Simple Question

todell

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T
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Feb 2009
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I am trying to use the move command to move a value of .98 to a data register. I get an error saying .98 is out of constant range. It will let me enter any number with out a decimal.
 
What PLC are you using? My first guess is where you trying to move to is not the same data format. .98 is either a float or a real. Where you move it to has to be the same.

If you can tell us what PLC you are using and post the move code you have created.
 
It's hard to offer a definitive answer since you didn't identify the brand or model PLC you're working with, but my guess would be that the destination register of your move command is limited to integer values. Different brands handle floating point values differently. Some reserve a specified range of addresses for floating point values. Some require you to declare variables as either floating point or integer.
 
Sorry for the incomplete details of the project. I am trying to build a orifice plate flow meter to measure water flow. I am using a Idec FC4A PLC. .98 is the discharge coefficient value for the plate I'm using. I am trying to use the .98 value in a multiplication line.
 
Yours is a simple RTFM question.

Does that model support floating point math or are you limited to integers? If it can't handle floating point calculations you're probably better off scrapping it and choosing a tool better suited to the task. If it can do floating point arithmetic, you need to figure what instructions and/or addresses to use.
 
I do not see where floating point is available. What would you suggest for a PLC? What does RTFM mean?
 
What would you suggest for a PLC?
Click to expand...
Once again, you haven't offered enough information to get a good answer. You seem to assume that anybody who reads this will immediately know exactly what inputs and outputs your system needs.

I can tell you a dozen or more brands of PLC that can do floating point arithmetic, but I don't know if this is all you need to do or if it's part of a larger system. If I tell you to use an Automation Direct DL06 PLC or a GE Fanuc VersaMax Micro, both of which can do floating point and you come back later and tell me you need a couple dozen channels of analog I/O we're no further ahead than when we started.
 
I am RTFM for the Idec FC5A. Web site says it will do floating point but I do not see anything about floating point in the manual. Sorry for frustrating you guys. I am self taught in PLC logic and have never tried to do math with a PLC. Just simple I/O with a analog input.
 
Not sure if this is your first attempt at programing a PLC or if this is your first attempt at building a control circuit but here are a few points

Idec is a low end PLC with lots of limitations. So you need to check your requirements very carefully.

Do you need Com's to another system
How Many Inputs and Outputs do you need
What kind of Inputs and Outputs do you need Analog or Discreet or both
How fast must you process
Do you need expandablity


All of these questions and a more that I have not mentioned decide which PLC you can use. Since we are not building your machine we can not give you any more than you supply.

FYI... In PLC's you have all types of data formats, Bits, Bytes, Double Intergers, Words, Double Words, Floats, Reals, Time, BCD....and the list goes one. Which ones your PLC can use is in your manual. Look under data types to find this info.
 
Simple Answer....

I don't see the fc4a listed there.

So far, sounds like steve's answer.

Don't forget to add a rung comment w/ your name, change you made and why, and phone number. Print out the rung w/ comment and paste it to the inside of the cabinet door w/ the flash drive that contains the saved copy of the last program you went online w/.
 
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