RU2287135C1 - Device for transformation of signal of electromagnetic flow meter - Google Patents

Abstract

FIELD: engineering of devices for selecting and transforming signals of electromagnetic-type flow meter.

SUBSTANCE: device contains pre-amplifier, adder, gated amplifier, gated integrator, synchronous detector, two selection and storage components, voltage-frequency transformer, control signals generator, excitation generator, current-lifting resistor, excitation current compensation component, optical coupler key. Output of pre-amplifier is connected to non-inverting input of adder. Output of adder is connected to input of gated amplifier. output of gated amplifier is connected to input of synchronous detector and to input of gated integrator. Output of gated integrator is connected to inverting input of adder. Output of synchronous detector is connected to input of first selection and storage component. Output of first selection and storage component is connected to first input of voltage-frequency transformer. First output of control signals generator is connected to controlling inputs of synchronous detector and excitation generator. Second output of control signals generator is connected to controlling input of gated amplifier. Third output of control signals generator is connected to controlling input of gated integrator. Fourth output of control signals generator is connected to control inputs of both selection and storage components. First output of excitation generator is connected to first output of excitation current compensation component, to first output of smoothing capacitor and to input of dampening component. Second output of excitation generator is connected to first output of current-lifting resistor, to non-inverting input of excitation current compensation component and to input of second selection and storage component. Output of second selection and storage component is connected to non-inverting input of excitation current compensation component and to second input of voltage-frequency transformer. Output of dampening component is connected to first output of consumption current modulator. Second output of current-lifting resistor is connected to second output of excitation current compensation component, to second output of smoothing capacitor and to second output of consumption current modulator. Output of voltage-frequency transformer is connected to input of consumption current modulator, to input of frequency-current transformer and to input of optical coupler key. As inputs of device, three inputs of pre-amplifier and two inputs of excitation generator are used. As outputs of device, first and second outputs of consumption current modulator, first and second outputs of frequency-current transformer and first and second outputs of optical coupler key are used.

EFFECT: expanded functional capabilities of device.

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Description

The invention relates to devices for isolating and converting a signal of an electromagnetic type flow sensor.

A device is known [US patent No. 006853928 B1, MC ⁷ G 01 F 1/00, 2005], containing adjustable and unregulated voltage stabilizers, a controlled current source, a measured signal converter and an output signal shaper. This device allows you to connect the flow sensor to the secondary device in a two-wire circuit with an output signal of 4-20 mA.

However, due to low energy consumption and considering that a significant part of the supplied energy is lost on a controlled current source and output signal shaper, this device can only be used with flow converters for small diameter pipelines in the absence of external electromagnetic interference.

In addition, the absence of a pulse number or encoded (for example, according to the HART protocol principle) output signal makes it difficult to use it as part of a liquid meter for commercial accounting. An obstacle to organizing the transmission of information by modulating the consumption current in this device is the inrush of the current consumption at the moments of switching the magnetic field excitation coils, which are almost impossible to reduce to the required level by using a smoothing capacitor.

The closest technical solution to the prototype of the claimed object on the set of essential features is the device ["Flow sensor ERIS. In (L) T. Operation manual. 230.01.00.000 RE", Tyumen, OJSC IPF Sibnefteavtomatika, 2003, p.33] containing a preamplifier, two sampling-storage nodes, an isolation capacitor, an amplifier, a synchronous detector, a voltage-frequency converter, a driver of control signals, a driver of excitation, a current collector resistor, a smoothing capacitor, a frequency-current converter, and opt nny key. This device allows its use with energy-intensive flow converters for large-diameter pipelines and in conditions of significant electromagnetic interference. The presence of analog and pulse output signals determines the versatility of using this device. For example, to indicate the flow rate, in flow control systems, as part of a liquid meter for commercial metering, etc.

The disadvantage of this device is the inability to connect it in a two-wire circuit. This drawback is also explained by current surges along the power circuit at the moments of switching the magnetic field excitation coil and the need to use a large-capacity smoothing capacitor along the power circuit of the flow sensor.

