SU757888A1 - Pressure sensor with frequency output - Google Patents

Description

The invention relates to instrumentation technology, in particular to sensors with a frequency output signal for measuring the pressure of gaseous and liquid media. '

Known frequency pressure sensors containing a cylindrical resonator, an electromagnetic exciter and a receiver [1]. With the help of an excitation system in a ferromagnetic 'θ cylindrical resonator of the sensor, oscillations with mode w = 1, η = 2 or m = 1, n = 4 are excited. oscillations and, therefore, the frequency of the output signal depends on the pressure difference acting on the wall of the cylindrical resonator.

Also known are frequency pressure sensors containing a cylindrical resonator, a magnetoelectric driver and a capacitive receiver located outside the resonator [2].

In these sensors, a cylindrical resonator can be made of any electrically conductive material and oscillations with mode π, = 1 and η = 2 are excited in it. The frequency of the output signal from the capacitive receiver also depends on the pressure difference acting on the wall of the resonator. Around cy- 30

2

There are permanent magnets in the number of a multiple of two that form a constant quadrupole magnetic field, between the poles of which are the electrodes of a capacitive receiver. The ends of the resonator are connected to an alternating current source. When the frequency of the alternating current is equal to the frequency of natural oscillations of the resonator with the mode ha - 1; η = 2 at the output of the capacitive receiver and, therefore, at the output of the sensor there is a signal of the same frequency. Since the natural frequency of oscillations of a resonator depends on the pressure difference acting on its wall, the measured pressure is thus converted into the frequency of the output signal.

The drawback of the device is that the output signal of the sensor depends not only on the measured pressure, but also on other influences, mainly on the ambient temperature surrounding the resonator, which leads to an error in the sensor.

The purpose of the invention is the expansion

(functionality and measurement accuracy.,

3

757888

This goal is achieved by the fact that in a pressure sensor with a frequency output ^- containing a housing, a cylindrical resonator connected to a supply transformer, permanent magnets forming the quadrupole field of the excitation system and electrodes of the capacitive vibration pickup system, eight identical uniformly distributed circumferentially are inserted into the excitation system additional magnets of alternating polarity, four of which are combined with the poles of the quadrupole system, and the removal system is made in the form of eight electrodes symmetrically located between max-nits, two opposite adjacent pairs of which are connected via resistivity to one of the inputs of the first; an amplifier, and two second pairs of adjacent ones; opposite electrodes are connected to another input of the first amplifier, and electrodes located relative to each other through one are connected respectively to the inputs of the second amplifier, while the resonator is connected to the secondary winding of the transformer, two primary windings which is connected to the outputs of the mentioned amplifiers, and the electrodes are interconnected and connected via a resistor to the source constantly! th voltage.

Each mode of the resonator has its own frequency of its own oscillations, which has its own dependence on the measured value (P) and disturbance (1 °)

= ^ρ -ί

= P ₂ (P; b °),;

where £ is the frequency of its own wheels |

Bayan resonator with. fashion; t = 1; η = 2; |

- the frequency of natural oscillations of the resonator with the mode go = 1; η = 4.

Therefore, knowing the relation (P; £ °) th P2 (P; Z ^O). Due posleduyuschey- processing signals from the first and second amplifier outputs may be defined as the measured value (P) without error by disturbance (£ °), so and “the indignation itself. Essential here is that two measuring channels are formed in one resonator, which ensures the same values of P and £ for these channels.

FIG. 1 shows the sensor section; in fig. 2-5 - section A-A in FIG. 1 with possible embodiments of a magnetic circuit that provides for the creation around the resonator of a superposition of quadrupole and octupole magnetic fields with coinciding poles; in fig. 6 is a diagram of the indicated magnetic fields and the pod-motor forces caused by them, acting on the current element flowing

I along the resonator (inside the cylindrical resonator, the interaction forces of the quadrupole field, the current field are shown, and outside, the octupole field, the possible numbering of the capacitive receiver electrodes and the deformations of the cross section of the resonator caused by the indicated forces are shown); in fig. 7 is a circuit diagram of a self-excitation system providing oscillations of the resonator at natural frequencies

^and Separation of signals corresponding to them. °

The sensor includes a cylindrical body 1 of a magnetically soft material (Fig. 2, Fig. 4) or a diamagnetic material (Fig. 3, Fig. 5) in which permanent magnets 2 are installed in a multiple of four located around a cylindrical resonator 3 fixed at one end on the cover 4 with the fitting of the inner strip of the resonator, and the second end - in the insulating block 8, which allows temperature longitudinal movement. The end resonators 5, as well as the electrodes of the capacitive receiver 6, are soldered to the sealed inlets 9, located on the lid 7 with the fitting of the external cavity of the resonator. Case 1; hermetically connected to the covers 4 and 7. In some embodiments, a magnetic circuit introduces diamagnetic liners 10 or magnetic flux concentrators 11. The latter are made of soft magnetic materials. The conductive walls of the resonator, together with the magnetic circuit, form a magnetoelectric exciter, which, when an electric current flows through the walls of the electric current, acts on the resonator (Fig. 6).

