----------------------------------------------------------------- Using the OBDScan Data Log function

OBDScan Data Acquisition Basics
The OBDScan Data Logger samples data at discrete points in time called sample points.  The time between the sample points can be set from as fast as the vehicle will respond to many seconds between samples.  Not all vehicles are created equal when it comes to data rate across the OBD-II interface, cars such as the RX-8 with a high performance CAN bus can run at over 50 samples/second and cars with the slower ISO-9141 can be as slow as 5 samples/second.  Why is the sample rate important? Because it's possible to miss too much data when sampling fast changing parameters.  This becomes especially important when more than one parameter is being sampled.  If you set the data log to 6 parameters on a slow ISO-9141 vehicle, it might take about 1 second for all 6 to get updated.  If you are trying to monitor an O2 sensor which switches 2-4 times per second, you won't be able to reliably see the proper operation.  It is for this reason that our Graphic Display window only displays one parameter at a time, you get the maximum resolution on the O2 sensor real time display which is important for troubleshooting O2 sensor problems.
The data logger has a maximum of 18,000 data points per channel which equates to 30minutes of data log at 100ms (0.1sec) sample time.  When the 18,000 sample limit is reached the software will stop logging data and ask you to save the data in a file.  You can chose to save the data or cancel out and not save it. You can also stop the log at any time with the STOP button,  you can then RESUME the data log, or QUIT the data log and save the file to disk.

Triggering
The OBDScan Data Logger has two possible triggers which can be AND'ed or OR'ed together.  Each trigger can be System Time Minutes, Speed and RPM. 

To use the OBDScan Data Logger you first start the OBDScan application, select either a COM port or USB connection and wait for the vehicle to respond.  The OBDScan application will automatically scan all the MODE1 sensors and OBD-II Monitors.  When the initial scan completes you can go to the Multiview menu item under the 'Data Monnitor and Log' menu.  Use the drop down boxes to select the parameters you want to view and/or log.  Select the number of samples, 2 to 6, and the Sample Time.  Remember, if the sample time setting is too low, meaning the Sample Rate is faster that the vehicle can support, the data logger will sample as fast as the vehicle will respond.  If you want to start on a trigger, then set the trigger now. Then click 'Start Log' to start the data logger.  If a trigger condition has been selected the data logger will wait for the trigger condition to become true before actual data logging starts.  You will see a "Waiting For Trigger" displayed on the window unitl the trigger condition is met.  Let the data log run for as long as desired then click "Quit".  You will be asked for a file name in a standard Windows dialog box.  Enter a file name and select the destination for the file then click "OPEN" in the dialog box.

Using the Logged Data

Now you have this data log file so what do you do with it?  The data logger stores data in the following format:

Ignition Advance -------
Air Flow ---------------
Absolute Load ---------
O2S1 Sensor -----------
"Start Time:2:33:37 PM"
-5,6.3,25,.9734685,.12
-5,6.37,25,.973011,.31
-5,6.34,25,.972706,.45
-5,6.34,25,.9719435,.621
-5,6.41,25,.9719435,.751
-5,6.37,25,.971181,.881
-5,6.34,25,.971181,1.011
-5,6.34,25,.9696865,1.141

This means the first column is Ignition Advance, second column is Air Flow, third column is Absolute Load and the fourth column is O2S1 Sensor ( in this case it's a Wide Band O2 sensor). Notice there is a fifth column, that is the system precision time recorded when the last parameter for that row was received from the vehicle.  By using the precision time you will always be able to construct a time line for the received data.  If the data was received within the Sample Time which was specified at the time the recording was made then you could ignore the fifth column.  The data is comma delimited, which just means there is a comma between each value in a row.  That makes it easy for Excel or the Star Office spreadsheet program to import the file.  Once the file has been imported then you have all of the power of Excel or other spreadsheet program to analyze or create plots of the data.  Shown below is a plot from data imported into Excel for a RX-8 running a quarter mile.  We were primarily interested in AFR ( Air/Fuel Ratio) at the higher RPM's with WOT (wide open throttle).  As you can see, the AFR drops considerably at the higher RPM's.