From what I heard, Pro-M went out of business a while ago. Some of the employees from Pro-M bought Pro-M's equipment at auction and started up PMAS. So essentially, PMAS is the heart of the old Pro-M.
According to one tidbit I just read, one of the engineers at the old Pro-M decided to make his own sensors under the old Pro-M name, don't know if that's real or not.