Rethink Sample System Automation

NeSSI provides new tools to tackle the challenges and improve performance.

By Robert N. Dubois, consulting analytical specialist

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Figure 4 shows a NeSSI-bus-enabled valve control module for actuating sample-system pneumatic valves as well as a NeSSI-bus-enabled pressure/temperature transmitter. The module is rated Division 1/Zone 1 and so can be mounted inside a sample system enclosure. When used with a gas chromatograph it can obviate separate pneumatic tubes between the chromatograph and the sample system. A single cable connection links the gas chromatograph to the valve control module.

Filter replacement routines. Do you know how effective your filter is or when to change it? Right now gauging system performance is a hit or miss activity. Use of a NeSSI-bus-enabled differential-pressure or moisture-breakthrough sensor (common in continuous emission monitoring systems) would give hard data. It would allow us to validate filter performance and move from preventive to predictive maintenance. Automation of the filter also will lead to adoption of more-intelligent filtration devices that predict life span and initiate self-cleaning routines.

Using the DCS to control analytical systems. The advent of low-cost miniature computing and control devices will enable sampling-system control functions to become distributed and local to the sample system. Simple programmable control applets will dominate, be interchangeable across platforms and available from third parties. Sensors and actuators associated with auxiliary systems such as carrier-gas generators, heat tracers, conditioners (vaporizing regulators, sample recovery systems, etc.) can be integrated on the NeSSI-bus. With these sensors we can monitor and apply set points to our auxiliary process-analytical support system. The process analytical SAM can significantly extend limited control functionality previously provided by the DCS and various controllers.

Thermostats for temperature control. We can replace thermostats with PID control loops. We already are doing this using commercially available smart heaters. Advantages include the ability to maintain higher temperatures thanks to tighter control of the heater. Although an explosion-proof heater can't run on intrinsically safe power, its temperature and set-point signals can be integrated into the NeSSI-bus. Reliability will be enhanced by being able to better monitor and control critical dew points and bubble points of the process sample.

NeSSI bus-enable module
Figure 4. Valve Control Module and
Transmitter: Module (left) comes with
a lockout to prevent actuation of
multiple valves at the same time.
Photo courtesy of Swagelok.

Gas cylinders for calibration and validation. More-precise flow and temperature control in a sample system affords the opportunity to opt for more permeation generators to calibrate and validate analytical sensors. Today we use bulky gas cylinders to do this chore. It would be a tremendous advantage from an installation and operational point of view to eliminate calibration cylinders when the components needed are available as permeation sources.

Maintenance resources and routine rounds.NeSSI can eliminate the need for continual checks and adjustments. The new generation of smart analyzers such as gas chromatographs will have visualization built into the sample system as part of their local human machine interface (HMI) and remote workstations, helping analyzer technicians properly troubleshoot. Indeed, troubleshooting will become more of a science than an art. Portable zone-2-rated laptop computers or PDAs can effectively serve as the new "adjustable wrench" for the technician.

Block and vent valves for gas chromatograph sample introduction. Typically to ensure constant molecular volume we reference the sample pressure to atmosphere using a block-and-vent-valve arrangement prior to injecting a sample into a gas chromatograph. The ability to use an absolute pressure sensor will allow more-precise measurement and better control without the need for block-and-vent hardware. Of course, this would require the sample system to communicate with the gas chromatograph.

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