Digital fluid flow rate measurement or control system

Abstract

A plurality of individually actuatable, value weighted digital bistable valve elements in parallel interconnect a fluid source to a fluid receiver. A linear relationship is preferably maintained between the resultant fluid flow rate from the source to the receiver and the product of a flow rate determinative fluid parameter times the sum of the weighted values of the digital valve elements in the open state. The fluid parameter is sensed, the states of the digital valve elements are controlled, and a flow rate representative signal is derived from the states of the valve elements and the fluid parameter. If the fluid is liquid, the parameter is the square root of the pressure difference across the valve elements, in the absence of cavitating venturis, and is the square root of the difference between the upstream pressure and the vapor pressure of the liquid in the presence of cavitating venturis. If the fluid is gas, the parameter is the source pressure divided by the square root of the source temperature. For measurement, the states of the digital valve elements are controlled to maintain the value of the fluid parameter constant. For control the states of the digital valve elements are controlled to establish a set point flow rate.

What is claimed is: 
     
       1. A digital fluid flow rate measurement or control system comprising: a source of fluid at a first pressure;   a fluid receiver at a second pressure lower than the first pressure;   a plurality of individually actuatable, value weighted digital bistable valve elements interconnecting the source to the receiver, each valve element assuming exclusively either an open state in which fluid flows from the source through the valve element to the receiver or a closed state in which no fluid flows from the source through the valve element to the receiver such that the resultant fluid flow rate from the source to the receiver is a function of the product of a flow rate determinative fluid parameter times the sum of the weighted values of the digital valve elements in the open state;   means for sensing the fluid parameter and generating a first signal representative of the value of the fluid parameter;   means responsive to the value of the fluid parameter and the states of the digital valve elements for generating a second signal representative of the value of the resultant fluid flow rate; and   means responsive to one of the signals for controlling the states of the digital valve elements so as to maintain constant the value represented by the one signal.   
     
     
       2. The system of claim 1, in which the fluid is incompressible, the fluid parameter is the square root of the difference between the first and second pressures, and the sensing means senses the square root of the difference between the first and second pressures. 
     
     
       3. The system of claim 1, in which the fluid is incompressible, each digital valve element has a passage from the source to the receiver which includes a converging-diverging nozzle designed to maintain the vapor phase of the fluid at its throat, the fluid parameter is the square root of the difference between the first pressure and the vapor pressure of the fluid, and the sensing means senses the first pressure. 
     
     
       4. The system of claim 1, in which the fluid is compressible, the fluid parameter is the absolute stagnation pressure divided by the square root of the absolute stagnation temperature, the sensing means senses the first pressure and the temperature of the fluid at the source, each digital valve element has a flow passage from the source to the receiver, a flow determining orifice formed in the flow passage, and a region in the flow passage through which the fluid flows at sonic velocity thereby isolating the flow passage upstream of the flow determining orifice from variations in the second pressure. 
     
     
       5. The system of claim 1, in which the fluid is compressible, the fluid parameter is the first pressure divided by the square root of the absolute stagnation temperature, and the sensing means senses the first pressure, the second pressure, and the temperature of the fluid at the source or receiver. 
     
     
       6. The system of claim 1, in which the controlling means comprises means for controlling the states of the valve elements to maintain the value of the fluid parameter constant. 
     
     
       7. The system of claim 6, in which the controlling means additionally comprises: a source of a third signal proportional to a desired fluid flow rate from the source to the receiver, and means responsive to the difference between the third and second signals for changing the states of the digital valve elements to reduce such difference.   
     
     
       8. The system of claim 6, additionally comprising an indicator responsive to the controlling means for displaying the states of the valve elements as a measurement of the fluid flow rate. 
     
     
       9. The system of claim 1, in which the controlling means comprises: a source of a third signal proportional to a desired fluid flow rate from the source to the receiver, and means responsive to the difference between the third and second signals for changing the states of the digital valve elements to reduce such difference.   
     
     
       10. The system of claim 9, in which the values of the respective digital valve elements are weighted according to a binary code, the third signal comprises a plurality of binary signals equal in number to the digital valve elements and weighted according to the binary code, and the second signal comprises a plurality of binary signals equal in number to the digital valve elements and weighted according to the binary code. 
     
     
       11. The system of claim 1, in which the fluid flow rate through at least some of the respective digital valve elements in the open state are weighted according to a geometric progression of two. 
     
