JP2008292287A - Flowmeter - Google Patents

Abstract

A flow meter having a simple configuration capable of accurately measuring the direction and flow rate of a fluid supplied through a pipe.
A thermal flow sensor that measures an instantaneous flow rate according to a flow direction of a fluid, a flow rate accumulation buffer that accumulates an instantaneous flow rate measured by the flow rate sensor and measures the accumulated time, and a flow rate accumulation The presence / absence of pulsation of the fluid is determined from the integrated flow rate and integration time accumulated in the buffer, and the flow rate accumulation buffer is reset when the pulsation is detected, and the fluid is not pulsating by this determination unit. When the flow rate is detected, a positive flow integration counter and a reverse flow integration counter are provided which individually integrate the integrated flow rates integrated by the flow rate integration buffer in accordance with the direction of fluid flow.
[Selection] Figure 5

Description

  The present invention relates to a flowmeter suitable for accurately measuring the flow direction and flow rate of a fluid supplied through a complicatedly installed pipe in a factory or the like.

  As a flow meter for measuring the flow rate of the fluid supplied through the piping, a sensor chip in which a pair of temperature sensing elements are arranged in the fluid flow direction with the heater element in between is used, and the ambient temperature in the vicinity of the heater element is determined. Paying attention to the fact that the temperature distribution in the vicinity of the heater element changes depending on the flow rate (flow velocity) of the fluid when the temperature of the fluid flowing along the sensor chip is increased by a certain temperature, the pair of temperature sensitive elements. There is known a thermal flow meter that measures the mass flow rate of the fluid with high accuracy from the difference in temperature obtained by each of the above.

In addition, in order to remove the influence of pulsation caused by pressure fluctuations of the fluid supplied through the piping, for example, the back flow of the fluid is detected and the back flow rate is integrated, and the flow rate is subtracted from the back flow rate. It is proposed to obtain accurately (for example, refer to Patent Document 1). Further, it has been proposed that each time a certain integrated flow rate is detected using a flow rate 升, the integrated flow rate is sequentially integrated to cancel the back flow rate associated with pulsation with the flow rate 例 え ば (for example, Patent Document 2). See).
JP 2002-5716 A JP 2004-93173 A

  By the way, pipes that are laid in factories or the like and supply fluids such as compressed air and various gases are often branched into a plurality of systems in accordance with the expansion of equipment. In addition, another fluid supply source may be connected in the middle of the pipe in order to compensate for a shortage of fluid supply through the existing pipe. However, when such branching and merging of the pipe is repeated, the pipe may be formed in a loop in rare cases. In addition, in order to avoid troubles in the piping path and ensure a stable fluid supply path at all times, a plurality of pipes may be intentionally provided in parallel between the fluid supply source and the fluid using equipment (facility equipment). is there.

  When supplying a fluid through a pipe having such a complicated path, it is important to accurately know in which direction and how much flow the fluid has flowed for each of a plurality of pipes. However, the conventional general flowmeter has a problem that it is impossible to grasp the occurrence of backflow because it only accurately measures the flow rate flowing in a predetermined direction as described above. .

  The present invention has been made in consideration of such circumstances, and the object thereof is simple, for example, that can accurately measure the direction and flow rate of a fluid supplied through a pipe having a complicated path. It is to provide a flow meter having a configuration.

In order to achieve the above-described object, the flow meter according to the present invention is:
<a> Measuring the instantaneous flow rate according to the flow direction of the fluid, for example, a thermal flow sensor,
<b> A flow rate integration buffer for integrating the instantaneous flow rate measured by the flow rate sensor and measuring the integration time;
<c> Judgment means for determining the presence or absence of pulsation of the fluid from the integrated flow rate integrated in the flow rate integration buffer and the integration time, and resetting the flow rate integration buffer when pulsation is detected;
<d> When it is detected by the determination means that the fluid is not pulsating, the integrated flow rate integrated by the flow rate integration buffer is changed to the positive / negative polarity of the integrated flow rate indicating the flow direction of the fluid. Accordingly, it is provided with a forward flow counter and a reverse flow counter that individually integrate.

