JPH0680407B2 - Impeller flow meter - Google Patents

Description

TECHNICAL FIELD The present invention relates to a flow meter.

[Prior Art] The flow in the suction pipe or the discharge pipe of a reciprocating pump or a compressor is pulsating. In connection with the operation of these fluid transportation machines, and especially when the development is intended to improve the performance of these machines, the instantaneous value or time average value of this pulsating flow may be required. Although there are various kinds of flowmeters that measure such a flow rate in principle, the impeller type flowmeter in which the impeller is installed in the pipe is preferable. In this, there is a flow meter of the type that knows the flow rate by the angular velocity of the impeller (Flow Measurement Handbook, edited by Kawada, Komiya, Yamazaki, 1979, Nikkan Kogyo Shimbun, pp. 199-218. -15562 publication). Alternatively, there is also a flow meter that connects the impeller with a motor driven by a constant voltage power supply and knows the flow rate from the motor current, etc.
-51282, Japanese Patent Publication No. 58-56414).

[Problems to be Solved by the Invention] The angular velocity detection type impeller flowmeter has high accuracy, but its dynamic response is very low. On the other hand, the impeller flow meter that uses a constant-voltage power supply motor has a higher dynamic response than the angular velocity detection impeller flow meter. However, there is a problem that the response is determined by the performance of the motor or is not as high as necessary. As described above, since the existing impeller flowmeter has low dynamic response, it is impossible to accurately measure the pulsating flow rate in the suction pipe or the discharge pipe of the reciprocating pump or the compressor. This invention
It is an object of the present invention to obtain a highly accurate and highly responsive flow meter capable of measuring such an instantaneous value or time average value of the pulsating flow rate.

[Means for Solving Problems] The basic concept of the flowmeter of the present invention will be described with reference to FIG.

The flow rate detecting element of this flow meter is the impeller 11, and the fact that the flow acts on the impeller 11 is used for the measurement. In this flow meter, the shaft of the impeller 11 is connected to the shaft of the motor 12. This will be referred to as the flow meter rotor 1. motor
12 is driven by a feedback type constant angular velocity control device (hereinafter, abbreviated as constant velocity control device) 2 that receives a voltage corresponding to the motor angular velocity. Then, even if the flow rate changes, the angular velocity of the flow meter rotor 1 is not affected by this and maintains a substantially constant value. At this time, the motor current has a one-to-one correspondence with the flow rate. This correspondence holds even when the flow rate changes rapidly. This motor current is detected and the current is input as
By reading the output voltage of the voltage converter 3, the instantaneous value of the pulsating flow rate can be measured.

[Operation] The operation of the flowmeter of the present invention will be described with reference to FIG.

An impeller 11 is installed in a cylinder 4 in which a fluid is flowing (flow rate q). The impeller 11 is rotating at the set angular velocity ω, and the direction of the angular velocity is opposite to that rotated by the flow. Then, it is assumed that a current i commensurate with this operation is flowing in the motor 12.

Now, consider that the flow rate suddenly increased, for example. Then, the angular velocity of the flowmeter rotor 1 decreases, and the difference from the set angular velocity increases. The constant speed control device 2 inputs a voltage proportional to the angular velocity of the flowmeter rotor 1 and a voltage proportional to the set angular velocity,
The voltage corresponding to the difference between the two voltages is used as the output voltage. Therefore, in the present case, the output voltage of the constant speed control device 2 increases. Since the motor 12 is driven by the constant speed control device 2, the motor current increases. Therefore, the angular velocity of the flow meter rotor 1 increases. Even if it says that the flow rate increases, it does not exceed the value before the flow rate increased, but stays at a value slightly smaller than the previous value. Then the motor current settles to a value corresponding to the new flow rate. When the flow rate drops, everything works in reverse. In this way, even if the flow rate q changes, the angular velocity ω of the flowmeter rotor 1 maintains a substantially constant value, and the motor current i always corresponds to the flow rate q. Note that the angular velocity can be set to zero, or can be set in the same direction as it is rotated by the flow.

The flowmeter rotor 1 has a moment of inertia. When there is an inertia moment, when the motor current changes, the change in the angular velocity of the flowmeter rotor 1 is always delayed, but since the gain of the constant speed control device 2 is made sufficiently large and the frequency characteristic is sufficiently extended, The angular velocity of the flowmeter rotor 1 changes immediately in response to changes in the motor current. The amount of change itself is very small. This is a flowmeter rotor 1
Corresponding to the equivalent reduction of the moment of inertia of.
In this way, by controlling the motor 12 at a constant angular velocity,
The motor current i can quickly follow the flow rate q.

Actually, in this control system, not only the flowmeter rotor 1 has a delay characteristic, but also the constant speed control device 2 has a delay characteristic. May be unstable. It is essential to equip the constant speed control device 2 with a phase correction circuit for avoiding this instability.

It should be noted that this motor current i is converted into a voltage by the current / voltage converter 3, and this is used as the indicated value of the flow meter.

[Embodiment] An embodiment of the flowmeter of the present invention will be described with reference to the drawings.

