Powder coating system incorporating improved method and apparatus for monitoring flow rate of entrained particulate flow

A method of monitoring flow of particulate material flowing from a feed hopper through a hose to a dispenser, comprising the steps of:

• monitoring the flow rate in the hose using an in-line flow meter to provide a first flow indication;
• weighing the feed hopper at predetermined time intervals;
• comparing the change in weight of the feed hopper over at least one of predetermined intervals to obtain a second flow indication;
• and
• comparing the first flow indication to the second flow indication to obtain a correction factor and applying the correction factor to the first flow indication to obtain a corrected flow rate, the first flow indication being provided using a venturi tube flow meter which includes pressure sensors and valving mechanisms to selectively connect the pressure sensors to atmosphere to produce a zero reading from the pressure sensors for calibration.

A system for monitoring the flow rate of particulate material entrained within an air stream, which comprises:

• a feed hopper providing a source of the particulate material;
• a hose for conveying the particulate material within the air stream;
• a pump for drawing the particulate material from the feed hopper and transporting the particulate material with the air stream through the hose;
• a venturi tube flow meter associated with the hose for measuring the mass flow rate of the particulate material through the hose and providing a first flow indication, the venturi tube flow meter including pressure taps and filters located in each of the pressure taps, the venturi tube flow meter including pressure sensors and valving mechanisms to selectively connect the pressure sensors to atmosphere to produce a zero reading from the pressure sensors for calibration;
• a device associated with the feed hopper for measuring the change in weight of the feed hopper over a predetermined time interval and providing a second flow indication;
• and
• a flow indicating device having electrical inputs connected to receive the first and second flow indications from the flow monitor and the weight measuring device, respectively.

A powder coating system, which comprises:

• a spray gun for spraying the powder onto a workpiece;
• a feed hopper providing a source of powder;
• a hose for conveying the powder material within an air stream;
• a pump for drawing the particulate material from the feed hopper and transporting the particulate material with the air stream from a pump output through the hose;
• a flow meter associated with the hose for monitoring the flow rate of the powder through the hose and providing a first flow indication;
• a device associated with the feed hopper for measuring the change in weight of the feed hopper over a predetermined interval and providing a second flow indication;
• and
• a controller which is connected to the pump and which receives the first and second flow indications, the controller using the first and second flow indications to adjust the output of the pump.

A venturi tube flow meter assembly for monitoring flow rate of a fluid, comprising:

• a housing block forming a venturi construction with a throat portion;
• a plurality of pressure taps in the housing block;
• a plurality of pressure sensors connected to the pressure taps;
• a supply of gas for purging the pressure taps;
• and
• a valving mechanism for selectively connecting the pressure taps to the gas supply for purging the taps of accumulated matter and for selectively connecting the pressure sensors to atmosphere for calibration.

A venturi tube flow meter assembly for monitoring flow rate of a fluid, comprising:

• a housing block forming a venturi construction with a throat portion;
• a plurality of pressure taps in the housing block;
• a plurality of pressure sensors connected to the pressure taps;
• a first supply of gas for purging the pressure taps;
• a second supply of gas at a regulated pressure;
• and
• a valving mechanism for selectively connecting the pressure taps to the first gas supply for purging the taps of accumulated matter and for selectively connecting the pressure sensors to atmosphere for calibration, the valving mechanism selectively connecting the pressure sensor to the second supply for calibration of the pressure sensors.

A venturi tube flow meter assembly for monitoring flow rate of a fluid, comprising:

• a housing block having an inlet and an outlet, the block forming a venturi construction with a throat portion;
• an elongated, substantially straight inlet tube connected to the inlet of the block;
• a plurality of pressure taps in the housing block, two of the taps being located in the throat portion;
• and
• a plurality of pressure sensors connected to the pressure taps.

A venturi tube flow meter assembly for monitoring flow rate of a fluid, comprising:

• a housing block having an inlet and an outlet, the block forming a venturi construction with a throat portion;
• an elongated, substantially straight inlet tube connected to the inlet of the block;
• a plurality of pressure taps in the housing block, two of the taps being located in the throat portion;
• and
• a plurality of pressure sensors connected to the pressure taps;
• a first supply of gas for purging the pressure taps;
• a second supply of gas at a regulated pressure;
• and
• a valving mechanism for selectively connecting the pressure taps to the first gas supply for purging the taps of accumulated matter and for selectively connecting the pressure sensors to atmosphere for calibration, the valving mechanism selectively connecting the pressure sensor to the second supply for calibration of the pressure sensors.

A method of monitoring flow of particulate material flowing from a feed hopper through a hose to a dispenser, comprising the steps of:

• monitoring the flow rate in the hose using an in-line flow meter to provide a first flow indication;
• weighing the feed hopper at predetermined time intervals;
• comparing the change in weight of the feed hopper over at least one of predetermined intervals to obtain a second flow indication;
• comparing the first flow indication to the second flow indication to obtain a correction factor and applying the correction factor to the first flow indication to obtain a corrected flow rate.

A method of monitoring flow of particulate material flowing from a feed hopper through a hose to a dispenser, comprising the steps of:

• monitoring the flow rate in the hose using an in-line flow meter to provide a first flow indication;
• weighing the feed hopper at predetermined time intervals;
• comparing the change in weight of the feed hopper over at least one of predetermined intervals to obtain a second flow indication;
• comparing the first flow indication to the second flow indication to obtain a correction factor and applying the correction factor to the first flow indication to obtain a corrected flow rate;
• and
• correcting subsequent first flow indications from the flow monitor according to a correction factor obtained from comparing a past second flow indication with a comparable first flow indication.