SLC 500 PLC Control

jimmycooker · Nov 4, 2010

Hi,

I am trying to setup a switch or pot in NI lookout to control an input in my SLC500 PLC.

I have managed to create input & output objects in lookout which mirror the PLC / ladder logic condition.

How do i map a switch to a digital PLC input? Or a pot to an analogue input?

Thanks,
James.

bernie_carlton · Nov 4, 2010

You typically do not control inputs (wshether discrete or analog) directly. The object of a discrete pushbutton to a SLC would typically be to a 'B' register location. The analog numeric word would be written to an 'N' register location.

jimmycooker · Nov 4, 2010

Hi Bernie,

Im sure you've helped me before too...cheers i'll have a go.....

jimmycooker · Nov 4, 2010

Bernie,

When i create a control object switch, how do i link that to a B register?

Marc_U · Nov 4, 2010

I presume that you are thinking of mapping it a PLC I:??/?? Data File address, as if it were a physical hardwired I/P into the PLC.

If so, you can't, as those address are tied to the I/O modules that are physically in the PLC rack.

You would have to map it to Binary (e.g. B3../..) Data File - for the Digital, or an Integer (e.g. N7:....) Data File for the Analog value; and then program the PLC program to use the value from there.

bernie_carlton · Nov 4, 2010

I havent used the NI system. But if you can direct the pushbutton to an input then in the same selection you should be able to choose a B register location.

jimmycooker · Nov 4, 2010

so there isn't a quick and easy way to create an on off switch in lookout to act as a PLC input.....bycreating expression or function in lookout? Could you give me a few google search parameters so i can look for more info on how to do this?

Thanks

Marc_U · Nov 4, 2010

jimmycooker said:
so there isn't a quick and easy way to create an on off switch in lookout to act as a PLC input.....bycreating expression or function in lookout? Could you give me a few google search parameters so i can look for more info on how to do this?

Thanks

I wouldn't be that negative. Are you trying to replace an existing hardwired pot/switch with a software pot/switch controlled via Lookout?

jimmycooker · Nov 4, 2010

Sorry, i've been at this since 8:00...progress is slow...

I have a PLC with no a few I/O cards. I've no istruments or equipment wired upto the cards so i'm trying to use lookout instead...setup a few switch that are mapped to inputs and use the ladder program in the background to turn on outputs and also map these to displays in outlook.

I've had 1 2 hour lab in SCADA where we used a little NI modbus box with pots, switche inputs and dicrete / analog output led's on it....

If i could use lookout switches & pots as PLC controls i'd be able to create and play around with the ladder programs a bit more....

jimmycooker · Nov 4, 2010

The short answer marc is yes im trying to replace a hard wired pot / switch with a software one..thanks...

Marc_U · Nov 4, 2010

jimmycooker said:
The short answer marc is yes im trying to replace a hard wired pot / switch with a software one..thanks...

What you need to do is identify a spare unused B3 file address N7 file address, e.g:

B3:0/1 (= Binary Data-file 3, Word 0, Bit 1) for your on/off switch

N7:3 (= Integer Data-file 7, Word 3)

And then you can use these addresses as if they were Input addresses.

Another possibility, if you have an O/P card in the PLC rack, you can map the directly to the Output address, assuming that that Output address is not being given a value by the PLC program.

jimmycooker · Nov 4, 2010

Marc,

My problem is how do i associate the switch control / graphic with that address....

I need some kind of Lookout expression to do this i think...

bernie_carlton · Nov 4, 2010

Try here

And here's some more

Marc_U · Nov 4, 2010

bernie_carlton said:
Try here

And here's some more

Bernie has beated me to the punch

Those links do explain fairly well what you need to do. Certainly better than what I could.

jimmycooker · Nov 4, 2010

Thanks both of you, going through those pages now (had looked at them already today but missed their significance).

Thanks.

SLC 500 PLC Control

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