     
       12. The system of claim 1, additionally comprising means for maintaining a linear function relationship between the resultant fluid flow rate and the product. 
     
     
       13. The system of claim 12, in which the valve elements are arranged so the fluid streams flowing through them are directed at each other. 
     
     
       14. The system of claim 1, in which the one signal is the first signal and the value of the fluid parameter is maintained constant by the controlling means. 
     
     
       15. The system of claim 1, in which the one signal is the second signal and the value of the resultant fluid flow rate is maintained constant by the controlling means. 
     
     
       16. The system of claim 1, additionally comprising switching means for alternatively applying to the controlling means the first signal to measure flow rate or the second signal to control flow rate. 
     
     
       17. The system of claim 1, in which the second signal generating means comprises a signal multiplier responsive to the first signal and the states of the digital valve elements. 
     
     
       18. The system of claim 17, in which the sensing and first signal generating means comprises transducer means for generating a signal proportional to the fluid parameter and a function generator for modifying the signal generated by the transducer means. 
     
     
       19. A digital liquid flow rate measurement or control device comprising: an upstream liquid manifold;   a downstream liquid manifold;   a plurality of at least three individually actuatable, digital valve elements, each valve element having a liquid flow passage leading from the upstream manifold to the downstream manifold, a sealable orifice in the passage, and a bistable plug positionable exclusively in a first state in which the plug seals the orifice to prevent liquid flow through the passage or a second state in which the plug unseals the orifice to permit liquid flow through the passage;   first liquid pressure sensing means located in the upstream manifold;   second liquid pressure sensing means located in the downstream manifold; and   means responsive to the liquid pressure difference sensed by the first and second pressure sensing means and the states of the digital valve elements for generating a signal representative of the resultant fluid flow rate from the upstream manifold to the downstream manifold.   
     
     
       20. The device of claim 19, additionally comprising means for controlling the states of the respective plugs to maintain the liquid pressure difference sensed by the first and second pressure sensing means at a substantially constant value. 
     
     
       21. The device of claim 20, additionally comprising an indicator responsive to the resultant fluid flow rate representative signal for displaying the liquid flow rate from the upstream manifold to the downstream manifold. 
     
     
       22. The device of claim 19, additionally comprising: a source of a set point signal proportional to a desired liquid flow rate from the upstream manifold to the downstream manifold, and means responsive to the difference between the resultant flow rate representative and set point signals for changing the plug states of the respective digital valve elements to equalize the desired flow rate and the actual flow rate.   
     
     
       23. The device of claim 19, additionally comprising means for maintaining a linear relationship between the resultant flow rate through the valve elements in the second position and the product of the sensed pressure difference times the sum of the effective cross-sectional areas of the valve elements in the second state. 
     
     
       24. A digital liquid flow measurement or control device comprising: an upstream liquid manifold;   a downstream liquid manifold;   a plurality of at least three individually actuatable, digital valve elements, each valve element having a liquid flow passage leading from the upstream manifold to the downstream manifold, a sealable orifice in the passage, a bistable plug positioned exclusively in a first state in which the plug seals the orifice to prevent liquid flow through the passage or a second state in which the plug unseals the orifice to permit liquid flow through the passage, and a cavitating venturi in the passage at which the liquid remains in its vapor phase when the plug is in the second state;   liquid pressure sensing means located in the upstream manifold; and   means reponsive to the liquid pressure sensed by the pressure sensing means and the states of the digital valve elements for generating a signal representative of the resultant fluid flow rate from the upstream manifold to the downstream manifold.   
     
     
       25. The device of claim 24, additionally comprising means for controlling the states of the respective plugs to maintain the liquid pressure sensed by the pressure sensing means at a substantially constant value. 
     
     
       26. The device of claim 25, additionally comprising an indicator responsive to the resultant flow rate representative signal for displaying the liquid flow rate from the upstream manifold to the downstream manifold. 
     
     
       27. The device of claim 24, additionally comprising: a source of a set point signal proportional to a desired liquid flow rate from the upstream manifold to the downstream manifold, and means responsive to the difference between the resultant flow rate representative and set point signals for changing the plug states of the respective digital valve elements to equalize the desired flow rate and the actual flow rate.   
     