In addition, this device has insufficient stability of the output signal with significant fluctuations in the electrochemical component of the signal induced on the electrodes of the flow transducer. Such fluctuation occurs, for example, when measuring contaminated or heterogeneous liquids. The instability of the output signal is explained by the fact that to exclude the electrochemical component of the signal, a differentiating RC chain with a large time constant is used.

The required technical result of the claimed device is an increase in consumer properties due to the possibility of connecting a flow sensor in a two-wire circuit without limiting the energy consumption of the flow transducer and increasing the stability of the output signal with significant fluctuations in the electrochemical EMF.

The prototype device contains the following essential features common with the features of the claimed object: a preamplifier, two sampling and storage nodes, a synchronous detector, a voltage-frequency converter, a driver of excitation signals, a driver of excitation, a current collector resistor, a smoothing capacitor, a frequency-current converter, and an optical key , and the essential distinguishing features of the claimed object include: an adder, a gated amplifier, a gated integrator, an excitation current compensation unit, damping node and the current consumption of the modulator, including appropriate communication therebetween.

It follows that the required technical result is ensured by the fact that the known device containing a preamplifier, two sampling and storage nodes, a synchronous detector, a voltage-frequency converter, a driver of excitation signals, a driver of excitation, a current collector resistor, a smoothing capacitor, a frequency-current converter and an optical switch is equipped with an adder, a gated amplifier, a gated integrator, an excitation current compensation unit, a damping unit and a consumption current modulator, with an input devices in general are three preamplifier inputs and two exciter driver inputs, the preamplifier output is connected to the non-inverting input of the adder, the adder output is connected to the input of the gated amplifier, the output of the gated amplifier is connected to the input of the synchronous detector and the input of the gated integrator, the output of the gated integrator is connected to the inverting integrator the adder, the output of the synchronous detector is connected to the input of the first sample-storage node, the output of the first sample-storage node is connected to the first input voltage-frequency converter, the first output of the control signal generator is connected to the control inputs of the synchronous detector and the excitation driver, the second output of the control signal generator is connected to the control input of the gated amplifier, the third output of the control signal generator is connected to the control input of the gated integrator, the fourth output of the control signal generator with control inputs of both sampling-storage nodes, the first output of the exciter former n with the first output of the excitation current compensation unit, with the first output of the smoothing capacitor and with the input of the damping unit, the second output of the excitation driver is connected to the first output of the collector resistor, with the inverting input of the excitation current compensation unit and with the input of the second sampling-storage unit, the output of the second node sample-storage is connected to a non-inverting input of the excitation current compensation unit and to the second input of the voltage-frequency converter, the output of the damping unit is connected to the first output of the modulator current consumption, the second terminal of the collector resistor is connected to the second output of the excitation current compensation unit, to the second terminal of the smoothing capacitor and to the second output of the current consumption modulator, the voltage-frequency converter output is connected to the input of the current consumption modulator, to the frequency-current converter input and to the input an optical key, wherein the outputs of the device as a whole are the first and second outputs of the consumption current modulator, the first and second outputs of the frequency-current converter and the first and second outputs ptronnogo key.

Note that from well-known sources of information (including patent), devices that are identical to the proposed and / or devices with a set of essential features (including distinctive ones) that are equivalent to the set of features of the proposed technical solution and exhibit the same new properties are not identified, allowing to achieve the required technical result during implementation. This allows us to argue that the proposed technical solution is new, non-obvious, has "significant" differences (etc.), that is, satisfies the "criteria" of the invention.

The graphic materials presented:

- figure 1 is a functional diagram of the inventive device;

- figure 2 timing diagrams of the main signals of the claimed device;

- figure 3 is a schematic diagram of the node compensation of the excitation current from figure 1;

- figure 4 is a schematic diagram of the damping node 14 of figure 1.

