JPS61116619A - Servo type volumetric flowmeter - Google Patents

Abstract

PURPOSE:To expand the dynamic range while elevating the sensitivity near the zero, by inputting the output of a differential pressure detector into a non- linear amplifier which has a small gain when the differential pressure signal level is high while having large gain when the level is small. CONSTITUTION:The differential pressure before and after a rotor 4 of a flowmeter 2 is detected with a differential pressure detector 5, the output of which is inputted into a non-linear amplifier 6. The non-linear amplifier 6 is so arranged to have a high gain when the differential pressure input is small while having a small gain when it is large. Then, the output of the non-linear amplifier 6 is inputted into a servo amplifier 5 through a non-linear controller 7. Moreover, the output of the servo amplifier 8 is fed to a servo motor 9 and the output of a tachogenerator 10 connected to the servo motor 9 is fed back to the servo amplifier 8 as speed feedback signal.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention uses a servo motor to drive the rotor so that the differential pressure before and after the rotor of a positive displacement flowmeter is zero. This invention relates to a servo-type positive displacement flowmeter that eliminates leakage from the flowmeter.

[Conventional technology]

In servo-type positive displacement flowmeters that have a servo mechanism, the differential pressure detection sensitivity of the flowmeter is limited. Therefore, an attempt is made to bring the differential pressure closer to zero by increasing the gain of the servo amplifier as much as possible.On the other hand, when increasing the gain, the component differential pressure detector,
The response delay of the amplifier, etc. causes a phase rotation in the control system, resulting in instability such as hunting. For this reason, stable control is performed by performing compensation through P, I, and D control. However, depending on the type of fluid and the transient state, the load fluctuations are large, so Ill! of each of P, I, and D! !
There was the annoyance of having to do this. Furthermore, increasing the gain of servo amplifiers, differential pressure detectors, etc. causes the dynamic range to be limited (increasing the gain of the servo amplifier, differential pressure detector, etc.).In transient conditions, this range may be exceeded, resulting in loss of control.For this reason, in the past, differential pressure When using a detector, there are two types: one that measures low differential pressure with high sensitivity and one that measures high differential pressure with low sensitivity. A differential pressure detector that detects a wide range of differential pressures was used, and control was performed to switch to a highly sensitive differential pressure detector when the target value was approached, so it was a failure.

[Problem that the invention seeks to solve]

The present invention has been made in order to solve the above-mentioned problems.

[Means for solving problems]

In the present invention, a low-sensitivity differential pressure detector with a wide measurement differential pressure range is used, and when the differential pressure signal level is large, the gain is small, and the output of the differential pressure detector is By inputting the input to a non-linear amplifier whose gain increases when , and this output characteristic changes depending on the size of the time constant of the differentiating circuit which has a differentiating circuit as a feedback loop. It has an elemental nature. This will be explained below using examples.

[Examples and effects]

Figure 181 is an embodiment of the present invention, and the differential pressure is detected in order to detect the differential pressure before and after the rotor 4 of the flowmeter 2 installed in the flow tube 1! I5 is provided, the output of which is input to the nonlinear amplifier 6. The human output characteristic of a nonlinear amplifier is that when the differential pressure input is small, as shown in FIG. 2A, it has a high gain, as shown by the dotted line B, and when the differential pressure input is large, it has a small gain. The output of the nonlinear amplifier is input to a nonlinear controller 7. The nonlinear controller is a circuit having a feedback loop consisting of a comparator 71, an integrating circuit 72, a differentiating circuit 73, and an amplifier 74. :I comparator 7
1 has a minute hysteresis width, and the input of the comparator is the output signal C of the nonlinear amplifier 6 and the amplifier 74.
It is compared with the feedback signal which is the output of Furthermore, the differential circuit 73
is connected in series with a capacitor 75 and a resistor 76, and the amplifier 7
4 is connected to a series of these capacitors 75 and resistors 76. The input to the servo amplifier 8 is connected to the output of the integrating circuit 72 of the nonlinear controller 7.

Generally, a servo motor (
A tacho energator (TG) 10 is coupled to the SM) 9, and the TG output is fed back to the servo amplifier as a speed feedback signal to provide damping.

The operation of this circuit will be described.

The differential pressure signal is detected with a high gain near zero, and is
Although it is amplified by a t#i amplifier, such a non-linear amplifier can be easily obtained by negative feedback of a circuit element that is a combination of a diode and a resistor, which is a non-straight circuit 1'l, with a linear 7 amplifier. This is a well-known method.

Next, the operation of the nonlinear controller will be described.

