The Acrylic Fiber Division of Sinopec Shanghai Petrochemical Company Limited is currently the largest professional acrylic fiber manufacturer in China, covering an area of 25.45 hectares. There are three major acrylic fiber production units: South Acrylic Unit, North Acrylic Unit and Jinyang Acrylic Unit. The main products are acrylic fiber and acrylic wool.

Second, the nature of the measured materials and the process requirements of this project are as follows:

(1) The conveying material is polypropylene acrylic

2）Particle diameter is 20-30um.

3）Moisture content is 45%-55%.

(4) The first automatic feeding system is centrifuge equipment, centrifuge discharging process is 16 minutes / times, each time out of 54kg, put into the lower reactor dosing system, a total of 5 times to the reactor dosing system in the material is about 270kg.

(5) Weighing reaction tank in the lower reactor to add materials, such as adding materials to reach 250kg, weighing reaction tank closed to stop adding materials, into the next cycle.

(6) 250kg of material is required to be discharged at a uniform speed within 30 minutes, with a measurement accuracy of 1%.

When the reaction kettle weighing calibration, equipment operation first incremental method on the centrifuge from the top of the reaction kettle charging measurement tracking. After four times of centrifuge charging or when the material in the reaction kettle is more than 250kg, the weighing control system sends a message to the centrifuge to prohibit the charging. Weighing control system to the centrifuge to send a signal to prohibit discharging, while discharging waiting state at any time to accept discharging instructions, dosage reduction method of measurement of the average speed in 30 minutes after discharging the material. After discharging, the weighing data and time can be saved.

Third, the control system to complete the function

1、SIWATOOLMS software calibration weighing

For SIWAREXMS module weighing software SIWATOOLMS is very easy to use, the operation can be independent of SIMATICS7-200 dosage debugging. Through the RS232 interface connected to the PC Com port, in the calibration interface, enter the weight of the standard weights, sent to the SIWAREXMS dosage module, and then in the empty scale, click on the "Zero Valid" button, put the 50KG standard weight weights, and then click on the "Weight Valid" button. After putting 50KG standard weights, click " Weight Valid", the calibration work can be completed instantly.

2、Set the low-pass filter frequency

In the on-line debugging can be based on the vibration of the two motor operation, to adjust the filter frequency, so that it is in the maximum conditions to limit the data of the vibration jumps, but does not produce too much lag in the data affects the accuracy of the generation of ultra-differential. Debugging in the dynamic process is very easy to adjust in the monitoring, more intuitive. Setting range from 0.05Hz to 5Hz between the seven optional frequency range. Truly from the point of view of the control application, a flexible solution to the impact of the two motor vibration.

3、PLC programmable weighing function

The PLC program can call the ready-made sub-programs provided by Siemens, which saves a lot of time in writing the weighing program, and only needs to call a few variables of the sub-programs, e.g.: tare, zero marking, displaying the tare weight, etc.. As shown in Fig. 5 SIWAREXMS weighing main program, the whole program is visualized and easy to operate.

4. Characteristics of the SIWAREXMS module

SIWAREXMS is a multipurpose metrology module for all simple weighing and force measurement applications. Its compact and modular design makes it easy to install in SIMATICS 7-200 systems. the SIWAREXMS module accesses the setup and weighing data directly in the S7-200 CPU, without the need for additional communication interfaces for data transfer with the PLC.

The SIWAREXMS module also offers the following advantages:

(1) Unified design using the STEP7-Micro/WIN software package, fully compatible with the S7-200.

(2) Measurement accuracy of 0.05%, with a resolution of 65,000, can be displayed after the decimal point of three or four decimal places

(3) Quick start-up of the weighing functions with the "Quick Start" software package.

4）With rich self-diagnosis function

5）With theoretical calibration function, no need to calibrate the weights.

6) Replacement of the weighing module without recalibration, all the calibration data of the load cells are stored in the CPU.

7) Easy to set up and calibrate the weighing module through SIWATOOLMS software, even if you have no PLC related experience, you can easily complete the calibration work.

8）It is certified as Ex-proof area, which is very suitable for chemical applications.

Project operation

The actual equipment debugging situation 250kg of material, the error is between 300g and 500g, accuracy of about 3 parts per thousand, much higher than the user's expectations of 1%. And two motors running at the same time fluctuations in the value of 200 grams, the entire discharge time control in 25 minutes. This result is very satisfactory for the customer, and the weighing method is also very satisfactory. Since the delivery of the equipment, there have been more than two months, the operation has been very stable.

V. Application experience

Previously used other manufacturers of PLC systems, the resolution of its analog module is the value of 4000 and 8000, and the previous weighing solutions also need to be equipped with traditional weighing instrumentation, and the conversion of analog data from different brands of products is very easy to cause data distortion. This time, after Siemens experts introduced, for the first time to use Siemens weighing solution, SIWAREXMS weighing module and Siemens PLC in the system data is directly converted to process weighing data, with high accuracy, stable performance and other characteristics, without excessive AD / DA / AD analog-to-digital conversion, and will not cause data distortion.