STEP-7 using timer data 3

[meatstu]

Hi everyone, this is my first time using Siemens gear (STEP-7, 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.

 

[controlsdude]

I believe it is as simple as a Load and transfer instructions. (MOV instrucion in AB)

Create data type that will be accepted by the instruction that you are trying use. Load the value you are using and transfer into the new variable.

Load REAL_variable
Transfer Dword_Variable

 

[meatstu]

Yes this has done the trick with a DI_I conversion at the end.

Thanks very much for the help.

 

[ozmosis]

Have a look at this link as it includes some "Tips & Tricks" for the S7-200 range. The download includes (usually) a pdf document explaining the tip and also a typical code in .mwp format as an example.

http://www.automation.siemens.com/microset/html_76/support/tipps/tt-steuerungstechnik.htm

 

[meatstu]

Thanks looks like some handy stuff.