15.16 Determining The Type Of Wire Break Condition From An Sm 1231 Module - Siemens SIMATIC S7-1200 System Manual

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Determining the type of wire break condition from an SM 1231

As described in the topic Measurement ranges of the analog inputs for voltage and current

(SB and SM) (Page 1471), the SM 1231 module returns an analog input value of 32767

(16#7FFF) for both a wire break condition or an overflow condition. If you want to determine

which of these two conditions occurred, you can include logic in your STEP 7 program to

make the determination. The method to determine the condition type consists of these tasks:

● Create a Diagnostic error interrupt OB to be called whenever there is an incoming or

outgoing diagnostic event.

● Include a call to the RALRM instruction.

● Set up an array of bytes for the AINFO parameter, which includes the information about

the condition type.

● Evaluate bytes 32 and 33 of the AINFO structure of the RALRM_DB when the CPU

triggers the Diagnostic Interrupt OB..

Creating a Diagnostic error interrupt OB

To be able to determine when a wire break condition occurs, create a Diagnostic error

interrupt OB. The CPU will call this OB whenever an incoming or outgoing diagnostic event

When the CPU calls the Diagnostic error interrupt OB, the input parameter LADDR will

contain the hardware identifier for the module with the error. You can find the hardware

identifier for the SM 1231 module in the STEP 7 device configuration for the SM 1231

Calling the RALRM instruction

To program the RALRM instruction call, follow these steps:

1. Add a call to RALRM in your STEP 7 program.

2. Set the F_ID input parameter to the hardware identifier in the LADDR parameter of the

Diagnostic error interrupt OB.

3. Use an array of bytes for the TINFO and AINFO input parameters. Use an array size of

34 bytes or greater.

S7-1200 Programmable controller

System Manual, V4.2, 09/2016, A5E02486680-AK

15.16 Determining the type of wire break condition from an SM 1231 module

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