Forcing Analog IO

Hi All,

I am working on RSLogix 5000 and trying to force a load cell value to test the PLC program but I can't. I am in need of advice to force analog values in RSLogix 5000.


Thanks in advance.

Well there are two possible ways, When I test programs I usually disable the call to the I/O's (I map them into bits/words) then you can force the bits/words. This is the standard way, I recommend this as it only requires to re-instate the calls to blocks for the I/O so for example map all physical inputs into internal bits in a block but not call that block while in simulation. (no need to map outputs unless you do not have the physical outputs). Another way is to build a simulator that simulates the loadcell, there are many circuits if you google them. I assume you are converting the analogue inputs to represent say lbs or kg etc. so will be using some sort of scaling so just disable the call that writes the values into the tag.
Here is a link to a doc with a circuit
http://hardyinst.custhelp.com/ci/fa...BJTIxJTIx/filename/load+cell+simulator+v2.pdf

What PLC are you using? If it is ControlLogix are you doing the analog scaling in the card? If it is CompactLogix then it is easier.


How I will do testing in a CompactLogix is I will create some Test_DINT and Test_Bit tags. Then in the SCP institution I will put the source as my Test_DINT. Then I will enter a value into the Test_DINT tag that is inside of the raw scale I am using in the SCP.


Another way is to put a simulator on the input (like parky said). This takes more time but does give you a complete check out of the system.


We have a great source for simulator as part of the PLC Talk Community. Check out http://plccable.com they have a bunch of different simulators and testers. I personally use them.

What I do as a programming standard is to read the analog input only once and MOV the value to a DINT or REAL tag. The rest of the program looks at that tag.

For troubleshooting put an AFI in the read line and then you can make the tag any value during testing. Instead of an AFI you can also put an XIC Enable_Read BOOL and toggle it on to test without having to edit it out later.