Abstract: Vortex-shedding flow meters provide an output signal having a frequency representative of fluid flow rate. At high flow rates the vortices are larger and easier to detect. Adjusting the gain of an output amplifier responsive to the output frequency extends the operating range, or turndown ratio, of a vortex flow meter.

Abstract: A paddlewheel flow sensor has two independently rotating paddlewheels in a flow passage. The spacing between the wheels can be selected to respond to most of the flow while simultaneously tolerating trash carried by the flowing fluid. Each wheel has its own rotation sensor, and an average of the two rotation sensor outputs can be used to determine flow rate.

Abstract: A vortex-shedding flowmeter uses two flow obstacles to provide stable generation of vortices that are detected as they pass through an ultrasonic beam between two transducers. The deleterious effects of acoustic signals reflected from the obstacles are minimized both structurally and electronically. The shapes of the obstacles are selected to reflect incident acoustic signals away from the beam between the transducers. Ultrasonic signals are generated simultaneously by two phase-opposed transducers and are detected in a time-windowed fashion in which the time window excludes extraneous reflected signals that have a longer path length.

Abstract: A heat flux probe uses a thermoelectric module to heat a relatively large sensing surface while cooling a substantially smaller one that is connected to the thermoelectric module by an elongated thermal conductor. A temperature difference between either the two sensing surfaces or the heated sensing surface and the cooled end plate of the thermoelectric module is controlled to have a selected value. Then the temperature change along the elongated thermal conductor is used as a measure of heat flux. This approach reduces inaccuracies arising from the thermal characteristics of the thermoelectric module and allows for in situ compensation for drift errors.

Abstract: A leaded piezoelectric transducer element is attached to the inside of the end surface of a closed-end cylindrical container such as a plastic cup. The outside end surface of the cup is intended for exposure to a fluid. The required components to isolate and/or resonate with the piezoelectric element are added, after which a rigid encapsulant is formed in the cup to make a single solid assembly strong enough to be clamped. The end of the cup is then thinned to yield a thin, compliant, and environmentally protecting acoustic window.

Abstract: The specific heat of a working fluid flowing along a channel is measured without having to provide an explicit flow rate correction. A specific heat sensing probe is configured with a stagnation enclosure surrounding a thermal transfer sensor. The stagnation enclosure is designed to provide a stagnation chamber in throttled communication with an outside of the enclosure so that the working fluid can flow into and out of the stagnation chamber at a seepage rate substantially less than the fluid flow rate. The thermal transfer sensor is operable to exchange heat with adjacent fluid and to provide a signal representative of the quantity of heat exchanged.

Abstract: Tangential forces present at the mating area between a clamp-on transducer and a pipe can be made very small in order to provide a higher quality, more stable acoustic coupling. In some cases this is accomplished by providing a low friction bearing on a surface of a transducer housing. This bearing may be a slippery surface portion, or may involve a rotary bearing mounted on the housing. In other cases, where a steel pipe is used, pairs of permanent magnets coupled by a yoke can provide the desired clamping force directed solely along a radius of the pipe.

Abstract: Thermal transfer measurements are useful for measuring either a mass flow rate or the specific heat of a fluid. Thermoelectric devices are desirable for this because of their ability to simultaneously heat one portion of the sensor while cooling another. However, the internal thermal resistance of thermoelectric devices has limited the accuracy of thermoelectric thermal transfer sensors. This problem is solved by using separate temperature sensors to measure selected temperature differences established by the thermoelectric portion of a thermal transfer sensor.

Abstract: An asymmetric heat flux sensor has two sensing surfaces separately thermally coupled to the end plates of a thermoelectric module so that one is heated and the other cooled. The heated sensing surface is constrained to have a wettable area much larger than the area of the cooled sensing surface. This allows the heated sensing surface to be nearly the same temperature as the fluid ambient while providing a relatively large temperature differential. Because bubbles, which degrade a heat flux measurement, form preferentially on a heated surface, the asymmetric design avoids bubble formation and hence provides enhanced accuracy.

Abstract: The accuracy of instruments used to measure the specific heat of heat transfer fluids is limited by the accumulation of bubbles, debris or loose surface films on an active measurement surface. Accumulated bubbles, debris or loose film may be reduced or eliminated by using an agitator to cause relative motion between a working fluid and an active surface of a specific heat sensor. The accumulation of bubbles, debris or loose film may also be reduced or eliminated by electrolytically cleaning an electrically conductive heat transfer surface.

