FBM205 Application of PLC in feed weighing and packinghttps://www.gsplcdcs.com/
http://www.gkong.com 2010-01-18 15:22 Guangzhou Kaishi Weighing Equipment Engineering Co., LTD
1. Preface
Feed weight measurement and packaging is an important production link in feed industry. The accuracy of feed weighing and packaging will directly affect the reputation and economic benefits of enterprises. In the past, mechanical weighing and manual bagging were used, with high labor intensity, slow speed and low precision. In recent years, although the static weighing accuracy can be greatly improved by using electronic weighing devices, its dynamic accuracy can not be guaranteed in the continuous production process of feed processing. Therefore, how to improve the dynamic weighing accuracy in fast automatic weighing has always been an urgent problem for feed processing enterprises.
FBM205 In the development of automatic feed production equipment, in order to coordinate with the batting process and realize the full automation of feed production, PLC is used as a dynamic weighing and packaging measurement and control equipment, and some measures and dynamic control methods are adopted in the hardware and software design, which better takes into account the contradiction between weighing speed and precision. The precision of dynamic weighing and metering in continuous feed production is realized.
2. Overall block diagram and working principle of the system
The measurement and control system composed of weighing sensor, amplifier and PLC is used to complete the production process of weighing, metering and packaging of feed, as shown in Figure 1. With PLC as the core, the system is equipped with weighing sensors, amplifiers, various electric actuators and mechanical devices to realize dynamic online weighing, metering and packaging of feed.
Above the weighing bucket is the finished product bin, the raw material in the bin is the feed bulk finished material produced from the feed mixing process. Under the finished product bin is a screw feeding device driven by a motor. When the motor is started, the powdered feed in the finished product bin enters the weighing bucket with the rotation of the transmission cage. Weighing bucket is equipped with three S-beam strain tension sensors, weighing bucket weight signal is directly converted by the sensor group into the corresponding voltage signal, the amplifier amplifies the voltage signal and sends it to PLC for data processing, when the predetermined value is reached, PLC control to stop feeding, and then PLC control to open the weighing bucket door. And control the automatic bagging machine by the conveyor belt sent out. Thus, the automatic process of feed weighing and packing is completed.
3. Hardware measures to improve the precision of dynamic weighing
FBM205 The influence on the static accuracy of weighing comes from the hardware system composed of sensors and amplifiers, as shown in Figure 2.
The system uses three tension sensors to convert the feed weight W into a linear voltage signal Ux, which is amplified by a two-stage amplifier. In the figure, Un represents the equivalent noise and interference voltage to the input of the amplifier, and ΔUi represents the equivalent drift voltage to the input. Set the magnification of the two-stage amplifier to A, then Uo=A(Ux+Un+ΔUi)=AUx+AUn+A·ΔUi formula in the second term mainly affects the sensitivity, the third term mainly affects the accuracy of the system.
(1) Factors affecting the sensor and solutions
FBM205 The stability of the sensor output signal not only determines the performance of the sensor itself, but also has a close relationship with the power supply and the installation of the sensor. The system uses three UH61-100u weighing sensors, each sensor is powered separately, and the output sensitivity K of the three sensors is the same by adjusting its bridge voltage, and the output voltage of the three sensors in series is Ux=K(E1+E2+E3). In order to improve the stability of the bridge power supply of each sensor, secondary voltage regulation is adopted, and the components are aging and selected after testing, especially the aging treatment and time-drift test of the reference voltage regulator 2DW233, and the time-drift is selected to work near zero temperature coefficient (<2ppm/℃) by adjusting its working current. The temperature stability of the entire sensor power supply is better than 10ppm/℃. Three tension sensors are installed between the weighing bucket and the weighing frame. If there is an alpha Angle between the weight of the sensor and the axis of the sensor, the lateral component force will be generated and the error ΔW=W-Wcos alpha will be introduced. This is for each weighing 25Kg, in the case of a bucket tare of 100Kg, that is, the actual load of three 100Kg sensors is 125Kg. When Alpha =4°, the weighing error is 0.43Kg. Therefore, when installing the sensor, try to ensure that the sensor can be vertically stressed.
(2) FBM205 Factors affecting the sensitivity of the system and solutions
The main factors affecting the sensitivity of the system are the internal noise of the detection circuit and the external interference voltage Un, which is related to the frequency band in which the amplifier operates. In the development, through the selection of low-noise devices, under the premise of meeting the acquisition speed required by a wide enough frequency band, through the selection of resistance to improve the amplifier circuit’s own common mode rejection ability, the whole detection system adopts double-layer shielding, sampling time is selected as an integer multiple of the power frequency cycle and other measures, so that the whole system can obtain the sensitivity of 5g weight.