JPH0258570B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic flowmeter that can automatically switch measurement ranges.

This type of ultrasonic flow meter is an analog measuring instrument, so it does not have the disadvantage of reducing measurement accuracy when the flow rate is in the middle range or higher of the measurement range, but the accuracy deteriorates significantly when the flow rate reaches the low range. This comes with the inconvenience.

This invention was made by focusing on the points mentioned above, and when the flow rate is above the middle range of the measurement range, the measurement range is widened, and when the flow rate is below the middle range, the measurement range is automatically narrowed to adjust the flow rate. An object of the present invention is to provide an automatic measurement range switching mechanism in an ultrasonic flowmeter that constantly maintains high measurement accuracy.

In addition, the present invention provides a pair of flow velocity measuring mechanisms including an ultrasonic transmitting element and an ultrasonic receiving element in a conduit through which a fluid to be measured flows, facing each other via the fluid flow, and also provides an ultrasonic transmitting element and an ultrasonic receiving element. Ultrasonic flow rate using a so-called phase difference method, in which a pair of flow velocity measuring mechanisms consisting of a sound wave receiving element and the flow velocity mechanism are arranged in different forward and reverse directions, and the flow rate is obtained by measuring the phase difference of ultrasonic signals. It is to provide a meter.

An embodiment of the present invention will be described below with reference to the drawings. Reference numeral 1 indicates an ultrasonic transmitter, and 2 and 3 indicate a pair of ultrasonic transmitting elements and ultrasonic receiving elements, which are provided facing each other via a fluid flow in a conduit 4 through which the fluid to be measured flows, and have a single flow velocity. A measuring mechanism 5 is configured. 6,
Reference numeral 7 designates another pair of ultrasonic transmitting elements and an ultrasonic transmitting element, which constitutes another flow rate measuring mechanism 8 and connects the aforementioned mechanism 5 to the conduit 4 in different directions with respect to the fluid flow. Arrange.

9 and 10 are preamplifiers that amplify the ultrasonic measurement signals received by the respective ultrasonic receiving elements 3 and 7; 11 and 1;
2 is each frequency dividing circuit, 13 is both circuits 11, 1
14 is a low-pass filter; 15 is a phase difference detector that receives the signal output from 2 and detects the phase difference;
is the output part of the weighing output signal.

Reference numeral 16 denotes a flow rate sensor that measures the approximate flow rate of the fluid flowing within the flow path 4 . This flow rate sensor 16
Instead, the received signal of one of the ultrasonic receiving elements, for example, 3, is branched to the output section 16a, and another ultrasonic receiving element 16b is attached to a part of the flow path 4, so that the difference in output between the ultrasonic received signals is reduced. Utilizing the fact that the flow rate is a function of the flow rate, the flow rate sensor 16 may be used to measure the approximate flow rate of the fluid. 17 is a preamplifier for amplifying the signal, 18 is a frequency division setting circuit, and 19 is a measurement range switching setting circuit.

The operation of this invention will be explained based on the above configuration.

The approximate flow rate of the fluid to be measured flowing in the flow path 4 is constantly measured by comparing the received signal outputs of the flow rate sensor 16 or branch output section 16a and other ultrasonic receiving elements 16b. That is, this rough flow rate measurement signal is amplified by the preamplifier 17 and input to the frequency division setting circuit 18 . This frequency division setting circuit 18 has the function of automatically switching the frequency division ratio according to the magnitude of the flow rate, so if the flow rate is large, the frequency division ratio will be a large value and the measurement range can be widened. However, the sensitivity decreases. However, since the flow rate range is widened, measurement accuracy can be ensured when the flow rate is large.

On the other hand, when the flow rate is small, the frequency division ratio is small and the measurement range is narrow, but the sensitivity is high and accuracy can be improved.

Therefore, the frequency division ratio 1/N is automatically set in the frequency dividing circuits 11 and 12 according to the magnitude of the flow rate, and the phase difference of the ultrasonic measurement signal is detected in the next stage phase difference detector 13, and the low-pass signal is detected. A flow velocity or flow rate signal can be transmitted from the output section 15 via the filter 14.

Since the present invention is constructed as described above, the measurement range of the fluid is automatically switched according to the frequency division ratio of the frequency divider based on the rough flow rate signal obtained from a different type of sensor or an ultrasonic measurement path, so that the flow rate is constantly maintained. It can be accurately measured regardless of size, and has the effect of improving measurement accuracy in the low flow rate range, which is a drawback of analog measuring instruments such as ultrasonic flowmeters.

[Brief explanation of drawings]

The figure is a circuit explanatory diagram showing an embodiment of an ultrasonic flowmeter according to the present invention. 1... Ultrasonic oscillator, 2, 6... Ultrasonic transmitting element, 3, 7... Ultrasonic receiving element, 5, 8... Flow velocity measuring mechanism, 11, 12... Frequency dividing circuit, 16... Flow rate sensor , 18... Frequency division setting circuit, 19... Measurement range switching setting circuit.

Claims (1)

[Claims] 1. Two sets of ultrasonic transmitters and receivers are disposed in the flow path of the fluid to be measured, facing each other in the flow direction with the same distance, and the ultrasonic transmitter An ultrasonic device that is driven by an ultrasonic signal oscillator that oscillates a fixed frequency, not limited to sine waves, and the flow rate is determined from the fact that the phase difference between the ultrasonic signals that occurs as the ultrasonic waves propagate is proportional to the flow velocity. The flowmeter is provided with a frequency divider that divides the frequency of the two sets of ultrasonic signals received by the ultrasonic receiver, and is also provided with a device that detects the approximate value of the flow rate, and the signal from the device or the ultrasonic receiver is provided. A frequency division setting circuit that automatically switches the frequency division ratio of the frequency divider according to the frequency divider value, and a phase comparator that compares the phase difference of the signal obtained by frequency division by the frequency divider are provided. A feature is that the flow rate signal is obtained from the output of the comparator, and the measurement range is kept optimal by automatically switching the frequency division ratio according to the value of the flow rate signal input to the frequency division setting circuit. Ultrasonic flow meter. 2. The ultrasonic flowmeter according to claim 1, wherein the frequency division setting circuit is provided with a circuit for setting one or more range switching points.