JPH0318237B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in a process quantity measuring device for measuring process quantities such as flow rate, pressure, and temperature.

[Technical background of the invention and its problems]

Conventionally, there is an electromagnetic flowmeter that measures the flow rate of fluid, which is one of the process quantities.

This electromagnetic flowmeter consists of a flow rate detection section that applies a magnetic field to the fluid and detects the electromotive force generated in the fluid as a flow rate, and a signal that converts the output of this flow rate detection section into a signal that can be read by a computer, indicator, etc. It is equipped with a conversion section. These flow rate detection section and signal conversion section have output characteristics as shown in A and B shown in FIG. That is, if the horizontal axis is the process amount Pro and the vertical axis is the detected voltage E, the flow rate detection unit can detect a wide range of process amounts 0 as shown in FIG. 1A.
Accurate detection voltage characteristics 1 can be obtained for changes in ~Pron. On the other hand, the signal converter cannot continuously and accurately convert signals over the entire range of the detected voltage 0 to En detected by the flow rate detector.

Therefore, conventionally, the flow rate has been measured by the following means. In other words, the process amount is 0~
Measurement flow scale (hereinafter referred to as
This method divides the measurement span (referred to as measurement span) into multiple parts. For example, as shown in FIG. 1B, the process amount is measured by changing the measurement span according to the process amount 0~ ^{Pro 1} , 0~Pro ² , . . . , 0~Pron. In this way, the entire range of process quantities can be measured with high precision.

However, the following problems arise with the above measuring means. For example, when a measurement span flow rate from 0 to Pro ¹ is measured, the error in the measured flow rate value is different between a process quantity close to 0 and a process quantity close to Pro ¹ . To explain this point with reference to FIG. 2, it is assumed that the full scale error in any measurement span is 1%. If a flow rate of 50% of full scale is measured over this measurement span, the error in the measured value will be approximately 2%. Furthermore, if a flow rate of 10% of the full scale is measured over this measurement span, the error in the measured value will be approximately 10%.
Therefore, when the flow rate is measured several times over the same measurement span, the error included in the measured flow rate value increases as the flow rate decreases. This means that it is difficult to measure accurate flow rates.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a process quantity measuring device that can accurately measure a flow rate without causing an error even when the flow rate changes.

[Summary of the invention]

The present invention amplifies the detection signal from the process quantity detection section, and when this amplified signal becomes above or below a predetermined level value, the measurement range is switched and at the same time the amplification factor corresponding to the switched measurement range is set. The process amount measuring device amplifies the detection signal and outputs a pulse signal having a pulse width according to the voltage level of the amplified detection signal and a DC voltage proportional to the pulse width of the pulse signal.

[Embodiments of the invention]

Hereinafter, an embodiment of the present invention applied to an electromagnetic flowmeter will be described with reference to FIG. This electromagnetic flowmeter includes a flow rate detection section 10 and a signal conversion section 20. The flow rate detection unit 10 includes a tubular body 11 through which fluid flows, two coils 12a and 12b that generate a magnetic field outside the tubular body 11 in a direction perpendicular to the flow direction of the fluid, and these coils 12a and 12b.
It is composed of a pair of electrodes 13a and 13b that detect an electromotive force generated in the fluid by a magnetic field generated by excitation of the fluid.

On the other hand, the signal conversion unit 20 includes a power supply 21, an excitation unit 22 that supplies excitation current to the two coils 12a and 12b, and a signal detected by the pair of electrodes 13a and 13b using the excitation current from the excitation unit 22. A differential amplification section 23 that performs differential amplification and a flow velocity level setting section 2
4, a pulse width modulation section 25, a calculation section 26, a power amplification section 27, and a timing signal generation section 28 that outputs a timing signal.

The flow velocity level setting section 24 includes an amplification section 24a that can be varied to a plurality of amplification factors, and a flow velocity level switching function when the amplification output of this amplification section 24a becomes above a predetermined set value or below a separately determined set value. A setting signal section 2 that performs the following and outputs a measurement level setting signal.
4b and a switching signal for setting the amplification factor suitable for the flow rate of the process amount to the amplification section 24a in accordance with the output of the setting signal section 24b, and an amplification factor signal indicating the degree of amplification factor to the arithmetic section. 26 and a flow velocity level switching section 24c.

