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bigredram87

Basic Timers

20 posts in this topic

I just recently started working with PLC's. I have no prior experience so please pardon the lack of knowledge. I am basically reading a book and starting to just go through it while practicing on my Micrologix 1100 with rslogix 500. My question is I have been using photoeye sensors to start a timer that when the time is met will shut off a motor through a relay.Basically a safety device simulating a box being jammed in a conveyor. Anyway as I was playing with the timers and latches I realized I dont know what function I would use to say start a motor for 5 seconds and than turn off? I know I may be missing something very simple but basically I know how to start a timer with an input(photoeye) but I dont know if the TON timer would be what I would use to just start a motor and than turn it off? If any one could point me in the right direction it would be very appreciated. Thanks in advance

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Use the photo eye to enable a TON and have a NOT .DN bit in parallel to latch in timer so it will continue to time after the photo eye is clear. The use the .TT bit to run the motor.

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Please be precise in how long the photoeye will be on relative to the 5 seconds of motor run.

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You might also think about a "standard" motor starter circuit using buttons and a relay (attachment). You would wire "conditions to start the motor" in parallel with the START button and "conditions to stop the motor" in series with the STOP button. To just start the motor and turn it off after a time, you would have an input start the motor (or some other condition internal to the PLC). You would add a TON instruction in an appropriate place to run while the motor is running and put the timer's DN bit in an appropriate place to stop the motor. Then, to use the photo eye, put another TON instruction (using a different timer address, of course) to run when the photoeye is blocked. Use this timer's DN bit to stop the motor. Note that, in either case, if your start signal is held on, the motor will take off as soon as the photoeye is cleared. If this is not what you want, you'll need to get a little fancier. Feel free to post whatever you come up with.

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Could I please have a little more guidance? I'm trying to figure out how to properly stop the motor from the .DN bit Thanks MOTOR CONTROL.RSS

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Add another XIO instruction like the one you have addressed with I:0/1 in rung 0. Also, you want to substitute O:0/2 for I:0/0 in rung 1 so the timer runs when the motor runs, not just when the button is pressed. Alternatively, you can add a branch around the output instruction on rung 0 and move the timer TON instruction there. MOTOR CONTROL.RSS

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Thanks so much, It makes so much sense now that I see it working. Thanks again I'm going to incorporate a couple photo eyes into the mix now for some practice.

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i am having trouble seeing if this code is right i never see the motor contact or safety pin outputs come on , they turn green but always say off. can someone shed some light on this please and ty in advance scissor lifts.RSS Edited by et8sec

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et8sec - at the top left of your RSLogix 500 window you will see it says 'Forces Installed'. Open it an choose 'Remove All Forces'. (Make sure that any controlled machine is in a safe state.

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OK i thought i had them off, why when i disable all forces does the box under it still say forces enabled?. and should this program work? as you see i am working on a scissor lift. after i push the start button the safety clamps should engage, then a 5 sec pause after that the motor will run for 30 sec and raise the lift. after lift is raised a pop out cylinder will come on and secure the lift from drifting down. i think i have it but i just realized that i need to add a solenoid to energize at the same time to open the pump while the motor is running. and now besides why it sdays forces enabled, i see i have another problem......back to the drawing board.

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All of the Micrologix series of controllers do that by default, it cannot be change.

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ok ty, i think i have it figured out now, can someone tell if this program will work before i go spend the money on a plc, and also how to i reset everything back at the end of cycle or will it auto rest once cycle is comple when i start the next cycle. SCISSOR LIFTS.rss

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OK i`m not sure what to do now i have tried latch and unlatch commands different timers but my output to my motor contact and solenoid are always energized i want them to turn on for 30 sec the go off until i start the down cycle.

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it seems to be working only 1 issue i see and that is rung zero and rung 14 the clamp at 0:0/0 pulses but if i untoggle the start bit my timers do not run everything else seems to work as planned SCISSOR LIFT A.RSS

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We can't tell enough about your system just from the ladder. Describe the 'Up' and 'Down' switches. Are they two separate switches. Is it possible for both to be on? Are they off if no one is operating them? If you had the system hooked up as you want then turned on the PLC but not touch any buttons what do you expect. Now describe each step. If you operate a button do you hold it or do you press and release it expecting the rest of the process to take place? So be careful to accurately describe what you are doing with the buttons and what outputs you expect to turn on, in what order. How do you expect to restart the sequence? Once all these are answered then the code will be much easier to write correctly and be fairly sure of its correctness before loading it into a PLC.

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I am changing the code now( the last worked fine in the emulator) the company i work for has no automation this will be the first, so they want to see a"demo" before they will buy a plc for me to play with i am trying to add a plc to a scissor lift first step is when we push equipment on to the lift, i was thinking of using a prox switch to sense it is there and turn on the safety clamps, then add a photo eye to the motor/pump latch and unlatch commands. ( not sure how they work any more been 15 years since i worked with them n/o or n/c i want the pe to be lit in down poss and once the up button is pushed the motor/pump run until the wheel crosses the light beam and then unlatch the motor/pump once that is done a 2 sec timer will run and then use the dn bit of timer to energize a saftey pop out cylinder to keep the lift from drifting down .........the of course start the down command from a second switch witch will olnly unlatch safety pins,turn on pump solenoid( motor does not run in down) and once down turn off clamps and prox sensor for 3 min so you have time to pull equip off to me it should be a simple project, but my head is hurting from beating it against the wall. i don`'t get anything from this at all other than a pat on the back and more work since this is a lift i run crazy yes it means faster work for me but it would really make my job easier.

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also the buttons are a push and release as it is now with no automation you hold the button down and it turns on the motor/pump solenoid and stop all when released

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in auto mode i want to just be able to push the buttons up or the down and walk away and let the program do the rest

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with that said this is what i have that is causing me to beat my head against the wall.......to many years not doing this has left me not even close to being rusty but more like a solid mass of oxidized crap SCISSOR LIFTS.RSS

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Does this describe the 'Auto' sequence? Sequence for lift (Note - this system needs positive feedback if it is in the lower or upper position! But I'll proceed without it.) We'll start out assuming that the lift is in the 'down' position. 1. 'Prox Switch for Clamps' is TRUE 2. Energize 'clamps' 3. 'Up' button is pushed 4. The 'Motor Contact' and 'Pump Solenoid' turns on. 5. The 'photoeye turns off' 6. The motor continues to run for 2 seconds. 7. The motor stops 8. The 'Safety Pins' are engaged 9. Wait for 'down' pushbutton 10. The 'Pump Solenoid' turns on allowing the lift to drop 11. Once the lift is 'down' (the method of detecting this is not stated) turn off the 'Pump Solenoid' 12. Wait 3 minutes. 13. Return to step 1. Use this method to describe the entire sequence. Then it becomes easier to write the program.

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