Merging Scanner & Datalogger results

[Jason Haines]

> > A short time ago, BobR posted some spreadsheets showing graphs of AFR &
> > other info, and it came out of the discussion that this was IIRC a
> > combination of Diacom results and his WB he was logging. Here's my
> > general question: how are logs from a scanner like Diacom, and a
> > datalogger recording other things (like measured AFR) not traced by the
> > scanner, combined/merged into one spreadsheet like BobR did.
> >
> > I'm not much of an Excel expert, so it might be obvious, but not to me.
> > Appreciate any good tips.

Combining multiple data streams is a common data acquisition problem. The
biggest problem will probably be getting a common variable for the different
data streams.

In Excel it is easy to graph the variables versus each other as long as you
have a common axis - even if the intervals are not the same. The "scatter
plot" style of graph actually uses the numerical value of the x-axis (unlike
the other graph modes that assume the axis are evenly spaced). As long as
you have a common axis (same variable) between the two, you can plot many
variables against each other. RPM is the easiest variable to use as the
x-axis but don't expect the data to be exactly in synch as different system
record the rpm differently, may round the rpm data up or down and may record
variables at different intervals (one after the other instead of multiple
data recordings at the same time). Getting time accurate enough and
synchronized between multiple systems is too much of a pain with most of the
data acquisition tools.

Another nice program for graphing multiple data streams against a common
axis (with different values for that axis) is Microcal's Origin. We are
using version 6.0 and it does a very nice job of plotting multiple curves.
It also has some very useful curve fit and function generation tools. It
also allows you to perform a lot of mathematical functions on graphs
(average multiple graphs to form a single graph, subtract or add graphs from
each other, etc.).

If you have to have the data at the exact same intervals (for example, every
100 rpm), you can do a curve fit to each variable (again versus some common
variable like rpm) and then recalculate the data at the required intervals.
This introduces a lot of chances for errors but it can work well in many
situations. If you have enough data points at high enough resolution you
could use an averaging algorithm to create values at set intervals but you
rarely have enough data points and resolution with data acquisition systems
like Diacom, Autotap etc...

Hope this helps,


Jason


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