CN2653452Y - Quality flow meter - Google Patents

Abstract

The mass flowmeter belongs to the measurement device of flow rate and mass flow, and its purpose is to further reduce the influence of various error factors on the measurement and improve the accuracy of the instrument. The utility model is equipped with an electromagnetic exciter on the vibration sensing tube, and at least two vibration sensors are arranged, and each vibration sensor outputs to a preamplifier, and each preamplifier outputs to a phase detector, and one of the preamplifier outputs is fed back The unit is sent to the electromagnetic exciter; one of the preamplifiers is output to the period measurement circuit unit, and the output signal T _S of the latter and the output signal ΔT of the phase detector are sent to the divider, and the Δt/T _S signal output by the divider is passed through the instrument precision conversion unit The final output is Q _m =k·Δt/T _S , which can eliminate multiplicative errors, obtain higher-precision measurement results, and significantly improve the accuracy of existing Coriolis mass flowmeters.

Description

Mass flowmeter

Technical field

The utility model belongs to the measurement mechanism of flow, mass flow.

Background technology

In the existing coriolis mass flowmeters (being called for short Coriolis flowmeter down), it as application number 96102362.7 patent " kort-type mass flowmeter " with at least one measuring tube, method for processing signals is: the oscillating movement signal that detects vibrating sensing pipe symmetry both sides earlier, ask for the mistiming of the absolute small phase place of these two oscillating movement signals again, the phase time extent just is directly proportional with the size of mass rate in the pipeline, at last the phase time difference signal is carried out the measurement result that scale transformation can obtain mass rate.Figure 1 shows that the Coriolis flowmeter of typical U type tubular construction.Q _mBe mass rate to be measured, in the vibrating sensing pipe 102 mass centre positions that pipeline connects on the pedestal 103 electromagnetic exciter 105 is housed, vibrating sensing pipe 102 symmetrical both sides are provided with vibration transducer 101 and 104, to detect vibration signal S1 and S2 respectively, this two signal is inputed to processing such as carrying out amplification filtering in the Circuits System, the small phase time that obtains two signals at last is poor, this phase differential is directly proportional with the mass rate of fluid media (medium) in the pipeline, so try to achieve the detection that the phase time difference has just realized mass rate.

In this class Coriolis flowmeter, the basic structure of signal processing circuitry as shown in Figure 2.Wherein the 201, the 202nd, prime amplifier, its effect is that vibration signal is amplified and Filtering Processing; The 203rd, feedback unit, its effect is to introduce the vibrational excitation feedback and set, and to produce positive feedback actuation drive signals F, keeps the vibration of system stability.The 204th, phase detector, its effect is a phase differential of asking for two signals, the phase place extent has promptly reflected the size of mass rate in the pipeline.The way of realization of physical circuit device can have two kinds of analog and digital counting formulas.

The Coriolis flowmeter of other pattern in input and processing, all is to adopt the aforesaid method of asking for the absolute phase mistiming of two signals except that vibrating sensing cast formula difference.But theoretical in-depth analysis and actual conditions all show, in the Coriolis flowmeter, condition that only be directly proportional with the mass rate size can not be guaranteed the phase differential size utterly with the resonance frequency of vibration transducer is irrelevant, has many factors can cause the property the taken advantage of error of instrument measurement equation.Therefore, the method for asking for the input of two signal absolute phase mistimings and the processing overall accuracy that is difficult to the dependable flow meter reaches higher level.

Summary of the invention

The utility model provides a kind of mass flowmeter, its objective is the influence of the various error components of further minimizing to measuring, and improves accuracy of instrument.

A kind of mass flowmeter of the present utility model, in vibrating sensing pipe mass centre position electromagnetic exciter is housed, vibrating sensing tube hub symmetria bilateralis is provided with two vibration transducers on the position at least, vibration transducer output electric signal respectively connects prime amplifier, each prime amplifier output electric signal connects the phase detector input, wherein prime amplifier output electric signal connects feedback unit, and feedback unit produces positive feedback actuation drive signals F electric signal and connects the electromagnetic exciter input; It is characterized in that one of prime amplifier output electric signal connects the period measurement circuit unit, the latter's output signal TS and phase detector output signal Δ T send into divider unit, divider output Δ t/TS electric signal connects instrument scale transformation unit, finally exports Qm=k Δ t/TS; Wherein Qm is that tested mass rate, k are that instrument scaling ratio, Δ t are that the vibration signal phase time that picks up of vibration transducer is poor, TS is the vibration period of vibration signal.

The utility model is handled and conversion any one signal wherein, in the hope of the period T of vibration signal after obtaining vibration signal S1 and S2 _S, ask for the phase time difference Δ t of vibration signal S1 and S2, at last with this phase time difference Δ t and period T _SBe divided by.After doing this processing, can try to achieve another signal parameter, promptly the relative phase mistiming (is defined as S _D=Δ t/T _S), final, circuit arrangement is with kS _D(k is an instrument scale transformation constant) is used as the measurement output signal of actual mass flow size.