Preferably, the determination means includes
<c1> A step of comparing whether the integrated flow rate integrated by the flow rate integration buffer with a preset effective integrated flow rate determines whether the integrated flow rate is a forward flow rate or a reverse flow rate effective for flow rate measurement. One means,
<c2> When the integrated flow rate is less than a flow rate effective for flow rate measurement, the integrated time is compared with a preset time limit, and whether the integrated flow rate is an invalid flow rate due to pulsation of the fluid A second means for determining whether or not
<c3> Third means for resetting the accumulated flow accumulated in the flow accumulation buffer and resetting the accumulated time counted in the flow accumulation buffer when the accumulated flow is an invalid flow. Configured.

  The flow sensor preferably has a sensor chip in which a pair of temperature sensing elements are arranged in the fluid flow direction and an ambient temperature in the vicinity of the pair of temperature sensing elements in the sensor chip along the sensor chip. The instantaneous flow rate of the fluid is determined from the difference between the temperatures required by the heating means (for example, a heater element provided between the temperature sensing elements) that increases the temperature of the flowing fluid by a certain temperature and the pair of temperature sensing elements. It comprises a thermal flow sensor provided with a desired instantaneous flow rate calculating means.

  According to the flowmeter having the above-described configuration, the accumulated flow obtained by the flow accumulation buffer when no pulsation is generated in the fluid is indicated by using the normal flow counter and the reverse flow counter. Since integration is performed individually according to the positive / negative polarity of the integrated flow rate, it is possible to accurately determine the integrated flow rate of the positive flow and the integrated flow rate of the reverse flow. In addition, the integrated flow rate during the pulsating flow integrated in the flow integration buffer is reset and excluded from the integration targets by the forward flow integration counter and the reverse flow integration counter. Can be eliminated. Therefore, for example, the integrated flow rates in the normal flow direction and the reverse flow direction can be accurately obtained without being affected by a temporary reverse flow caused by pressure fluctuation caused by opening and closing of a valve provided in the pipe.

  In the present invention, the integrated flow rate integrated by the flow rate integration buffer is compared with a preset effective integrated flow rate to determine whether the integrated flow rate is effective for flow measurement. A large flow rate exceeding 1 can be accumulated without a time delay by the forward flow counter and the reverse flow counter. On the other hand, when the integrated flow rate is very small, which is less than the effective flow rate measurement, the integrated time is compared with a preset time limit so that the integrated flow rate is an ineffective flow rate due to the pulsation of the fluid. It is determined whether or not there is. If the flow rate is invalid, the accumulated flow accumulated in the flow accumulation buffer is reset and the accumulated time measured in the flow accumulation buffer is reset. Therefore, fluctuation in the fluid flow direction (effect of pulsation) It is possible to achieve an effect such as being able to be easily eliminated effectively.

Hereinafter, a flow meter according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a schematic configuration of a flow meter according to this embodiment. Reference numeral 1 denotes a flow sensor that is incorporated in a pipe (not shown) and detects the flow rate of a fluid (for example, gas) flowing through the pipe. (Flow rate signal detection unit). This flow sensor is mainly composed of a sensor chip in which a pair of temperature sensitive elements Ru and Rd are formed on a semiconductor substrate (for example, a silicon substrate) B with a heater element Rh therebetween as shown in FIG. . Incidentally, the heater element Rh and the pair of temperature sensing elements Ru, Rd are made of, for example, a thin film resistor of platinum (Pt). The heater element Rh and the pair of temperature measuring elements Ru, Rd are shown in FIG. As schematically shown in the structure, they are arranged side by side along a fluid flow direction F on a thin diaphragm D provided by bridging a cavity (concave portion) C formed in the semiconductor substrate B. In the drawing, Rr is a temperature detection element that is provided at a position away from the diaphragm D of the semiconductor substrate B and detects the ambient temperature of the sensor chip, and hence the temperature of the fluid.

