Control ladder diagram of liquid mixing device

PLC control ladder diagram design of liquid mixing device From the above analysis,
it can be seen that this is a typical step control, which can be easily implemented using the shift register instruction
(SFT) program. The ladder diagram program is as shown in the figure.
    The explanation is as follows:
    1) Considering that the shift pulse of the shift register is a narrow pulse, so
each start button signal and each liquid level sensor signal are converted into narrow
pulses using differential instructions. 2) When the start button is pressed, use the MOV instruction to set the lowest bit HR000
    of the shift register channel to "1", and this bit controls the output relay 01001 to be turned on, so that the external YV1 solenoid valve is energized and opened, and liquid A flows into the container. While the start button is pressed , keep relay HR0100 on and latched.     3) When the liquid level rises to I, the liquid level sensor I is closed, the input relay 00003 is turned on, and its rising edge is differentiated to turn on 20100 for one scan cycle (as shown in Figure 7-10: Step 7 ),and. 20100 is used as the shift pulse of the shift register to shift each bit in the HROO channel by one bit, namely HROO01-1. Since the input logic of the shift relay is 25314. This is a special function register that always remains OFF , thus ensuring that "O" is moved to the lowest bit of the HROO channel every time it is shifted. At this time, the output relay 01001 is disconnected, causing the YV1 solenoid valve to be powered off, while HROO01=1 controls the output relay 01002 to be connected, causing the external YV2 solenoid valve to be energized and opened, and liquid B is emptied into the container.     4) When the liquid level reaches H, input relay 0003 is turned on, and its rising edge is differentiated so that 20100 is turned on for another scan cycle, causing each bit of the shift register channel HROO to shift one more bit, that is, HR0002 =1. At this time, the output relay 01002 is disconnected, so that the YV2 solenoid valve is de-energized and the output relay 01000 is connected, which energizes the external contactor KM coil, the motor starts and runs, and the internal timer TIMOOO starts timing at the same time.     5) When the 60s timer of timer TIMOOO expires, its normally open contact is closed , turning on 20100, and each bit in the shift register channel HROO moves one bit t, that is, HR0003 -1. At this time, the output relay 01000 is turned off. , the KM contactor coil is powered off, the motor stops, and the output relay 01003 is turned on, which energizes the external YV3 solenoid valve, and the mixed liquid is discharged to the next process.     6) When the sleeping position drops below the sensor position I, the liquid level sensor I is turned off, and the input relay 0004 is turned off. After differentiation by the falling edge, 20100 is turned on for one scan cycle, and the bits in the shift register HROO move again. One digit, that is, HR0004=1. On the one hand, it controls the YV3 solenoid valve to continue to be energized, and at the same time, it causes the internal timer TIMO01 to start timing.     7) When the 2s timer of timer TIMO01 expires, its normally open contact closes, turning on 20100, and each bit in the shift register channel HROO moves one more bit, that is, HR0005-1. At this time, the output relay 01003 is disconnected, causing the YV3 solenoid valve to be powered off, completing a cycle of work. At the same time, the HR0005 contact is closed so that the M()V instruction is executed, setting the lowest bit HROOO of the shift register channel to "l", thus starting a new cycle.     8) When the stop button SB2 is pressed, the input relay 00001 is turned on, which resets the holding relay HR0100 and the normally open contact of HR0100 is disconnected. Therefore, when the liquid is discharged and the delay time of timer TIMO01 expires, the internal relay 20100 is no longer turned on, but the MOV instruction is executed to clear all the shift register channels HROO to 0", causing the whole machine to stop working.     (4 ) Conclusion A prominent feature of this method is that the shift register is programmed to have only one "1" move . This ensures the interlocking between the various parts, so there is no need to The empirical design method relies entirely on contacts for interlocking, and often "focuses on one thing but not the other", thereby simplifying the design process. This is more advantageous in step control with a large number of parts and complex control requirements .