Experts

Instrumentation and Control

Instrumentation and Control by Greg McMillan, principal consultant, TAC Worldwide, and Cecil Smith, president, Cecil L. Smith, Inc.

Greg McMillan is principal consultant at TAC Worldwide, Austin, Tex. He spent more than 30 years at Monsanto and Solutia and then was a professor at Washington University, St. Louis. Honored as one of the 50 most influential people in the history of the field, he regularly speaks and writes about instrumentation and control topics; his books include “Process/Industrial Instruments and Controls Handbook” and “Advanced Temperature Control.”

Cecil Smith is president of Cecil L. Smith, Inc., Baton Rouge, La., a firm specializing in automation technology that he founded after leaving the faculty of Louisiana State University. Also cited as one of the 50 most influential people in the field, he teaches courses on control topics and has authored or co-authored 14 books, including “Digital Control of Industrial Processes” and more than 100 articles.

---

Can you explain a split range controller?
Regarding split range controller:

1. Is it normal to have a control valve with two different sizes?
2. Why use a split range controller and where can we it?
3. My application: I am planning to use at outlet of condenser. The outlet will have condensate liquid and non-condensate vapor. Will it work here?

Category: Instrumentation and Control

Can you explain linearity and accuracy of flowmeters?
I am confused on linearity and accuracy of flowmeters such as oval meters. In some references they are mentioned as the same but in some others they are not the same. Should I only rely on linearity for selection for measuring custody transfer or another flowmeter characteristic?
Category: Instrumentation and Control

Can you recommend a flowmeter?
We are going to install a flowmeter for lube oil loading as custody transfer. The flowrate may alter between 140-280 CMH (two-speed motor) having viscosity 150cSt at 40C. Simple installation and setting up on the line and reasonable cost as well as pressure drop are preferred. The pump can generate 8barg pressure. What would be the recommended flow measuring type to support the requested service?
Category: Instrumentation and Control

Where should I install the control valve on the hot oil line?
I am going to use hot oil for heating a process in a jacketed vessel and I am going to make a control loop for controlling the vessel content. The hot oil enters at the bottom of the jacket and exits from the top. The control elements are RTD, controller, and control valve. My question: Where should I install the control valve on the hot oil line? Is it up stream or down stream of the vessel?
Category: Instrumentation and Control

Why is there a discrepancy of solids at sampling points?
Ours is a fertilizer industry and within the premises we transfer phosphoric acid from the phosphoric acid production facility to the fertilizer production facility. The distance of the pipeline might be around 400m but the difference in issue and receipts generally comes out to be 100s of tons per day. Can you tell me what could be the possible problem? Other info required:

1. Phosphoric acid has around 5% solids
2. Sampling point in phosphoric acid tank is at the bottom
3. Sampling point in the fertilizer plant is at a higher level(25 ft) and is preceded by a lot of bends.

Could this be an issue with the sampling points or the data analysis?
Category: Instrumentation and Control

Is there any standard for painting critical instruments?
Is there any standard/code for coloring (painting) of critical instruments related to Plant/Process Safety devices? What color should be used for painting critical instruments for easy identification from other normal instruments of the plant?
Category: Instrumentation and Control

Are there limitations when installing a wafer-type butterfly valve?
Are there limitations (straight run pipe distances, etc.) that must be considered when installing a wafer-type butterfly valve in a chilled water system and the valve is used as the control valve?
Category: Instrumentation and Control

Can a DCS react fast enough to prevent loss of the booster compressor?
I have two four-stage centrifugal air compressors (electrical driven) running in parallel, feeding a turbo-driven booster compressor. When an air compressor shuts down I lose the booster compressor because of overspeed or low suction pressure at the booster compressor. Can a DCS react fast enough to prevent loss of the booster compressor?
Category: Instrumentation and Control

Which Programming Language Should I Learn For Process Control?
I am concerned with the role that is played by programming languages in process control. In the first course of my undergraduate study, we went through Visual Basic; our teacher was encouraging us to master it since it is of great importance in our specialty. Recently I found out, on Google, that most people prefer C/C++ to VB as far as engineering is concerned. According to your experience, which language best fits process control engineering, especially for someone interested to work for BP or Shell Oil Companies?
Category: Instrumentation and Control

