JPH0749388Y2 - Vortex generator type flow meter circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a vortex shedding type flow meter (vortex shedding).
flow meter) electrical circuit, and in particular, to a circuit useful for operating a sensor connected to a vortex generating flow meter to reduce energy consumption and temperature rise.

The eddy current type flow meter has a bluff bod
It is used to measure the volumetric flow rate of a fluid by placing a non-streamlined obstacle called y). When the flowing fluid separates around the obstacle, vortices naturally occur downstream from the obstacle, alternating from one side to the other. The number of these vortices per unit time is directly proportional to the volumetric flow rate. Therefore, counting the number of vortices can provide a measure of flow rate.

To detect the passage of these vortices, it is known to utilize a bridge circuit having one resistor or other element that changes as each vortex passes. The circuit element is connected to the bridge circuit to count the passage of the vortex thus sensed and to provide a signal proportional to the flow rate of the fluid to be measured.

A transformer is used to energize one side of the bridge and extract the signal from the other side of the bridge. When a large energizing voltage is used, the sensor bridge will heat up and will tend to lose accuracy due to drift and also compromise useful life. Moreover, many transmitter applications cannot utilize this high power on a continuous basis.

The present invention seeks to provide an improved circuit for energizing and sensing signals from a sensing bridge used in a vortex generating flow meter.

AC (rather than continuously energizing the bridge)
It has been found to be beneficial to use the signal to actuate the bridge sensor in individual single-cycle pulse bursts that are widely spaced. Thus, the sensor is biased to sense the passage of vortices only during individual pulse bursts, giving the sensor a low average power,
As a result, the sensor is maintained in a stable state with an extended product life.

Accordingly, it is an object of the present invention to provide a circuit for operating a vortex-generating flowmeter sensor having an energizable sensor member having an output that varies according to the frequency of vortex generation, and in this circuit, It is characterized in that the bridge circuit including the sensor member is activated only during each burst by a series of pulse bursts consisting of AC1 cycle burst so that the time interval between these bursts is longer than the duration of each burst.

The sensitivity is improved because the sensor is energized at high peak power. This is because sensitivity is directly related to peak drive output. This realizes the main purpose of the present invention.

Yet another object of the present invention comprises a sensor that changes state depending on the frequency of vortex generation, and means for applying AC single cycle bursts to the sensor with a time interval greater than the duration of each burst. A vortex generating type flow meter including an urging circuit connected to the sensor and a sensor circuit connected to the sensor for generating a signal corresponding to a vortex generation frequency.

It is another object to provide isolation between the sensor and the output circuit to prevent ground interaction.

Yet another object of the present invention is to provide a sensor circuit for a vortex generating flow meter which is simple in design, robust in construction and economical to manufacture.

Referring now to the drawings, FIG. 1 shows an exemplary circuit that may be used to implement the present invention. The bridge, which is generally designated by the numeral 10, is composed of _four resistors R _{1 to} R ₄ . The bridge is used as a strain gauge to sense the passage of a vortex across a bluff body of a vortex generating flow meter.

One of the resistors R ₁ acts as an active element of the bridge and responds to the passage of vortices by changing the resistance. Another resistor, for example R ₄ , acts as a dummy resistor and cooperates in a known manner with the two balancing resistors R ₂ and R ₃ .

The bridge energizing transformer T ₁ is connected to the north and south terminals 14 of the bridge 10.
And a coil 12 on one side connected between 16 and 16.
The coil 20 on the other side of the energizing transformer T ₁ has two transistors
Connected to the collectors of Q ₁ and Q ₂ . Transistor Q ₁ and
The emitter of Q ₂ is connected to circuit common point 22. The bases of transistors Q ₁ and Q ₂ are excited by first and second energizing signals applied to terminals 24 and 26, respectively, as shown in FIGS. 3 and 4, respectively. These energizing signals correspond to the upper and lower half cycles of the waveform of FIG.

