JPH07109376B2 - Composite sensor output signal processing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a composite sensor output signal processing method that improves measurement accuracy by using two types of flow rate sensors.

[Conventional technology]

Using a fluidic flow sensor with a gas flow meter,
There is a drawback in that the sensitivity drops sharply in the low flow rate region, and satisfactory measurement cannot be performed. Therefore, a method has been proposed in which a sensor using a different method capable of measuring up to a low flow rate range, for example, a thermal semiconductor flow rate sensor and the above fluidic flow rate sensor are combined to enable measurement from a low flow rate range to a high flow rate range. There is. The characteristics when the fluidic flow sensor is used for the gas flow meter are shown in FIG. 4 (a), and the characteristics when the thermal semiconductor flow sensor is used for the gas flow meter are shown in FIG. 4 (b). In FIG. 4, the horizontal axis represents the flow rate and the vertical axis represents the sensor output.

[Problems to be Solved by the Invention]

The fluidic flow rate sensor measures the volumetric flow rate of gas, whereas the thermal semiconductor flow rate sensor measures the mass flow rate of gas.Therefore, if the temperature, density, or gas mixture ratio of the gas changes, the measured values of both will differ. Occurs. This is shown in FIG. In FIG. 5, the horizontal axis is the volume flow rate, and the vertical axis is the sensor output. S1 is the output of the fluidic flow sensor when there is a temperature change, etc., and S2 is the output of the thermal semiconductor flow sensor when there is a temperature change. Indicates. As shown in FIG. 5, the thermal type semiconductor flow rate sensor shows different characteristics depending on temperature changes. Therefore, depending on the temperature, the thermal type semiconductor flow rate sensor is switched to the fluidic flow rate sensor or the fluidic flow rate sensor is changed to the thermal type semiconductor flow rate sensor. When switching to the flow rate sensor, a jump in the flow rate measurement value, that is, a rapid change in the flow rate measurement value occurs.

The present invention has been made in view of the above circumstances, and an object of the present invention is to eliminate the deviation of the flow rate measurement value in the sensor switching when using two types of flow rate sensors and to improve the measurement accuracy. It is to provide a signal processing method.

[Means for Solving the Problems]

In order to achieve such an object, the present invention measures and displays a flow rate value by a first flow rate sensor below a first predetermined flow rate, and displays a flow rate value above a second predetermined flow rate by a second flow rate value. In a composite sensor output signal processing method for measuring and displaying by a flow rate sensor, when the flow rate to be measured is a value between a first predetermined flow rate and a second predetermined flow rate, a flow sensor with high accuracy of the two flow rate sensors. The data calibration of the flow sensor with lower accuracy is automatically performed.

[Action]

In the composite sensor output signal processing method according to the present invention,
The flow rate measurement value does not change suddenly when switching the flow rate sensor and is a smooth value.

〔Example〕

First, the outline of the present invention will be described. Provide a range where both sensors operate simultaneously near the switching point of the two flow rate sensors,
The data of the low-precision sensor is calibrated with the data of the predetermined high-precision sensor of the two data obtained when the measured value falls within this range. The correction count used for this calibration is used for data correction of the low precision sensor until the next calibration.

FIG. 3 is a system diagram showing a gas flow meter using a thermal semiconductor flow sensor 1 as a first flow sensor and a fluidic flow sensor 2 as a second flow sensor. 3 and 4 are flow rate values FA and A signal processing circuit for outputting FB, 5 is a microcomputer for inputting and processing the flow rate values FA, FB, and G is a gas. In FIG. 1, the fluidic flow sensor 2 is a high-accuracy sensor, the thermal semiconductor flow sensor 1 is a low-accuracy sensor, and data calibration of the thermal semiconductor flow sensor 1 is performed within a certain range of flow measurement values of the fluidic flow sensor 2. To do.

FIG. 1 is a flow chart for explaining an embodiment of a composite sensor output signal processing method according to the present invention, and FIG. 2 is a graph showing characteristics of two kinds of sensors (a thermal type semiconductor flow sensor and a fluidic flow sensor). is there. In FIG. 2, the horizontal axis is the flow rate, the vertical axis is the sensor output value, S _FA is a curve showing the characteristics of the thermal semiconductor flow rate sensor 1, and S _FB is a curve showing the characteristics of the fluidic flow rate sensor 2. See also S _FAC
Is the measured output value of the thermal semiconductor flow sensor 1 after data calibration.

Next, a method of calibrating data will be described with reference to FIGS. Considering that the error in the measured output value of the sensors 1 and 2 is caused by the sensitivity change of the sensor, if the actual flow rate is F and the change from the predetermined sensitivity of each of the sensors 1 and 2 is ΔSA, ΔSB, FA = F (1 + ΔSA) (1) FB = F (1 + ΔSB) (2) In addition, the sensitivity change of the sensor is due to the change of ambient temperature,
It is caused by the difference in the measurement gas component, the change over time, and the like.

Considering the characteristics of the sensor as | ΔSA | >> | ΔSB | When the interval is reached (steps 11 to 13 in FIG. 1), the value of the measured value FA of the thermal semiconductor flow sensor 1 is calibrated using the value of the measured FB of the fluidic flow sensor 2. That is, the value of the correction coefficient k in the following equation is determined (step 1 in FIG. 1).
Five).

k · F (1 + ΔSA) = FB (3) After that, the flow rate measurement value FB is the sensor output value F1 and F2 in FIG.
The measured value FA of the sensor 1 is multiplied by k and displayed until the interval between and. The value obtained by multiplying the measured value FA of the sensor 1 by k is expressed as FAC. FAC = k · FA = k · F (1 + ΔSA) (4) By doing this, the thermal semiconductor flow sensor 1 Display accuracy is improved, and the measured value of fluidic flow sensor 2
It is possible to eliminate the shift when switching to the FB.

