Minimise plant downtime with Siemens S7-PDIAG

Siemens Ltd. - S7-PDIAG version 5.3 is the latest version of the process diagnostics configuration tool for Siemens S7 controllers. S7-PDIAG enables the user to configure the process diagnostics required in Step 7 for display on Siemens HMI panels or WinCC SCADA. Process faults can therefore be diagnosed by the operator directly from the HMI device without need for programming knowledge or a PC.

Some of the highlights of the latest version include:

• S7-PDIAG now uses the new license types: Floating License and Trial License, consistent with Step 7 and the automation licence manager
• Inconsistency warning when loading changed blocks - the offline blocks in STEP7 are taken into consideration when downloading
• Support of foreign language character sets as introduced with STEP7 V5.3 SP2.

Diagnostics

In a market place where competition is every increasing, the productivity level of machines is a critical factor in the success of the overall operation. The productivity of the plant is dependent both on the output capability of the machines and their availability. Minimizing downtime and ensuring high availability relies on being able to diagnose and correct faults in the shortest time with minimal disruption to the plant.

System and Process Diagnostics

Faults and tools to diagnose them can be broken into two types: system and process faults.
System faults are typically hardware or software faults within the control system. Internal diagnostics that indicate these faults are standard today. SIMATIC® provides particularly effective integral system diagnostics for detecting and displaying these faults within Step 7 or on Simatic HMI devices and WinCC SCADA.
Process diagnostics detect and indicate faulty states in the process allow problems to be rectified quickly where they arise. Process faults account for 80% of faults during normal operation, so process diagnostics has an important part to play. Process faults are faults located outside the control system. Examples include:

• Limit switch not reached
• Interlock condition not fulfilled
• Watchdog time elapsed

These conditions are plant-specific and cannot therefore be integrated into the PLC hardware or firmware. Therefore process diagnostics must be configured as part of the user program. This can lead to extremely high engineering costs for implementation and maintenance depending on the tools available.

Conventional implementation of process diagnostics

With other systems process diagnostic functions are programmed separately from the actual control program. This has many problems:

• High engineering overhead - the addition diagnostics code can easily be as large as the control program
• No automatic display method for HMI devices
• Extremely costly to maintain - if control program is modified, the monitoring functions will usually have to be reprogrammed. This is often not done correctly, if at all, and the process diagnostics are not longer synchronized with the control code. The resulting incorrect messages are worse than no messages at all and could actually increase the downtime of the system.

The engineering cost and maintenance issues usually prevent the implementation of this important downtime reducing tool.

Process diagnostics with Siemens

The engineering cost and maintainability of process diagnostics can be considerably improved by using the SIMATIC diagnostic tools S7-PDIAG and PROAGENT.
The most important user benefits are: 

• Easy configuration
• Automatic change management
• User-friendly automatically created diagnostic displays
• Preventative maintenance

Easy configuration with S7-PDIAG

The process diagnostics are integrated into the standard program and do not require additional code. Simply mark variables to be monitored and define the error state. Configuration of process diagnostics with programming languages ladder, statement list and FBD requires the Step 7 add-on S7-PDIAG. This functionality is included in the languages Graph and Hi-Graph.

Automatic Change management

As the process diagnostics are integrated with the control code, any changes to the control code will be automatically reflected in the process diagnostics. This removes the need for additional engineering and knowledge to maintain both control and diagnostics code, while also ensuring the process diagnostics is automatically synchronised with the control program.

Automatic generation of user friendly diagnostics screens with PROAGENT

When an error occurs, the precise condition in the network or the logical operation that resulted in the error can be displayed. The diagnostic system will trace the error cause through multiple runs of logic and even through different programming blocks until the root cause is found. This information is then automatically displayed on Siemens HMI devices with the add-on PROAGENT.
In the example below the safety fence is preventing the machine from starting. The operator will be able to immediately diagnose this from the HMI screen shown underneath without specialist knowledge or a PC, greatly reducing the downtime due to this fault.

Preventive maintenance
Disturbances in the process sequence can be detected at an early stage and analysed allowing faults to be prevented. For example, tool wear is indicated by increasing frictional forces. The process diagnostics can monitor these forces and a new tool can be obtained and used to replace the old one before it wears out.