The device (see Fig. 1) consists of a preamplifier 1, an adder 2, a gated amplifier 3, a gated integrator 4, a synchronous detector 5, two nodes 6 and 7 of the sample-storage, a voltage-frequency converter 8, a driver 9 of the control signals, a driver 10 excitation, collector resistor 11, node 12 compensation of the excitation current, the smoothing capacitor 13, the damping node 14, the modulator 15 of the current consumption, the Converter 16 frequency-current and the optocoupler 17. The input of the device as a whole are three inputs of the preamplifier 1 and two input yes exciter 10, the output of the preamplifier 1 is connected to the non-inverting input of the adder 2, the output of the adder 2 is connected to the input of the gated amplifier 3, the output of the gated amplifier 3 is connected to the input of the synchronous detector 5 and to the input of the gated integrator 4, the output of the gated integrator 4 is connected to the inverting input adder 2, the output of the synchronous detector 5 is connected to the input of the sample-storage unit 6, the output of the sample-storage unit 6 is connected to the first input of the voltage-frequency converter 8, the first output is formed For 9 control signals, it is connected to the control inputs of the synchronous detector 5 and excitation driver 10, the second output of the control signal generator 9 is connected to the control input of the gated amplifier 3, the third output of the control signal generator 9 is connected to the control input of the gated integrator 4, and the fourth output of the control signal generator 9 connected to the control inputs of both nodes 6 and 7 of the sample-storage, the first output of the exciter 10 is connected to the first output of the node 12 compensation current excitation of waiting, with the first output of the smoothing capacitor 13 and with the input of the damping unit 14, the second output of the excitation driver 10 is connected to the first output of the collector resistor 11, with the inverting input of the excitation current compensation unit 12 and with the input of the sampling-storage unit 7, the output of the sampling unit 7 storage is connected to a non-inverting input of the excitation current compensation unit 12 and to the second input of the voltage-frequency converter 8, the output of the damping unit 14 is connected to the first output of the consumption current modulator 15, the second terminal of the current collector the resistor 11 is connected to the second output of the excitation current compensation unit 12, to the second output of the smoothing capacitor 13 and to the second output of the consumption current modulator 15, the output of the voltage-frequency converter 8 is connected to the input of the consumption current modulator 15, to the input of the frequency-current converter 16 and the input of the optocoupler key 17, while the outputs of the device as a whole are the first and second outputs of the modulator 15 current consumption, the first and second outputs of the Converter 16 frequency-current and the first and second outputs of the optocoupler 17. their materials 1 (to explain the principle of operation of the apparatus) by additional reference numerals 18 ... 40 denote portions corresponding number of electric circuits.

The device operates as follows.

When describing the operation of the device, the following conventions are adopted:

U _xx is the voltage value in the section of the circuit xx;

I _xx is the current value in the section of the circuit xx;

F _xx - the value of the signal frequency in the section of the circuit xx;

T _xx - the value of the signal period in the section of the circuit xx,

where xx is the number of the circuit in Fig.1.

Shaper 9 control signals generates the following logic signals:

- U ₁₈ (see figure 2), which is a meander with a period T ₁₈ switching the direction of induction of the magnetic field of the flow transducer (see figure 1 on the left, a separate position is not indicated);

- U ₁₉ , the active first quarter (t ₀ ) of each half-period T ₁₈ to control the gain of the gated amplifier 3;

- U ₂₀ , the active last quarter (t ₃ ) of each half-period T ₁₈ for controlling the gated integrator 4;

- U ₂₁ , the active third quarter (t ₂ ) of each half-period T ₁₈ for controlling the nodes 6 and 7 of the sample-storage.

The excitation driver 10, made according to the well-known bridge circuit (for example, the L6201 chip manufactured by SGS-THOMSON Microelectronics), switches the direction of the current I ₂₂ in the excitation coil and, accordingly, the direction of the magnetic field induction in the flow transducer by the signal U ₁₈ .

The EMF arising on the electrodes of the flow transducer relative to the housing is supplied to the preamplifier 1, made in the form of a tool amplifier, where it is pre-amplified (signal U ₂₃ ).

