Dosimeter for monitoring working areas

Claim 1

An improved dosimeter that has an electric motor, a power source, an exhaust port and a filter means in which particles or vapors present in an air stream being pumped through the dosimeter at a controlled constant flow rate are collected on the filter means; the improvement in use therewith comprises a variable drive multicylinder pump, tubularly connected to the filter means and coupled to the electric motor, draws the air stream through the filter means; an orifice being positioned in a tube attached to the pump and to an exhaust port, wherein the air stream is pumped through the orifice and thereby creates an air pressure drop; a differential pulsation pressure filter position in a tube connected to the exhaust port and in parallel with the orifice and reduces pulsations in the air stream; a differential pressure switch positioned in a tube connected in parallel to the differential pulsation filter is activated by a change in the air pressure drop of the air stream and creates a low voltage electrical input signal; an integrator circuit electrically connected to a power source and to the pressure switch uses the low voltage input signal generated by the pressure switch and integrates this signal; an amplifier circuit electrically connected to the power source and connected in series to the integrator circuit and to the electric motor which amplifies the signal generated by the integrator circuit and feeds the amplified signal to the electric motor thereby controlling the speed of the motor driving the pump in relationship to the signal generated by the pressure switch to maintain the air stream at a controlled constant flow rate.