Due to the differential pressure input signal: the output of the F amplifier rake 71 is immediately saturated and input to the integrating circuit. Since the time constant of the integrator circuit is selected to be a small value, the integrator circuit also saturates immediately, and the servo motor operates at the maximum number of times. In this case, the gain is high and there is no phase compensation, so the system oscillates and becomes unstable. On the other hand, if a closed circuit is used in which the feedback signal is applied to the comparison input of the comparator, the DC component is removed by the capacitor 75 of the differentiating circuit in the feedback circuit &:, and the tributary component in the integrating circuit 72 is returned to ff1b. This is because the time constant of the differentiating circuit is set in seconds, which corresponds to the delay in the control system, whereas the time constant of the integrating circuit is set in milliseconds.

Therefore, in such a closed circuit, oscillation at a low frequency of a hertz, which is determined by the slew rate of the comparator, the hysteresis width, the phase delay of the feedback signal, etc., is suppressed. In this circuit, the output of the comparator is an ON@ pulse IP corresponding to the deviation between the differential pressure signal and the RIM signal, which is converted into an analog signal by the integrating circuit 72. The magnitude of this analog signal is proportional to the 08 width and is input to the servo amplifier as a phase advance control signal. The differential time constant is changed by adjusting the variable resistor 76 of the differentiating circuit. A time constant that is longer than the delay of the normal control system is set. The amplifier 74 adjusts the damping gain.

As shown in FIG. 3, the relationship between the differential pressure signal and the nonlinear controller output is such that when the amount of negative feedback is increased, the gain of the nonlinear controller is decreased, and conversely, when the amount of negative feedback is decreased, the gain of the nonlinear controller 2 is increased. Therefore, the delay in the control system can be dealt with by adjusting the differential time constant, and the gain in the control system can be dealt with by adjusting the damping gain. Incidentally, since the capacitor 75 of the differentiating circuit blocks direct current feedback, offset in the steady state can be removed.

〔Effect of the invention〕

As described above, according to the present invention, in order to widen the dynamic range of control and increase the sensitivity near zero differential pressure before and after the compressor, it is possible to・The complexity of switching between a differential pressure detector with a wide differential pressure measurement range and a differential pressure detector depending on the size of the differential pressure can be reduced by simply modifying the low-sensitivity wide differential pressure detector and 7 amplifiers according to the present invention. Since the same effect can be obtained, a flow meter can be provided at a lower cost, and reliability is also improved because the number of components is reduced.

Furthermore, in the conventional PID controller 11g, P, I%D
Optimum control requires a lot of practice because each adjustment is required, but according to the present invention, the differential time constant and damping gain can be adjusted, so the optimal conditions can be found easily.

[Brief explanation of drawings]

Figure 1 shows the control block of the servo positive displacement flowmeter of the present invention, Figure 2 shows the output characteristics of the non-linear amplifier of the present invention, and Figure 3 shows the output characteristics of the non-linear controller of the present invention. . Procedural amendment written format) December 19, 1985 1, 1L Indication of patent application No. 145493 of 1988 2, Title of invention Servo-type positive displacement flowmeter 3, Person making the amendment Relationship to this case Patent application Person Postal code: 161 Name: Oval Equipment Industrial Company 4; Date of amendment order: November 6, 1985 (Delivery date: January 26, 1985) 5: [Brief description of drawings] Q) JgAJ6, “3rd” written on page 8 @ line 15 of the statement of contents of the amendment was changed to “3rd”.
The figure is corrected.

Claims (2)

[Claims] (1) A differential pressure detector that detects the differential pressure that occurs before and after the rotor of a positive displacement flowmeter, a nonlinear amplifier whose gain decreases as the output from the differential pressure detector increases, and the output of the nonlinear amplifier. It consists of a nonlinear controller that converts into a control signal, and a servo motor driven by the output of an amplifier that amplifies the output of the nonlinear controller, and the rotation of the servo motor is generated in the rotor of the positive displacement flowmeter before and after the rotor. A servo-type positive displacement flowmeter that transmits differential pressure so that it approaches zero. (2) The nonlinear controller in the servo-type positive displacement flowmeter described in paragraph (1) includes a comparator that compares the input signal from the nonlinear amplifier with the feedback signal, an integrating circuit that integrates the output of the comparator, and the integrating circuit. The servo-type positive displacement flowmeter according to claim 1, wherein the output of the servo-type positive displacement flowmeter is used as an output signal, and the output signal is used as a feedback signal via a differentiating circuit and an amplifier circuit.