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S7-200, using timers to calc speed.

7/20/2009 1:43 PM	Rate (0)
meatstu Posts: 4 Rating: (0)	Hi everyone, this is my first time using Siemens gear (ladder logic and CPU224) and I would appreciate any ideas anyone can offer. Basically I have a pick-up sensing a wheel with a single tooth giving me an aprox 1Hz square wave signal with a low M/S ratio. The frequency of this signal will vary a small amount, so I would like to use this signal to generate a variable that can be adjusted using a math function, and then applied to the PT of another timer. The timer then turns on a punch, so basically I am trying to create a speed compensation system. So far I have the following: 1. I have used a BGN_ITIME and CAL_ITIME instructions to find my time value - a DWORD value. 2. Next I take the DWORD value, use a MULT_R instruction and multiply my time value by a coefficient, generating a new REAL value output. 3. Now I'm stuck, I've tried applying my REAL value output directly to the PT of my final TON timer but I get an error - data type is not valid for the instruction operand. I'm guessing the data type is the wrong size for the PT input, so my question is how do I convert it? I've tried the convert instructions but none seem suitable. Anybody point me in the right direction? Or am I going about this the wrong way, is there an easier more straight forward way? Sorry for the long post and thanks for looking if you've got this far.
meatstu Posts: 4 Rating: (0)
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7/20/2009 1:47 PM	Rate (0)
Robster Platinum Member Joined: 5/28/2008 Last visit: 1/15/2026 Posts: 1344 Rating: (141)	Hi, a REAL value you can convert to DWORD using the ROUND instruction. If DWORD is also wrong for timer, then you have to convert the DWORD into a WORD. But just try to round and getting the dword. regards

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7/20/2009 1:54 PM	Rate (0)
meatstu Posts: 4 Rating: (0)	Ok, thanks I will have a look, but I do think I will need to convert from a DWORD to a INT which is smaller than an DWORD yes? How might I do that? Cheers.
meatstu Posts: 4 Rating: (0)
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7/20/2009 1:59 PM	Rate (0)
meatstu Posts: 4 Rating: (0)	Ok I've tried that but my issue is still now trying to get from a DINT to INT to input to the PT of my timer. Any ideas? Cheers
meatstu Posts: 4 Rating: (0)
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7/20/2009 3:40 PM	Rate (0)
Robster Platinum Member Joined: 5/28/2008 Last visit: 1/15/2026 Posts: 1344 Rating: (141)	its like I wrote: Convert-instruction DWORD to Word. Word is same like INT in relation to the size.

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7/20/2009 3:54 PM	Rate (0)
meatstu Posts: 4 Rating: (0)	Yes sorry you're correct, I couldn't find the instruction but I have now. Many thanks for your help, it's much appreciated.
meatstu Posts: 4 Rating: (0)
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