Next, the pulse width modulation section 25 receives the output voltage of the amplification section 24a and outputs a pulse signal having a pulse width corresponding to the level of this output voltage. The calculation unit 26 is
The pulse signal of the pulse width modulation section 25 is converted to the amplification section 24a by the amplification factor signal from the flow velocity level switching section 24c.
The signal is returned to the voltage level before amplification, converted to a DC voltage signal, and output. Further, the calculation section 26 has a conventional flow velocity level switching section 26a. The power amplification section 27 amplifies the DC voltage signal and sends the signal to the display section 30. The display section 30 is the power amplifier section 2.
7 signal is displayed. Timing signal generator 28
This is to eliminate the influence of noise by adjusting the timing of each operation of the excitation section 22, flow rate level switching section 24c, and pulse width modulation section 25.

The operation of one embodiment configured as above will be explained. After the power is turned on, the excitation section 22 causes an excitation current to flow through the coils 12a and 12b at the timing of the timing signal generation section 28. coil 12
a, 12b generate a magnetic field in a direction perpendicular to the fluid due to this current. As a result, the electromotive force generated in the fluid is detected by the pair of electrodes 13a and 13b.
The detected voltage detected by the flow rate detection section 10 in this manner is sent to the signal exchange section 20. This signal converter 20 converts this detection signal into a signal that can display the flow rate. At this time, the flow rate level switching section 26a
Assume that, for example, a flow velocity level of 6 [m/s] is set in the calculation unit 26. Then, while measuring the flow rate at this flow rate level, the fluid flow rate is 3
Assume that the vehicle has decelerated to less than [m/s]. This results in
The output of the flow rate detection section 10 decreases and is sent to the signal conversion section 20. This detection output is differentially amplified by the differential amplifier section 23 and sent to the flow velocity level setting section 24 .

Therefore, the flow velocity level setting section 24 performs the following operation. First, the amplifying section 24a amplifies the amplified voltage of the differential amplifying section 23 by a predetermined amplification factor and outputs the amplified voltage. Then, the setting signal section 24b includes the amplification section 24a.
Detect the voltage level of the output voltage. Amplification section 24
The output voltage from a decreases due to the deceleration of the fluid flow rate and becomes lower than the preset voltage value. Therefore, the setting signal section 24b sends a signal to the flow velocity level switching section 24c to set the flow velocity level to 3 [m/s]. As a result, the flow velocity level switching unit 24c changes the flow velocity level from 6 [m/s] to 5 [m/s].
s] → 4 [m/s] and finally 3 [m/s]. At the same time, the amplification factor of the amplifying section 24a is set to an amplification factor corresponding to the flow velocity level 3 [m/s]. Then, the flow rate level switching section 24c sends an amplification factor signal to the calculation section 26 for returning the voltage level to the voltage level before being amplified by the amplification section 24a. In the current state, the amplification factor signal is set to 3 [m/s] in the flow velocity level switching section 24c and 6 [m/s] in the flow velocity level switching section 26a built in the computing section 26. This is a signal that is multiplied by 3/6.

By the operation of the flow velocity level setting section 24 as described above, the output voltage of the amplification section 24a is changed to the pulse width modulation section 25.
sent to. The pulse width modulation section 25 includes the amplification section 24
The pulse width is varied according to the voltage level of the output voltage of a, and the pulse width is sent to the calculation unit 26 as a pulse duty signal. The arithmetic unit 26 multiplies the voltage level of the pulse duty signal by 3/6 times using the amplified signal, converts the pulse duty signal into a DC voltage corresponding to the duty ratio, and outputs the DC voltage. Then, the power amplification section 27 amplifies the DC voltage from the calculation section 26 and sends it to the display section 30 . As a result, the display unit 30 displays the flow rate using a meter such as a recorder or a totalizer. Here, the timing signal generating section 28 sets the operation timings of the excitation section 22, the flow velocity level switching section 24c, and the pulse width modulation section 25. Further, the flow velocity level is switched in a pulse width section a that does not affect the measured values shown in FIG. Fourth
b in the figure is a sampling section when measuring the flow rate.