  The fluid flow rate detection using such a flow rate sensor (sensor chip) 1 is performed by the instantaneous flow rate calculation unit 2 while the heater element Rh is driven to generate heat while the pair of temperature sensitive elements Ru and Rd are in the vicinity of the temperature. Is detected, and the temperature difference is obtained as an instantaneous flow rate of the fluid flowing along the sensor chip. Specifically, the heater element Rh is driven to generate heat, and the ambient temperature in the vicinity of the temperature sensitive elements Ru and Rd is increased by a certain temperature from the ambient temperature (fluid temperature) detected by the temperature detection element Rr. Then, the temperature distribution in the vicinity of the temperature sensing elements Ru and Rd raised by a certain temperature changes depending on the flow rate (flow velocity) Q of the fluid flowing along the sensor chip. The temperature is detected as a difference between temperatures detected by the temperature elements Ru and Rd, and the mass flow rate of the fluid is obtained from the temperature difference.

  FIG. 4 shows the configuration of the instantaneous flow rate calculation unit 2 that drives the heater element Rh of the flow rate sensor (sensor chip) 1 to generate heat and detects the flow rate from the temperature difference detected using the temperature sensitive elements Ru and Rd as described above. An example is shown. The instantaneous flow rate calculation unit 2 will be briefly described. The instantaneous flow rate calculation unit 2 is roughly composed of a drive unit 2a for the heater element Rh and a temperature difference detection unit 2b using a pair of temperature sensitive elements Ru and Rd. Is provided.

  The drive unit 2a for the heater element Rh includes a first bridge circuit 11 for temperature control configured using the heater element Rh, the temperature detection element Rr, and a pair of fixed resistors R1 and R2, and a power supply voltage Vcc. In response, the transistor 12 for changing the driving voltage of the bridge circuit 11 and the bridge output voltage (potential difference between the bridges) of the bridge circuit 11 are obtained, and the operation of the transistor 12 is feedback-controlled so that the bridge output voltage becomes zero. The differential amplifier 13 is configured. By the feedback control of the transistor 12 based on the output of the differential amplifier 13, the heat generation temperature of the heater element Rh is controlled to be always higher than the ambient temperature T detected by the temperature detection element Rr by a constant temperature ΔT. The

  On the other hand, the temperature difference detection unit 2b uses, for example, a pair of temperature sensing elements Ru, Rd and a pair of fixed resistors Rx, Ry provided in the fluid flow direction with the heater element Rh interposed therebetween. And a bridge output voltage (potential difference between the bridges) corresponding to a change in the resistance value of the temperature sensitive elements Ru and Rd in the first bridge circuit 14. And a differential amplifier 15. Since the resistance values of the temperature sensitive elements Ru and Rd vary depending on the temperature, the bridge output voltage of the bridge circuit 14 detected by the differential amplifier 15 flows along the flow sensor (sensor chip) 1. Information on the temperature difference according to the flow rate of the fluid, in other words, the flow rate signal detected using the flow rate sensor 1 is output.

  That is, the temperature difference detection unit 2b is configured to control the temperature sensing elements Ru, Rd in a situation where the heating temperature of the heater element Rh is always higher than the ambient temperature T by a constant temperature ΔT under the control of the driving unit 2a. Is detected as a change in the temperature distribution in the vicinity of the temperature sensitive elements Ru and Rd according to the flow rate of the fluid flowing along the flow sensor (sensor chip) 1 and detected by the differential amplifier 15. The bridge output voltage of the bridge circuit 14 is output as a flow rate signal (sensor signal).

