Programing analog I/O

[NewToUnitronics]

Hello

I just bought a Unitronics M91-2-UA2 PLC.

I am trying to program the analog I/O, but I cant get them to talk together.

I have a loop calibrator on the analog input 4-20ma.

On the analog output i have a multimeter that i can recieve 4-20ma. 

The problem is when i give the input 4ma, the output showa 16ma. When I adjust the input to 8ma, the output shows 12ma... 

Can anyone help me with the ladder diagram to get the output to communicate with the input.

 

[Joe Tauser]

You probably have your scaling set up incorrectly.  The analog inputs are 14 bit (0-20 mA = 16384) while the outputs are 12 bit (0-4095 = 0-20 mA).

If you're doing a straight map of one to the other it won't match.

Can you post your program?

Joe T.

[NewToUnitronics]

This is my program. I still have a problem with the low readings. 

When it's 4mA on the analog input, it shows 9,6mA on the analog output.

When it's 20mA on input, its 19,8mA on output.

 

[Joe Tauser]

It's been so long since I've played with an M91 I may have forgotten some of their idiosyncrasies.  It sounds like the scaling is still off.

Have you played with different constant values?  You're not going to break the PLC by trying. 

I think I know what value you need to stuff into SI 82 but I wouldn't want to take your fun away.  Beat on it and let us know what you find.

Joe T.

[Flex727]

48 minutes ago, Joe Tauser said:

but I wouldn't want to take your fun away

This IS the fun part, isn't it?