Infrared Spectroscopy and how the Datamaster Works - Challenging the machine and winning

In Michigan, police agencies now use the Datamaster DMT for breath testing, which has replaced the BAC Datamaster. The new Datamaster uses infrared spectroscopy, which captures a sample of breath from the client. This sample may contain alcohol, which absorb infrared energy.

A known sample of infrared light is sent through the chamber, and if any ethanol is present, it absorbs that infrared light. The remaining light is measured by a detector; this “loss” of energy is then measured and you get an alcohol reading. This measurement is only as accurate as the device and the procedure allows.

Before reaching this point, the machine goes through a number of steps including purging where the internal plumbing is cleansed of any residual substances from prior samples. If it is clear, there will be a .00 reading displayed. The machine will then do it’s ambient zeroing, which an interference filter is inserted in the infrared path to check for contaminants in the ambient air sample. These filters are used to separate ethanol from potential interference such as acetone.


The machine then does a blank test and a .000 will appear on the display if no contaminants are detected. The final step is the internal standard check where a quartz filter is dropped into the infrared light source path. The filter absorbs infrared energy which is a known amount, determined during the calibration of the machine.

The infrared detector receives a reduced amount of infrared energy that was transmitted by the infrared source. The reduced intensity is evaluated by the microprocessor in the Datamaster, and a predetermined result is achieved. This step evaluates the machine’s electronic system, signal analysis, and proceeding system to determine that everything is working properly.

While all of these precautions sound impressive, they mean nothing if the machine doesn’t alert the operator that some of these components that do the internal checks are not working properly.

Datamaster operators will testify under oath that there is a hole in the assumption that things are working properly, because they are not trained on anything other than pressing buttons, and rely on the machine itself to tell them that is working properly. This is like going to the doctor for a medical opinion, then coming back two minutes later for a second opinion, there is no true checks and balance system, because the machine checks itself.