一拖一手动旁路柜是由三个高压隔离开关QS1、QS2、QS3组成。手动旁路柜严格按照“五防”联锁要求设计，变频器输出QS2和旁路高压隔离开关QS3机械闭锁，完全能够保证变频调速系统安全运行。
1)在变频运行状况下，QS1、QS2闭合，QS3断开。
如需手动切换至工频运行时，系统先停止变频器输出，断开用户开关，再由机械操作依次断开QS1、QS2，然后机械操作闭合QS3，使电机切换至工频侧，再合上用户开关，使电机工频运行；
2)在工频旁路运行状况下，QS3闭合，QS1、QS2断开。
如需手动切换至变频运行时，系统先断开用户开关，由机械操作断开QS3，然后由机械操作依次闭合QS2、QS1，使电机切换至变频侧，再合上用户开关。
2. 控制系统方案
为了更方便的操作，变频器的起停在机旁箱进行控制，在DCS上进行监控。频率调节通过前级的传感器返回的电流模拟量信号（4—20mA）进行PID控制。其具体控制信号如下：
2.1 与高压开关柜联锁信号
1）合闸允许：常开接点，闭合有效，此信号串联在供电高压开关柜的合闸回路中，当变频器自检完成或系统处于工频状态时，信号闭合，允许用户合高压电；
2）高压跳闸：常闭接点，断开有效，此信号并联在供电高压开关柜的分闸回路上，当变频器发生重大故障或急停信号有效时，分断用户高压电；
2.2 变频器DO信号
以上输出信号全部为独立无源干接点，默认为常开接点，闭合有效，容量大小为250V AC 5A。
2.3 变频器DI信号
以上输入信号仅需客户提供独立无源干接点，脉冲信号，除急停外，其它信号均默认为常开接点，闭合有效；
2.4 变频器AI信号
2.5 变频器AO信号
四、现场实际运行照片
现场变频器运行照片
现场电机照片
五、 改造后的效果：
1. 变频调速的节能 steps
(1) Set the parameters and check whether the packaging film is installed and whether the color code photoelectric is intact.
(2) Press the manual button to test whether the packing bag is intact.
(3) Press the automatic button to randomly sample and measure whether it meets the requirements.
2.2 equipment process flow
According to the production requirements, the process is shown in Figure 2.1
3. Scheme determination
The program flow of pillow packaging machine looks very simple, but the internal calculation is very complicated. Now most domestic businesses in the industry are still using some single chip microcomputer or some low-cost PLC (Panasonic). Due to the increasingly fierce demand and competition of some foreign customers, they also began to upgrade the equipment function and brand. Siemens PLC entered the industry under this environment, At the beginning of the design, due to the consideration of price, Siemens S7-200 series PLC was selected at the initial stage. In the final debugging stage, it was found that the scanning cycle of PLC was more than 5 times larger than Panasonic PLC. Due to the use of the
