Ask Control Engineering
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What's the problem with overshoot?
September 10, 2010
Dear Control Engineering: I was looking at Back to Basics in the August issue about closed loop control. What is the main concern about overshoot? Why is it a problem, and can’t a controller prevent it? An ideal controller should be able to move a process variable quickly to the desired setpoint without shooting past. Sometimes controllers will push the... » more
( 1 Comment )
September 10, 2010
Dear Control Engineering: I was looking at Back to Basics in the August issue about closed loop control. What is the main concern about overshoot? Why is it a problem, and can’t a controller prevent it? An ideal controller should be able to move a process variable quickly to the desired setpoint without shooting past. Sometimes controllers will push the... » more
( 1 Comment )
Finding an oil / water interface level
September 03, 2010
Dear Control Engineering: I was reading the article on differential pressure sensors, and I was wondering if I could use that density calculating feature to determine the interface point between oil and water in the same tank? Let’s think about how that feature works and see how to solve your problem. As the article pointed out, if you have two taps on the... » more
( No Comments )
September 03, 2010
Dear Control Engineering: I was reading the article on differential pressure sensors, and I was wondering if I could use that density calculating feature to determine the interface point between oil and water in the same tank? Let’s think about how that feature works and see how to solve your problem. As the article pointed out, if you have two taps on the... » more
( No Comments )
Pressure gage ranging and accuracy
August 29, 2010
Dear Control Engineering: I was reading the recent article on differential pressure sensors, and I had a question coming out of that discussion. The author made the following statement: “The pressure in the line may be upwards of 1,000 psi, but the pressure drop is usually very small. Using two separate gage pressure devices and subtracting the readings... » more
( No Comments )
August 29, 2010
Dear Control Engineering: I was reading the recent article on differential pressure sensors, and I had a question coming out of that discussion. The author made the following statement: “The pressure in the line may be upwards of 1,000 psi, but the pressure drop is usually very small. Using two separate gage pressure devices and subtracting the readings... » more
( No Comments )
Analog to digital: Frequency
August 20, 2010
Dear Control Engineering: I was looking at the discussion about bit rate, but can you go into more depth on how frequency works in this context? If bit rate is the vertical or y-axis on our graph, frequency is the horizontal or x-axis. Bit rate says how many divisions you have on y, and frequency says how often you make a mark. Here’s an analogy. Say you... » more
( No Comments )
August 20, 2010
Dear Control Engineering: I was looking at the discussion about bit rate, but can you go into more depth on how frequency works in this context? If bit rate is the vertical or y-axis on our graph, frequency is the horizontal or x-axis. Bit rate says how many divisions you have on y, and frequency says how often you make a mark. Here’s an analogy. Say you... » more
( No Comments )
Analog to digital: Counting the bits
August 13, 2010
Dear Control Engineering: I was reading a release about an analog-to-digital converter that says it’s 12-bit. What does that mean exactly? Is 12-bit better than eight-bit? Bit counts are all about trying to convert analog measurements to digital. Let’s say you’re trying to measure the diameter of a coin with a ruler. You put the ruler on the coin and... » more
( No Comments )
August 13, 2010
Dear Control Engineering: I was reading a release about an analog-to-digital converter that says it’s 12-bit. What does that mean exactly? Is 12-bit better than eight-bit? Bit counts are all about trying to convert analog measurements to digital. Let’s say you’re trying to measure the diameter of a coin with a ruler. You put the ruler on the coin and... » more
( No Comments )
How much oil was lost in the gulf?