     
       28. A digital gas flow measurement or control device comprising: an upstream gas manifold;   a downstream gas manifold;   a plurality of at least three individually actuatable, digital valve elements, each valve element having a gas flow passage leading from the upstream manifold to the downstream manifold, a sealable orifice in the passage, a bistable plug positionable exclusively in a first state in which the plug seals the orifice to prevent gas flow through the passage or a second state in which the plug unseals the orifice to permit gas flow through the passage, and a critical flow orifice through which gas flow at sonic velocity is maintained when the plug is in the second state;   absolute gas pressure sensing means located in the upstream manifold;   absolute temperature sensing means located in the upstream manifold; and   means responsive to the absolute pressure sensed by the pressure sensing means divided by the square root of the absolute temperature sensed by the temperature sensing means and the states of the digital valve elements for generating a signal representative of the resultant fluid flow rate from the upstream manifold to the downstream manifold.   
     
     
       29. The device of the claim 28, additionally comprising means for controlling the states of the respective plugs to maintain the absolute pressure sensed by the pressure sensing means divided by the square root of the absolute temperature sensed by the temperature sensing means at a substantially constant value. 
     
     
       30. The device of claim 29, additionally comprising an indicator responsive to the resultant flow rate representative signal for displaying the gas flow rate from the upstream manifold to the downstream manifold. 
     
     
       31. The device of claim 28, additionally comprising: a source of a set point signal proportional to a desired gas flow rate from the upstream manifold to the downstream manifold, and means responsive to the difference between the resultant flow rate representative and set point signals for changing the plug states of the respective digital valve elements to equalize the desired flow rate and the actual flow rate.   
     
     
       32. The device of claim 28, in which the critical flow orifice comprises the throat of a converging-diverging nozzle. 
     
     
       33. A digital gas flow measurement or control device comprising: an upstream gas manifold;   a downstream gas manifold;   a plurality of at least three individually actuatable, digital valve elements, each valve element having a gas flow passage leading from the upstream manifold to the downstream manifold, a sealable orifice in the passage, and a bistable plug positionable exclusively in a first state in which the plug seals the orifice to prevent gas flow through the passage or a second state in which the plug unseals the orifice to permit gas flow through the passage;   first gas pressure sensing means located in the upstream manifold;   second gas pressure sensing means located in the downstream manifold;   temperature sensing means located in one of the manifolds; and   means responsive to the pressures sensed by the first and second pressure sensing means and the temperature sensed by the temperature sensing means and the states of the digital valve elements for generating a signal representative of the resultant fluid flow rate from the upstream manifold to the downstream manifold.   
     
     
       34. The device of claim 33, additionally comprising means for controlling the states of the respective plugs to maintain the pressure sensed by the first pressure sensing means divided by the square root of the absolute temperature sensed by the temperature sensing means at a substantially constant value. 
     
     
       35. The device of claim 34, additionally comprising an indicator responsive to the resultant flow rate representative signal for displaying the gas flow rate from the upstream manifold to the downstream manifold. 
     
     
       36. The device of claim 33, additionally comprising: a source of a set point signal proportional to a desired gas flow rate from the upstream manifold to the downstream manifold, and means responsive to the difference between the resultant flow rate representative and set point signals for changing the plug states of the respective digital valve elements to equalize the desired flow rate and the actual flow rate.   
     
     
       37. A method of measuring the flow rate in a fluid line between a source of fluid at a first pressure and a fluid receiver at a second pressure lower than the first pressure, the method comprising the steps of: interconnecting a plurality of individually actuatable, value weighted digital bistable valve elements in parallel in the fluid line between the source and the receiver, each valve element assuming exclusively either an open state in which fluid flows from the source through the valve element to the receiver or a closed state in which no fluid flows from the source through the valve element to the receiver such that the resultant flow rate through the fluid line is a function of the product of a flow rate determinative fluid parameter times the sum of the weighted values of the digital valve elements in the open state;   sensing the .Iadd.flow rate determinative .Iaddend.fluid parameter;   controlling the states of the digital valve elements to maintain .[.the.]. .Iadd.a .Iaddend.fluid .[.parameter.]. .Iadd.characteristic in the line .Iaddend.constant .[.as the flow rate through the fluid line varies..]..Iadd.;   sensing the digital valve elements in the open state; and   indicating the resultant flow rate through the fluid line from the sensed flow rate determinative fluid parameter and the sensed digital valve elements in the open state. .Iaddend.   
     
     
       38. The method of claim 37, additionally comprising the step of maintaining a linear function relationship between the resultant flow rate through the valve elements in the open state and the product. 
     
