JPS6152516B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an arithmetic circuit suitable for use in a differential pressure flow meter using an orifice plate.

Differential pressure flowmeters are most widely used to measure the flow rate of fluid flowing in a steady flow through a pipe. The principle of this flowmeter is to provide an orifice plate in a pipe and measure the flow rate from the pressure difference before and after the orifice plate.

Here, there is a relationship between the flow rate q and the pressure difference (P ₁ −P ₂ ) as shown in the following equation.

Note that k is a constant determined by the structure, and ρ is the density of the fluid.

Therefore, when you want to know the pressure difference from the flow rate, you need to calculate the square, and when you want to know the flow rate from the pressure difference, you need to calculate the square root.

There are several conventionally known arithmetic circuits of this kind, but all of them have the drawback of being complex.

This invention was made to eliminate these conventional drawbacks, and its purpose is to:
An object of the present invention is to provide an arithmetic circuit that can perform square or square root operations with a simple circuit configuration.

In order to achieve such an object, the present invention compares a reference signal such as a triangular wave that periodically repeats a proportional slope with an input signal using a comparator, and turns on a switch depending on the polarity of the reference signal. is supplied to a filter and smoothed to obtain a signal that is the square of the input signal. In addition, this square calculation circuit is placed in the back circuit, and the smoothed output of the filter is input to the operational amplifier along with the input signal, and an output signal is output by controlling both inputs to be equal. Feedback as input signal of comparator,
It is configured to obtain a signal that is the square root of the input signal.

Hereinafter, this invention will be explained in detail based on examples.

FIG. 1 is a circuit diagram of an embodiment in which the arithmetic circuit according to the present invention is used as a square arithmetic circuit, and FIG. 2 is a waveform diagram of each signal.

In the figure, reference numeral 1 denotes a reference generator, which emits a triangular wave reference signal that periodically repeats a proportional gradient as shown in FIG. 2A. 2
is a comparator, the reference signal is input to the inverting input terminal, and the input terminal 3 is input to the non-inverting input terminal.
An input signal e IN having an analog value output from a sensor or the like is inputted through the input signal e _IN . Reference numeral 4 designates a changeover switch whose movable contact is normally turned on at the fixed point a, but acts to turn on the fixed contact b in response to an operating signal output from the comparator 2. 5 is a filter consisting of a resistor R and a capacitor C and acts as an integrating circuit; 6 is an output terminal.

In such a circuit configuration, when the input signal e _IN is a constant voltage e ₁ , the comparator 2 compares this voltage e ₁ with a reference signal, and if the reference signal is smaller than the voltage e ₁ , an operating signal is output. . In response to this operation signal, the changeover switch 4 is switched and the movable contact turns on the fixed contact b, so that a reference signal as shown in FIG. 2B is supplied to the filter 5. This reference signal is smoothed and integrated by a filter 5, and a voltage e ₂ corresponding to the area is sent to an output terminal 6 as an output signal e _OUT .
is output to. If the peak voltage of the triangular wave of the reference signal is e _T , its 1/4 period is T, and the period during which the reference signal is lower than the voltage e ₁ is 2t, then t = e ₁ /e _T
There is a relationship called T. Furthermore, since the relationship e _2T = 1/2te ₁ holds, e ₂ =t/2Te ₁ = 1/2e _{Te 1} ² . Since e _T is constant, e ₂ =e ₁ ² can be obtained by appropriately selecting the magnitude of e _T .

Moreover, when the input signal e _IN is the voltage e ₃ (=2e ₁ ), the comparator 2 and the changeover switch 4 operate in the same way, and a reference signal as shown in FIG. A voltage e ₄ is obtained as the signal e _OUT . At this time, the relationship e ₃ ² = e ₄ (=4e ₂ ) holds between the voltages e ₃ and e ₄ . In other words, when the input voltage doubles, the output voltage quadruples, and there is e _IN between the input signal e _IN and the output signal e _OUT .
The relationship ² = e _OUT is obtained. Thus, the square value can be calculated with a simple circuit configuration.

FIG. 3 is a circuit diagram of an embodiment used as a square root calculation circuit. The same parts as in FIG. 1 are given the same numbers. 7 is an operational amplifier, the input signal e _IN from the input terminal 3 is input to the non-inverting input terminal, and the smoothed signal e _FIL output from the filter 5 is input to the inverting input terminal. The output signal e _OUT of the operational amplifier 7 is output to the output terminal 6, and at the same time is input to the non-inverting input terminal of the comparator 2 and fed back.

With this configuration, operational amplifier 7
is controlled to output an output signal e _OUT such that e _IN =e _FIL . As a result, the following relational expression holds true.

e _IN =e _FIL ...(1) Also, from the example in Figure 1, e _OUT ² =e _FIL ...(2) From formulas (1) and (2), √ _IN =e _OUT ...(3) Thus, it is easy The square root value can be calculated with a simple circuit configuration.

In this way, since the square value or square root value of a predetermined analog quantity can be easily calculated, the relationship between the flow rate and the pressure difference can be easily calculated in a differential pressure type flowmeter using an orifice plate.

In the above embodiment, the reference signal is 3
Although a square wave is used, various signals having a periodically repeating proportional slope can be applied, such as a sawtooth wave or a waveform intermediate between a triangular wave and a sawtooth wave. Further, the changeover switch is not a contact type switch, but various electronic type non-contact switch means can be used.

In addition to differential pressure type flowmeters, the present invention can also be applied to differential pressure transmitters to compensate for detection sensitivity characteristics having square-law characteristics and to obtain linear output characteristics very easily.

As described above, the arithmetic circuit according to the present invention can perform square or square root calculations with a simple circuit configuration, and is very effective when used in differential pressure flowmeters, differential pressure transmitters, and the like.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of one embodiment of an arithmetic circuit according to the present invention, FIG. 2 is a wave diagram of each signal, and FIG. 3 is a circuit diagram of another embodiment. 1... Reference generator, 2... Comparator, 3... Input terminal, 4... Selector switch, 5... Filter, 6... Output terminal, 7... Operational amplifier.

Claims (1)

[Claims] 1. A reference generator that transmits a reference signal that periodically repeats a proportional gradient, and inputting and comparing this reference signal and an input signal,
It consists of a comparator that outputs an operating signal according to the polarity of the comparison value, a switch that turns on a reference signal output circuit in response to this operating signal, and a filter that smoothes the reference signal that is output when the switch is turned on. An arithmetic circuit that outputs a signal that is the square of the input signal from a filter. 2. A reference generator that emits a reference signal that periodically repeats a proportional gradient, an operational amplifier that inputs an input signal and outputs an output signal, inputs and compares the reference signal and output signal, and determines the polarity of the comparison value. It consists of a comparator that outputs an operating signal according to the operating signal, a switch that turns on the reference signal output circuit according to this operating signal, and a filter that smoothes the reference signal that is output when this switch is turned on. An arithmetic circuit that inputs a smoothed signal to the operational amplifier, controls the output signal so that the input signal and the smoothed signal are equal, and makes the output signal a square root of the input signal.