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Lecturer Ph.D Truong Dinh Chau, Department of Automatic Control, Faculty of Electrical – Electronics Engineering, HCM. City University of Technology tdchau@hcmut.edu.vn 091. 543-74-40 Industry Automation Outcome 7 Chapter - Latches, Timers, Counters and More Events include Time delays - use timers Previous events - use counters, latches and system variables +V Push Button Device Push Button Device Device (Logical Response) (Event Response) On/Off time A B C D event too short to be noticed (aliasing) Timing Diagram A D A C B D L U Latches An Example I/0 I/1 I/0 I/0 I/1 O/0 O/1 O/1 O/2 O/2 L U I/0 I/1 O/0 O/1 O/2 Flip-Flops for Latching Values S R Q Q A B Q Q A B Timers retentive nonretentive on-delay off-delay RTO TON RTF TOF TON - Timer ON TOF - Timer OFf RTO - Retentive Timer On RTF - Retentive Timer oFf An On-delay timer A TON Timer example Preset 4000 Accumulator 0 A example.DN (EN) (DN) example.ACC 0 3 4 0 3 6 9 14 17 19 example.EN 2 13 example.TT example.DN B B Retentive On-delay Timer A RTO Timer example Preset 4000 Accum. 0 A example.DN (EN) (DN) example.ACC 0 3 4 0 3 6 9 14 17 19 example.EN 10 example.TT Off-delay timer A TOF Timer example Preset 3500 Accum. 0 example.DN (EN) (DN) example.ACC 0 3 3.5 0 3 6 10 16 18 20 example.EN 9.5 example.TT A Heating control TON Timer heat Delay 10s TOF Timer cooling Delay 300s Horn Heating Coils Auto heat.TT heat.DN Auto Auto StopStart Fan cooling.DN Design Case: Design a system to flash a light continuously, so that it is on for one second, and then off for two seconds. Counters CTU A Counter example Preset 4 Accum. 2 (CU) (DN) example.DN example RES X B An Example cnt_up cnt_down reset output_thingy example.DN cnt_up cnt_down reset example.DN output_thingy CTU example preset 3 CTD example preset 3 RES example Another Example CTU Counter parts_cnt Preset 6 CTU Counter parts_max Preset 11 part_present parts_cnt.DN part present pneumatic cylinder parts_max.DN parts_cnt parts_max RES RES Master Control Relays A MCR MCR B C L D U X Y Y Design Case Problem: Develop the ladder logic that will turn on an output light, 15 seconds after switch A has been turned on. A TON Preset 15s delay delay.DN Light Solution: Problem: Develop the ladder logic that will turn on a light, after switch A has been closed 10 times. Push button B will reset the counters A CTU Preset 10 Accum. 0 count B count RES count.DN Light Design Case Design Case a system that will turn on a light ‘L’ when input ‘A’ has been turned on between 10 and 15 times. Problem: Develop a program that will latch on an output B 20 seconds after input A has been turned on. After A is pushed, there will be a 10 second delay until A can have any effect again. After A has been pushed 3 times, B will be turned off. On CTU Preset 3 Accum. 0 count On TON Time base: 1.0 Preset 20 t_0 On A L Light t_0.DN L t_0.DN TON Time base: 1.0 Preset 10 t_1 On t_1.DN U Light count.DN U Design Case Design Case Computer power button. Design Case Computer power button + light. Deadman Switch Problem: A motor will be controlled by two switches. The Go switch will start the motor and the Stop switch will stop it. If the Stop switch was used to stop the motor, the Go switch must be thrown twice to start the motor. When the motor is active a light should be turned on. Go CTU Preset 2 Accum. 1 count Motor Stop C5:0 Motor Light RES Motor count.DN Stop Motor Solution: Design Case Conveyor Problem: A conveyor is run by switching on or off a motor. We are positioning parts on the conveyor with an optical detector. When the optical sensor goes on, we want to wait 1.5 seconds, and then stop the conveyor. After a delay of 2 seconds the conveyor will start again. We need to use a start and stop button - a light should be on when the system is active. Light Light Go Stop Part Detect TON Preset 1.5s incoming incoming.DN TON Preset 2s stopped incoming.DN Light Motor stopped.DN incoming RES stopped.DN stopped RES Design Case Accept/Reject Sorting Problem: For the conveyor in the last case we will add a sorting system. Gages have been attached that indicate good or bad. If the part is good, it continues on. If the part is bad, we do not want to delay for 2 seconds, but instead actuate a pneumatic cylinder. Design Case Light Light Go Stop Part Detect TO N Preset 1.5s incoming incoming.DN TO N Preset 2s stopped stopped.EN Light Motor stopped.DN incoming RES stopped.DN stopped RES Part_Good incoming.DN TO N Preset 0.5s rejected Part_Good rejected.EN Cylinder rejected.DN rejected RES rejected.DN A toggle start switch (TS1) and a limit switch on a safety gate (LS1) must both be on before a solenoid (SOL1) can be energized to extend a stamping cylinder to the top of a part. 2. While the stamping solenoid is energized, it must remain energized until a limit switch (LS2) is activated. This second limit switch indicates the end of a stroke. At this point the solenoid should be de-energized, thus retracting the cylinder. 3. When the cylinder is fully retracted a limit switch (LS3) is activated. The cycle may not begin again until this limit switch is active. 4. A cycle counter should also be included to allow counts of parts produced. When this value exceeds 5000 the machine should shut down and a light lit up. 5. A safety check should be included. If the cylinder solenoid has been on for more than 5 seconds, it suggests that the cylinder is jammed or the machine has a fault. If this is the case, the machine should be shut down and a maintenance light turned on. SOL1 extend.DN LS2 SOL1 CTU Preset 5000 Accum. 0 part_cnt SOL1 RTO Preset 5s extend extend.DN LIGHT RESET extend RES SOL1 TS1 LS1 LS3 part_cnt.DN L U part_cnt.DN L Shear Press Design Case Packing system Design Case Packing system Syswin Packing system Step7