FIELD OF THE INVENTION

This application relates to the field of fluid measurement devices. More specifically, this application relates to an ultrasonic flow meter calibration system and method for determining a zero-offset during active flow.

BACKGROUND

Ultrasonic flow meters utilize transducers to send and receive ultrasonic signals through a flow stream to measure the velocity of flow through a conduit. Where the transducers include an upstream transducer and a downstream transducer, the flow meter is configured to measure a “time-of-flight” of an ultrasonic signal transmitted between the two, spaced apart, transducers. The ultrasonic signal travels from a first transducer, along an ultrasonic signal path through the fluid and/or gas flowing through the conduit, to be received by a second transducer. The elapsed time between when the signal is sent from the first transducer and received by the second transducer is the time-of-flight. The signal may then be sent in a reverse direction to determine a reverse time-of-flight. The time differential between the forward vs. backward “time of flight” is referred to as the ΔT, which can be used to calculate the velocity of the flow through the conduit. The velocity of the flow through the conduit can, in turn, be used to calculate a flow rate and/or flow volume.

However, the “time of flight” forward versus backwards through a conduit may vary for reasons other that a flow through the conduit. No flow meter matches the theory perfectly. For example, the “time of flight” may vary based on transducer alignment, inconsistencies in the conduit, etc. To account for such variance, meters may be set to have a large value for uncertainty or may be calibrated the meter based on the variance. Giving a large uncertainty value may reduce meter accuracy and, as such, is impractical for some application. When calibrating a meter, during manufacturing, ultrasonic flow meters are calibrated to a “factory zero” where the “time of flight” is consistent forward and backwards during zero flow.

To determine the amount of such calibration, ΔT is calculated without any flow through the conduit. The ΔT is used to calibrate the ultrasonic flow meter.

Even following such factory calibration, variances may be reintroduced during the installation where the flow meter will be used. For example, one type of flow meter are clamp on flow meters that may be affected by the alignment of the meter, the section of conduit onto which the meter is clamped, etc. These factors can also drift over time, affecting the flow meter calibration. Accordingly, it is preferred that the flow meter be calibrated during installation and recalibrated as needed to be calibrated to an “in situ zero” where, once again, the “time of flight” is consistent forward and backwards during zero flow.

However, it is often impractical to arrange fix there to be zero flow through the conduit being measured. This is particularly the case where the flow meter is being recalibrated periodically and/or as needed to account for drift. What is needed is a flow meter and, method of recalibrating the flow meter to allow the flow meter to be calibrated to an “in situ zero” without requiring zero flow through the associated conduit.

SUMMARY OF THE INVENTION

The present invention provides an ultrasonic flow meter that includes an ultrasonic flow meter configured to measure a flow within a conduit configured for autozeroing during active flow operation of the flow meter. The flow meter includes a printed circuit board including circuitry for conducting ultrasonic transit time flow measurements, the printed circuit board including transducer swap relays and first and second transducer cables connecting the first and second transducers, respectively, to the transducer swap relays. The flow meter further includes a programmable processor configured to generate flow measurement data based on an ultrasonic flow meter calibration performed by the ultrasonic flow meter in situ while measuring flow through the conduit. Calibration includes determining a zero offset value, determining a swap offset value by measuring transit time forward and backward between the first and second transducers through the flow in the conduit, activating the transducer swap relays to physically swap the first and second transducers, and measuring transit time forward and backward between the swapped first and second transducers through the flow in the conduit, determining a flow zero value based on the zero offset and swap offset, and generating flow rate data based on the flow in the conduit and the flow zero offset.

In one more detailed aspect, determining a swap offset value includes generating a forward average based on a plurality of measurements taken before activating the transducer swap relays and generating a reverse average based on a plurality of measurements taken after activating the transducer swap relays.

In another embodiment of the invention, generating flow rate data includes calculating an average of a standard flow rate based on one or more measurements taken before activating the transducer swap relays and a swapped flow rate based on one or more measurements taken after activating the transducer swap relays.

In, another embodiment of the invention, the processor is configured to initiate ultrasonic flow meter calibration based on a user input or periodically.

In another more detailed aspect, the processor is configured to monitor the flow rate to identify a steady flow rate prior to initiating ultrasonic flow meter calibration.

In another embodiment of the invention, a computer-implemented method for autozeroing an ultrasonic flow meter configured to measure a flow within a conduit using a processor of the flow meter implementing autozeroing instruction stored in non-transient memory. The method includes determining a zero offset value based on measured transit time forward and backward between first and second transducers through a flow in a conduit and determining a swap offset value by measuring transit time forward and backward between first and second transducers through the flow in the conduit, activating transducer swap relays on a printed circuit board of the flow meter that is connected to the first, and second transducers by first and second transducer cables, respectively, to physically swap the first and second transducers, and measuring transit time forward and backward between the swapped first and second transducers through the flow in the conduit. The method further includes determining a flow zero value based on the zero offset and swap offset and generating flow rate data based on the flow in the conduit and the flow zero offset first and second transducers.

Other aspects of the invention, besides those discussed above, will be apparent to those of ordinary skill in the art from the description of exemplary embodiments which follows. In the description, reference is made to the accompanying drawings, which form a part hereof, and which illustrate examples of the invention.