     
       39. A digital fluid flow rate measurement or control system comprising: a source of fluid at a first pressure;   a fluid receiver at a second pressure lower than the first pressure;   a plurality of individually actuatable, value weighted digital bistable valve elements interconnecting the source to the receiver, each valve element assuming exclusively either an open state in which fluid flows from the source through the valve element to the receiver or a closed state in which no fluid flows from the source through the valve element to the receiver;   means for maintaining a linear relationship between the resultant fluid flow rate from the source to the receiver and the product of a flow rate determinative fluid parameter times the sum of the weighted values of the digital valve elements in the open state;   means for sensing the fluid parameter; and   means responsive to the value of the fluid parameter and the states of the digital valve elements for generating a signal representative of the resultant fluid flow rate.   
     
     
       40. The system of claim 39, additionally comprising means for controlling the states of the valve elements to maintain the value of the fluid parameter constant. 
     
     
       41. The system of claim 39, in which the generating means is responsive to the sensed value of the fluid parameter and the states of the digital valve elements, the system additionally comprising means for controlling the states of the digital valve elements responsive to the signal representative of the resultant fluid flow rate. 
     
     
       42. The system of claim 39, in which the fluid is incompressible, the fluid parameter is the square root of the difference between the first and second pressures, the sensing means senses the square root of the difference between the first and second pressures, and the means for maintaining a linear relationship comprises means for establishing a sufficiently low maximum difference between the first and second pressures to prevent formation of vena contractas having pressure dependent cross-sectional areas downstream of the valve elements in the open state. 
     
     
       43. The system of claim 39, in which the fluid is incompressible, the fluid parameter is the square root of the difference between the first and second pressures, the sensing means senses the square root of the difference between the first and second pressures, and the means for maintaining a linear relationship comprises means for directing the streams from the valve elements in the open state at each other to dissipate the vena contractas. 
     
     
       44. The system of claim 39, in which the fluid is incompressible, the fluid parameter is the square root of difference between the first pressure and the vapor pressure of the fluid, the sensing means senses the first pressure, and the means for maintaining a linear relationship comprises a cavitating venturi in each valve element. 
     
     
       45. The system of claim 39, in which the fluid is compressible, the fluid parameter is the absolute stagnation pressure divided by the square root of the absolute stagnation temperature, the sensing means senses the first pressure and the temperature of the fluid at the source, and the means for maintaining a linear relationship comprises a critical flow orifice in each valve element through which fluid flows at sonic velocity. 
     
