The basic concept of weightless scale and the main points of conception
The weightlessness scale is a kind of weighing equipment with intermittent feeding and continuous discharging. Because the loss control is carried out in the hopper, it can achieve higher control accuracy and the structure is easy to seal. Therefore, the screw scale is used for powder control. Compared to that is a big improvement. It is suitable for the control batching of fine materials such as cement, lime powder and coal powder. The weighing hopper and the feeding mechanism are used as the entire scale body, and the weight signal of the scale body is continuously sampled by the weighing instrument or the upper computer, and the rate of change of the weight per unit time is calculated as the instantaneous flow rate, and then through various software and hardware Filtering technology processing, get the actual flow that can be used as the control object. The acquisition of this flow is very important and is the basis for the accuracy of the weightlessness scale. FC uses PID feedback algorithm to perform control calculations to approach the target flow, and output adjustment signals to control feeder controllers such as frequency converters. It can be seen from the principle that it is not affected by the mechanical changes of the scale body and the feeding mechanism, but only calculates the weight difference (differential weight). Compared with the traditional dynamic measurement method, the advantages are self-evident. When the control object is the flow rate, and the material can be transported well, and the measurement accuracy is high, the weight loss method can be used as an ideal solution. Attention must be paid to the design of a weightless scale, so as not to affect the accuracy. First, determine the correct delivery rate range. Generally, the actual working range is 60% to 70% of the rated delivery volume. If AC speed regulation is adopted, the corresponding frequency conversion rate is 35~40Hz. This ensures a wide adjustment range, because when the delivery rate is too low, the stability of the system is poor. The sensor range is selected appropriately, and the sensor also uses 60%~70% of its range. The signal variation range is wide, which is beneficial to improving the accuracy. The mechanical structure design must ensure good material fluidity, and at the same time, ensure that the replenishment time is short. If it is too frequent, it is generally required to make up the feed every 5 to 10 minutes. The supporting transmission system must ensure stable operation and good linearity.