Is there a flow meter that will be reliable, even with moderate particulate in the air stream?
One of my processes has a dust-collection line to eliminate nuisance dust. The same line is tapped for a supporting process in the room. The problem we have experienced is that the dust collection adversely affects the product yield if flow rates are too high. We don't have a way of quantifying an acceptable flow range. I would like to install a flow meter so we can determine such a range and make it part of the operation procedure. The line is about 4 inches in diameter. I've looked at a few flow meters, but would like your thoughts on which type would be best suited for this application. I want to find something that will be reliable, even with moderate particulate in the air stream. Of course, the more economical the solution, the better the chance it will have of happening.
Category: Instrumentation and Control

Flow Meters: What is the appropriate length of reducer and expander?
I have to install a flow meter size 900mm on a 1,600mm water pipe line. Gravity flow with 5,600 cubic meters/hr flow rate. What will be the effect on the flow profile? Line pressure? What will be the pressure drop? Will it affect/resist flow? Meter length would be around 500mm. Please suggest appropriate length of reducer and expander.
Category: Instrumentation and Control

Choosing Dry or Wet Reference Legs
In the d/p Level transmitters, what is your criteria to choose dry or wet reference legs? I now that wet leg is used for fluids that condensate. How do you check if a fluid condensates? By checking the vapor pressure? Is it only for ambient temperatures?
Category: Instrumentation and Control

Installing a close loop for temperature control
We want to install one new close loop for temperature control. Before tuning the control valve, what should be the initial P, I, D value?
Category: Instrumentation and Control

Extracting RMS value
The plant I support has two existing speed controlled simplex diaphragm pump installations (manual stroke adjustment) w/ Coriolis mass meter configured so Flow adjusts stroke speed. Flow has a pulsing frequency of ~ 1sec. Because these are simplex pumps, pulsing affects flow more than 5%, in spite of the pulsation dampener. The second flow is ratio controlled from the first flow. I would like to take advantage of the constant volume characteristic of the metering pump to compare the flow generated by the pump to the flow measured by the cmm, as a plausibility check of the health of the cmm and pump. In a sense an on-line prover. This seems straight forward: stroke speed *volume* cmm density where volume is the calibrated volume @ a stroke setting. However the computed value is in effect a smoothed value while the meter is instantaneous. I imagine I need an RMS value from the Micro Motion. First Any advice on how to extract or generate the value? Secondly, I am trying to determine whether ratio control with the computed values or the RMS values will reduce downstream variability induced by the feed control & pump system. What computation would I make with vendor data, to show which is likely to work better? (If there is a way, where would I find the method?)
Category: Instrumentation and Control

Control Valve Sizing
I would like to know, why reducer and expander is provided in inlet and outlet line of Control valve? Is there any perticular reason for it?
Category: Instrumentation and Control

Improve thermocouple response time
How do you improve thermocouple response time? In one of my plants, I am checking thermocouple response time (K-type) in main steam temperature measurement. The response time is coming 22 sec without a thermowell. How do I achieve a response time of 7 to 10 sec.?
Category: Instrumentation and Control

Measuring waterwater pH
We know that the pH of wastewaters is important if we want to release them in rivers, lakes or seas, etc. I want to know the best methods that measure the pH of wastewater in a lab.
Category: Instrumentation and Control

Instrumentation and control resources
I am an instrumentation and control engineer. Even though I design process control systems, I want to become more knowledgeable in that field. Kindly suggest a few resources that make learning process control interesting and can help me understand the basics thoroughly.
Category: Instrumentation and Control

Transmitter nozzle orientation
I have a question about the installation of a DP Level Transmitter. Is there any obligation to select both nozzles of a side DP transmitter in the same orientation? I have heard tube length shall be restricted in high temperature services to preventing condensation and we have to select both nozzles in same orientation. Please clarify.
Category: Instrumentation and Control

Number of wires required for RTD sensors
What is the distance a signal conditioning transmitter will reach with a 2-wire RTD sensor? When is it best to use a 3- and 4-wire RTD?
Category: Instrumentation and Control

