Electronic flowmeter system and method

A method of operating a flowmeter with an accuracy of at least one percent over at least three orders of magnitude of varying flow rates, the flowmeter being of the type having a rotatable turbine provided with a plurality of vanes and disposed at least partially within a body having a passage through which a liquid fluid whose flow is to be measured passes, the method comprising the steps of:

• (a) providing sensor means for detecting rotation of the turbine by sensing the passage of the vanes past a predetermined location, the sensor means including optical means for optically detecting the presence and absence of vanes of the turbine in the predetermined location, the optical means being provided with first and second optical fibers, a light source for providing light to a first end of the first optical fiber, and a substantially transparent window for transmitting light emanating from a second end of the first optical fiber to the predetermined location and back to one end of the second optical fiber, said transparent window means being capable of resisting at least 100 atmospheres of pressure, said sensor means producing an electromagnetic input signal whose period is inversely proportional to the rate of rotation of the turbine;
• (b) in a digital electronic controller converting the input signal into a first numerical value whose magnitude is proportional to the period of the input signal and inversely proportional to the rate of rotation;
• (c) in the controller selectively adjusting the first numerical value to compensate for any predetermined nonlinearity between the rate of rotation indicated by the electronic input signal and the rate of fluid flow through the body at least in a low flow region of operation of the flowmeter, thereby producing a second numerical value;
• and
• (d) producing a digital output signal whose magnitude is derived at least in part from the second numerical value, and wherein step (c) includes at least the substeps of:
• (1) providing a group of predetermined linear approximation (LA) values with each such LA value being associated with a particular range of flow rates,
• (2) selecting one of the LA values based upon the magnitude of the first numerical value, and
• (3) scaling the first numerical value in accordance with the selected LA value to produce the second numerical value.

A method of accurately measuring liquid flow over a range of flow rates spanning at least three decades using a flowmeter of the type having body provided with a substantially cylindrical bore in which a turbine provided with a plurality of vanes is disposed for rotation about an axis collinear with the axis of the bore, which is generally in line with the direction of flow of the liquid whose flow is to be measured, the method comprising the steps of:

• (a) detecting the rotation of the turbine by sensing the passage of the vanes past a predetermined location of the cylindrical bore, and producing an electromagnetic input signal whose period is inversely proportional to the rate of rotation of the turbine, said sensing being accomplished with optical sensing means including an artificial light source and photodetector remote from the body of the flowmeter and an optical conduit for directing light from the light source to the predetermined location;
• (b) in a digital electronic controller converting the input signal into a first numerical value whose rate of rotation is proportional to the period of the input signal by (1) providing a time base signal having a frequency at least in the Megahertz range and a pulse rate at least ten times that of the maximum expected pulse rate of the input signal, (2) providing a digital counter having a capacity of at least 24 bits for counting pulses of the time base signal, (3) gating the time base signal with the input signal, and (4) using the accumulated count in the counter resulting from one cycle of the input signal as the first numerical value;
• and
• (c) in the controller selectively adjusting the first numerical value to compensate for any predetermined nonlinearity between the rate of rotation indicated by the electromagnetic input signal and the rate of fluid flow through the body at least in a low flow region of operation of the flowmeter to produce a second numerical value by (1) providing a group of predetermined linear approximation (LA) values with each such LA value being associated with a particular range of flow rates, (2) selecting one of the LA values based upon the magnitude of the first numerical value, and (3) scaling the first numerical value in accordance with the selected LA value to produce the second numerical value.