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Submitted by 2verb on Fri, 08/11/2006 - 13:43

Hi All,

I am trying to work through the math in the Theory of Operation section of the DMC-21x2/21x3 manual.

On page 187 the discrete model for the Digital Filter section is explained. There is also an equivalent continous model given. One of the parameters for the continuous model is given as
a = 1/T ln = (1/B)

I am guessing this is a typo. (Where is the argument for the ln if not?)

Does someone know what should go there?

Thanks!

Comments 6

2verb on 08/11/2006 - 13:47

BTW that is page 187 rev 1.0d of the manual. It's 192 in the latest from the website. (Same text though.)

Just look for the section in Chapter 10 on the Digital Filter in the system modeling section.

Galil_RobinR on 08/14/2006 - 16:26

2verb-
Yep, you win the prize. That's a typo. Delete the second '=' and it will all make sense...
I've updated our paper manuals so no-one else has to deal with the error. Thanks for bringing it to my attention.

2verb on 08/15/2006 - 08:54

Ok,

So a= ln(1/B)
-------
T

?

Or a= 1
---------
T*ln(1/B)

?

I am doubly confused because niether case seems to fit the example that follows on the next page.

Galil_RobinR on 08/15/2006 - 09:23

a=(1/T)*ln(1/B)
You can see the formula written again in the following pages. The very last page of Chapter 10 (right before the Appendix) has the formulas again, in the 'Equivalent Filter Form'
And, if you review the description for the PL command in the Command Reference, you'll see the formula achoed once again.

2verb on 08/15/2006 - 12:34

OK,

I see the equation and I understand the order of precedence. The problem I have now is that the example on page 188 that comes right after the various models does not make sense.

It says that PL=0.75. We know from the previous page that PL=B.

T=0.001 s.

So a=(1/T)*ln(1/B) is
a=(1/0.001)*ln(1/0.75)
a=287.7 roughly.

The example has 250.

Is there a unit conversion I'm missing?

Thanks for the patience.

Galil_RobinR on 08/16/2006 - 09:13

Your calculation is correct. Apparently, that section of the manual was written before calculators, as you're seeing a rather pronounced rounding error.