  Returning to the description of the configuration of the flow meter shown in FIG. 1, the flow rate signal obtained by the instantaneous flow rate calculation unit 2 as described above is sent to the forward / reverse flow / pulsation determination unit (determination unit) 3 that determines the direction of fluid flow. Given. The forward / reverse flow / pulsation determination unit 3 includes a flow rate integration buffer 4 and has a function of sequentially integrating the flow rate signals (instantaneous flow rate) obtained by the instantaneous flow rate calculation unit 2 using the flow rate integration buffer 4. Prepare. Further, the forward / reverse flow / pulsation determination unit 3 is based on the function of determining the direction of fluid flow from the polarity of the flow rate signal (sensor signal), the integrated flow rate integrated by the flow rate integration buffer 4 and the integration time. It has a function of determining the presence or absence of pulsation of the fluid and resetting the flow rate accumulation buffer 4 when pulsation is detected.

  Specifically, when the polarity of the flow signal (sensor signal) is plus (+), the forward / reverse flow / pulsation determining unit 3 forwards the fluid from the upstream side of the pipe toward the downstream side thereof. When the polarity of the flow signal (sensor signal) is negative (−), it is determined that this is a reverse flow in which fluid flows from the downstream side to the upstream side of the pipe. Further, when the absolute value of the integrated flow accumulated in the flow accumulation buffer 4 exceeds a preset minimum flow value as described later, the forward / reverse flow / pulsation determining unit 3 determines that the fluid is upstream of the pipe. Alternatively, when it is determined that the flow is a forward flow or a reverse flow flowing toward the downstream side, and the absolute value of the integrated flow rate integrated by the flow rate integration buffer 4 is less than a preset minimum flow rate value By monitoring the flow rate integration time, it is determined whether or not it is a pulsating flow.

  When the normal / reverse flow / pulsation determining unit 3 determines that no pulsating flow is generated, the normal flow counter 6 and the reverse flow counter 7 provided in parallel as the total recording unit 5 are used to perform the normal flow. The flow rate and the backflow rate are individually integrated. In other words, when it is determined that the flow is normal, the integrated flow calculated by the flow integration buffer 4 at that time is integrated by the positive flow integration counter 6 and when it is determined that the flow is reverse. Is integrated by the counter counter for reverse flow 7 at that time. Thus, the respective integrated flow rates in the forward flow direction and the reverse flow direction obtained by the forward flow integration counter 6 and the reverse flow integration counter 7 are read out and selectively displayed on the display unit 8 or in parallel. Is displayed.

  The determination of the forward / reverse flow and the pulsating flow in the forward / reverse flow / pulsation determination unit 3 and the flow rate integration processing by the counters 6 and 7 based on the determination result will be described in a little more detail. Is executed in accordance with, for example, the processing procedure shown in FIG. That is, first, the aforementioned sensor signal Vs is obtained from the flow rate sensor 1 (step S1), and the instantaneous flow rate calculation unit 2 calculates the instantaneous flow rate Q (= F (Vs)) from the sensor signal Vs (step S2). 〉. Then, the instantaneous flow rate Q is applied to the flow rate integration buffer 4 and integrated, and the integrated flow rate X obtained in the flow rate integration buffer 4 is updated as [X ← X + Q] (step S3). At the same time, the integrated time <integrated number of instantaneous flow rates> for obtaining the integrated flow rate X is updated by the flow rate integrating buffer 4 (step S4). Note that the integration time t by the flow rate integration buffer 4 is obtained by counting the timer clock indicating this cycle since the acquisition of the sensor signal Vs from the flow rate sensor 1 described above is performed at a constant cycle, for example. .

  Thereafter, it is determined whether or not the absolute value of the integrated flow rate X obtained by integrating the instantaneous flow rate Q in the flow rate integration buffer 4 is smaller than a preset effective integration lower limit value (step S5). Needless to say, it may be determined whether or not the absolute value of the integrated flow rate X is greater than or equal to a preset effective integrated lower limit value. If the absolute value of the integrated flow rate X is equal to or greater than the effective integrated lower limit value, it is determined that this is the flow of the fluid whose flow rate is to be measured, and the flow rate integration buffer 4 that is the flow rate value is obtained. It is determined whether the integrated flow rate X shows a positive value or a negative value <step S6>.

