TEOM® monitors where introduce about fifteen years ago to provide engineers with real-time information about the particulate mass concentrations of diluted diesel exhaust. The instrument has gone though a number of changes over the years to reflect the current state of technology and the changing state of particulate regulations. This paper discusses the changes that have taken place in the instrument and performs a series of tests to determine the impact of: filter temperature, filter face velocity, filter pressure drop, and filter conditioning. The testing identified the item with the greatest impact is temperature. Lastly a method for setting up TEOM® monitor to optimize the filter loading and data quality is set out.