June 19, 2013

Sharing pH Control Expertise

Hi everybody! I’m Jim Cahill, author of the Emerson Process Experts blog and am delighted to be able to guest post here on the Analytic Expert site. The objective of my blog is to be your connector with the experts around Emerson Process Management, including the Rosemount Analytical team. I’ve featured their expertise over the years in the Analyzer category.

Instead of pretending to be an expert, I’ll highlight the work of Greg McMillan and pH control. If you’re not familiar with Greg, he was named as a Process Automation Hall of Fame member by ControlGlobal.com in 2001. He authors the Control Talk blog and is a frequent contributor on the ISA Interchange blog.

He is also the author of numerous process automation-related books including Advanced pH Measurement and Control, 3rd Edition. He also founded the ISA mentor program to pass along his wisdom to the next generation of process control and instrumentation professionals.

Here’s a presentation Greg gave on pH Control Solutions from two years ago.

The presentation includes 3 major sections: pH opportunity and challenge (slide 7), modeling and control options (slide 24), and plant design and maintenance (slide 71). Each section concludes with key points to summarize concepts and practical guidance for you.

For example, in the pH opportunity and challenge section, one of Greg’s key points is:

Slope of the titration curve at the set point has the greatest effect on the tightness of pH control as seen in control valve resolution requirement. The next most important effect is the distance between the influent pH and the set point that determines the control valve rangeability requirement.

An example from the modeling and controls section is:

Filter the feedforward signal to remove noise and make sure the corrective action does not arrive too soon and cause inverse response.

I’ll also add that accurate pH measurement is a critical component in closed loop pH control and selection guides are available based on your application.

If your or one of your colleague’s responsibilities includes pH control strategies, I highly recommend reviewing the presentation and getting your hands on his book.

June 5, 2013

Flame Detection in Coastal Areas

by Ken Elledge, business development manager, Net Safety Monitoring

Today I would like to talk to you about the considerations for flame detectors when installed in a coastal environment. There are several things you have to keep in mind when working through these applications like location, temperature, humidity, power consumption, voltage range, weight, mounting options, maintenance, warranties and cost.

When considering what type of flame detector would best suit your application, you should first determine what technologies are available. Your options consist of ultraviolet (UV), ultraviolet/infrared (UV/IR), and triple infrared (IR3). You need to determine if it will be for indoor or outdoor use. A UV flame detector would be best for indoor use, whereas a UV/IR would offer a dual technology for an indoor or outdoor application. You may also choose a triple IR detector for indoor or outdoor coverage as well, and at the same time, maximize your ability to minimize false alarms.

Offshore-Petro-facility-(vert)It is almost guaranteed that the customer will use a stainless steel enclosure due to the salty air of coastal sites. Using stainless steel will most certainly increase the cost of the project. Salt can be very harsh on aluminum enclosures and could potentially cause the detector to malfunction or completely shut down due to corrosion. It can also make maintenance difficult if the threaded areas are compromised.

Salt build-up on the lens is certainly an issue as well, which means someone will have to clean the lens more frequently than in a non-coastal environment. High winds are also a big factor as the flame detectors must be mounted to a steady object as to not sway or vibrate. You should also be aware that heavy fog can render most flame detectors blind. If they can’t see through the fog then they can’t see the fire.

The location of the site is critical as well. You know that if it is located onshore then power is not always an issue. However, if you are located offshore, power consumption then becomes one of the most critical options. Also, having a detector with a wide voltage range, like 10-32 VDC, is a great option. On offshore platforms the power can fluctuate causing some detectors to reset themselves and create lots of issues for the technicians on site.

You should also be aware of the mounting options available for your flame detectors and ensure that the mounting bracket isn’t considered an additional accessory by the manufacturer you choose. Another one of the more critical features of a device for offshore applications is weight. The weight of each device on a platform is most important. Most companies do weight calculations every day on their offshore rigs. Choosing a lightweight flame detector with a compact design and the same for the mounting bracket is key for offshore. Let’s not forget about temperature range. You want to make sure you choose a detector that can withstand the high as well as the low temperature conditions we see around the globe as well.

There are several other considerations for coastal conditions but I’ve touched on the most critical ones. I hope this gives you a better understanding of what options are available and the ones that you should be aware of when deciding what flame detectors to use for your coastal application.

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