  When the integrated flow rate X shows a positive value, it is determined that the fluid is a positive flow flowing from the upstream side to the downstream side of the pipe, and the above-described integration is performed using the positive flow integration counter 6. The flow rate X is integrated to the positive integrated flow rate value T1 obtained so far (step S7). When the integrated flow rate X shows a negative value, it is determined that the fluid is a reverse flow flowing from the downstream side to the upstream side of the pipe, and the integration is performed using the backflow integration counter 7. The flow rate X is integrated with the integrated flow rate value T2 of the reverse flow that has been obtained so far (step S8). That is, depending on whether the flow rate detected as described above is in the forward flow direction or in the reverse flow direction, the forward flow integration counter 6 and the reverse flow integration counter 7 are alternatively used. The flow rate is integrated.

  Therefore, only the flow rate of the fluid flowing in the forward flow direction is sequentially accumulated in the forward flow integrating counter 6 to obtain the accumulated flow value, and only the flow rate of the fluid flowing in the backward flow direction is sequentially accumulated in the counter flow integrating counter 7. Therefore, the integrated flow rate value is obtained. When the integration of the detected flow rate by the forward flow integration counter 6 or the reverse flow integration counter 7 is completed, the above-described flow rate integration buffer 4 is reset and the above-described integration time t is reset <Steps S9 and S10>. The processing from step S1 is repeatedly executed under the operation cycle.

  On the other hand, when the absolute value of the integrated flow rate X obtained by the flow rate integrating buffer 4 is smaller than the preset effective integrated lower limit value (step S5), the above-described integrated time t is set in advance. It is determined whether or not the determination time has been reached <step S11>. If the accumulated time t is less than the determination time, the processing from step S1 is repeatedly executed under the above-described operation cycle, that is, at the next instantaneous flow rate detection timing. Therefore, when a flow rate smaller than the effective integration lower limit value is repeatedly detected, the minute flow rate is sequentially accumulated in the flow rate accumulation buffer 4 (steps S3 and S4). Then, it is determined whether or not the integrated flow rate obtained by integration in the flow rate integration buffer 4 has reached the above-mentioned effective integration lower limit value (step S5).

  In spite of this, when the integrated flow rate is less than the effective integrated lower limit value, the above-described determination of the integrated time t is performed again (step S11). When the accumulated time t has reached a preset determination time, it is determined that this is a pulsating flow with fluctuations in the fluid flow direction, and the detection flow rate during that period is invalidated as described above. The flow integration buffer 4 is reset and the integration time t described above is reset <steps S9 and S10>. Then, the processing from step S1 is repeatedly executed under the operation cycle described above.

  That is, when a pulsating flow of fluid temporarily occurs due to a pressure change associated with opening and closing of a valve provided in the pipe, a fluctuation occurs in which the flow direction of the fluid alternately changes. Then, since the instantaneous flow rate Q detected every predetermined cycle becomes a positive value or a negative value, the value of the integrated flow rate X obtained by integrating the instantaneous flow rate Q in the flow rate integration buffer 4 is There is almost no increase. Therefore, in the determination unit 3, when the integrated flow rate X obtained by the flow rate integration buffer 4 is less than the effective integration lower limit value, and the integration time t passes a predetermined time, this is described above. It is determined that a flow is occurring. Then, by excluding the detected flow rate in the pulsating state from the measurement target, as described above, the integrated flow rate of the fluid flowing in the forward flow direction and the integrated flow rate of the fluid flowing in the reverse flow direction are obtained individually. It has become.

