We use a LN2 unit made by Vacuum Barrier Corp. (781-933-3570). We have a model called a Linerter. We bought it used for about 15K. It works great and is fairly easy use and maintain. Not sure on specific dosing rates as the controller just uses arbitrary numbers, but we set it as high as we can without the LN2 causing foaming issues before the crowner. It's pretty obvious when you have too much.