In many chemical industry plants, a safety controller ensures the required level of safety — in the event of danger, it switches off. In order to do justice to this task, it decides, like a watchman, which signals from the field level may be forwarded to higher-level systems and which not. Field device diagnostics for maintenance and optimization have so far been left out of the scope. For the first time, a solution jointly developed by Endress+Hauser and Hima also grants access to advanced diagnostics from instruments applied in safety loops.
Although process automation is heading towards digitization, a look at the field reveals the opposite: 4…20 mA is still the dominant technology for signal transmission, and although many field devices are now equipped with the Hart protocol, in most cases this is only used during commissioning.
This impression is confirmed by Dr.-Ing. Andreas Ziegler, Senior Automation Engineer at the Automation Technology Center at BASF in Ludwigshafen. Together with his colleagues in the Regulated Automation Solutions group, he virtually sets the standards for safety controls within BASF. This includes the creation of specification sheets, the use of proven function blocks or the development of complex, model-based PLT safety solutions. “We have to find a viable way of using automation technology, not just here in Ludwigshafen, but globally,” explains Ziegler. For him, therefore, the big difference between what is possible in theory and what happens in the field is not a surprise.
Nonetheless, BASF is pushing ahead with digitization under the heading of BASF 4.0. According to Ziegler’s experience, all concepts that allow for simpler and more efficient maintenance are successful. This applies, for example, to monitoring the fouling of heat exchangers, the diagnosis of vibrations in large machinery such as turbo compressors or the diagnosis of actuators.
An even more careful approach is naturally taken in safety control applications. The importance of intelligent diagnosis is on the increase, however, particularly because the sensors and actuators used in this field are so essential to the process.
While there are some diagnostic routines, “We don’t have access to the truly interesting diagnostic data when it comes to safety-related applications,” Dr.-Ing. Martin Roser, Senior Automation Manager of the Regulated Automation Solutions Group states regretfully in light of the current situation. “But this is precisely the type of data we need in order to further increase the degree of diagnosis. This allows the period between repeat inspections to be prolonged, for example.” The challenge lies in the fact that common safety controls have so far not permitted such additional information from the field to be read.
Joint Idea Triggered a Breakthrough
In the scope of the Open Integration partner program, Endress+ Hauser and Hima have now developed a special solution for this purpose. The Himax safety controller can now trigger self-monitoring functions and read the diagnostic data from Endress+Hauser Proline flowmeters with Heartbeat Technology in the SIL loop. This function provides a so-called HBSI (Heartbeat Sensor Integrity) value, which detects corrosion and deposits, among other things.
The concept also includes an integrated Hart firewall of SIL 3 quality: the safety control decides which signals can be transferred between the field device and a higher level of automation, and which cannot. For example, read-only access can be permitted for field devices, blocking any write commands. The features of the safety control implemented by this process therefore correspond to a safety concept in accordance with IEC 62443 for Hart device access.
Thanks to Heartbeat Technology, periodic inspections can be carried out through the safety control even if the devices are SIL-locked in installed safety guards. The safety controller determines the optimum implementation time to run the device self-tests. The process is fully automated from the point when the device is unlocked, through comprehensive device verification to the relocking of the device. This process is controlled via the Hart interface as well as in a manner that is NE 154 compliant.
The concept is particularly interesting since it provides the opportunity to prolong test cycles. Ziegler refers to the high personnel costs involved in periodic inspections, especially if a device requires disassembly or is due for calibration. “This already takes up a lot of time at present and is likely to take even more time in future, as sensors and actuators are becoming increasingly complex.” The newly developed solution offers many advantages for the maintenance of Coriolis flowmeters, with further measurement processes set to follow. The devices can be inspected without the need for disassembly or any plant downtime. In fact, it is an automatic inspection and a secure technical process that avoids systematic errors while providing clear inspection results. This process also provides extensive monitoring parameters for the simple implementation of predictive maintenance.
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