Linearization

[redhunter]

Hi,

In the u90 is it possible to linearise 3 analog inputs? I have regularly done 2 in the ladder but would like to be able to do 3 for the next job.

Thanks, 

Craig

[Isakovic]

You can linearise as many analog inputs as PLC has them. You can linearise other numeric values, I don't think there's any limit.

[Ausman]

Just remember that it seems to go against the programming rules, because you repeat the use of the same system operands for each linearization.

cheers, Aus

[redhunter]

Thanks for your replies, yes it does seem to be a bit wrong!

Craig

[sanyc]

On 5/7/2020 at 2:34 PM, Ausman said:

Just remember that it seems to go against the programming rules, because you repeat the use of the same system operands for each linearization.

cheers, Aus

Any remedies for this condition?

[Flex727]

4 hours ago, sanyc said:

Any remedies for this condition?

It doesn't really require a remedy, but the remedy would be to use the Vision or UniStream product lines.

[sanyc]

3 hours ago, Flex727 said:

It doesn't really require a remedy, but the remedy would be to use the Vision or UniStream product lines.

OK, thanks

[Isakovic]

Will reusing the same operands (system or standard) in several places in program be a problem? I often use the same memory place as auxiliary variable for several calculations in the same scan.

[Joe Tauser]

Not at all.  I do that all the time for intermediate calculation buffers.  The only time I put different MIs in the middle of a calculation is on the rare occasion that my code doesn't work perfectly the first time and I need to figure out where the problem is.

Joe T.

[sanyc]

One thing that bothers me with multiple linearization inputs is that when going online the y1,y2 parameters get the readings from the second AI, no matter what their store blocks command them.

Is that because of the scan time of the program and it doesn't have the time to "update" the stored values, so it "shows" the last stored values in them?

[Flex727]

Last one always wins with PLCs.

Also remember that the update frequency of your VisiLogic is on-line mode is relatively slow. It has to go out to the PLC and read every operand value and display it. It generally take longer than a single scan to accomplish that.

[Ausman]

8 hours ago, Joe Tauser said:

I do that all the time for intermediate calculation buffers. 

Joe, I think it would be worth expanding on this for clarification, perhaps with some screenshots.  My comments were only about the use of the linearization operands, which is somewhat different to the area you and Isakovic are touching on.

cheers, Aus

[Joe Tauser]

Here's an example in Visilogic where I calculate a flow rate for a dispensing gun given the time it's on and the weight of the product dispensed.  There are two guns in the system.

Gun 1:

ML 7 is a scratch register that contains the result of MI 21 x 6000.  I immediately use that value in the DIV block.  Then I don't care about it anymore.

The STL View shows how the PLC actually solves this network:

The line following the MUL instruction is STore the output of it in ML 7.  This happens immediately, and the PLC retrieves it in order from the same memory location (ML 7) it just wrote it to.  

This also shows why it's a good idea to look at the STL View when a network doesn't act how you think it should.  It will show the real operation flow.  This is also why you shouldn't get overly complicated with your networks.   You don't win any prizes for cramming a whole bunch of logic into one net.

Gun 2:

There's ML 7 again, holding the result value for only the few microseconds that I care about.  I can use this same register as many times as I want for this purpose.

This same scratch register technique applies to Jazz or any other brand of PLC.  Move the data into your working registers and then move it out. 

Joe T.