1 Preface

In the resin mixing production process, the dosing is in an important basic position, the dosing product that is the liquid quality indicators of the advantages and disadvantages of the subsequent resin production operations have an important impact. The main quality indicators of calcium ratio, fineness, aluminum-silicon ratio and fineness are achieved by adjusting the ratio of methanol, polyurethane and other materials entering the raw material mill and the flow rate (weight of material per hour).

The original dosing equipment and methods used are: the use of two skirt-type plate machine with the above two kinds of materials, relying on the adjustment of its drive motor slip motor speed to complete, that is, there are technicians relying on the pump weighing the weight of the two kinds of materials at different speeds, and then simply estimate a series of different speeds corresponding to the flow rate of the two kinds of materials, the operation of the room, and then the feed machine operator in accordance with the adjustment indexes of the personnel's orders, according to the In the operation room, the operator of the feed machine will adjust the ratio and flow rate of the materials according to the order of the person who adjusts the index and rely on the manual adjustment of the motor speed in this table. This method has the following shortcomings: on the one hand, due to the performance limitations of the slip speed motor itself, when the plate machine is running at a low speed, the speed of the plate machine is often in a kind of unstable state, that is, in the normal range of speed regulation often occurs due to the unstable performance of the governor obvious deviation, every week or so, you need to electrician to the governor overall calibration in order to be able to use it normally, and due to the sealing of the slip clutch is not good, the clutch is easy to be dusty, the clutch is easy to be used as the main equipment, and it is easy to be used as the main equipment. Not good, the clutch is easily blocked by dust or foreign objects and cause flying (out of control) phenomenon. As a result, the measurement is not accurate and difficult to meet the production process control requirements, resulting in a low pass rate of the grinding liquid into the slot, the need for follow-up in the small slot in the second or even three times to adjust the indicators in order to qualify the slot, so that the subsequent process has become complex. On the other hand, the plate machine speed weighing instrumentation in the field and the lack of online testing and dosage equipment, which requires feed machine operators to regularly irregularly to the scene inspections, records, calculations, adjustments, etc., labor-intensive. Furthermore, the plate machine is more than the electronic scale maintenance, cleaning workload, high cost. In view of the above problems, we use DCS dosage system, frequency conversion electronic scale and its control weighing instrumentation, etc. on the dosage system for transformation.

2 working principle and application of frequency conversion speed control system

2.1 Each part of the device selection and its function:

DCS system using FOXBORO company I / A, S centralized distribution system (here only list the functions related to the control of this part) its role as:

(1) According to the overall process and dosage equipment to provide two electronic scales (two kinds of materials) of the proportion of material and flow given.

(2) Completion of explosion-proof electronic scale start, stop the automatic control, and including fault alarm and shutdown.

(3) Completing the interlocking protection control function with other related dosage equipment.

The weighing instrument uses TS900, a high-performance control weighing instrument specially designed for electronic scales, whose role is to compare the given flow value provided by DCS with the returned instantaneous flow value, and then change the given speed of the frequency converter through the operation of its internal PID regulator to adjust the instantaneous flow so that its value is equal to the given flow value.

The frequency converter uses LG's iG5 (3.7kW) series.

PTM-1000 is used for frequency conversion and speed control. The weighing module is YZC-516-500kg. The speed measurement module is Ni3-EG08-ANGX.

2.2 Working principle (automatic control):

Take an electronic scale as an example: first of all, manually electrify the electrical circuits of each part of the electronic weighing system, so that it has the conditions for automatic operation: close the circuit breakers QF1, QF2 and QF3, the weighing instrument TS900 gets power and carries out self-checking, and sends out a signal of readiness to the DCS system after its hardware is free from any problem (KA2 is closed), which means that it is permitted to start the car, and then put the SA in the automatic position (KA1 is closed). (KA1 absorbed). So far, it has the condition of automatic control operation, when the operator in the main control room needs it to run, he can start the electronic scale in the main control room through the microcomputer mouse (DCS system), at this time, the KA3 coil is electrified, and its normally open contact is closed, the frequency converter starts and at the same time, sends out the answer signal (KA4 absorbs) in the weighing instrument, the weighing instrument starts to work after getting the instruction, and adjusts the frequency converter to adjust the running speed of the electronic scale according to the flow rate given in the DCS. According to the flow value given by the DCS, the frequency converter adjusts the running speed of the electronic scale. Since there is a period of fabrication when the electronic scale starts to operate, the weighing instrument does not carry out PID regulation or alarm (except for the speed alarm) during the set fabrication time, but it carries out the calculation of the flow rate and the calculation of the totalization value at any time. If the load factor is detected during the feeding period