Electrodes capacitive receiver

- With ₈ * placed between the poles of the octupole field and form with the outer cylindrical surface of the resonator 3 capacitors, which are electrically interconnected and connected through a resistor to the source 12 of constant voltage. In addition, each of the electrodes is connected through a resistor to the inputs of differential amplifiers 13 and 14. The ends of the resonator are connected to the secondary winding of the supply transformer 15.

The sensor works as follows.

The measured pressure through the nozzle is supplied into the internal cavity of the resonator 3, which, together with the magnetoelectric exciter, capacitive receiver and amplifiers 13 and 14, forms a dual-circuit electromechanical self-oscillatory system providing in the resonator non-damping oscillations with two parts

757888

ό

| Stacks £ ^ 2 ^and 4, corresponding to 'modes with wavenumbers rn = 1, η = 2 and c = 1, η = 4, respectively. The placement of the electrodes - C ₈ and the distribution of the exciting forces on the surface of the resonator are such that 5

at its two-frequency oscillations, a change in capacitance and C ₂ (and corresponding others) creates a common-mode signal for the mode m = 1, η = 2: and an antiphase signal for the mode m = 1, η = 4. Therefore, summing up at the input of the differential amplifier 13 signals from capacitances and C _g , receive at its output a signal due only to the mode of oscillation u = 1; η = 2, and you, _ reading the same signals at the input of the differential amplifier 14, receive the signal only from mode w = 1, η = 4. Thus, the group of electrodes 1, 2, 5, 6, which are connected antiphase to the electrodes. 20

3, 4, 7, 8 to the input of the amplifier 13, allows you to get at its output a signal proportional to the oscillations of the resonator with a frequency of £ 42., Corresponding to the mode m = 1, η = 2. Analogy 25, electrodes 1, 3, 5, 7, which are connected antiphase to the electrodes 2, 4, 6, 8 to the input of the amplifier 14, produce at the output of this amplifier a signal proportional to the oscillations of a 30 э ₄ frequency and mode t = 1, η =

= 4 Due to the symmetrical and close mutual positioning of the electrodes and the resonator, as well as antiphase activation of the electrodes, an additional 35

external pickups at the outputs of amplifiers are compensated

Phase characteristics of amplifiers

13 and 14 in the operating frequency range is chosen so that the first frequency of 40 self-oscillations is equal to the natural frequency of the resonator with the mode

t = 1, η = 2, and the second frequency of self-oscillations - the frequency of natural oscillations of the resonator with mode w - 1, 45

η = 4. When an alternating current flowing along a resonator has these harmonic frequencies, these forces act on the resonator to support oscillations.

The output signals of the amplifiers 13 and

14 are simultaneously output signals of the sensor, and their frequencies have

different dependences of the measured / measured pressure and perturbation, which makes it possible to determine each of the indicated values in the subsequent processing of these signals and thereby increase the measurement accuracy.

Claims (1)

Claim Pressure sensor with frequency output, comprising a housing, a cylindrical resonator connected to a power transformer, permanent magnets forming the quadrupole field of the excitation system and electrodes of a capacitive vibration pickup system, characterized in that, in order to extend the functionality and improve measurement accuracy, into the excitation system introduced eight identical uniformly distributed around the circumference additional magnets of alternating polarity, four of which are combined with the poles of the quadrupole sy themes, and the removal system is made in the form of eight electrodes symmetrically located between the magnets, two opposite adjacent pairs of which are connected via resistance to one of the inputs of the first amplifier, and two second pairs of adjacent opposite electrodes are connected to another input of the First amplifier, and the electrodes located each other relative to each other through one, connected respectively to the inputs of the second amplifier, while the resonator is connected to the secondary winding of the transformer, the two primary windings of which are connected to the outputs of the mentioned amplifiers, and the electrodes are interconnected and connected through a resistor to a constant voltage source.