Siemens Graph Actions

Hi All

I am working on a set of sequences in a TIA V15 project using graph FBs. I would like to condition the graph actions to open a given valve dependant on the value of an REAL. If REAL = 1.0 THEN Valve1.Out, If REAL = 2.0 THEN Valve2.Out. Below is an extract from the help files.


In actions you can assign an operand with the value of another operand or mathematical expression or the result of an instruction. Use the following syntax for this:

Assigning the value of an operand: A:=B

Assigning the value of a mathematical expression: A:=B<Operator>C

You can use the following operators: + (Addition), - (Subtraction), * (Multiplication), / (Division), % (Modulo), AND (AND logic operation), OR (OR logic operation), XOR (Exclusive OR logic operation)

Assigning the result of an instruction: A:=<Instruction>(B)



As you are not allowed to use the compare instruction within an action I am hoping there is a way to achieve this with a mathematical expression. Anyone got any pointers on how I might be able to achieve this?

Thanks

You could use the permament post-instructions, e.g.

Thanks.

I should probably have mentioned that the REAL value is a setpoint relating to the selected tank and so can not be written from the PLC. I am currently using the pre-instructions to set a series of bits conditioned by the setpoint but would like to be able to reference the setpoint directly from the action to keep things as simple as possible.