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Control Global

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Personal, professional growth accrues over time

Tue, 20 Mar 2018 10:04:00 -0400

As we grow, we go through several awakening stages.

The electric grid continues to be cyber vulnerable and susceptible to catastrophic impacts

Tue, 20 Mar 2018 00:09:00 -0400

The Russians have been in the US electric grids since at least 2014. The Defense Science Board stated the US critical infrastructure doesn’t have the ability to prevent damage. What is happening to provide resilience and recovery?

Data cable solutions for the flourishing smart factory

Mon, 19 Mar 2018 12:31:00 -0400

Data cables are increasingly being used to create more information transparency within factories, allowing raw sensor data to be easily and quickly pieced together into higher-value context information.

Control's 10 most-read articles from February 2018

Mon, 19 Mar 2018 11:22:00 -0400

From choosing the right valves and controllers to the top companies in the industry, these were the most-read articles on during February 2018.

Subject matter experts necessary to support digitalization

Fri, 16 Mar 2018 17:40:00 -0400

Quick commissioning of preconfigured systems defers the need to learn new technology.

How to eliminate uncertainty, risk when performing partial stroke tests

Fri, 16 Mar 2018 17:26:00 -0400

When implemented correctly, partial stroke tests enhance the final element (i.e., the valve) by reducing its PFDavg contribution (50%) to the safety instrumented function.

OPA Forum expands open, interoperable standard for process control device interfaces - Part 2

Fri, 16 Mar 2018 16:24:00 -0400

ExxonMobil Research and Engineering Co., Lockheed Martin gain ground with complementary initiative

OPA Forum expands open, interoperable standard for process control device interfaces - Part 1

Fri, 16 Mar 2018 11:42:00 -0400

ExxonMobil Research and Engineering Co., Lockheed Martin gain ground with complementary initiative

Product roundup: PLCs, PACs & PCs get connected

Thu, 15 Mar 2018 11:20:00 -0400

Today's PLCs, PACs and PCs are well-networked and protected to perform anywhere.

Can we resolve the climate debate? - part 3

Wed, 14 Mar 2018 11:48:00 -0400

How warming affects winds, precipitation, hurricanes and ocean currents

Fertility Clinic Liquid Nitrogen Incidents – could they have been hacks?

Wed, 14 Mar 2018 03:37:00 -0400

Two different fertility clinics on opposite sides of the country had almost simultaneous failures of their liquid nitrogen systems that appear to be process sensor-related and possibly cyber-related. What are the implications to these and other industries using liquid nitrogen?

Yaskawa America's Sigma-7 400 Volt servo motor, amplifier

Tue, 13 Mar 2018 13:40:50 -0400

New amplifier design offers advantages to machine builders and end users

Saudi Aramco handles increasing digitalization in the processing

Tue, 13 Mar 2018 11:46:00 -0400

Saudi Aramco has sought to alleviate increasing obsolescence in its automation systems and networks since 2010

The particulars of particles-in-liquid

Mon, 12 Mar 2018 17:49:00 -0400

Accurate turbidity determinations depend on technique as well as technology

SINET Security Conference Summary and Observations March 7-8, 2018

Mon, 12 Mar 2018 11:59:00 -0400

I participated in the 2018 SINET Security Conference in Mt. View, CA. The agenda can be found at There was a dearth of control system cyber discussions and a lack of control system cyber security understanding by many.

Among colleagues

Fri, 09 Mar 2018 12:46:00 -0500

There's nothing like face-to-face meetings with people who know what's going on.

Solutions to Prevent Harmful Feedforwards

Thu, 08 Mar 2018 21:20:00 -0500

Here we looks at applications where feedforward can do more harm than good and what to do to prevent this situation. This problem is more common than one might think. In the literature we mostly hear how beneficial feedforward can be for measured load disturbances. Statements are made that the limitation is the accuracy of the feedforward and that consequently an error of 2% can still result in a 50:1 improvement in control. This optimistic view does not take into account process, load and valve dynamics. The feedforward correction needs to arrive in the process at the same point and the same time as the load disturbance. This is traditionally achieved by passing the feedforward (FF) through a deadtime block and lead-lag block. The FF deadtime is set equal the load path deadtime minus the correction path deadtime. The FF lead time is set equal to the correction path lag time. The FF lag time is set equal to the load path lag time. If the FF arrives too soon, we create inverse response and if the FF arrives too late, we create a second disturbance. Setting up tuning software to identify and compute the FF dynamic can be challenging. Even more problematic are the following feedforward applications that do more harm than good despite dynamic compensation. (1) Inverse response from the manipulated flow causes excessive reaction in the opposite direction of load. The inverse response from a feedwater change can be so large as to cause a boiler drum high or low level trip, a situation that particularly occurs for undersized drums and missing feedwater heaters due misguided attempts to save on capital costs. The solution here is to use a traditional three element drum level control but added to the traditional feedforward is an unconventional feedforward with the opposite sign that is decayed out over the period of the inverse response. In other words, for a step increase in steam flow, there would be initially a step decrease in boiler feedwater feedforward added to the three element drum level controller output that is trying to increase feedwater flow. This prevents shrink and a low level trip from bubbles collapsing in the downcomers from an increase in cold feedwater. For a step decrease in steam flow, there would be a step increase in boiler feedwater feedforward added to the three element drum level controller output that is trying to decrease feedwater flow. This prevents swell and a high level trip from bubbles forming in the downcomers from a decrease in cold feedwater. A severe problem of inverse response can occur in furnace pressure control when the scale is a few inches of water column and the incoming air manipulated is not sufficiently heated. The inverse response from the ideal gas law can cause a pressure trip. An increase in cold air flow causes a decrease in gas temperature and consequently a relatively large decrease in gas pressure at the furnace pressure sensor.  A decrease in cold air flow causes an increase in gas temperature and consequently a relatively large increase in gas pressure at the furnace pressure sensor. (2) Deadtime in correction path is greater than the deadtime in the load path. The result is a feedforward that arrives too late creating a second disturbance and worse control than if there was no feedforward. This occurs whenever the correction path is longer than the load path. An example is a distillation column control when the feed load upset stream is closer to the temperature control tray than the corrective change in reflux flow.  The solution is to generate the feedforward signal for ratio control based on a setpoint change that is then delayed befor[...]

OPC Foundation, FieldComm Group developing standard information model

Thu, 08 Mar 2018 16:27:00 -0500

The two organizations formed a joint working group late in 2017 to develop a protocol-independent companion specification for process automation devices.

NovaTech donates controls to USC Aiken lab

Thu, 08 Mar 2018 16:00:00 -0500

The company donated its D/3 Process Control System to the Control Systems Laboratory at the University of South Carolina Aiken to give Industrial Process Engineering (IPE) students the opportunity to experience a more hands-on approach.

ARC Forum makes sense of digitalized future

Thu, 08 Mar 2018 15:46:00 -0500

About 900 visitors attend 50 sessions at ARC Advisory Group's 22nd annual conference