The signal U ₂₃ through the adder 2 is fed to the gated amplifier 3, which in the period of time t ₀ (signal U ₁₉ ) has a gain equal to zero. Thus, the effect of impulse noise induced on the electrodes of the flow transducer at the time of switching the excitation current to the conversion accuracy is eliminated.

Gated integrator 4 in the period of time t ₃ (signal U ₂₀ ) sets the zero signal level U ₂₄ at the output of gated amplifier 3. The rest of the time it is in storage mode. This eliminates the effect of interference caused by fluctuations in the electrochemical EMF on the electrodes of the flow transducer on the stability of the output signal of the flow sensor.

The synchronous detector 5 by the signal U ₁₈ converts the bipolar signal U ₂₄ into a unipolar signal U ₂₅ .

The node 6 sample-storage in steady state (time period t ₂ ) by the signal U ₂₁ samples the signal U ₂₅ and stores this level the rest of the time. Thus, the signal level U ₂₆ at the output of the sampling-storage unit 6 is determined only by the EMF induced on the electrodes of the flow transducer when the electrically conductive fluid moves in a magnetic field, and is proportional to the speed of the measured medium.

On the collector resistor 11, the signal U ₂₇ is proportional to the current absolute value of the current I ₂₂ in the excitation coil.

The node 7 of the sample-storage signal U ₂₁ selects the amplitude value of the signal U ₂₇ in steady state (time period t ₂ ) and holds this value (signal U ₂₈ ) until the next sampling time. Those. the signal level U _{28 is} proportional to the excitation current and, accordingly, the value of the magnetic induction during sampling.

The signals U ₂₆ and U ₂₈ are fed to the voltage-frequency converter 8, made according to the double integration scheme and performing the function

F ₂₉ = K × U ₂₆ / U ₂₈

Where:

F ₂₉ - the frequency of the signal U ₂₉ ;

K is the proportionality coefficient determined during calibration of the flow sensor.

The use of such a conversion function eliminates the influence of instability of the magnetic field induction on the signal frequency U ₂₉ due to temperature changes in the parameters of the excitation coil. Thus, the frequency of the signal U _{29 is} proportional to the flow rate of the measured medium and does not depend on external factors (for example, temperature change, electromagnetic interference, etc.).

The consumption current modulator 15 generates packs of current pulses along circuit 30 (I ₃₀ ) with a carrier frequency F _carried and a modulation frequency F ₂₉ , wherein

F _carried ≫F _29max ,

Where:

F _29max - the frequency of the signal U ₂₉ at the maximum flow rate of the measured medium.

The main points that prevent the transfer of current pulses from circuit 30 to power circuit 31 are:

- inrush current consumption I ₃₁ at the moments of switching the excitation coil of the flow transducer;

- the presence of a smoothing capacitor of large capacity along the power circuit of the flow sensor.

The solution to this problem, which is absent in the known similar devices, is as follows.

The signals U ₂₇ and U ₂₈ are supplied to the node 12 compensation of the excitation current, made, for example, according to the circuit shown in figure 3.

The parameters of the node 12 compensation of the excitation current are selected so that the condition:

I ₃₂ = (U ₂₈ -U ₂₇ ) / R ₁₁ + I _cm ,

Where:

I ₃₂ - current consumption of the node 12 compensation of the excitation current;

R ₁₁ - the value of the collector resistor 11;

U ₂₈ - the current signal level 28;

U ₂₇ - the current signal level 27;

I _cm - the minimum current consumption required for the linear operation of the node 12 compensation of the excitation current, and really is 1 ... 3% of the total current consumption of the device.

