By Rob Dubois
One can safely say that a modern refrigerator has more automation than your average process analytical sample system. Why is this?
Since the launch of the New Sampling/Sensor Initiative (NeSSI), significant strides have been made to advance automation in the process analytical community. One tangible result has been the introduction of physically small, low-power, intrinsically safe (IS) buses—IS CAN-in-Automation and Siemens' I2C—which are tailored specifically for process analytical requirements.
However, despite these efforts and others over the past 10 years, the move to sampling system automation has been glacial. Could the lack of a small, programmable PC to manage the sub-systems, provide simple control and deal with signal requirements be regarded as the greatest contributor to this delay?
What is SAM?
The Sensor Actuator Manager (SAM), as proposed by NeSSI, is a small, hockey puck-sized, programmable, low-cost, process automated controller (PAC)-type device rated for hazardous area operation and packaged for operation across a wide range of environmental conditions. It's a mini-PC equivalent for process analytical systems. SAM serves four major functions (Figure 1):
- It connects to a powered serial bus communicating with sensors, actuators and remote I/O modules. This bus can be intrinsically safe or non-intrinsically safe depending on the application. (This can be considered as a purpose-based bus similar to USB.)
- It acts as a container for transportable, industry-standard "applets" that are used for automating repetitive sampling, analyzer shelter and analytical measurement tasks.
- It provides a universal connectivity solution to a secure plant DCS.
- It connects to local and remote maintenance devices, handheld configurators (including portable PCs) and the Internet. This connection would be considered non-secure and "hermetically sealed" from other SAM functions. This connection may be wireless.
To better understand these issues, let's look at SAM through the eyes of various process analytical stakeholders, and see what features of a SAM would have value for them. Can SAM serve as a common denominator for these diverse needs?
For example, to an operator, the most important element is confidence. Nothing will be more damaging to the credibility of an installation than running a process based on an assumption that the data is correct when it isn't. Operators don't need detailed information; they need a performance factor. That's why the simple concept of a traffic light—red light (bad data), green light (good data), and yellow light (impending failure)—is used as an operator alert system. To have confidence, an operator needs to know the status of the complete analytical system, which includes the analyzer + sampling system + auxiliary systems.
For maintenance staff, automation is a boon if it makes troubleshooting and configuration easier, and provides better performance. It must be simple to use and not require complex programming. Having remote and local connectivity to troubleshoot and monitor an analytical system, having a way to visualize flow paths and a mechanism to access service documentation in the field are all important. Being able to control sample flows, pressures and temperatures within the analytical environment is maintenance friendly.
Similarly, system integrators would benefit from having:
- Interoperability with disparate system connectivity.
- Seamless sub-system connectivity of shelter, analyzer, pre/post conditioner, HVAC and sample system.
- Integrated heater and heat-tracing controls.
- Ability to self-test each module prior to drop-shipping.
In addition, DCS system and IT gatekeepers require that the data transmitted over their networks and into their distributed control systems (DCS) systems be as secure as Fort Knox. Wireless can be a dirty word. Security and data integrity is paramount.
Meanwhile, analytical sensor developers and analyzer manufacturers find it difficult and costly to penetrate the process analytical marketplace. Not only do they need to come to grips with sample systems, but they also need to come to terms with DCS connectivity, system validation and electrical hazardous classifications. There is a strong desire to have a universal way to connect to anyone's DCS or SCADA system. The analytical sensor designer may need custom programming requirements, packaged for industry, to control their device.
Also, for analytical system designers, it is now evident that much of the hard-won learning is complete with respect to sampling, and that the crystallization of this knowledge needs to be captured in standard practices for deployment on future projects. There needs to be a flexible way of repurposing analytical designs to satisfy the nuances of each new project. The ability to link together various subsystems gives design flexibility, reduces cost and speeds design.
Is Embedded SAM the Sole Solution?
Embedding the SAM in intelligent analyzers such as gas chromatographs (CG) may seem like the complete answer, but it is not. Still, two major GC manufacturers (Siemens Industry and ABB) are doing so, even though 95% of the analyzers purchased in the process industries are not GCs.