SCP with RSLogix 5k

[robw53]

On RS500 you can use SCP to give an analogue signal out to a VFD what is the function you would use in RS5K

Cheers

Rob

 

[sthompson]

On RS500 you can use SCP to give an analogue signal out to a VFD what is the function you would use in RS5K

Cheers

Rob

There is a SCL Instruction for Function Block and Stuctured Text, but not Ladder Logic. In Ladder Logic, I usually use the CPT Instruction, but you could use simple math. Also, the ControLogix Analog Cards allow you to do the Scaling in them.

Stu....

 

[daba]

On RS500 you can use SCP to give an analogue signal out to a VFD what is the function you would use in RS5K

Cheers

Rob

previous reply only hints at the capabilities of doing the scaling on the card, here's more info.

once scaling on the module is configured, everything you do from then on is in engineering units, and that includes (also "on the module"), HH, H, L, LL process alarms (with deadband control), rate of change alarm (eng. units per second), program mode/fault mode output response.

all of the setpoints for these functions are in the module's "C" tag, nothing is actually retained on the module, so there is no need to worry about swapping a module out in case one fails, just put the new module in, and it gets configured by the processor. Dynamic changes can be accommodated, put new values into the "C" tag, and issue a "Module Reconfigure" message to update the module.

Seriously, having everything up-scaled to engineering units makes these modules a dream to use, and of course there is zero processor overhead when using them.

 

[rstech]

I like the SCP command so when I started using RSLogix5000 I made my own SCP instruction in ladder logic as an Add-on instruction. Works great and I just copy it to any other application I need it in.

In the logic for the Add-on instruction I am using a CPT command but I like the Add-on instruction so I can assign the local tags to it such as Unscaled Minimum, Unscaled Maximum, Scaled Minimum, Scaled Maximum, Input, and Output.

 

[daba]

I like the SCP command so when I started using RSLogix5000 I made my own SCP instruction in ladder logic as an Add-on instruction. Works great and I just copy it to any other application I need it in.

In the logic for the Add-on instruction I am using a CPT command but I like the Add-on instruction so I can assign the local tags to it such as Unscaled Minimum, Unscaled Maximum, Scaled Minimum, Scaled Maximum, Input, and Output.

Seems to me you are doing a lot of work that is totally unnecessary, and I would bet that your purpose built code doesn't do half as much as the modules themselves can do without any effort on your part....

Analog Inputs...
a. Scaling to engineering units
b. HH,H,L,LL Process Alarms
c. Rate of Change Alarm

Analog Outputs...
a. Scaling from engineering units
b. Low and High limits (clamps)
c. True ramping (eng. units per second)
d. Programmable fault response

And all of this with ZERO controller overhead, i.e. no code, no additional data handling, no additional memory requirements.

The modules are already doing "default" scaling (-10.0 to +10.0) anyway, why not just change the defaults to the ranges you require, and do away with the added complexity of user-generated code.

Remember that in the Logix5000 system, analog input modules can be "shared" between multiple controllers, so getting the module to produce engineering unit scaled data to all consumers means you don't have to go and change any code in any controller if you have to re-scale an input range.

IMHO 1756 analog modules are the best I have seen, and I salute the developers.

 

[rstech]

Seems to me you are doing a lot of work that is totally unnecessary,

It's not a lot of work. Takes about 0.2546 seconds (give or take 1 millisecond) to copy and paste. Not a lot of work at all. How long does it take you to configure an analog card on every project you do? 30 seconds or so.

I'm not knocking your method, it works, just like mine. I've scaled in the card and prefer the method I use. Like most things, there are many ways to do the same thing. Like I said, I like the SCP command, and so I continue to use it.