The compressor weighing module in the current refrigeration industry controls the capacity of the compressor based on the maximum cooling capacity of the screw compressor under the given operating conditions. However, during use, due to various reasons, it is required to change the gas output to adapt to the actual cooling load, enabling a continuous and stepless adjustment of the gas output ranging from 10% to 100%, and also allowing for no-load startup. Therefore, screw compressors currently commonly use slide valve regulation.

The weighing module adopts an industrial control distributed control method. It consists of a main unit and multiple slave units connected through a network. The main unit delegates control tasks to each slave unit for execution. The weight is picked up by pressure, and the picked-up weight signal is amplified, filtered, and then sent to the A/D converter for conversion from analog to digital. It is then sent to the weighing instrument for signal analysis and processing. The results are output through the RS232C communication serial port to the industrial control. At the same time, corresponding reactions and operations are made based on the signal results. The control system can freely switch between manual operation mode and automatic operation mode in a certain sequence.

The alarm and interlock protection function is a digital alarm. The overload signal of the compressor is given by the thermal relay in the electrical control cabinet. The exhaust pressure is converted into a standard current signal by the weighing module and sent to the control system. A high alarm value is preset, and when the exhaust pressure is higher than this alarm value, the system alarms and displays the corresponding alarm information. During operation, the unit detects various digital and analog signals in real time, determines whether an alarm occurs, and takes corresponding alarm and protection measures.

The energy regulation control system of the compressor realizes the regulation of compressor energy by controlling the on-off of two energy regulation solenoid valves. When load needs to be increased, the load increase solenoid valve is opened, and the energy level slide valve is pushed to the load increase position through the corresponding oil circuit to achieve the load increase operation. Similarly, when load needs to be reduced, the load reduction solenoid valve is opened. In the automatic operation mode, the system regulates the energy of the compressor based on the comparison result of the current value of the suction weighing module and the control set value. When the suction pressure is higher than the control set value, the load is increased; when the suction pressure is lower than the control set value, the load is reduced.

The weighing module uses the Siemens S7-200 CPU226XM as the control core. As the most powerful CPU module in the S7-200 series, CPU226XM has more input/output points, stronger module expansion capability, faster running speed, and more powerful internal integrated special functions. It is used for higher requirement control systems.

The EM231RTD module is used in combination with the PT100 platinum resistance to detect temperature signals. The weighing module has an input resolution of 0.1°C, 15-bit A/D conversion accuracy, a full-channel refresh cycle of 405ms, and can connect two temperature inputs. At the same time, this module can set multiple types of thermocouple circuits and has functions such as thermocouple circuit break detection.

The compressor detects the pressure signal through the weighing module, and the position of the angle displacement sensor detects the energy level position, the content volume ratio slide valve position, and the current signal of the compressor motor. It has 12-bit A/D conversion accuracy, a digital-to-analog conversion time of less than 250ms, can detect 4 voltage or current signals, and can set multiple input types.

The text display TD200 is used as the human-machine interface for display and operation. Information is displayed in simplified Chinese characters, the interface is friendly, and programming is very convenient. Its data and code are stored in the PLC's memory, and a command wizard can be used in the PLC programming environment to complete the programming work quickly. The connection of TD200 is very simple. Just plug it into the PPI interface of the CPU module using the provided connection cable, and no separate power supply is required.