I may be wrong, but I think what you are wanting to test is the integrity of your grounging electrodes. If you are, you probably want to go to the AVO (Biddle) web site. They offer several earth resistivity test sets. These will allow you to determine the effectivness of your grounding...
I don't know how much HP you need but, you may be able to use a stepper motor and drive to do this application. The programming is usually straight forward. The pricing will be less than a servo, you can control speed accuratly, position is no problem. Good luck.
Allen Bradley and Toledo Scale have a package in the Jaguar series that provides a straight interface from the scale to the PLC. They also have some "canned" applications for culling and marking product.
