Vernier Tech Info Library TIL #1234

Question

Can I Collect Percent Transmittance Data in Data Pro (on a Palm handheld)

Answer

We calculate Absorbance, A, from percent transmittance,%T, in Data Pro, using the formula, A = log(100/%T). Even though we measure %T (and sometimes calibrate in this unit), the program actually converts it to the more useful Absorbance, A, using the above expression. To answer your question, we do not actually keep track of %T values after doing this conversion.

However, if you want to obtain %T values, you can do so by creating a calculated column, after the data collection. To do so (I'll describe it after the fact):

1. What you want to do here is create a New Column for %T. To do this, we solve the equation above for %T. This gives you the equation:

%T = 100/10^A

2. You can create this column in two steps. First, tap on the Data button (or Data Table toolbar button). Then tap on New Column.

3. When the Calculated Column dialog comes up, you will want to create the first of two calculated columns, X^A. Do this by:
a. Give it a simple name like Z, with a label of Z (this isn't your final column, so the name and label don't really matter).
b. Choose an equation from the pull-down menu. Choose this one: 10^X
c. For the Column, choose CH1: ABSORBANCE
d. Tap OK
e. Now you have your column X^A created.

4. Now you need to create the final column, 100/10^A (which is now going to be 100/Z, Z being the previous column created in 3.)
a. Tap on Data again.
b. Tap on the Column Options button.
c. Give it a name (T), and a label (%).
d. Choose the equation X/A.
e. For the Column, choose the column you created (Z)
f. Tap OK
g. If you want to display %T on the graph, just tap on the Y axis label (ABS), and tap on %T. If you want to view the %T data, just tap on the data table toolbar button.
h. Once you have created the columns, you can actually collect additional data runs for %T.

Created by: dholmquist on October 24 2003
Last updated by: dholmquist on October 24 2003