Alco Sensor IV PAS Device

The Alco Sensor IV is a hand held Preliminary Alcohol Screening (PAS) device designed to analyze a person's blood alcohol concentration (BAC). The California Highway Patrol (CHP) utilizes the Black Dot (4797) software version of the Alco Sensor IV screening device. There are other software versions distinguished by the presence of a colored dot (approximately 3/16 of an inch in diameter) emblem on the face of the PAS device.

Other California law enforcement agencies utilize the Black Dot version, as well. The Black Dot version has memory retention, which means that all tests administered are stored and the printouts are available through the Discovery procedures governing criminal cases (Penal Code Section 1054, et seq.) and California Public Record Requests.

The Alco Sensor IV weighs approximately six (6) ounces and uses a nine volt alkaline battery which the California Highway Patrol DUI Enforcement Manual contends should last for approximately 600 tests. This PAS device can be used every 15 to 30 seconds if no alcohol is encountered. However, the CHP manual directs that the operator administering the preliminary should wait two minutes if a positive alcohol reading has registered on the Alco Sensor IV.

The Alco Sensor IV utilizes fuel cell technology to analyze the concentration of alcohol in a breath sample. When certain chemicals are introduced into the unit, the fuel cell (through the process of oxidation) will produce electrical energy. This energy is produced when a chemical exposed to the active surface of the fuel cell releases electrons.

When activated, the Alco Sensor IV draws one cubic centimeter (CC) of the DUI suspect's breath by way of an electrically operated piston sampling pump within the device from a manifold into the fuel cell for analysis. An amplifier powered by the nine volt batter provides an output curve of the fuel cell response which is then digitized and analyzed by a microprocessor. The result of the analysis is automatically displayed as a three digit reading which is recorded by the officer administering the PAS test.

The Alco Sensor IV uses a devise call a thermistor to determine when a minimum breath sample has been collected. The thermistor in the manifold monitors breath flow and causes sampling of deep lung air or alveolar breath at the end of exhalation. The deep lung air and any alcohol which is detected will be more in equilibrium with the blood than breath collected at the beginning of the exhalation cycle.

The automatic collection of a breath sample will not occur if an individual is unable or unwilling to exhale into the Alco Sensor IV with a certain minimum pressure. Individuals who suffer from asthma or drivers who have been in collisions often are not able to provide a sample with sufficient pressure for the device to automatically collect a breath sample. Some officer who conduct DUI investigations have a preference for manually trapping a driver's breath sample.

Manual Trapping of a Breath Sample

If a person is unable or unwilling to provide a sufficient breath sample, a manual sample may be obtained by the Alco Sensor IV. The operator must depress a button on the front of the PAS which is identified by the word "Manual." The strength of the sample may effect the reading. A sample collected at the beginning of the exhalation cycle may have a lower reading than a sample from the same subject collected at the same time later in the exhalation cycle.

Accuracy Checks and Calibration

The accuracy of each Alco Sensor IV PAS device is to be checked a minimum of every ten (10) calendar days or 150 tests, whichever occurs first. Each California Highway Patrol Field Office assigns one or two officers who are designated at the PAS Coordinator and backup PAS Coordinator whose duties include checking the accuracy, calibrating, and performing maintenance on the Alco Sensor IV PAS devices.

The California Highway Patrol PAS Coordinator will typically check the accuracy of each PAS device once a week on the same day. As a practical matter, 150 or more PAS tests are ordinarily not administered in any seven day period on any given PAS device.