Audit Neutral Density Filter Sales and Service

Environmental Monitor Service, Inc. manufactures quality, precision neutral density filters for use in all of the most popular Opacity Monitors. Used for EPA audits and service, our filters are NIST traceable, fully certified and manufactured with high quality optical substrate material.  Each filter has a unique serial number and comes with its own scanned trace which is dated and signed. The filters are labeled with the value in both Optical Density and Opacity.

Along with manufacturing our own neutral density filters, EMS can recertify any competitor’s model. Our filter certification service sets the standard in the industry for speed and cost, contact us today for details.

The values for filters which EMS sells are found in the table below.

Nominal Density (O.D.) % Opacity
0.02 5
0.04 8.8
0.1 20.57
0.2 36.9
0.3 49.88
0.4 60.19
0.5 68.38
0.6 74.88
0.7 80.05
0.8 84.15
0.9 87.41
1.0 up 90 up Special Order