What is the best way to connect the EL-USB-4 data logger to a Mettler Toledo M400 Transmitter to record data

While we are not familiar with that specific device I did take a quick look at it and it appears to have 4 programable analog outputs that can output either a 0-20mA or 4-20mA signal. For use with the EL-USB-4 you would want to output a 4-20mA signal. You would simply connect the leads from the logger to the output channel you wish to monitor on your device. For additional details on connecting the logger please see the user manual which is available on the “manuals and resources” tab on the product page of our website.