New to PLC Programming Please Help

[Daniel81]

Hello Guys,

I'm new to PLC programming and a course I'm currently studying has asked a question and requested we use a shift register.

The question is to use a single push button to select either 1 sec, 2 sec, 3 sec or 4 sec delay times for a motor to start using a shift register and timers.

I can shift inputs 1's into the B3:0 register but don't understand how to get zero's shifted in by just using one input switch.

I had thought to map the time delays to binary numbers such as
1 sec = 001
2 sec = 010
3 sec = 011
4 sec = 100

But due to my lack of knowledge and experience I cannot generate the zero's I require.

Would it be possible if one of you guys could point me in the right direction and point out what I am missing or doing wrong.

Your help is much appreciated.

Thank you

Daniel

 

[gclshortt]

http://accautomation.ca/plc-programming-example-shift-register-conveyor-reject/

Take a look at the above post. It will discuss the shift register. The shift register generally has three inputs
Input - Move a 1 or 0 into the register
Clock - This determines when the bits shift in the register
Reset - Set all of the bits in the register to 0

Regards,

 

[Daniel81]

Hello Again,

I forgot to mention that I am using BSL register
File #B3:0
Control R6:0
Bit Address I:0/0
Length 15

 

[Daniel81]

Thanks for the reply Gary,

With the previous reading I have done, it also says that shift registers require the three inputs as you say. As I am using an AB micrologix 1000 PLC it looks as if I only have the provision for one input into the BSL register. Do you have some familiarity with this PLC?
Do I have to use more that one BSL register?

 

[Steve Bailey]

The single input to the BSL instruction is the clock signal. Each time it makes the transition from false to true, the pattern of ones and zeroes over the address range of B3:0/0 to B3:0/15 gets shifted left by one position. That means B3:0/15 takes the value of B3:0/14, B3:0/14 takes the value of B3:0/13, etc. The vacated bit at B3:0/0 gets set to a zero or one based on the state of I:0/0. There is no reset command in the Micrologix BSL instruction.

 

[Daniel81]

Thanks Steve,

Now this makes sense now. Now that I have configured the BSL the correct way I am getting my clock input and I do see my input data shifting through the register. The problem now is I can only use one input to switch through my four selectable time delays. Is there a way to capture the binary data after each time I press the input switch so I can map that data to the time delays? I was thinking about using counters to count each time the B3 binary's are used but this seems like a clumsy way to do it. If I latch the first binary input say B3;0/0 the problem is that when it unlatches it will just latch again as soon as I hit the input switch and will not see anything further.
Anyway sorry for dumping this on you. If you can advise me on a different or better approach it would be most appreciated.

 

[Steve Bailey]

I don't think I would have selected a shift register as the right tool for the job, but if that's what the instructor wants...
While you hold the pushbutton closed, enable a timer with a preset of one second, Use the timer's .DN bit as the clock input to the shift register. Also use the timer's .DN bit to reset the timer, so the .DN bit pulses once per second. The longer you hold the pushbutton closed, the more bits are set in the shift register. Use the number of bits set to choose the preset of your motor start delay timer. Hold the pushbutton closed for five seconds or longer to clear all of the bits in the shift register so can select a different motor start delay.
You could eliminate the shift register if you were to simply measure how long you hold the pushbutton closed and use that time as the preset for the motor start time delay.
As you are programming this exercise, give some thought to how an end user could inadvertently or intentionally screw things up and try to come up with methods to prevent it.

 

[Sergei Troizky]

Hello Guys,
The question is to use a single push button to select either 1 sec, 2 sec, 3 sec or 4 sec delay times for a motor to start using a shift register and timers.
Daniel

The goal is not clear from such description.
Learn to formulate goals clearly and avoiding ambiguities.
Do you need to change a value as the button is repeatedly pressed?
Or change a value repeatedly as the button is held pressed?
Or something else?

 

[Daniel81]

Hello Sergai,

To change a value as the button is repeatedly pressed. If I press the button then I have selected time delay one. If I press the button again then I have selected time delay two etc etc.

 

[Daniel81]

Hi Steve,

I agree. From all the reading I have done shift registers are really used for conveyor lines tracking items.

 

[Sergei Troizky]

After the value reaches 4, what should happen on the next pressing of the button?
When the value should be reset?
Should it be reset to 1 or to 0?

 

[Daniel81]

Hi,

After you have selected the 4 second delay the next button press automatically goes back to the 1 second delay.

 

[Sergei Troizky]

Change the extension of the attached file to .rss

 

[gclshortt]

If the instructor wants a shift register then use the push button as an input to the shift register (Bit 0). Use a time bit of 1 second to shift the register. (clock) Use the bits in the shifted register as a delay to latch the start.
Bit 2 - 1 second
Bit 3 - 2 second
Bit 4 - 3 second

Regards,

 

[yog_july81]

Hi,
Sorry to Interrupt in this post.
I am in need of your help.we are trying to do migration for Old PV600 running on Devicenet with SLC 5/05 .We done conversion for the .PVA file in Rsview studio ME edition.We are trying to connect the PVPLUS 700 which we are using after migration on ethernet.On pinging i can see both SLC and PVPLUS 700 on Ethernet.I can do upload/download but my PVPLUS 700 is not communicating with SLC 5/05.Is there any changes required SLC programm to read the HMI.Your help Highly Appreciated.

Thanks

Yogi