Views: 0 Author: Site Editor Publish Time: 2022-01-25 Origin: Site
Piston-type water meter detection device
The liquid flow standard device is widely used in the experiment and verification device of liquid flow meter, especially for flow meter manufacturers, there are a large number of instrument verification work and product development experimental work, a set of efficient and reliable liquid flow standard device is produced. Activities are important. In industrial applications, the flow standard device should not only have sufficient accuracy and reliability, but also have a relatively high verification efficiency. Factors such as the construction cost of the device, the operating cost, and the technical requirements of the operator should also be considered.
The traditional liquid flow standard devices are mostly standard devices based on the mass method and the volume method. The generation of the flow source relies on the water pump to provide the flow, but the flow is pulsating, the flow stability is poor, and the flow point adjustment is not accurate. With the rapid development of these devices, these devices can no longer meet the requirements. In order to meet the requirements of liquid flow meter verification, calibration, factory inspection and the growing trend of new flow meter production.
Our company has designed and manufactured an active piston liquid flow standard device with water as the medium. This standard device has a unique design. Its basic working principle is to compare the volume flow of the fluid discharged by the piston and the volume flow of the tested flowmeter within a certain time interval. In contrast, the volume of fluid displaced by the piston is obtained by multiplying the cross-sectional area of the piston cylinder by the displacement of the piston.
Driven by the servo motor to reduce the disturbance to the liquid flow, it has many advantages such as stability and reliability, good repeatability, high degree of automation, and easy operation, avoiding the shortcomings of the start-stop effect or the commutator effect of the traditional liquid flow standard device. It is beneficial to improve the measurement uncertainty level. The device also has the characteristics of self-contained, compact structure, high efficiency and energy saving, no need to build a pool, no need to put forward special structural requirements for buildings, and is very suitable for production testing and product development testing of small flow metering instruments.
1. Device uncertainty: ≤0.2%(k=2) Flow stability ≤0.2%;
2. The working pressure of the device: 0-1MPa;
3. The working temperature of the device: 5-85℃;
4. The number of inspection meters: ultrasonic or ordinary water meters: DN15: 10 only, DN20: 10 only, DN25: 8 only, and the number of clamps for other meters is calculated according to the length of the pipeline;
5. Communication interface: M-BUS, RS485;
6. Control system: Siemens PLC, industrial control touch screen;
7. The verification process is automated, with functions such as visual interface control, automatic data saving, and report generation.
1. Piston composition
The active piston liquid flow standard device is shown in Figure 1, which is mainly composed of a frame, a piston rod, a piston cylinder, a motor, a ball screw, a supporting optical axis, a sensor, and a protective casing. The piston rod is in close contact with the piston cylinder through the Y-shaped sealing ring, and the three together form a sealed cavity. The movement of the piston rod is realized by the servo motor, coupling, ball screw, supporting optical axis, etc. The rod is connected by a screw nut, and the movement direction is controlled by a servo motor and a ball screw. A water suction pneumatic valve and a drainage pneumatic valve are installed at the outlet of the piston cylinder. Install high-precision temperature and pressure sensors.
2. Hardware characteristics of the control system
The control system is mainly composed of industrial computer, PLC control system, servo motor, grating ruler, various temperature and pressure sensors, pneumatic ball valve, platform software, etc. The industrial computer has strong anti-interference, which can make the verification process more stable and reliable; the PLC and servo motors are internationally renowned brands with high precision and high reliability, and the control and data processing software are written in accordance with the relevant national verification regulations.
(1) grating ruler
The standard cumulative flow of the active piston liquid flow standard device is the product of the internal cross-sectional area of the piston and the piston displacement in the time period. Therefore, the accurate measurement of the piston displacement is one of the key factors to reduce the uncertainty of the device. In order to improve the accuracy of displacement measurement, the device uses a grating ruler to measure the displacement of the piston. The output signal of the grating scale is an AB quadrature signal, which is improved by 4 times on the basis of the original accuracy.
(2) Servo motor
The driving element of this servo system is a Panasonic servo motor. The servo motor converts the voltage signal into torque and speed to drive the control object. Changing the voltage signal can change the speed and direction of the servo motor. The servo has a built-in 23-bit encoder, which has higher control accuracy. The servo system accurately drives the displacement of the piston according to the instantaneous flow and calibration signal sent by the host computer. The servo motor has large starting torque, wide operating range, no rotation phenomenon, and positioning accuracy. High features, widely used in various automation control systems.
The sensor mainly has a temperature sensor and a pressure sensor, which are located at the water outlet of the piston cylinder, which are respectively used to measure the temperature and pressure of the liquid, and then transmit the information to the PLC and software system in time.
Sensors are important components for collecting analog quantities such as temperature, pressure, humidity, etc. Its accuracy and performance will directly affect the accuracy of the measurement results of the device. Therefore, it is necessary to comprehensively consider various factors to select the most cost-effective sensor products. In this device, the temperature measurement range of the temperature sensor is (0～100)ºC, and the accuracy grade is not lower than A; the pressure measurement range of the pressure sensor is (0～1.6)MPa, and the accuracy grade is not lower than 0.5%.
(4) PLC control system
The PLC control system of this device adopts Siemens S7200smart system, adopts ladder programming language, and mounts analog input and output modules to collect and control temperature and pressure signals.
PLC is essentially an industrial control computer, which uses programmable memory to store and execute instructions such as logical operations and sequential operations, and controls machinery or production processes through digital and analog input and output. The interface connecting the PLC with the industrial process It has the advantages that the general computer does not have, and the PLC itself has a better programming language suitable for control requirements. The device is made in accordance with CE safety standards and has numerous protections and sound and light alarms, such as low air pressure alarm, low water tank level alarm, watch clamp not in place alarm, piston overtemperature alarm, piston overpressure alarm, piston limit alarm, etc.