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O
'
M
PERATOR
S
ANUAL
Exponential Decay Time Constant Excel Parameter (Excel Example 1)
This example calculates the time constant of an exponentially falling pulse, such as the light output of a phosph
or.
The first figure shows a typical pulse, including pseudo-random noise, generated by a VBScript.
(1 – t/TC1)
-t/TC2
The pulse was generated by a formula of the form e
* e
, where TC1 and TC2 are time constants, The
requirement is to measure the time constant TC2, using the portion of the trace where TC1 has negligible effect.
This was done using Function F1, which is not a p
art of the measurement process.
For the actual measurement, Parameter P1 was set up as an Excel call. In Excel, the s
elected portion of the trace
was converted to logarithms, and the Excel function SLOPE was used, as shown here.
Here we see the input data in column B (with a time scale in A) created using the contents of cell F9, Horizontal
Per Step. The logarithmic data are in column D, with the time scale repeated in C. The output appears in cell H3,
using the formula =1/SLOPE(D21:D51,C21:C51).
181
WRXi-OM-E Rev C
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