Analog input for 'flasher' circuit?

[steelblue48310]

I'm working on a bench project to learn more about the basics. I have created a 'flasher' circuit with 2 timers, and that works. I would like to control the 'rate' of the flash by utilizing the analog inputs of my ML1100 (it also has a IF20F2 module)

I am thinking that the rate should be from once per minute to as much as 150 per minute, based on the 0-10 Volt input. I'm guessing that I would have to 'scale' the input with some math functions and such.

Also, is it possible to set one of the analog outputs to be a steady +10 Volts, so I can use that as my reference voltage for the potentiometer input?

Been reading, searching, experimenting... finally at a point to ask a question! Thx... Mike B.

 

[steelblue48310]

OK... figured out one part! I did manage to get +10 volts out of O0.0 with a MOV function; value of 31100. Now onward to the 'input'!

 

[Mickey]

Scaling the input and then moving that value to the timers preset should do it.

http://www.wikiplc.com/index.php?option=com_content&task=view&id=61&Itemid=36

 

[Brijm]

You can do it without scaling, but you will need to do some math at some point to get your flash rate. Normally it is easier to convert the units to engineering units in the PLC for troubleshooting.

Here is the basic concept of scaling. EU = input / InputSpan * EUSpan
Now if you have an offset on your low value, you need to account for that on either the input or output of the equation. ie...EU = (input - inputZero) / InputSpan * EUSpan + EUZero

So for example lets convert a 4-20mA signal to 3-15 PSI with an input of 8mA. First we need to convert our input to a percentage. We have an offset of 4, that we want to get rid of, to get 0-100%. Subtract 4 from our input and the input high number. Now we have 4mA out of a span of 16. which gives us 25%. Next we multiply our output span by this percentage. For 3-15 PSI we have a span of 12. 0.25*12 = 3. Finally we need to add our offset (3PSI) which will give us 6PSI.

Your numbers will vary (depending on the input configuration) You will need to look up what your input gives you at 0 an 10V.

RS500 also contains a scale (SCL) function which find the slope and enter the offset (I'm not sure if it is available on the ML1100)I like the method above, because once you learn it, you can apply it to any PLC. It also helps you to understand scaling. Also, I'm not sure if the ML1100 has the compute instruction (CPT). This will allow you to type in an equation, which will use less intermediate addresses, than individual Multiply and Divide operations.

I typed this out quickly, I hope it helps

 

[Mickey]

FYI: The ML1100 has a "SCP" instruction also. Easier to use then the SCL. See PDF.

 

[steelblue48310]

Thanks for the info! I'm making progress...

 

[Brijm]

I do like the SCP function. Used a couple of processors without it, and completely forgot

 

[steelblue48310]

Got it to work... SCP is very handy! Next, I'm trying to get the LCD display to show the actual 'frequency' of the so-called 'flashes'. (Per minute)

I got it to display a value that was stored in a N7 register, but my potentiometer isn't linear... much more reading to do!

Thanks to all who replied.

 

[iant]

it should not matter if the pot is nonlinear.
at the end of the day the scaled value (SCP) is for exapmle 0~100
which is still 0 ~ 10V the difference is how far you turn the pot.
the RPM is still only needed to be done by calculations