Dosimeter having constant flow pump

Claim 1

An improved dosimeter that has an intake port connected to a filter means in which particles or vapors present in an air stream being pumped through the dosimeter are collected on the filter means, a variable drive pump is connected to the filter means and draws the air stream through the filter means and pumps the air stream through the dosimeter, an electric motor is coupled to the variable drive pump and operates the pump, an electric power source is coupled to the electric motor, an air reservoir connected to the pump retains any excess air supplied by the pump to maintain a constant flow rate of the air stream, an orifice positioned in a tube attached to the air reservoir whereby a pressure drop is created when the air stream is pumped through the orifice, a differential pressure switch positioned before the orifice that is activated by a change in air pressure of the air stream and creates a low voltage electrical input signal; an integrator circuit electrically connected to the power source and to the pressure switch uses the low voltage input signal of the pressure switch and integrates this signal, an amplifier circuit electrically connected to the power source and the integrator circuit which amplifies the signal from 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 constant flow rate; the improvement in use therewith comprises: an accumulator positioned before and connected to the variable drive pump which retains air and maintains an even flow of air to the inlet of the pump and a pulsation air pressure filter assembly positioned between the orifice and the pressure switch which reduces pulsations in the air stream in contact with the pressure switch thereby limiting the activity of the pressure switch to substantial changes in air pressure of the air stream.