  Thus, according to the flowmeter configured as described above, the integrated flow rate of the fluid flowing in the forward flow direction through the pipe and the integrated flow rate of the fluid flowing in the reverse flow direction can be individually determined. In addition, the integrated flow rates of the fluid in the forward flow direction and the reverse flow direction can be obtained with high accuracy without being affected by the pulsating flow accompanied by fluctuations in the flow direction. Therefore, even in a pipe having a complicated path, it is possible to accurately grasp how much fluid flows in which direction through the pipe. Also, when the flow direction of the fluid changes with the opening and closing of the valve, it is possible to estimate the piping path that forms a closed loop from the relationship between the piping and the valve, for example. In practice, it is possible to effectively deal with the laying mistake and the like.

  The present invention is not limited to the embodiment described above. In the embodiment, the instantaneous flow rate Q obtained by the instantaneous flow rate calculation unit 2 is once written in the flow rate accumulation buffer 4 and then pulsation is determined. The absolute value of the instantaneous flow rate Q obtained by the instantaneous flow rate calculation unit 2 is as follows. May exceed the effective integration lower limit value, the instantaneous flow rate Q may be applied to the forward flow integration counter 6 or the reverse flow integration counter 7 without using the flow rate integration buffer 4 for integration. Although the case where a thermal flow sensor is used has been described here as an example, it is of course possible to use other types of flow sensors capable of measuring the normal flow rate and the reverse flow rate. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.

The block diagram which shows schematic structure of the flowmeter which concerns on one Embodiment of this invention. The figure which shows the example of a thermal type flow sensor. The figure which shows the cross-section of the thermal type flow sensor shown in FIG. The figure which shows the structural example of the drive circuit of the thermal type flow sensor shown in FIG. The figure which shows the example of the rough process sequence of the flow volume detection in the flowmeter which concerns on one Embodiment of this invention, its determination process, and the integration process of an integrated flow rate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Flow rate sensor 2 Instantaneous flow rate calculation part 3 Forward / reverse flow / pulsation judgment part 4 Flow rate accumulation buffer 5 Accumulation recording part 6 Forward flow accumulation counter 7 Reverse flow accumulation counter 8 Display section

Claims (3)

A flow sensor that measures the instantaneous flow rate according to the flow direction of the fluid;
While integrating the instantaneous flow rate measured by this flow sensor, the flow rate integration buffer for measuring the integration time,
Determining means for determining the presence or absence of pulsation of the fluid from the integrated flow rate integrated in the flow rate integration buffer and the integration time, and resetting the flow rate integration buffer when pulsation is detected;
When the determination means detects that the fluid is not pulsating, the integrated flow rate integrated by the flow rate integration buffer is determined according to the positive / negative polarity of the integrated flow rate indicating the flow direction of the fluid, respectively. A flow meter comprising a forward flow counter and a reverse flow counter that individually integrate. The determination means determines whether the integrated flow rate is a normal flow rate or a reverse flow rate effective for flow measurement by comparing the integrated flow rate integrated in the flow rate integration buffer with a preset effective integrated flow rate. First means to:
When the integrated flow rate is less than the effective flow rate measurement, the integrated time is compared with a preset time limit to determine whether the integrated flow rate is an invalid flow rate due to the pulsation of the fluid. A second means to:
And a third means for resetting the accumulated flow accumulated in the flow accumulation buffer and resetting the accumulated time counted in the flow accumulation buffer when the accumulated flow is an invalid flow. The flow meter according to claim 1. The flow sensor is a sensor chip in which a pair of temperature sensing elements are arranged in the direction of fluid flow; and
Heating means for raising the ambient temperature in the vicinity of the pair of temperature sensing elements in the sensor chip by a certain temperature from the temperature of the fluid flowing along the sensor chip;
The flow meter according to claim 1, further comprising an instantaneous flow rate calculating means for determining an instantaneous flow rate of the fluid from a difference in temperature respectively determined by the pair of temperature sensing elements.

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