Monday, July 17, 2017

Foundation Fieldbus – Part Two

storage tanks
Almost any operation can benefit from incorporating
Foundation fieldbus
Since automatic control decisions in FOUNDATION fieldbus are implemented and executed at the field instrument level, the reliance on digital signals (as opposed to analog) allows for a streamlined configuration of direct control system ports. If the central control device were to become overloaded for any reason, tasks related to control decisions could still be implemented by operators in the field. This decentralization of the system places less burden and emphasis on the overall central control unit, to the point where, theoretically, the central control unit could stop functioning and the instrumentation would continue performing process tasks thanks to the increased autonomy. Allowing for the instrumentation to function at such an increased level of operation provides a proverbial safety net for any system related issues, with the capacity for independent functionality serving as both a precaution and an example for how process technology continues to evolve from analog solutions to fully end to end digital instrumentation.

Even in terms of the FOUNDATION compliant instrumentation itself, there were two levels of networks being developed at this increased level of operation, initially: the first, H1, was considered low speed, while H2 was considered high speed. As the design process unfolded, existing Ethernet technology was discovered to fulfill the needs of the high speed framework, meaning the H2 development was stopped since the existing technology would allow for the H1 network to perform to the desired standards. The physical layer of the H1 constitutes, typically, a two-wire twisted pair ungrounded network cable, a 100 ohm (typical) characteristic impedance, DC power being conveyed over the same two wires as digital data, at least a 31.25 kbps data rate, differential voltage signaling with a defined threshold for both maximum and minimum peak receive rates, and Manchester encoding. Optical fiber can be used on some installations in lieu of the twisted pair cable.

Most of these specifications were exactly designed to withstand extremely challenging process control environments while still not abandoning the philosophy of being easy to build and implement, especially in terms of new system establishment. The most crucial aspects of many process control systems are streamlined together, allowing for consistent communication and synchronization. All aspects are viewable from both the legacy central controller and also via each individual device. Despite the data rate of 31.25 kbps being relatively slow, what is sacrificed in terms of speed is more than made up for in terms of the system being compatible with imperfect cables and other hiccups which may destabilize a network with faster speeds. The evolved technology, ease of installation, and durability have made the H1 network a widely used implementation of the FOUNDATION fieldbus technology. The standard is currently considered one of a few widely adopted industrial process control communications protocols.

Foundation Fieldbus Equipped Instrumentation – Part One

Foundation filedbus capable pressure transmitter
Foundation fieldbus capable instruments and devices
provide benefits to process operators
Image courtesy Autrol
Autonomous control and digital instrumentation are two capabilities enabling highly precise or complex execution of process control functions. FOUNDATION fieldbus instrumentation elevates the level of control afforded to digital field instrumentation where, instead of only communicating with each other, instruments involved in particular process control systems can independently facilitate algorithms typically reserved for instruments solely dedicated to controlling other instruments. Fieldbus capable instrumentation has become the standard instrumentation for many process industry installations due to the fact the FOUNDATION design principle streamlines process systems. A large contributor to FOUNDATION’s success has been faster installation as opposed to operational controllers which do not feature the fieldbus configuration. Newer process companies, or process control professionals seeking to establish a new system, have gravitated towards fieldbus due to the combined advantages of system conciseness and ease of implementation.

In a typical digital control system, dedicated controllers communicate with field instrumentation (the HART protocol is a prime example of digital communication at work in the industry). The host system controls configuration of instruments and serves as a central hub where all relevant control decisions are made from a single dedicated controller. Typically, these networks connect controllers and field devices through coupling devices and other ‘buses’ which streamline many different instruments into a complete system.

FOUNDATION fieldbus approaches the same network scheme with an important difference. Whereas in a legacy or more conventional system, either algorithmic or manual decisions would need to be implemented via the dedicated system level controllers, instruments utilizing FOUNDATION fieldbus architecture can execute control algorithms at the local device level. The dedicated controller hub is still present, so that operators can view and monitor the entire network concurrently and make status changes. Algorithmic execution of control functions becomes entirely device reliant thanks to the FOUNDATION protocol. Additionally, even though FOUNDATION implements an advanced configuration, some operators use the capabilities introduced in the fieldbus upgrade to implement specific algorithms via each device while concurrently maintaining algorithms in the central controller. This dual algorithmic configuration allows for several advantages, including the ability for increased system precision.

Since individual devices in the control process are calibrated and able to execute their own control functions, issues in the process with particular devices can be isolated and dealt with in a more specified manner by technicians using the instruments in the field. The central operator retains the capacity to use the control hub to alter and direct the control system.

Saturday, July 8, 2017

In Situ Gas Measurement Instrument for Emission Monitoring and Combustion Control

in situ gas monitor
Model GM 35 in situ gas monitor
Image courtesy of Sick USA
The measurement of gas component concentration, especially in operations involving combustion, is necessary to assure regulatory compliance, as well as levels of fuel consumption efficiency. Measurement instrumentation that is reliable, easy to maintain, and accurate delivers needed information without a substantial burden.

What are some attributes of a gas measurement instrument that may prove useful for industrial installations?

  • Ability to measure multiple constituents, such as CO, CO2, H2O, or N2O with a single instrument. 
  • Built-in capability for zero and span test without the need for test gases.
  • In place continuous operation with real time measurement output, eliminating the need for gas sampling or transport. Measurement is accomplished in the process flow.
  • Measurement of temperature and pressure included in unit function.
  • Model available in cross duct and single ended probe type versions.
  • Rugged, properly rated, enclosures for installation outdoors in challenging industrial environments
Each installation scenario will have its own challenges, and each process its own set of measurement requirements. Share your application specifics with a process measurement specialist, combining your own knowledge and experience with their instrument application expertise to develop an effective solution.