Therefore, if the flow rate level (a value slightly larger than the predicted maximum flow rate value) is set in the flow rate level switching unit 26a built in the calculation unit 26, even if the flow rate decreases significantly, the flow rate range setting unit 24 Since the output of the differential amplification section 23 is amplified by a predetermined amplification factor and returned to the voltage level before amplification in the arithmetic section 26, it is possible to accurately measure the flow rate without causing an error.

Furthermore, if a fine flow velocity level is set by combining a plurality of flow velocity levels provided in the flow velocity level switching section 24c, the measurement accuracy of the flow rate can be further improved.

In addition, the flow velocity level of the flow velocity level switching section 24c is
10 [m/s], and the flow rate can be measured without setting the flow rate level using the flow rate level switching unit 26a built into the calculation unit 26. In this case, the display section can be digitally displayed to display the entire range of the measured flow rate, making it possible to accurately measure the flow rate.

The display unit 30 does not need to use a multi-scale recorder, totalizer, etc., and may be a display device such as a one-range recorder, totalizer, etc.

Note that the present invention is not limited to the above embodiment. In the above embodiment, only the flow rate is measured, but by changing the flow rate detection section 10, measurement of various process quantities can be performed. For example, each of the flow rate detection units 30 to 30 shown in FIG.
It is like 32. Figure 5a shows the electromotive force (e ₁₎ generated in the thermocouple 30a and the voltage drop e ₂ across the resistor R.
This is a temperature detection section 30 for measuring the temperature by detecting the difference _eX = _e1 - _e2 ). FIG. 5b shows a temperature detection section 31 for measuring temperature similarly to FIG. 5a. This temperature detecting section 31 is provided with a measuring resistor RT in a bridge circuit and detects a voltage difference caused by unbalance of the bridge circuit due to temperature change. FIG. 5c shows a rotation speed detection section 32 that detects the rotation speed of the rotating body. The rotational speed detection section 32 uses a tachometer generator 32a, and detects an electromotive force generated in the tachometer generator 32a. As described above, if each of the detection units 30 to 32 is used, various process quantities (in addition to pressure, force, etc.) can be detected.
can be measured accurately, and the measurement accuracy is not lower than when measuring flow rate.

〔Effect of the invention〕

The present invention provides a highly accurate process amount measuring device that can accurately measure process amounts without causing errors, regardless of whether the process amount is large or small, such as when the process amount decreases rapidly within the same measurement span. Can be provided.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the output characteristics of the flow rate detection section and the signal conversion section, Fig. 2 is a diagram explaining the error rate generated by a conventional electromagnetic flowmeter, and Fig. 3 is a diagram showing the electromagnetic flow rate according to the present invention. A block diagram showing one embodiment of the meter,
Figure 4 is a diagram showing the timing of flow rate level switching;
FIGS. 5a, 5b, and 5c are diagrams showing each detection section applied to an embodiment of the present invention. 10...Flow rate detection section, 20...Signal conversion section, 2
2...Excitation section, 23...Differential amplification section, 24...Flow velocity level setting section, 24a...Amplification section, 24b...
Setting signal section, 24c...Flow velocity level switching section, 25
... Pulse width modulation section, 26 ... Calculation section, 27 ...
Power amplifier section, 28... Timing signal generation section, 3
0...Display section.

Claims (1)

[Claims] 1. A process quantity measuring device that measures the entire range of the process quantity by dividing it into a plurality of measurement spans corresponding to the process quantity, which includes a detection section that detects the process quantity and amplification of the detection signal output from this detection section. a setting signal section that outputs a measurement level setting signal that switches the measurement level when the output level of the amplifier section becomes equal to or higher than a set value or lower than a separately determined set value in each measurement span; , receives the measurement level setting signal output from this setting signal section, controls the amplification factor of the amplification section so that the amplification factor corresponds to this measurement level, and returns the amplification factor to the amplification factor before this variable amplification factor. a level switching section that outputs an amplification factor signal; a pulse width modulation section that converts the output level of the amplification factor into a pulse duty signal corresponding to the output level of the amplification section; and amplification of the pulse duty signal converted by the pulse width modulation section from the level conversion section. 1. A process amount measuring device comprising: a calculation section that receives a rate signal and converts it into a DC voltage signal corresponding to a duty ratio at a previous output level variably amplified by the amplification section and outputs the signal.