August 06, 2010
Dear Control Engineering: Please help me understand how much oil was spilled in the Gulf of Mexico. We’ll never know exactly how much oil was released from the blown-out Deepwater Horizon well over the past few months, but it is safe to say that it was the largest oil spill ever. One estimate that seems to be gaining acceptance is that roughly 5 million... » more
( No Comments )
August 06, 2010
Dear Control Engineering: Please help me understand how much oil was spilled in the Gulf of Mexico. We’ll never know exactly how much oil was released from the blown-out Deepwater Horizon well over the past few months, but it is safe to say that it was the largest oil spill ever. One estimate that seems to be gaining acceptance is that roughly 5 million... » more
( No Comments )
DC electrical transmission growing
July 30, 2010
Dear Control Engineering: It seems that using dc for electrical distribution is growing. How is this practical? You shouldn’t expect to have your residential electrical service converted to dc anytime soon. The considerations that made utilities adopt ac almost universally over the last century continue to apply for most uses. Still, there are applications... » more
( No Comments )
July 30, 2010
Dear Control Engineering: It seems that using dc for electrical distribution is growing. How is this practical? You shouldn’t expect to have your residential electrical service converted to dc anytime soon. The considerations that made utilities adopt ac almost universally over the last century continue to apply for most uses. Still, there are applications... » more
( No Comments )
What is medium voltage? It depends on application, industry
July 26, 2010
medium voltage is far from uniformly defined, with specifications varying widely by industry, application, standards organizations, and other sources. At the broad system level, IEEE (Institution of Electrical and Electronic Engineers) Std. 100 defines nominal medium voltage (MV) as ... » more
( 1 Comment )
July 26, 2010
medium voltage is far from uniformly defined, with specifications varying widely by industry, application, standards organizations, and other sources. At the broad system level, IEEE (Institution of Electrical and Electronic Engineers) Std. 100 defines nominal medium voltage (MV) as ... » more
( 1 Comment )
Apple's problems and wireless instrumentation
July 16, 2010
Dear Control Engineering: It’s been interesting following some of the problems that Apple is having with its iPhone 4. Should I be concerned about similar reception difficulties with wireless instrumentation devices? It’s difficult to compare a cell phone network and wireless instrumentation in a typical industrial plant, but some of the issues of... » more
( No Comments )
July 16, 2010
Dear Control Engineering: It’s been interesting following some of the problems that Apple is having with its iPhone 4. Should I be concerned about similar reception difficulties with wireless instrumentation devices? It’s difficult to compare a cell phone network and wireless instrumentation in a typical industrial plant, but some of the issues of... » more
( No Comments )
Where has Control Engineering been?
June 29, 2010
Control Engineering, part of CSE Media, along with Consulting-Specifying Engineer and Plant Engineering, has relaunched on the web on June 29, 2010. June-July issues are expected in mid-July. » more
( No Comments )
June 29, 2010
Control Engineering, part of CSE Media, along with Consulting-Specifying Engineer and Plant Engineering, has relaunched on the web on June 29, 2010. June-July issues are expected in mid-July. » more
( No Comments )
Using 2-wire proximity sensors
June 22, 2010
Dear Control Engineering: Is it practical to replace a 3-wire proximity sensor with 2-wire type? » more
( 4 Comments )
June 22, 2010
Dear Control Engineering: Is it practical to replace a 3-wire proximity sensor with 2-wire type? » more
( 4 Comments )
Coal mine safety
June 22, 2010
Dear Control Engineering: Aren’t there sensors and other safety devices that could make coal mining less hazardous? » more
( No Comments )
June 22, 2010
Dear Control Engineering: Aren’t there sensors and other safety devices that could make coal mining less hazardous? » more
( No Comments )
Lifespan of flash memory
April 03, 2010
Dear Control Engineering: It seems that more devices, including industrial controllers, are using flash memory to store and transfer data and programs. How long does this kind of memory last? » more
( No Comments )
April 03, 2010
Dear Control Engineering: It seems that more devices, including industrial controllers, are using flash memory to store and transfer data and programs. How long does this kind of memory last? » more
( No Comments )
Large-scale fieldbus installations
March 27, 2010
Dear Control Engineering: I’ve been investigating using fieldbus architecture for field device wiring in a process unit, and it has the potential to be a fairly large installation if we proceed. Given that this technology has been around for many years now, how broadly has it been used in high-device-count installations? » more
( No Comments )
March 27, 2010
Dear Control Engineering: I’ve been investigating using fieldbus architecture for field device wiring in a process unit, and it has the potential to be a fairly large installation if we proceed. Given that this technology has been around for many years now, how broadly has it been used in high-device-count installations? » more
( No Comments )
Safety certifying automotive components
March 13, 2010
For electronics to make their way onto commercial airliners, extensive testing and failure modes must be determined before they are certified for flight. Is there a similar requirement for automobile fly by wire systems? » more
( No Comments )
March 13, 2010
For electronics to make their way onto commercial airliners, extensive testing and failure modes must be determined before they are certified for flight. Is there a similar requirement for automobile fly by wire systems? » more
( No Comments )
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