RU2572461C2 - Medium flow rate meter - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: flow rate meter comprises the following components connected in series with an input channel: a summator, a discharge flow meter and a flow divider, a reverse flow rate meter connected to it, a device of flow rate components and a flow rate indicator, according to the invention, upstream the summator for the reverse flow there is a pump connected with the "pressure-flow" characteristic, operation of which is switched off by a signal from the device for comparison of flow rates of discharge and reverse flows.

EFFECT: expanded range of flow measurement, its separation into two parts, with reduction of measurement level in the first part of the range, not reducing the upper value of the second part of the range, reduced error of the measurement circuit of the first part of the range, considering changes in values of discharge and reverse flows as information signals between links of the measurement system, as a meter built on the opposite connection of links with negative feedback, possibility to produce different functional connection between values of discharge and reverse medium flows.

2 cl, 2 dwg

Description

The invention relates to the field of measuring equipment and can be used in systems for measuring gaseous and fluid media, as well as in commercial calculations.

Known devices for measuring the flow rate of the medium, in which the medium is supplied from the highway through a pump, flowmeter and workload (Kremlevsky P.P. Flow meters and quantity counters. Reference book // L., Engineering, 1989, 702 S.). A disadvantage of the known devices is the location of the measuring device in a series of flow rate consumption devices, which does not provide sufficient accuracy of the flow measurement.

A known device for measuring a jet flow meter (RU 1295230, A1, 03/07/1987) with an insufficient sensitivity zone, which limits the working area and the measuring range. A disadvantage of the known device is the existence of conflicting requirements and the impossibility of overcoming them when implementing only one physics of the flow of the medium when using one jet generator. These requirements are reduced to two parameters: the minimum measured flow rate and the maximum allowable pressure drop across the flowmeter at the maximum point in the range.

A known device for measuring fluid flow (RU 2157967, C2, 05.21.1998), adopted as a prototype. A part of the medium flow after the main flow meter is returned through the auxiliary flow meter and the restrictive throttle to the line in front of the pump and the flow rate for the working load is determined as the difference between the flow rates through the main and auxiliary flow meters. This technique allows you to shift the measuring area of the main flow meter to the required reduced range.

The disadvantages of the known device is the requirement that a measuring device has a pressure device (pump) installed in the trunk, because without it, the complex is inoperative.

In addition, the pump must comply with the main flow rate, which is associated with the fulfillment of other design requirements: increased dimensions, weight, resource, price, etc.

In addition, there must be a functional relationship between the direct feed line and the main flow meter and its load, which requires that their parameters be coordinated with each other. Otherwise, the operation of the complex is impossible if the load absorbs the main flow without residue. In addition, the second measuring device (auxiliary flowmeter) must have a measurement error that is obviously less, which burdens the complex with additional measurement technology of a different range with a forced calibration, price, dimensions, weight, etc.

In addition, the main and auxiliary flowmeters continuously operate in the full range, which reduces the resource of the measuring part of the complex, located in the return line of the part of the stream, which, however, is intended only to expand the boundary in the lower part of the range, and when measured in the accepted (without lowering) range does not make sense to function.

In addition, the measurement range is shifted in the presence of a return flow line, which lowers the sensitivity threshold and together with it reduces the upper measurement limit (practically the reverse flow is dumped as part of the flow rate into the tank), which significantly narrows the measurement range and suggests underutilization of the resulting reserve along the upper boundary of the main flow meter.

In addition, the flows of the main pipeline and the reverse are interdependent. There is no such state when one stream is constant in magnitude and the other stream changes and can be independent.

In addition, when analyzing the well-known complex as a measuring device, it was shown that the links of the measuring circuit (two flowmeters) are connected in a counter-parallel connection with positive feedback, i.e. with an increase in flow in the main pipeline, the return flow through the auxiliary flow meter simultaneously increases. Such a compound in the complex significantly increases the measurement error not only in the zone of lowering the range to the threshold of sensitivity, but also after, because in this case, the errors of the links are summed up. (Braslavsky D.A. Instruments and sensors of aircraft. M., Mechanical Engineering, 1970, p.108).

