Yes we have done it successfully before. You can check our web http://is.gd/iDdebv for references.

If it is a new installation is quite simple. For an existing installation it is trickier and obviously it depends on the design of the mill base plates to work out where you are going to position the load cells. The output could be placed on a large display screen for the operator(s) to see as to activate them on adding more balls (as the pebbles would normally be part of the feed into the mill)

The adding of load cells assist with optimal grinding but the amp meter on the mill motor is generally used as an indication of ball loading.

Yes, you add load cells to existing SAG Mills; it depends on the type of mill bearing support system. They are normally button type compressive cells. With Polysius mills they are integral in the Feed end bearing pedestals and provide a load signal out via an amplifier and integrator. Check out http://is.gd/GioSt3 .

The output is normally tied into the weight-o-meter feeding the mill, or directly to the VSD that controls the feed conveyor. In this way, there is minimal lag between load cell reading and feed rate change - allows for stable mill operation and "real-time" control. In new plants, the load cell signal is shown on the mimic display as “tons in mill" or similar.

Your details are 100% correct and as it would be implemented in a modern day milling operation. Obviously this load cell control arrangement would apply to all types of milling operations.

Some of the old timer experienced operators would simply "listen" to the milling sounds to know when to add balls. Unfortunately those guys are getting less and any new installation should have the latest technology installed to control the grind and optimize the production rate.

Using Audio to "listen" to mill load is still in use, however more in dry grinding mills. I have installed several of these systems in wet mills; however this was used to check mill speed rather than load, to listen to where the charge is impacting on the "toe". It is difficult in my opinion to use audio to monitor charge load. I also agree that the Amp-meter on the motor(s) is still the preferred way to determine when to add balls and increase / decrease feed rates.

Load Cells in my experience give a better and more rapid indication than bearing back-pressure 'interpolated' systems. I have tried to install them on all new milling installations; however, explaining the merits to a cash-strapped Client is difficult to overcome! The control of a SAG circuit can be more useful with load cells, but you also could benefit from knowledge of charge movement as well to get a better understanding of charge motion, load (ball and rock) and power. It does depend upon the mill base plates, in order to retrofit.