Given that the current value of current I ₂₂ in the excitation coil is determined by the formula:

I ₂₂ = U ₂₇ / R ₁₁ ,

the total current I _{33 of the} device’s consumption through the power circuit, given the negligible power consumption of the remaining parts of the device, can be determined by the following formula

I ₃₃ = I ₂₂ + I ₃₂ = U ₂₇ / R ₁₁ + (U ₂₈ -U ₂₇ ) / R ₁₁ + I _cm = U ₂₈ / R ₁₁ + I _see

Thus, the current consumption of the device through the circuit 33 remains stable at any time, regardless of the parameters (or changes in these parameters) of the excitation coil of the flow transducer and does not distort the shape of the current pulses generated by the consumption current modulator 15.

The smoothing capacitor 13 filters the short "surges" of the current I ₃₃ associated with the limited speed of the node 12 compensation of the excitation current.

The damping unit 14 limits the rate of rise-fall of the current I ₃₄ during the charge-discharge of the smoothing capacitor 13 and can be performed, for example, according to the scheme shown in figure 4. The time constant τ _{14 of the} damping unit 14 (see figure 4) is selected from the condition

τ ₁₄ = R ₅ × C ₁ ≫1 / F _carried ,

Where:

R ₅ , C ₁ - denominations of the corresponding elements.

Thus, the current pulses I ₃₀ created by the consumption current modulator 15 and carrying information about the current flow rate of the medium being measured are not shunted by the smoothing capacitor 13 on the circuit 35-34, which makes it possible to isolate and process them with a secondary device on the circuit 31-36 when connected to flow sensor in a two-wire circuit.

The frequency-current converter 16 generates in a circuit 37-38 a galvanically isolated standard 4-20 mA output current signal corresponding to the flow rate of the medium to be measured and intended for use in control and indication systems of the current flow rate.

The optocoupler switch 17 is intended for matching the pulse output signal of the flow sensor in circuit 39-40 with various types of counting-indicating secondary devices when connected to the flow sensor in a four-wire circuit.

Thus, the set of essential features (including distinguishing ones) of the proposed device ensures the achievement of the required technical result, meets the criteria of "invention" and is subject to protection by a title of protection (patent) of the Russian Federation in accordance with the request of the applicant.

Claims (1)

A signal converting device for an electromagnetic flowmeter containing a preamplifier, two sampling and storage units, a synchronous detector, a voltage-frequency converter, a driver of control signals, a driver of excitation, a current collector resistor, a smoothing capacitor, a frequency-current converter and an optical key, characterized in that it is equipped an adder, a gated amplifier, a gated integrator, an excitation current compensation unit, a damping unit and a consumption current modulator, while the input three in general are three inputs of the preamplifier and two inputs of the excitation driver, the output of the preamplifier is connected to the non-inverting input of the adder, the output of the adder is connected to the input of the gated amplifier, the output of the gated amplifier is connected to the input of the synchronous detector and the input of the gated integrator, the output of the gated integrator is connected to the inverter the adder, the output of the synchronous detector is connected to the input of the first sample-storage node, the output of the first sample-storage node is connected to the first input voltage-frequency generator, the first output of the control signal generator is connected to the control inputs of the synchronous detector and the excitation driver, the second output of the control signal generator is connected to the control input of the gated amplifier, the third output of the control signal generator is connected to the control input of the gated integrator, the fourth output of the control signal generator with control inputs of both sampling-storage nodes, the first output of the exciter is connected to the first output of the excitation current compensation unit, with the first output of the smoothing capacitor and with the input of the damping unit, the second output of the excitation driver is connected to the first output of the collector resistor, with the inverting input of the excitation current compensation unit and with the input of the second sampling-storage unit, the output of the second sampling unit is storage is connected to a non-inverting input of the excitation current compensation unit and to the second input of the voltage-frequency converter, the output of the damping unit is connected to the first output of the modulator consumption, the second terminal of the collector resistor is connected to the second output of the excitation current compensation unit, to the second terminal of the smoothing capacitor and to the second output of the consumption current modulator, the voltage-frequency converter output is connected to the input of the current consumption modulator, to the frequency-current converter input and to the input an optical key, while the outputs of the device as a whole are the first and second outputs of the consumption current modulator, the first and second outputs of the frequency-current converter and the first and second outputs of the opt the key.

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