In addition, in the known measurement complex, the characteristic of the link located in the feedback is not inverse, which does not allow us to consider the system as a counter-parallel connection with negative feedback, which reduces the overall measurement error of the entire measurement complex.

The technical result is the expansion of the range of flow measurement, its separation into two parts with a decrease in the measurement level in the first part of the range, without lowering the upper value of the second part of the range, reducing the error of the measuring circuit of the first part of the range, considering the changes in the pressure and return flows as information signals between the links measuring system, like a meter built on the opposite parallel connection of links with negative feedback, the possibility of obtaining different functional relationship between the pressure and return flows.

The technical result is achieved by the fact that in the proposed flow meter, which contains an adder connected in series with the input channel, a pressure flow meter and a flow divider, a return flow meter connected to it, a flow comparison device and a flow indicator, according to the invention, a pump is connected to the return adder with an inverse characteristic, the operation of which is turned off by the signal of the device for comparing the costs of pressure and return flows.

In addition, a flow meter measuring the medium, in which a check valve is additionally installed in the channel between the pump and the adder.

Figure 1 shows the structural diagram of the flow meter with a reduced initial level of measurement (threshold), figure 2 is a characteristic of the meter in the coordinates of "QP", figure 3 is a sequence diagram of work with an arbitrary flow rate Q of the medium at the input through channel 1 into the meter.

The meter comprises a combiner 2 (hydraulic supply tee) connected in series with the input channel 1, a channel 3 with a pressure flow meter 4 and a flow divider 5 (hydraulic exhaust tee), a return flow meter 9 connected thereto, a device 11 for comparing the readings of the pressure flow meters 4 and 9 reverse flow, flow indicator 12, as well as for the functioning of the reverse flow 7, a pump 8 is connected (for example, a PN pump) with an inverse characteristic “Q-P”, the location of which together with the flowmeter 9 is reverse of the flow in the feedback creates an OOS (negative feedback) on the flow rate, which is turned off by the signal of the device 11 comparing the flow rates 4 of the pressure and return 9 flows.

The return flow 7, measured by its flowmeter 9, is formed under the influence of a pump (for example, a micropump) 8, forming a forced circulation 7 of the return flow through the flowmeter 4. The pump is controlled through the power supply 10 by the signal comparison device 11.

The pressure stream 1 of the medium passes through the adder 2 streams, forming a total stream 3 by attaching a return stream 7, which is separated from the total stream 3 in the separator 5, in the device 11, the value of the return stream 7 is subtracted from the total stream 3 and the signal of the actual pressure flow rate is fixed flow 1 on indicator 12. It is assumed that after the subtraction procedure, that flow 6 that has passed through the load is considered equal to the pressure flow 1 and is measured with some error ζ. When changing the magnitude of the pressure flow 1 changes, for example, proportionally, with the opposite sign (inverse), the magnitude of the reverse flow 7.

The entire measurement range (Fig. 2) is divided into two parts: in the first, the return flow 7 works, in the second the return flow does not work, in the first part of the range, the return flow 7 is forcibly directed to the pressure flow 1, the value of the return flow 7 is changed:

- increase it with decreasing pressure flow 1 to a consistent (selected lower) value of the first part of the range, or

- reduce its value to zero as the pressure stream 1 increases to a consistent (selected upper) value of the first part of the range.

In the first part of the range, the return flow 7 is subtracted from the total flow 3, fixing the value on the indicator 12, in the second remaining part of the measuring range, when the return flow 7 is zero, the pressure flow 1 is measured by a flowmeter 4, the signal of which directly passes through the device 11 to the indicator 12, fixing the flow rate of the pressure stream 1 in the second range.

