Digital devices—commonly called “intelligent devices”—are easier to calibrate because it can be done semi-autonomously or at least without the interaction between zero and span of older analog devices. However, they compensate for easier calibration by making configuration more complex.
Many end users believe digital devices can't be calibrated in the field, or at least not as well as their factory default settings. So instead of calibrating a device, they run a reference check to verify that when a known input is presented to the sensor input, the device responds within acceptable limits. They note that the definition of acceptable limits is often not specified, and left to the technician's discretion. Other facilities have full quality programs requiring traceability to a certifiable standard. The correct answer when it comes to calibration, reference check and level of repeatability, as with most things, is that it depends on the application. Custody transfer is much more rigorous than a monitor-only signal.
The good news is that digitally transmitted signals, either as wired fieldbus transmissions or as wireless sensor communications, will be more accurate than an analog output because there are fewer analog/digital converters. Plus, the signal itself is digital and normally in engineering units, so the reading won't deteriorate during transmission.
Since most of today’s process transmitters support HART as a minimum, technicians should use the digital signal not just to communicate with the calibration parameters, but also to verify the analog measurement. Let’s use the intelligence we have intelligently.
Going back to intelligent devices, ISA108, “Intelligent Device Management—Part 1: Concepts and Terminology,” defines an intelligent device as a “device having digital communication and supplementary functions such as diagnostics in addition to its basic purpose.” These supplementary functions are the reason for development of the ISA-108/IEC 63082 series of documents, and they complicate the use of intelligent devices.
ISA108 Part 1 was published as a technical report (TR) by ISA in 2015, and it should be available from IEC in 2017. In addition to the main committee, three new working groups were recently formed to accelerate development of the balance of the documents, explaining how the information available from intelligent devices can be used effectively as part of an integrated management system. The working groups are roughly aligned with the role of the team that will use the resulting documents:
- Working Group A: Build and Maintain—Configuration and Change Management. This group will develop documents focused on plant operations and related activities, including describing how to implement with appropriate explanations, generic work processes mainly for maintaining configuration of the system, and intelligent devices throughout the facility lifecycle from project concept through design, construction, commissioning, operations (including turnarounds) and finally decommissioning.
- Working Group B: Condition Management. By focusing on the engineering and planning (i.e. plant desk role) aspects of intelligent devices, this group will address how to implement an intelligent device management (IDM) program by defining and explaining generic work processes mainly for maintaining performance of the system and intelligent devices, including availability and reliability throughout the facility lifecycle.
- Working Group C: Program and Technology—Enterprise Resource Management. The results of this group will be more corporate or enterprise-oriented and broader in scope, explaining how to define and implement an IDM program and generic work processes related to enterprise activities common to facilities. The group will address the need for corporate work processes to establish the program, as well as other corporate processes to manage and maintain it.
Each of the working groups will develop two document types: one describing the requirements, and a second showing implementation of requirements specific to an industry in some cases. Though a critical part in the lifecycle of any device, as we can see with today’s intelligent devices, they're just one piece of the puzzle. If you're interested in helping to participate in defining the balance of the puzzle as a member of ISA108, please contact me directly. Many hands make light work, and the resulting diverse input will result in stronger and better documents.