I launched my multi-channel temp/external logger and I received a voltage graph (not temperature) from the external channel.

When launching multi-channel data loggers you need to enable or disable the channels that you want to use. Additionally, you must select the appropriate sensor within the software. The external channel is set to voltage. If you launched your H8 data logger without choosing the correct external sensor, the following is an unreleased application that has been made available on the internet in its current, untested form at the request of customers who wish to convert the external measurement in their datafile.

There is no help file available with this program, but it does come with an installation program. This program only works with the H8 family of data loggers and will only convert the external channel readings from volt to temp, or visa versa. To use this program, after the install, simply drop the .dtf file that needs to be converted onto the program. Find the download here.
The file name is: H8 File Converter