     
       46. The system of claim 45, in which the orifice is the throat of a converging-diverging nozzle. 
     
     
       47. A method for operating a digital fluid flow control system having a plurality of individually actuatable, value weighted digital bistable valve elements interconnecting a source of fluid at a first pressure to a receiver at a second pressure lower than the first pressure, each valve element assuming exclusively either an open state in which fluid flows from the source through the valve element to the receiver or a closed state in which no fluid flows from the source through the valve element to the receiver such that the resultant fluid flow rate from the source to the receiver is a function of the product of a flow rate determining fluid parameter times the sum of weighted values of the digital valve elements in the open state, the method comprising the steps of: sensing the fluid parameter and generating a first signal representative of the value of the fluid parameter;   generating a second signal representative of the product of the value of the fluid parameter and the states of the digital valve elements; and   controlling the states of the digital valve elements responsive to one of the signals so as to maintain constant the value representated by the one signal. .Iadd. 48. A digital fluid control system comprising:   a first fluid manifold;   a second fluid manifold;   a plurality of individually actuatable, value weighted digital bistable valve elements interconnecting the first manifold to the second manifold, each valve element assuming exclusively either an open state in which fluid flows from the first manifold through the valve element to the second manifold or a closed state in which no fluid flows from the first manifold through the valve element to the second manifold such that the resultant fluid flow rate from the first manifold to the second manifold is a function of the product of a flow rate determinative fluid parameter times the sum of the weighted values of the digital valve elements in the open state;   means responsive to the value of the flow rate determinative fluid parameter and the states of the digital valve elements for generating a signal representative of the value of the resultant fluid flow rate;   means for sensing a control parameter in the system; and   means responsive to the sensed control parameter for controlling the states of the digital valve elements so as to maintain the sensed control parameter constant. .Iaddend..Iadd. 49. The control system of claim 48, in which the sensed control parameter is the pressure in one of the manifolds. .Iaddend. .Iadd. 50. The control system of claim 49, additionally comprising an indicator responsive to the signal representative of the value of the resultant fluid flow rate. .Iaddend..Iadd. 51. The control system of claim 50, in which the fluid flow rate determinative parameter and the sensed control parameter are identical, the generating means being responsive to the sensing means. .Iaddend..Iadd. 52. The control system of claim 51, in which the fluid is incompressible, each valve element has a passage from the first manifold to the second manifold which includes a converging-diverging nozzle designed to maintain the vapor phase of the fluid at its throat, the fluid parameter is the square root of the difference between the pressure in the first manifold and the vapor pressure of the fluid, and the sensing means senses the pressure in the first manifold. .Iaddend..Iadd. 53. The control system of claim 48, additionally comprising an indicator responsive to the signal representative of the value of the resultant fluid flow rate. .Iaddend..Iadd. 54. The control system of claim 48, in which the fluid flow rate determinative parameter and the sensed control parameter are identical, the generating means being responsive to the sensing means. .Iaddend. .Iadd. 55. A digital fluid control system comprising:   a source manifold;   a receiver manifold;   a plurality of individually actuatable, value weighted digital bistable valve elements interconnecting the source manifold to the receiver manifold, each valve element assuming exclusively either an open state in which fluid flows from the source manifold through the valve element to the receiver manifold or a closed state in which no fluid flows from the source manifold through the valve element to the receiver manifold such that the resultant fluid flow rate from the source manifold to the receiver manifold is a function of the product of a flow rate determinative fluid parameter times the sum of the weighted values of the digital valve elements in the open state;   means for sensing the flow rate determinative fluid parameter;   means responsive to the sensed flow rate determinative fluid parameter and the states of the digital valve elements for generating a signal representative of the value of the resultant fluid flow rate; and   means for controlling the states of the digital valve elements so as to maintain the value of a fluid characteristic in the system constant. .Iaddend..Iadd. 56. The control system of claim 55, in which the fluid characteristic is the pressure in one of the manifolds. .Iaddend. .Iadd. 57. The control system of claim 56, additionally comprising an indicator responsive to the signal representative of the value of the resultant fluid flow rate. .Iaddend..Iadd. 58. The control system of claim 55, in which the fluid is incompressible, the flow rate determinative fluid parameter is the square root of the difference between the pressures in the source manifold and the receiver manifold, and the sensing means senses the square root of said pressure difference. .Iaddend..Iadd. 59. The control system of claim 55, in which the fluid is incompressible, each digital valve element has a passage from the source to the receiver which includes a converging-diverging nozzle designed to maintain the vapor phase of the fluid at its throat, the flow rate determinative fluid parameter is the square root of the difference between the pressure in the source manifold and the vapor pressure of the fluid, and the sensing means senses the pressure in the source manifold. .Iaddend. .Iadd. 60. The control system of claim 55, in which the fluid is compressible, the flow rate determinative fluid parameter is the absolute stagnation pressure divided by the square root of the absolute stagnation temperature, the sensing means senses the pressure and the temperature of the fluid in the source manifold, each digital valve element has a flow passage from the source manifold to the receiver manifold, a flow determining orifice formed in the flow passage, and a region in the flow passage through which the fluid flows at sonic velocity thereby isolating the flow passage upstream of the flow determining orifice from variations in the pressure in the receiver manifold. .Iaddend..Iadd. 61. The method of claim 37, in which the fluid characteristic is the flow rate determinative fluid parameter. .Iaddend. .Iadd. 62. A method for operating a digital fluid flow control system having a plurality of individually actuatable, value weighted digital bistable valve elements interconnecting a source of fluid at a first pressure to a receiver at a second pressure lower than the first pressure, each valve element assuming exclusively either an open state in which fluid flows from the source through the valve element to the receiver or a closed state in which no fluid flows from the source through the valve element to the receiver such that the resultant fluid flow rate from the source to the receiver is a function of the product of a flow rate determinative fluid parameter times the sum of the weighted values of the digital valve elements in the open state, the method comprising the steps of:   sensing the flow rate determinative fluid parameter;   generating a signal representative of the product of the value of the flow rate determinative fluid parameter and the states of the digital valve elements; and   controlling the states of the digital valve elements so as to maintain the value of a fluid characteristic in the system constant. .Iaddend.