Cumulative flow measurement instrumentation
What is the instrument that can take a cumulative flow measurement of an effluent slurry containing fibers? I am required to measure the quantum of effluent that I send to a common effluent treatment plant. The effluent was generated by the dying operation of jute yarn and it contains jute fibers. Vanes of the flow meters (water meter) stops its running by these fibers. Is there is any electronic device like the energy meter (that is used to measure power consumption) available? Can a mass flow meter be used in this application?
Category: Instrumentation and Control

Cause and effect charts
Cause and effect charts used for system shutdowns, etc. is a concept/technique commonly used, but there seems to be no standardized methodology, and the format or the data produced varies as well. As you get deeper in the subject, you find that there is a wide variation in what is included and the definitions. We searched for "days" and visited with others in our industry looking for some source of documentation (book) or even an guideline by an organization such as ISA, etc., but at the end of the day, there was nothing. Do you have any reference book or source of information that may be of value? It is such an important "analysis," one would think there would be some form of consistency and "rules."
Category: Instrumentation and Control

ChemicalProcessing.com
Would PLC be suitable or a hybrid controller to control the temperature and air/fuel ratio of 12 zones of a continuous annealing furnace?
Category: Instrumentation and Control

Control pressure at discharge
I have five pumps running parallel, transferring water. Due to pressure fluctuation at discharge, which depends on the flow requirements of the user, I am planning to install a pressure control valve at the pump discharge to keep the pump running at an optimum condition. My candidate is a globe valve, but because the line size is quite big (14 in.), the globe valve is not adequate. An engineering consultant suggested a butterfly type. According to past experience, using this kind of valve is not effective for pressure control. What kind of valve is best for a 14-in discharge?
Category: Instrumentation and Control

Pneumatic conveyor sensor
My company used pneumatic conveying for dust handling. I want to put a level sensor/transmitter in blow tank/transporter/blowpot. The problem is the sensor reliability. The space (in the blow tank) is high pressure. The level sensor often leaks at that condition. Could you please recommend a type of level sensor that is suitable for the system?
Category: Instrumentation and Control

Control conveyor velocity
I want to control the conveying velocity of dust pneumatic conveying. What kind of instrument should be installed on the conveying line? My focus is to reduce air consumption, so I need to control compressed air to have an effect on velocity conveying.
Category: Instrumentation and Control

Avoid excessive heat flux
How does one set the constraints (startup or operation) to avoid excessive heat flux or pressure change that result in bumping or boil over of an evaporator or batch stripper, especially at vacuum? What correlations for pressure change and or heat flux would be used to establish prudent rate of change constraints?
Category: Instrumentation and Control

Signal error in coriolis flow meter
What are the possible causes that could contribute to signal error in coriolis flow meter? I experienced a case in which my flow meter showed that there was a 300 L/min flow in the flow meter while there actually was no flow in the meter.
Category: Instrumentation and Control

Learning process control
Are there any elementary books or articles for learning process control on a self-study basis? I am woefully weak in this area and it is really messing up my job hunt.
Category: Instrumentation and Control

Reliable methods of measuring the level in ammonia chillers
We have solvent dewaxing unit with liquid ammonia refrigeration as coolant in our process chillers. Our chillers cool process liquid by evaporating liquid ammonia in the shell side and process fluid flows in the tube side. All of our chillers are provided with level trolls with stainless steel floats type level transmitters for measuring the level. Often we find that these indications are malfunctioning and resulting in liquid ammonia carry over to vapour lines and causing serious problems in our ammonia compressor. Is there a more reliable method of measuring the level in ammonia chillers? If so, what are the available options?
Category: Instrumentation and Control

Cyclone blockage
We have been facing continous (unsolved) problems with cyclone blockage in the reactors on our plant. These cyclones regularly get blocked due to the catalyst inside the reactor. Many options have been considered , each with its own disadvantage. Mechanical hammers/other mechanical solutions usually has the disadvantage of short life span due to the corrosive nature of the catalyst. Magnetic solutions are a possibility as long as it does not influence the reaction to the fact that the catalyst must form a fluidised bed. The reactor is also at very high temperatures (350 degrees celcuis). I wish for any advice or best pratices on cyclone blockage prevention.
Category: Instrumentation and Control