Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F15/00—Details of, or accessories for, apparatus of groups G01F1/00 - G01F13/00 insofar as such details or appliances are not adapted to particular types of such apparatus
  • G01F15/07—Integration to give total flow, e.g. using mechanically-operated integrating mechanism
  • G01F15/075—Integration to give total flow, e.g. using mechanically-operated integrating mechanism using electrically-operated integrating means
  • G01F15/0755—Integration to give total flow, e.g. using mechanically-operated integrating mechanism using electrically-operated integrating means involving digital counting
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F15/00—Details of, or accessories for, apparatus of groups G01F1/00 - G01F13/00 insofar as such details or appliances are not adapted to particular types of such apparatus
  • G01F15/02—Compensating or correcting for variations in pressure, density or temperature
  • G01F15/022—Compensating or correcting for variations in pressure, density or temperature using electrical means
  • G01F15/024—Compensating or correcting for variations in pressure, density or temperature using electrical means involving digital counting

Definitions

• the invention relates to an arrangement for flow measurement according to the preamble of the main claim.
• Mass flow measuring arrangements which work with a tube through which the fluid to be measured flows and which is set to resonance frequency, the mass flowing through being calculated from phase shifts within this tube.
• the measurement inaccuracies of these arrangements are undesirably large if the measuring tube is flowed through by a heterogeneous two-phase mixture, if the measuring arrangement is installed in a line through which various liquids are pumped, and if between these liquids the line is flushed with a gas If, at the beginning and at the end of each liquid dosage, heterogeneous areas occur in which this liquid is mixed with a part of the purge gas.
• the object of the invention is to minimize the measurement inaccuracies during the time in which a heterogeneous two-phase mixture flows through the measuring tube.
• the measurement error should be reduced during the time in which there is a recognizable faulty measurement by the mass flow meter by evaluating an artificially generated signal instead of the faulty measurement signal.
• FIG. 1 is a schematic diagram of a system in which the arrangement for mass flow measurement is used
• FIG. 3 shows the measurement signal from FIG. 2 at the end of metering
• Fig. 5 shows a comparison of the signal output by the measuring device with the signal received by the counter during the start time of a dosage
• Fig. 6 shows a comparison as in Fig. 5, but at the end of the same dosage.
• B denotes a container to which various raw materials R1, R2, R3 can be supplied via a line L. Between the feeds for the raw materials and the container B. an arrangement for mass flow measurement M is provided. In addition to the raw materials R, purge gas G can also be supplied to the container B via the line L. This rinsing takes place after each metering in which a certain raw material R is pumped into the container B. The scope of each dosage or purging is determined by opening and closing valves V1, V2, V3 for the raw materials and Vg for the purging gas.
• the measuring device Mg within the arrangement for mass flow measurement M has an output signal in the form of pulses, the frequency of which changes with the mass flow through the measuring device. The frequency increases with the mass.
• the mass flow rate cannot be as great as later, since at the beginning the pipe and the measuring tube are not yet completely flowed through by the raw material R, but there is also purge gas in these pipes.
• Some of the high-frequency measurement signals give at the start of dosing. Conveying performance again that the pump used can not bring up.
• Fig. 3 makes it clear that a similar phenomenon can be observed when the metering is ended.
• the measurement signal simulates a mass that is substantially greater than the mass actually flowing through.
• Mg is the measuring device within the arrangement for mass flow measurement, which gives a measuring signal to the counter Z. Since this measurement signal - as can be seen from FIGS. 2 and 3 - consists of pulses, the measuring device output is followed by a frequency comparator K which enables a signal path of the measuring pulses to the counter Z if the frequency of these measuring pulses is within the tolerance range.
• the tolerance range can be specified, for example, by only evaluating frequencies which correspond to a delivery rate up to the maximum delivery rate of the connected pump.
• a signal synthetically generated by an oscillator 0 is fed to the counter Z.
• the oscillator shown in FIG. 4 has the possibility of generating three different frequencies.
• the oscillator switches a switch S in such a way that its output signal corresponds to the target delivery quantity of the currently connected pump.
• a frequency of 90 Hz at the output of the measuring device Mg corresponds to the maximum delivery capacity of the pump.
• the frequency comparator K does not emit an output signal in the event that the frequency of the measuring device output does not exceed 100 Hz.
• the switching point of 100 Hz is adjustable and can be at other frequencies for other measuring devices.
• the logic gate "UND1" now has the measuring device signal on the one hand and the negated output signal of the frequency comparator on the other hand, so that both inputs of this "UND1" gate receive a signal.