The fluidic flow rate sensor 2 cannot instantaneously obtain a flow rate value, and a certain amount of measurement time or more is required for accurate measurement. For this reason, when performing calibration, the flow rate is measured for a certain period of time, and the average flow rate during that period is taken as the measured value FB.
The thermal semiconductor flow rate sensor 1 can continuously measure, but during calibration, the measurement is continued within the same time as the fluidic flow rate sensor 2, and the average flow rate during that time is used as the flow rate value FA. This process is the process shown in steps 14 and 15 of FIG. 1, and this process will be described later. By performing such a process, even if a flow rate fluctuation occurs within the measurement time, it is not affected and a highly accurate calibration becomes possible. During this simultaneous measurement, the output value FB of the fluidic flow sensor 2 is integrated (steps 13, 14, 20 in FIG. 1). In addition, the flow rate changes during the simultaneous measurement and the output value F1 shown in Fig. 2
If it goes out of the range of to F2, the calibration calculation is stopped and normal measurement is resumed. The output value of fluidic flow sensor 2
If FB is smaller than output value F1, thermal semiconductor flow sensor 1
The output value FA of is corrected and integrated (steps 12, 1 in Fig. 1)
7-19).

The sensor output values F1 and F2 that determine the data calibration range are determined as follows. F0 ≤ F1 <F2 ≤ F3, where F0 is the lower limit that can be satisfied with the fluidic flow sensor 2 and F3 is the upper limit that can be satisfied with the thermal semiconductor flow sensor 1. Select output values F1 and F2 as shown in (5).

The thermal semiconductor flow rate sensor 1 can continuously measure, but the fluidic flow rate sensor 2 can obtain the measurement result only intermittently. Therefore, when the flow rate of the gas G changes abruptly,
If the section from F2 to F2 is too small, it may pass through this section before measurement, and the correction calculation described above may not be performed. In addition, if the section from F1 to F2 is wide, the probability that a measured value will enter this section is high, but since the measurement is performed twice here, the power consumption increases, which is not preferable for a gas flow meter driven by a battery. Therefore, F1 and F2 are determined within the range of the equation (5) shown above while considering the actual usage conditions. For example, when F0 = 100l / h and F3 = 300l / h, F1 = 150l / h
Select as h, F2 ＝ 180l / h.

There are the following methods to prevent the power consumption during data calibration described above. A timer is provided in the arithmetic unit, and the timer is reset every time data is calibrated (step 1 in FIG. 1).
16). After that, even if the measured value falls between F1 and F2, data calibration is not performed until the time T1 preset in the timer has elapsed (steps 13, 14, 20 in FIG. 1), and after the time T1 has passed. Make sure to calibrate data for the first time (1st
(Steps 14 and 15 in the figure). The time T1 is determined according to the rate of temperature change of the gas and the rate of change of the gas component. That is, the time T1 is short under the fast-changing measurement conditions and the time T1 under the slow-change conditions.
Choose long. By doing so, data calibration is not performed more frequently than necessary, and wasteful power consumption can be prevented.

〔The invention's effect〕

As described above, according to the present invention, when the flow rate to be measured is within the flow rate range that exceeds the first predetermined flow rate by a certain amount, the first and second flow rate sensors simultaneously measure, and the two flow rate sensors are stable. A highly accurate flow sensor can easily increase the stability of the flow sensor that is prone to drift over time by automatically performing data calibration of the flow sensor that is prone to drift over time. There is an effect that it is possible to eliminate the deviation of the flow rate measurement value when switching the sensor when the flow rate sensor is used.

[Brief description of drawings]

FIG. 1 is a flow chart for explaining one embodiment of a composite sensor output signal processing method according to the present invention, FIG. 2 is a graph showing characteristics of two kinds of flow rate sensors, and FIG. 3 is a composite sensor output according to the present invention. FIG. 4 is a system diagram showing a gas flow meter to which an embodiment of the signal processing method is applied. FIG. 4 is a graph showing characteristics of the fluidic flow sensor and the thermal semiconductor flow sensor.
FIG. 5 is a graph showing changes in output values of the fluidic flow sensor and the thermal semiconductor flow sensor due to temperature changes and the like. 1 ... Thermal semiconductor flow sensor, 2 ... Fluidic flow sensor, 3, 4 ... Signal processing circuit, 5 ... Microcomputer, G ... Gas.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-59-12316 (JP, A) JP-A-1-308921 (JP, A) SAIKAI HEI 2-93716 (JP, U)

Claims (3)

[Claims] 1. A flow rate value is measured and displayed by a first flow rate sensor below a first predetermined flow rate, and a flow rate value is measured and displayed by a second flow rate sensor above a second predetermined flow rate. In the composite sensor output signal processing method, the first flow rate sensor can measure simultaneously with the second flow rate sensor even in a flow rate range that exceeds the first predetermined flow rate by a certain amount.
When the flow rate to be measured is in the flow rate range measured by the first flow rate sensor and the second flow rate sensor at the same time, the flow rate sensor with high stability out of the two flow rate sensors causes a drift with time to easily occur. A composite sensor output signal processing method that automatically performs data calibration. 2. A composite sensor output signal processing method according to claim 1, wherein a fluid sensor and a thermal semiconductor sensor are used as the two flow rate sensors, and data is calibrated by an arithmetic unit. 3. The composite sensor output signal processing method according to claim 2, wherein a timer is added to the arithmetic unit so that calibration is not performed until the timer set time has elapsed.