The key elements of the NeSSI Generation II Specification are as follows.
* Adoption of a digital communication bus (NeSSI-bus) that is specifically tailored for process analytics and intended to replace 4-20 mA systems. This bus can handle up to 30 devices. (This bus would be equivalent to a plug-and-play USB bus on a personal computer but with special requirements.)
* For electrical equipment in hazardous areas, classifying the interior of an enclosure handling hazardous (flammable) fluids (e.g. hydrogen and ethylene) as Division 1/Zone 1 rather than Division/Zone 2.
* Adopting the use of a safe low energy, globally accepted method of electrical protection called intrinsic safety for the NeSSI-bus.
* Adopting the use of miniature smart/automated electronic devices including sensors (flow, pressure temperature), on/off and proportional actuators and enclosure heater controls.
* A move away from the use of local indicating devices such as gauges and rotameters in order to reduce labor-intensive manual checking (rounds).
* A move away from centralized control (automation) model to a local/field control model which is represented by a small computing device called the Sensor Actuator Manager (SAM).
* Adopting the concept of portable, commercially available software smart applets for the purpose of automating specific sample system functions. These applets would be resident in the SAM.
* Employing an Ethernet network between the SAM, the DCS and the Operator & Maintenance (O & M) user station. (NeSSI refers to this bus as the ANLAN)
* Introduction of a Graphical User Interface (GUI) for better visualization of physically compact sampling systems.
The first prototype of a multi node/miniature Generation II system was demonstrated by Siemens Process Analytics in 2006. Siemens has adapted an existing bus system called IC to operate in an intrinsically safe mode. This work was undertaken once it was determined that existing intrinsically safe capable digital communication systems such as Foundation Fieldbus and Profibus could not meet the requirements of reduced physical size as well as the lower cost and power draw defined by the NeSSI-bus. Whether or not this bus will go into wide commercial production is unknown at this time.
A nonprofit organization, CAN in Automation (CiA) released a 2007 Draft Standard Proposal (DSP-103), that specifies the physical layer of an intrinsically safe bus. [CAN = Controller Area Network] The specification has been developed by members of the CiA organization among them ABB, Pepperl+Fuchs, Texas Instruments, and Siemens. By using a lower voltage (9.5 V) for its power supply, this bus can provide more current (up to 1,000 mA) to power multiple devices in a hazardous environment. This group has standardized upon the 5-pin M8 pico connector for providing both power and signal to the devices. A commercial implementation of a process analytical system using this bus has yet to be demonstrated.
An interim development called Generation 1.5 uses both conventional 4-20 mA analogue sensors and discrete signals to actuate valves. A Programmable Logic Controller (PLC) is used as the Sensor Actuator Manager (SAM).