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Alco-Sensor III Accuracy Check Procedure

An Accuracy Check should be performed periodically. The frequency should be determined by your Quality Assurance Program. Below are basic Accuracy Check instructions for the Intoximeters Alco-Sensor III breath testing instrument.

Tools Required: Before beginning have items available: instrument, calibration standard, new mouthpiece

Alco-Sensor III Accuracy Check Procedure Part 1
  • Dry Gas Standard & Regulator
  • True-Cal or True-Cal II Device
  • Alco-Sensor III
  • New Mouthpiece


Note: A calibration standard can be a:

  • Mini-Alco Can (for non-evidentiary testing applications only),
  • Dry Gas Cylinder and Regulator
  • Wet Bath Simulator and Solution


For this demonstration, a dry gas cylinder is used as the standard – value (at sea level) of.082%.

  • A True-Cal device was used to give the true value of the standard at the time of our demonstration
  • the True-Cal will display an adjusted, or expected, gas value for the current atmospheric pressure
  • Therefore, the target value for this demonstration is .081

True-Cal displays .081

Alco-Sensor III Accuracy Check Procedure Part 2
Accuracy Check – Alco-Sensor III

  1. Check temperature strip on back of Alco-Sensor III – any visible number verifies that the instrument is at proper operating temperature.

Temperature window display

  1. Depress read button, .000 should be seen for at least 5 to 10 seconds.

READ button depressed ASIII displays .000

  1. If .000 is not seen, depress SET button and recheck in one minute. (Follow Step 2 again. The unit must display .000 for 5 to 10 seconds before proceeding with the Accuracy Check).
  2. Depress set button on Alco-Sensor III.

SET Button Pressed

  1. Follow instructions on the dry gas standard to mount the regulator.
  2. If this is the first test from the dry gas standard today, purge regulator by depressing button/valve on regulator for approximately 3 to 4 seconds.
  3. Attach a mouthpiece to the Alco-Sensor III and then to the Standard’s output port.


Alco-Sensor III Accuracy Check Procedure Part 3
  1. You should know the expected value of the standard – this will be used to compare against the actual result determined by the instrument.
  2. The True-Cal II device displays .081, this is the expected value of the Standard used for this demonstration.



  • Submit a gas sample from the standard to the Alco-Sensor III for at least six (6) seconds. On the 4th or 5th second of the count, depress the read button and hold it down.

(NOTE: The vapor must continuously flow

through the mouthpiece until one second after the read button is depressed).

  1. Continue to hold the read button until the displayed result stablizes for 5 to 6 seconds.


Submit a gas sample
READ button is depressed

  1. Carefully detach the Alco-Sensor III from the standard and observe the displayed reading until it becomes stable for 5 seconds. The stable number is the final result.
  2. The difference between the final result and the expected value of the standard should be within the tolerance allowed in the Quality Assurance Plan set for your program.
  3. If the difference is greater than the specified tolerance, the unit requires a calibration adjustment.  (Follow instructions for CALIBRATION).
  4. The expected value of the standard used for this demonstration was .081, so our result of .080 is within an acceptable tolerance
Observe the final result


To demonstrate compliance with your program’s QAP it is best to keep a record or a Calibration Log for each device used for testing.  The log should contain the results of all accuracy checks and calibrations for each instrument.  This log may become a crucial piece of evidence should your test results be challenged.  The log may include information such as:

  • Date
  • Time
  • Procedure performed (Accuracy Check or Calibration)
  • Name of Technician performing procedure
  • Location
  • Identification of the Standard including Lot Number of the Standard
  • Expected Value of the Standard
  • Result of the Accuracy Check or Calibration

For more information about procedures for your Intoximeters instrument, please refer to your

  • Operator’s Manual
  • or email Intoximeters Tech Support
  • or phone the Technical Support Department at 314-429-4000

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