• the output signal of this "AND1" gate is also 1. It is fed to the logic "OR” gate and from there to the counter Z.
• the oscillator 0 simultaneously produces a synthetic signal, the frequency of which corresponds to the frequency of the measuring device output at the desired delivery rate of the connected pump.
• This signal generated by the oscillator is fed to the logic gate "UND2" as the first input, which is therefore equal to 1.
• An output signal from frequency comparator K is equal to 0 as a second input at logic gate "UND2". This is the output of this logic gate also at 0 and no signal is supplied to counter Z from here.
• the logic gate "UND1" is the first input of this measuring device signal, so that this input is logically equal to 1.
• the frequency comparator K also produces an output signal which is logically equal to 1. However, since this is negated before the second input of the "UND1" gate, 0 is present there. There is therefore no signal from this logic gate via the "OR” gate to the counter Z. Instead, the output signal of the frequency comparator K is present at the logic gate “UND2” at an input which is therefore logically equal to 1 and the synthesized is at the other input of this logic gate Signal of the oscillator 0, so that this second input is logically equal to 1. A signal is thus passed from this logic gate “UND2” to the “OR” gate and through this to the counter Z.
• Fig. 5 shows on the one hand the actual measurement signal that is passed on from the measuring device Mg to the comparator and on the other hand the signal that is behind the
• Correction circuit arises and the counter Z supplied leads.
• 5 shows the start of metering, ie the point in time after a raw material R has been pumped through line L to the arrangement for flow measurement M and is present there in the measuring tube together with the remaining purge gas G as a heterogeneous mixture. 5 that the measuring device first emits an output signal for this switch-on process, the frequency of which is several times higher than the normal frequency corresponding to the nominal delivery rate of the pump.
• the "measurement signal" synthetically generated by the oscillator is fed to the counter for this period of the unbelievably high measured values and only when the output signal of the measuring device reaches realistic values is this information supplied to the counter.
• a measurement error during the start of dosing, despite the correction circuit, may be that the mass flow rate given by the oscillator in the meter tube does not correspond to the mass actually flowing through, since the meter tube also has residues of the flushing gas G.
• the error between this actual filling of the measuring tube and the TARGET filling of the measuring tube assumed by the oscillator is significantly less than the difference between the one indicated by the measuring device Mg, e.g. T. often excessive delivery rate and the actual. It is clear from FIG. 1 why the correction circuit for the mass flow measurement essentially only has to come into force at the start phase of a metering, whereas it is not necessarily required at the end phase of this metering.
• valves V1, V2 or V3 are closed at a point in time at which the arrangement for mass flow measurement M does not yet indicate the value of raw materials R1, R2 or R3 that is to get into the container B.
• This supposedly premature closing of the valves V1 to V3 does not mean the end of the metering of the respective raw material, since the amount of raw material still gets into the container B, which is between the .Valve V and the measuring arrangement M in the line L and has not yet been measured.
• the valve VG is opened and the line L is subsequently flushed with the flushing gas G, the remainder of the line L is pressed into the container B by the measuring arrangement M and during this time a heterogeneous two occurs again in the measuring device.
• the mass which is located between the measuring arrangement M and the individual valves V1 to V3 in the line L, is a fixed quantity for each of the individual raw materials R1 to R3 and therefore no longer needs to be detected by the measuring arrangement M. Therefore, the second phase, in which the measuring device Mg supplies inaccurate values, falls within a time range in which no measurement of the flow mass is necessary. The entire measuring arrangement is therefore not required during the end of dosing.

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• Physics & Mathematics (AREA)
• Fluid Mechanics (AREA)
• General Physics & Mathematics (AREA)
• Measuring Volume Flow (AREA)
• Details Of Flowmeters (AREA)

Applications Claiming Priority (2)

Publications (1)

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• 1987
  • 1987-03-31 DE DE19873710682 patent/DE3710682A1/de active Granted
• 1988
  • 1988-03-25 EP EP19880104877 patent/EP0285932B1/de not_active Expired - Lifetime
  • 1988-03-25 DE DE8888104877T patent/DE3865486D1/de not_active Expired - Lifetime
  • 1988-03-25 EP EP88902843A patent/EP0356440A1/de active Pending
  • 1988-03-25 ES ES198888104877T patent/ES2026592T3/es not_active Expired - Lifetime
  • 1988-03-25 US US07/423,432 patent/US5224387A/en not_active Expired - Fee Related
  • 1988-03-25 AT AT88104877T patent/ATE68594T1/de not_active IP Right Cessation
  • 1988-03-25 WO PCT/EP1988/000252 patent/WO1988007662A1/de not_active Application Discontinuation
  • 1988-03-30 CA CA000562872A patent/CA1329270C/en not_active Expired - Fee Related

Non-Patent Citations (1)

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