The error component that influences the Coriolis flowmeter precision is a lot, and wherein many factors are the property taken advantage of errors.Be described as follows with equation: if the instrument measurement equation is Q _m=C ₀Δ t (Q _mBe tested mass rate, C ₀Be the instrument scaling ratio, Δ t is the absolute phase mistiming of asking for), but the property taken advantage of error factor, mismachining tolerance as the vibration survey pipe, the inconsistency of two pipes, the large-scale variation of temperature, pressure and Media density etc. all can cause the instrument scaling ratio to depart from former design load C ₀And become C=C ₀+ Δ C, mass rate just becomes Q ' like this _m=(C ₀+ Δ C) Δ t has directly produced instrument measurement error delta Q _m=Q ' _m-Q _m=(C ₀+ Δ C) Δ t-C ₀Δ t=Δ C Δ t.And method for processing signals of the present invention is: try to achieve absolute phase mistiming signal X=(C ₀+ Δ C) Δ t afterwards, also tries to achieve periodic signal Y=(C simultaneously ₀+ Δ C) T _S, like this, above-mentioned two signals are made the signal Processing of division arithmetic, obtain relative phase mistiming signal S _D=X/Y=(C ₀+ Δ C) Δ t/ (C ₀+ Δ C) T _S=Δ tT _sAfter carry out scale transformation again, just can eliminate the property taken advantage of error, obtain the higher measurement result Q of precision _m=K Δ t/T _S(wherein K is final instrument scaling ratio).So advantage of the present invention is to improve accuracy of instrument significantly.

Description of drawings

Fig. 1 is the Coriolis mass flowmeter synoptic diagram of U type tubular construction;

Fig. 2 is existing Coriolis mass flowmeter signal processing circuit synoptic diagram;

Fig. 3 is a mass flowmeter signal processing circuit synoptic diagram of the present utility model.

Embodiment

Fig. 3 is a kind of basic form of implementation of the utility model signal processing circuit, wherein prime amplifier the 201, the 202nd, identical circuit, the second-order bandpass filter that is made of the high input impedance type operational amplifier realizes that the concrete model of operational amplifier can be selected OP07 type precision operational-amplifier for use.Feedback unit 203 is realized by two-stage amplifier, the first order is the proportional amplifier of Gain Adjustable, vibration signal is amplified to a desired value, the second level is that open loop amplifier band is recommended power-output amplifier, the first order, second level amplifier can be made up of a slice dual operational amplifier, as LM358 type operational amplifier, recommend power amplification then adopt in power recommend triode and form.

Phase detector 204, specifically can detect the zero crossing of two tunnel sinusoidal signals respectively by two zero-crossing comparators, form pulse signal, obtain the time pulsewidth of two signal phase differences then with logic gates, with stable high-frequency count pulse pulsewidth is counted and tried to achieve phase differential time size, zero-crossing comparator can be made of LM311 type comparer; Logic gates is that core constitutes with 74LS86 type XOR gate; Counter then can adopt the cascade of multi-disc 74LS93 counter to constitute, and total counting figure place is determined a desired value in conjunction with the frequency of count pulse and the processing word length of microprocessor.The 205th, the period measurement circuit unit, its effect is to ask for the vibration signal period T _s, the treatment circuit unit of available pulse pad count or other standard is realized.

205 is identical with 204 structure in fact, obtained the positive half cycle of vibration signal earlier by a zero-crossing comparator, asks for the time size of positive half cycle again with method of counting, can obtain the periodic quantity of vibration signal.The enforcement device of wherein concrete zero-crossing comparator and counter is with 204.The 206th, divider, its effect is to realize Δ t/T _SDivision function, the 207th, instrument scale transformation unit, its effect is that relative phase mistiming signal is carried out linearity or nonlinear operation, is finally reflected a standard output signals of mass rate size, and shows with the engineering unit of mass rate.

Constitute signal processing system because this flowmeter normally is core with the single chip microcomputer, so the computing of division and precision converting unit can be finished by the CPU software programming, and single chip microcomputer can adopt 51 or 96 type CPU.

Claims (1)

1. A mass flowmeter, an electromagnetic exciter is installed at the mass center of the vibration sensing tube, at least two vibration sensors are arranged at symmetrical positions on both sides of the vibration sensing tube center, and the vibration sensor outputs electrical signals to connect to the preamplifier respectively , the output electrical signals of each preamplifier are connected to the input of the phase detector, and one of the preamplifier output electrical signals is connected to the feedback unit, and the feedback unit generates the positive feedback excitation drive signal F and the electrical signal is connected to the input of the electromagnetic exciter; it is characterized in that the preamplifier One of the output electrical signals is connected to the period measurement circuit unit, the output signal T _s of the latter and the output signal ΔT of the phase detector are sent to the divider unit, and the Δt/T _s electrical signal output by the divider is connected to the instrument scale conversion unit, and finally outputs Q _m = k·Δt/T _s ; where Q _m is the mass flow rate to be measured, k is the instrument scale coefficient, Δt is the phase time difference of the vibration signal picked up by the vibration sensor, and T _s is the vibration period of the vibration signal.