FIG. 2 shows that the shaft of the impeller 11 is connected to one end of the shaft of the motor 12, and the shaft on the opposite side of the motor 12 is connected to the shaft of the angular velocity detector 21, and these are supported by the support component 5. It is shown that it is mounted inside the cylinder 4. However, the motor 12 and the angular velocity detector 21 may be outside the cylinder.

Next, FIG. 3 is a simplified circuit diagram showing one embodiment of this flow meter, and the constant speed control device 2 is an example corresponding to the embodiment described in claim 2. is there.

The configuration of the constant speed control device of this embodiment will be described.

The voltage of the angular velocity setting power supply 22 is e ₀ . A subtracter 23 produces a difference Δe between the output voltage e of the angular velocity detector 21 and this voltage e ₀ . This difference voltage Δe is input to the phase compensator 24. This output voltage is input to the amplifier 25, and this output voltage
It drives the series circuit of 12 and the motor current detection resistor 26. Then, a current i flows through the motor. In this way, the operation of the motor constant angular velocity control device described in the section [Operation] can be realized. The control circuit has been described above.

Next, a circuit (a part of FIG. 3) of the current / voltage converter 3 which produces the indicated value of the flow meter will be described. The voltage follower 27 receives the voltage across the motor current detection resistor 26. The output voltage of this is a voltage proportional to the motor current and is the actual reading of the flow meter. However, in this embodiment, the output voltage of the voltage follower 27 is input to the linearizer 28, and the output voltage of the linearizer 28 is used as the indicated value of the flowmeter. This linearizer 28 will be described. Considering the case of using a permanent magnet field type (or shunt winding type) DC motor as the motor, the motor current is proportional to the square of the flow rate, so the indicated value of the flowmeter becomes very small at a small flow rate. . In order to improve this, a two-quadrant square root calculator is used as the linearizer 28. Since the square root calculator has a very large gain when the input voltage is small, the indication value of the flow meter can be made proportional to the flow rate by using this. In the graph of FIG. 4, the solid line shows the flow rate and the output voltage of the voltage follower 27 (which is also the input voltage of the linearizer 28), and the broken line shows the relationship between the flow rate and the output voltage of the linearizer 28. However, this is the relationship when the set angular velocity is zero.

Here, from the viewpoint of obtaining a flow meter with a high response speed and a high accuracy, a preferable form will be given for the main ones among the constituent elements.

First of all, the impeller 11 is preferably an axial-flow impeller because it can be used even in reverse flow and has a small energy loss. Next, if a permanent magnet field type (or shunt winding type) DC coreless motor is used for the motor 12, a flowmeter with good performance can be obtained.

As the angular velocity detector 21, a pulse encoder or a frequency generator can be used in addition to the DC tacho generator. The DC tachogenerator whose output voltage is proportional to the angular velocity is the best in terms of the circuit simplification, but other ones are better in terms of the small friction torque. The angular velocity can be detected without using a dedicated detector. For example, if a Wheatstone bridge is constructed using a permanent magnet field type (or shunt winding) DC motor armature on one side and resistors on the other three sides, the connection point between the motor and the series resistor The difference between the electric potential of No. and the electric potential of the corresponding connection point is the voltage representing the motor angular velocity (no explanatory diagram).

[Effects of the Invention] The flowmeter of the present invention can have a very high response speed as compared with the conventional impeller flowmeters. Therefore, using this, it is possible to accurately measure an instantaneous value or a time average value of a severe pulsating flow rate such as a pulsating flow rate in the suction pipe or the discharge pipe of the reciprocating pump or the compressor. The flow meter using the constant speed control device described in claim 2 has a simple structure. Although the flow meter of the present invention is intended to measure the pulsating flow rate, it is naturally possible to measure the steady flow rate.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining the basic concept of the flow meter of the present invention, FIG. 2 is a view showing a flow meter rotor mounted on a cylinder, and FIG. 3 is an embodiment of the flow meter of the present invention. It is a simplified circuit diagram. Further, FIG. 4 is a diagram showing the relationship between the flow rate as the measured amount, the output voltage of the voltage follower, and the output voltage of the linearizer. In FIG. 1, 1
Is a flow meter rotor, 11 is an impeller, 12 is a motor, 2 is a constant speed controller, and 3 is a current / voltage converter.

Claims (2)

[Claims] 1. A current / voltage converter (3) having a flowmeter rotor (1) as a main body, which is formed by connecting a shaft of an impeller (11) and a shaft of a motor (12), and which inputs a motor current. In a flow meter that indicates the flow rate by the output voltage of the flow meter, the constant angular velocity control device (2) that inputs the motor angular velocity controls the angular velocity of the motor (12) to be constant regardless of the flow rate value. . 2. The flowmeter according to claim 1, wherein the constant angular velocity control device (2) has the following structure. A) An angular velocity detector (21) for detecting the angular velocity of the motor (12), an angular velocity setting power supply ( 22 ), and a subtractor that inputs the output voltage of the former and the voltage of the latter and creates the difference between both input voltages. ( 23 ) a) Phase compensator ( 24 ) that receives the output voltage of this subtractor ( 23 ) c) Use the output voltage of this phase compensator ( 24 ) as an input, and use the output to output the motor (12) and motor current. Amplifier ( 25 ) driving series circuit of sense resistor ( 26 )