In the circuit of FIG. 1, the feedback link 14 serves as a feedback flow meter 9 and a pump 8, which has an inverse “flow-pressure” characteristic with respect to a change in the flow rate (potential) of the pressure flow, the direct chain link 13 is a flow meter 4, a flow splitter 5 .

Links 13 and 14 are included in a counter-parallel circuit to reduce the relative error ζ, measuring the circuit, which is calculated by the well-known formula (D. Braslavsky. Instruments and sensors of aircraft. M., Mechanical Engineering, 1970, p. 108):

ζ = ψ ₁ ζ ₁ + ψ ₂ ζ ₂ ,

where ψ ₁ = 1 / (1 + S ₁ S ₂ ) is the influence coefficient of link 1 and ζ ₁ is its relative error,

ψ ₂ = -S ₁ S ₂ / (1 + S ₁ S ₂ ) is the influence coefficient of link 2 and ζ ₂ is its relative error,

here S ₁ - the steepness of the characteristic "pressure-flow rate" of the direct chain link,

S ₂ is the slope of the pressure-flow characteristic of the feedback link.

Since ψ ₂ with such a scheme of switching on the links is always with a minus sign, the overall relative error of the measurement circuit in the first part of the measurement range is reduced in comparison with the relative error of the general circuit.

The expansion of the flow measurement range is achieved by dividing it into two parts with a decrease in the measurement level in the first part of the range. The value of the return flow 7 of the feedback link 14 allows to increase the sensitivity of the flowmeter 4 to the agreed lower measurement boundary, adding a part of the flow rate that is not enough to start the reliable operation of the flowmeter 4. In the known device, the return flow returns to the highway (tank, tank), in which the information the field is close to zero in magnitude of the pressure signal since the pump located after the point of summing the flows determines the potential value before the load, and a vacuum (suction of the flow) is created in front of the adder 2 and the potential is close to zero. In the proposed meter, the return flow returns to the information line with a pressure of a value other than zero. In this case, to implement a counter-parallel circuit with negative feedback, an inverse pressure-flow characteristic of the feedback link is required. Those. with increasing potential (pressure) and flow rate of the measured flow Q at the summation point, the flow rate of the reverse flow 7 decreases according to the characteristic “Q-P” of the feedback link regardless of the control signal for its decrease. The control signal from the comparison device 11 coincides in sign with the sign of decreasing the flow rate of the pump 8 according to the “Q-P” characteristic and is necessary to stabilize the flow rate through channel 3 and maintain it at a constant level, to preserve the environmental protection and reduce the error of the flow measurement circuit in the first part of the range.

Work (figure 3, see line "Q ₂ ", column 1) of the return flow 7 begins with a conditional zero, for example Q ₂ = 20 l / h, the working point of the interval between the point of reliable operation of the flow meter 4 (for example, Q ₁ = 40 l / h) and a reduced agreed measurement limit (e.g. Q = 20 l / h).

If there is insufficient total flow rate through channel 3, for example, Q <20 l / h (line “input Q”, column 1) and Q ₁ = Q + Q ₂ <40 l / h passing through flowmeter 4, indicator 12 does not show the measurement process (line “Q indicator”, column 1). Those. flow rate Q <20 l / h is not measured at all.

With sufficient Q ₁ = Q + Q ₂ ≥40 l / h, the total flow rate through channel 3 passing through the flowmeter 4, indicator 12 shows the measurement process Q = Q ₁ -Q ₂ ≥20 l / h. The value 10 is initially set in the device 10 — a “conditional” zero Q ₂₀ = 20 l / h is set for comparison with the incoming flow increment from the flow meter 4. In the same device 10, the increment δQ = Q ₂ -Q ₂₀ ≥0 is fixed, which is a signal to a change in the performance of the pump 8, and the value of Q _{2 of the} return flow 7 decreases by the amount of excess over the value of 40 l / h, maintaining the value of 40 l / h constant (line “Q ₁ ”, column 2), and so on, the value of Q _{2 is the} return flow 7 with increasing pressure flow 1 (line "input Q", column 2) decreases by command Comparison system 11 by the power unit 10 of the pump 8 of the return flow 7.