The east and west terminals of the bridge 10 are connected to both ends of one side coil 28 of the isolation signal transformer T ₂ . The signal received from the bridge 10 is supplied to the sample and hold circuit 32 by the other side coil 30 of the transformer T ₂ . The sample-and-hold circuit 32 is connected to the two inputs of the differential amplifier 34.
And second switches S ₁ and S ₂ . Switches S ₁ and S ₂ operate in conjunction with capacitors C ₁ and C ₂ to transform transformer T ₂
It provides a full wave rectification of the output signal from. The differential amplifier provides a circuit common reference signal and has an output indicating the difference between the signals on capacitors C ₁ and C ₂ . In that case, the waveform at the output of intensifier 34 represents a sampled aspect of the vortex frequency, sampled at intervals determined by the peaks in FIG.

3 and FIG. 4 shows a waveform of a signal applied to terminals 24 and 26 for biasing the transistors Q ₁ and Q _2. The signals represented by 40 and 42 are single-cycle bursts with large intervals
It consists of 44 and 46. Thus, a typical duty cycle of 10% is applied to the bridge energizing voltage applied to terminals 24,26. The frequency of the bridging energization is selected to be at least 5 times, preferably 10 times the maximum vortex frequency to be measured. Thus, the sensor in the form of a bridge 10 is gated on by wide-spaced bursts in a single cycle. This allows for increased energization levels of about 10: 1, while at the same time allowing operation at low total power schemes as specified by known 4-20mA two wire transmitter based technology.

The present invention also allows a bridge energization level that is typically 10 times higher than when using low but continuous energization levels without introducing additional heating problems.

Therefore, typically a 10x improvement in sensitivity is obtained with the duty cycle switching technique. In addition, a two-fold increase is obtained due to the full wave action of the sample and hold circuit and the signal path transformer typically contributes a five-fold increase in signal voltage.

Having described the invention, it should be noted that many modifications can be made within the spirit of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a circuit used in the present invention, and FIG.
FIG. 4 is a waveform diagram showing a typical waveform applied to a bridge in the circuit of FIG. 1, FIG. 3 is a waveform diagram showing a biasing waveform applied to an input 24 of the circuit of FIG. 1, and FIG. Is a waveform diagram of the same applied to the input point 26. 10: Bridge R _{1 to} R ₄ : Resistor T ₁ : Bridge energizing transformer 12, 20: Coil Q ₁ , Q ₂ : Transistor T ₂ : Isolation transformer 28, 30: Coil 32: Ampoule and hold circuit 34 : differential increase width vessel S _1, S _2: switches C _1, C _2: capacitor

 ─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-53-6062 (JP, A) JP-A-54-137370 (JP, A) JP-A-55-159166 (JP, A) Actual development Sho-51- 140696 (JP, U) Japanese Patent Sho 51-2266 (JP, B1) Actual Japanese 42-4877 (JP, Y1)

Claims (2)

[Scope of utility model registration request] 1. A sensor composed of a bridge circuit composed of one active element and a balancing element that change state with vortex generation frequency, and an alternating current (AC) for energizing the sensor to change its state with vortex generation frequency. ) A single cycle burst of), the energizing circuit connected to the input side of the sensor having means for alternately applying to the opposite end of the sensor at a time interval longer than the time of each burst, said alternating current The frequency of a single-cycle burst of (AC) is at least 5 of the maximum value of vortex generation frequency.
A biasing circuit selected to be doubled, and an output circuit connected to the output side of the sensor to generate a signal corresponding to the rate at which the sensor changes its state, the biasing circuit comprising: Providing a bridge energizing transformer having an output coil and an input coil connected to the bridge, providing a positive half cycle of each burst to one end of the input coil and a negative half cycle to the other end of the input coil The output circuit is an insulating transformer having an input side coil connected to a bridge and an output side coil, a sample and holder circuit connected to the output coil, and the sample and holder circuit. Flow meter circuit having a differential amplifier connected to the vortex generator. 2. The energizing circuit comprises a first transistor connected to one end of the input side coil and a second transistor connected to the other end of the input side coil, each of the transistors being a positive and a negative of each burst. A circuit as claimed in claim 1, each including a base which can be linked to determine a half cycle.