A new, computer based, improved version of airborne dust concentration monitor is presented. Thanks to the application of electronic circuit reducing GM counter dead time, exchangeable radiation source collimators, rotary measuring unit and personal computer as a control and processing unit, considerable improvement of exploitation parameters was achieved.
The principle of operation of the gauge is based on the measurement of beta absorption by the dust mass deposited on air filter from an air volume which is proportional to the pumping time. For count rates up to 4000 c/s from GM counter the count loss is 6.0%. A set of exchangeable radiation source collimators with different diameters aperature permits to use the same 37 MBq Pm-147 source for a period not shorter than 10 years. The precision of the measurement of the deposited dust mass in typical operating conditions is 10-15 mg, which permits to obtain a relative precision of dust concentration measurement 1.0-1.5% when the collected dust mass is equal to 1 mg. The lower detection limit does not exceed 2 mg/m³. Thanks to the measurement of a reference sample at the start and the end of the measuring cycle, variations of ambient temperature and pressure are compensated. A personal computer employed as processing and display unit of the gauge makes the programming of measuring cycles easy and permits to display measuring results in a convenient form for the user.