As Industrial Automation and Controls professionals, a majority of our time is spent on troubleshooting or debugging code other people wrote, with little documentation to reference. A key tool in your troubleshooting arsenal is “Cross Referencing”.

Cross referencing is the act of finding where a variable in the system is actively used in order to find the root-cause of an anomaly in the system. A lot of cross-referencing is done inside the PLC and HMI programs to find why certain functions are not executing when the input signal is sent. 

This article will discuss how to use cross-referencing in Siemens TIA Portal to solve a common industrial controls problem.

Typical Controls Issue

“The motor does not turn on when the button on the HMI is pressed.”

This is a common occurrence in industrial manufacturing and process plants. Below shows a common controls architecture for motor control using an HMI.

Simple motor control architecture

If, after all electrical wiring and mechanical structures are verified to be in working condition (with the machine operator), the motor still doesn’t turn, you can jump into the HMI and PLC in order to follow the logic bread crumbs to figure out why the motor isn’t turning.

Having no prior knowledge of how the system was programmed, the logical path in troubleshooting is to start from the HMI button. 

I will use the Siemens TIA Portal platform to demonstrate cross-referencing.

HMI Screen

Open up the HMI prioject in TIA portal and cross reference the “Motor On” button.

Right click on the button and review the link
The button is linked to HMI tag "HMI_cmdMotorOn"
The HMI tag is linked to the PLC tag with the same name
The PLC tag is found under the "Default tag table" under the PLC project
Cross-reference the PLC tag in the "Default tag table"
"HMI_cmdMotorOn" is used in "FB_MotorControl" on Network 1

At this point we get online with the PLC to see the current state of variables in “FB_MotorControl”.

We find that the VFD that powers the motor has a fault and we continue to cross-reference
We find that the VFD is signaling to the PLC that it is sensing high temperatures at the motor

Using Cross-Referencing as our main tool we were able to find that the motor will not turn due to the VFD signaling a “motor over temp” fault. The motor should be checked for issues along with the wiring between the motor thermistor and VFD. All this could be bypassed if the HMI had an alarm for Motor Over Temp.

Cross-referencing is an indispensable tool in troubleshooting issues quickly and logically. The majority of industrial controls software platforms have cross-referencing capabilities.

Automation One