Abstract: Power at a selected frequency in the high frequency region of the spectrum is supplied by a power converter having a wide range of input voltages. The power converter uses a source oscillator and a NOR gate. The source oscillator generates a rectangular wave at the selected frequency and supplies that signal to one of the NOR gate inputs. The rectangular wave is differentiated and the differentiated signal is supplied to the second NOR input along with a feedback signal from an amplifier controlled by the NOR gate's output.

Abstract: Ultrasonic transit time flow meters using transducers mounted on insertion probes spaced apart along a pipe axis provide an economical way to measure fluid flow. The accuracy of these flow meters can be improved by providing additional transducers to measure the current speed of sound of a working fluid; the actual spacing of the probes; and the diameter of the pipe through which the fluid is flowing.

Abstract: An ultrasonic transit time approach is used for measuring both a speed of sound of a fluid and a diameter of a pipe through which the fluid flows. A reflecting structure is provided to split an acoustic beam generated by a transducer into two portions. One of these portions traverses an acoustic path of known length in order to determine the speed of sound in the fluid. The second portion of the beam may be directed along a path that includes reflections from an inner surface of the pipe. In this case the second portion of the beam can be used to measure the diameter of the pipe. Alternately, the second portion of the beam may extend to a second transducer that is spaced apart along the pipe from the transducer generating the split beam.

Abstract: A time-of-flight ultrasonic flow meter uses transducers placed on streamlined heads of probes that are spaced out along a pipe. The placement of the transducers and probes is selected so that an acoustic signal can propagate between the transducers on the two probes along a path that involves at least one reflection from an internal surface of the pipe.

Abstract: The specific heat of working fluids used in commercial heating systems commonly change with temperature and composition. Conventional heat metering systems assume a fixed value of the specific heat at a nominal temperature. This source of inaccuracy is removed by measuring the specific heat of a working fluid as a heating system operates and using the currently measured value in calculating the heat transferred. The real time specific heat measurement may be made by using a specific heat sensor having either a resistive heating element or a thermoelectric module.

Abstract: A clamp-on acoustic flow meter for measuring the rate of flow of a fluid in a pipe uses a transducer stack mounted in a housing that includes a rigid polymeric foam body in which the stack is embedded. This transducer configuration is used in combination with a clamping mechanism operable to supply a clamping force directed substantially entirely along a radius of the pipe for clamping the exposed portion of a transducer stack end piece to the pipe.

Abstract: Acoustic windows that are portions of an ultrasonic sensor used to measure a rate of flow of a fluid are wetted whenever the fluid is present. These windows may become coated with a contaminant film during operation. The contaminant may be removed by applying an acoustic cleaning signal to the same ultrasonic transducers used in the flow measurement. The cleaning signal frequency is commonly on the order of one to a few tens of kilohertz, which is substantially less than the measurement signal frequency, which is commonly on the order of a few megahertz. Several approaches are described that isolate the cleaning and measurement functions and that provide protection to signal amplifiers that are used in the measurement process and that could be damaged by high cleaning voltages.

Abstract: Tangential forces present at the mating area between a clamp-on transducer and a pipe can be made very small in order to provide a higher quality, more stable acoustic coupling. In some cases this is accomplished by providing a low friction bearing on a surface of a transducer housing. This bearing may be a slippery surface portion, or may involve a rotary bearing mounted on the housing. In other cases, where a steel pipe is used, pairs of permanent magnets coupled by a yoke can provide the desired clamping force directed solely along a radius of the pipe.

Abstract: A time-of-flight flow meter that is particularly useful for measuring the flow of gases, such as steam, uses a spark gap periodically energized with an electrical pulse to generate an acoustic pulse. The pulse is detected by upstream and downstream acoustic detectors that may be capacitive transducers having flexible plates wetted on both sides by the fluid so that no external venting is required. The acoustic detectors may be electrically heated to avoid condensation effects. In some cases the interior of the pipe or other conduit is shaped near the source so as to define acoustic beams aimed at the detectors and so as to concentrate the received acoustic energy on the detectors.

Abstract: An in-line magnetic flow meter has an electrically insulated quasi-annular voltage sensing path defined between an internal wall of a meter body and an outer wall of an axially disposed hollow tube. Although less than 100% of the fluid flow passes through the sensing region, the choice of an inner tube reduces flow impedance introduced by the meter, when compared to other meters providing a quasi-annular sensing path. In addition, by forming two electromagnet coils on a single core and using axially separated pairs of electrodes, the present arrangement allows one to provide two flow meters in the space normally occupied by one.