0 and A1 below.

Coefficients of the equation

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The last feature provided by the weightFunctionXAxis.db is to generate an array for the X-axis of the chart, containing the translation to nanosecond for each tick count. This is held by the aSub record BLEN:$(AREA):$(POS):$(INST)_WF_TIME, using the function calcTimeArray() available in the file asubWeightXAxis.c. The input for the record is the PV AmcClkFreq already described before.

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AUTO_A0_A1 AUTO_A0_A1

Auto adjustment of weight factors A0 and A1