Speed and fluid flow controller
First Claim
1. A gas monitoring apparatus, comprising:
- a sensor testing gas samples for contaminants;
a pump communicating with the sensor, the pump providing the gas samples to the sensor;
a motor driving the pump;
a motor driver providing drive signals to the motor to control operation of the motor; and
a sampling unit sampling motor back electromagnetic force (EMF) during intervals between the drive signals, the motor driver adjusting the drive signals based on the back EMF sampled, wherein the motor driver comprises a controller that, during sampling of the back EMF, at least one of delays the onset of at least one drive pulse of the drive signals, increases an interval between two adjacent drive pulses, reduces a width of at least one of the drive pulses, and eliminates at least one of the drive signals.
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Accused Products
Abstract
A system and method for measuring fluid flow rate in a system where fluid is pumped, such as a gas monitoring instrument where gas is pumped from a space such as a room or enclosure through a conduit to a sensor. The flow of gas through a pump is determined by measuring motor back-e.m.f. which is proportional to motor speed. In a system where motor speed is regulated by pulse width modulation of the motor drive voltage, the back-e.m.f. is sampled during intervals between the drive pulses applied to the motor, and in a further aspect the sampling is done at selected, spaced-apart or infrequent intervals such as once for every ten or once for every hundred motor drive pulses. Advantageously, in an instrument that uses a microprocessor and analog-to-digital converter to measure gas-concentration, the same microprocessor and converter can provide the PWM control of the pump, in response to the back-e.m.f. generated by the pump motor between the drive pulses. The microprocessor compares the output of the analog-to-digital converter, corresponding to the back-e.m.f., which in turn corresponds to the pump motor speed, to a set-point value, representative of the desired pump motor speed. The processor then adjusts the PWM to control the pump motor to achieve and maintain the desired speed. As a result, in a gas monitor, the gas-flow rate may be maintained close to a desired gas flow rate regardless of the voltage supplied by the battery or other voltage source, regardless of the degree to which the gas is filtered, and under a wide range of operating conditions.
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Citations
36 Claims
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1. A gas monitoring apparatus, comprising:
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a sensor testing gas samples for contaminants; a pump communicating with the sensor, the pump providing the gas samples to the sensor; a motor driving the pump; a motor driver providing drive signals to the motor to control operation of the motor; and a sampling unit sampling motor back electromagnetic force (EMF) during intervals between the drive signals, the motor driver adjusting the drive signals based on the back EMF sampled, wherein the motor driver comprises a controller that, during sampling of the back EMF, at least one of delays the onset of at least one drive pulse of the drive signals, increases an interval between two adjacent drive pulses, reduces a width of at least one of the drive pulses, and eliminates at least one of the drive signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 13, 14, 15, 16, 17, 18)
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10. A gas monitoring apparatus, comprising:
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a sensor testing gas samples for contaminants; a pump communicating with the sensor, the pump providing the gas samples to the sensor; a motor driving the pump; a motor driver providing drive signals to the motor to control operation of the motor; and a sampling unit sampling motor back electromagnetic force (EMF) during intervals between the drive signals, the motor driver adjusting the drive signals based on the back EMF sampled, wherein the motor driver generates drive signals separated by different first and second intervals, the second interval being longer than the first interval, the sampling unit sampling the back EMF during the second interval.
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19. A method for controlling a gas monitoring apparatus having a sensor, a pump for providing gas samples to the sensor, and a motor for driving the pump, the method comprising:
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driving the pump with the motor to provide gas samples to the sensor at a predetermined flow rate; testing the gas samples at the sensor for contaminants; generating drive signals to power the motor; sampling back electromagnetic force (EMF) of the motor during intervals between the drive signals; adjusting the flow rate of gas samples to the sensor by changing the drive signals based on the back EMF sampled from the motor; and determining a low flow condition, based on the back EMF sampled, when a target motor speed is not maintained and displaying information indicating the low flow condition. - View Dependent Claims (20, 21, 22, 23, 24, 25, 27)
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26. A method for controlling a gas monitoring apparatus having a sensor, a pump for providing gas samples to the sensor, and a motor for driving the pump, the method comprising:
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driving the pump with the motor to provide gas samples to the sensor at a predetermined flow rate; testing the gas samples at the sensor for contaminants; generating drive signals to power the motor; sampling back electromagnetic force (EMF) of the motor during intervals between the drive signals; and adjusting the flow rate of gas samples to the sensor by changing the drive signals based on the back EMF sampled from the motor, wherein the drive signals are separated by different first and second intervals, the second interval being longer than the first interval, the sampling of the back EMF samples occurring during the second interval.
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28. A handheld portable gas monitoring instrument, comprising:
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a housing sized and shaped to be handheld and portable; a battery for powering the instrument; a sensor for testing gas samples for contaminants; a pump, provided in the housing and communicating with the sensor, the pump providing the gas samples to the sensor; a motor, provided in the housing, for driving the pump; a motor driver for providing drive signals to the motor to control operation of the motor; a sampling unit for sampling motor back electromagnetic force (EMF) during intervals between the drive signals, the motor driver adjusting the drive signals based on the back EMF sampled; and a microprocessor determining a low flow condition when a target motor speed is not maintained. - View Dependent Claims (29, 30, 31, 32, 33, 34, 35, 36)
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Specification