If the flow rate is Q> 40 l / h or more (line “input Q”, column 3 or 7.8), then the PN pump is turned off, the flow rate Q ₂ is zero (see line “Q ₂ ”, column 3), and only flowmeter 4 works, measuring Q ₁ = Q in the second part of the measuring range (line “indicator Q”, column 3, 7, 8).

Figure 2 shows that the flow rate Q _{1 is} maintained (horizontal line) along the channel 3 constant and equal, for example, 40 l / h This maintenance of the flow rate Q ₁ = const at the selected level is necessary for the coordinated operation of the reverse flow pump 8 with an inverse characteristic (flow rate reduction) to increase the pressure drop in the inlet pipe 1 at the summation point 2.

In another embodiment, the connection between the flow rate of Q ₁ and Q ₂ can be assumed that Q ₁ = var≤60 l / h and Q ₂ = const = 20 l / h, when Q ₁ = 60 l / h is reached, feedback link 14 shuts down from work. With this type of operation, reminiscent of the operation of the prototype circuit, in which the pump operates continuously, there are two drawbacks.

The first drawback is that, according to its technical data, pump 8 should be able to overcome the level of potential in channel 1 while increasing the flow rate, for example, to 60 l / h, because with an increase in flow rate Q at inlet 1, the pressure drop at the summation point increases. In the proposed meter, the PN pump in the circuit is located upstream of the adder 2 in the return flow 7, and not after, and only the reverse flow 7 is pumped.

The second - the most important drawback - in such a summation scheme (like the well-known) of the pressure and return flows, POS (positive feedback) occurs instead of the OOS, which increases the measurement error in the range from a reduced threshold (20 l / h) to the start of reliable operation of the flow meter (40 l / h).

The fundamental difference between the schemes for lowering the threshold level of sensitivity in the proposed method and in the prototype in terms of determining the measurement error consists in changing the essence of the feedback - the PIC is replaced by the OOS.

The proposed method provides the opportunity to obtain various functional relationships between the pressure and return flows of the medium. For example, to reduce the time constant of the links of the direct chain, the pump 8 is turned on proactively.

When in the process of increasing the pressure flow 1 the reliable operation point of the flow meter 4 is reached, then by this moment the return flow 7 is close to zero (Fig. 2) and a further increase in the pressure flow 1 brings it to complete disappearance. The link 14 is switched off from the measurement operation of the pressure stream 1 and a transition is made to the second part of the measuring range, in which the flow Q of the pressure stream 1 is measured only by the flow meter 4. The measuring range of the second part remains the same, which does not decrease when the first part of the range is included in the operation. The overall measurement range has been expanded and lowered the lower level of measurement of the flowmeter 4, which was previously inaccessible before turning on the reverse flow 7, without lowering the upper value of the second part of the range. The bore is closed for circulation of the flow 7 when the pump is idle and the idle pump 8 does not let flow 7 through itself.

With the open passage section of the idle pump 8, its channel can be used as a bypass with recalculation of the transmittance of the flow through the entire circuit, increasing the overall throughput of the measuring circuit and expanding the overall measuring range. In this case, part of the pressure flow passes through the bore of the pump 8 (Fig.2, the upper curve of the characteristic "P-Q"). In the case of using the bypass channel, the expansion of the second part of the measuring range is achieved by increasing the maximum flow rate.

For small bypass cross-sections, when measured in the second part of the range, this flow can be neglected.

Claims (2)

1. A flow meter of a medium flow comprising an adder connected in series with the input channel, a pressure flow meter and a flow divider, a return flow meter connected thereto, a flow comparison device and a flow indicator, characterized in that a pump with the characteristic “ pressure-flow "associated with the device for comparing costs and connected by its signal. 2. The flow meter of the medium according to claim 1, in which a check valve is additionally installed in the channel between the pump and the adder.

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