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| 1 |
A look at 4 - 20 Milliamp Signals (38KB)
4 - 20 Ma; the analog signal of choice. Its characteristics,
its use to represent process variables, control,
retransmission, transmitter outputs, set point, position,
and feedback signals. Signal converter inputs and outputs |
| 2 |
Buying a Temperature Controller? Understand the
Specification Before you Order
(210KB)
A thorough look at the many ingenious features of the
discrete temperature controller. How it has adapted itself
to fit every known heat process and application. This tells
you how to be an informed user and how to select the
best buy. |
| 3 |
Calibrating and Testing Control Components on Your Heat
Process. What, when and how should I calibrate? (64KB)
All about best calibration practices, features of
calibrators for linear and the many non-linear signals from
transducers signal conditioners and temperature sensors.
Calibration of controllers recorders and indicators. |
| 4 |
Cascade Control. Handle Processes that Challenge Regular PID
Control (87KB)
Control sluggish processes that are too much for normal PID
control. How to tighten them up using cascade control.
Example. |
| 5 |
Compare your Energy Prices Easier Said than Done (26KB)
How to cut through the jungle of different energy price
offers that are designed to confuse and defeat your right to
make the best deal. eal. |
| 6 |
Understand your Heat Process Problems and How PID Control
Deals with Them (300KB)
Understand what makes a process hard or easy to control. How
PID is defined. Look at these and other control refinements
and how they are put to work. |
| 7 |
Is Electrical Interference Crippling your Control System?
Understand it and You can Defeat It (172KB)
Look at the various mechanisms of electromagnetic
interference, how they hurt your process and how to fight
them. |
| 8 |
Wasting Energy: How does your Plant Rate? (22KB)
A case history. How a power-hungry extruder was analyzed and
put to work on a lean diet. |
| 9 |
Engineering Units in the Process Heating Workplace; How
Handy are they to Visualize and Use? (72KB)
How to get your mind round engineering units in the process
heating workplace.. Here's how they look and feel. Free
yourself from the handcuffs of those quaint antique units;
work easier and faster. |
| 10 |
Where Feedback Benefits your Process (180KB)
How feedback works for you when controlling your process.
Makes circuits stable, robust and linear. Makes your
actuator go exactly where the signal told it in the face of
friction and line pressure. Gives your heater the exact
power the controller demanded. |
| 11 |
Feedforward on Temperature Control Systems. Fast
Compensation for Disturbances (185KB)
Feedforward watches your process and warns the controller to
immediately deliver a measured response to changes. This
leaves the sensor and overall control loop with much less
work to do in chasing and correcting deviations. An example. |
| 12 |
Final Control Elements. The Devices that Modulate Process
Heat (159KB)
They provide the muscle for your process. Magnetic and solid
state contactors, SCRs, Electric motor and electro pneumatic
actuators for valves and dampers. Motor speed controllers. |
| 13 |
How Ground Loops Harm your System (83KB)
When you see malfunctions or gross measurement errors look
at the components of your system and check for
misconnections or components that share a common line or
ground. |
| 14 |
How Instrumentation Can Reduce Hazards to People and Plant
An account of an expensive refinery accident and the many protective features and techniques available on modern controllers. |
| 15 |
Heating Billets ready for Diecasting (22KB)
Choose the coil arrangement, power and frequency for
induction heating an aluminum billet |
| 16 |
Your Heater Material and Design Dictate how you Control it
(84KB)
Look at the characteristics of four common heater element
materials and consider how best to control them them |
| 17 |
Troubleshooting Temperature Control Equipment (221KB)
Tool and tips for finding and clearing process problems |
| 18 |
Master Slave Temperature Control, Three Ways to Achieve it.
(98KB)
An example of a two-platen press where the second platen is
required to track the temperature of the first platen. The
principles here are applicable to a great variety of
processes. |
| 19 |
Understand the Instrumentation on your Heat Process (66KB)
A description of the features of the many installed
instruments on your process and a discussion of those of a
different class: the test and trouble-shooting instruments
you will need to start up and maintain the process cess |
| 20 |
Non-contact Temperature Sensing (66KB)
arious ways to sense the temperature of the untouchable
using thermocouples, RTDs and optical thermometers. |
| 21 |
Power Factor. Two Myths and some Words of Comfort (177KB)
A review of the different aspects of power factor; how low
power factors can cost you money. How to define it in SCR
power control. |
| 22 |
Protective Devices for Electrical Control Equipment (184KB)
All about Fuses, Circuit breakers, SCR Chop off Circuits,
Crowbars, Thermostats over-temperature shut-offs and fusable
links |
| 23 |
Ramp and Soak Applications (71KB)
A case history. the buckling oven. Techniques and versatile
features of temperature programming systems. |
| 24 |
Ratio Control. Some of its Applications and Imperfections
(110KB)
How to make two process variables keep the same ratio
regardless of how wild and variable they are. are. |
| 25 |
A Book on Electroheat by A.C. Metaxas: Worth a Look (23KB)
For anyone interested in the many ways of delivering
electroheat this book is well worth a study. It is based on
courses on Electroheat given in the Engineering Department
of Cambridge University. Here Metaxas combines mathematical
treatment of the principles of electroheat with descriptions
and sketches of a wide variety of real industrial
applications |
| 26 |
SCR Control of Electric Heaters (109KB)
The many ways that SCRs are used to control and manipulate
electric power in the face of difficult heaters and unstable
power sources. |
| 27 |
Silicon Controlled Rectifiers and Transformers in Power
Control. (400KB)
How transformers extend the capabilities of SCRs. Examples
of single-phase, three-phase, wye and delta connections,
Scott T connections for three to two or to one phase |
| 28 |
You want good Control? Check the Location and Construction
of your Temperature Sensor (43KB)
The best controller can be defeated by a badly designed or
located temperature sensor. Here are some examples of these
problems followed by some solutions and precautions. |
| 29 |
Signal Conditioners. The little hidden boxes that manipulate
your process signals
(56KB)
Modifying your process? Have some jobs that cannot be
performed by the regular control system? You need an extra
device of some kind. Look in your catalogue for small
hockey-puck shaped or DIN rail mounted components. These are
Signal conditioners - essential items in the inventor's tool
kit. |
| 30 |
Smart Field-mounted Control Components They obey your
commands and tell you how they're doing. (115KB)
Those dumb and obedient field devices - control valves,
power control devices, temperature sensors, signal
converters, transducers and motor drives have for some time
been evolving smart features. This has opened up process
diagnostics, aided preventive maintenance and plant up time
and don't forget - greatly simplified plant wiring. |
| 31 |
Traps and Color Confusion in Thermocouple Wiring. (131KB)
Multiple so-called national standards for color codes of
thermocouple extension cables have been responsible for many
cases of process instabilities and upsets. Here is a costly
example. Internationally agreed standards, in use since 1989
are still rare in N America. ica. |
| 32 |
Thermocouples: Eight established types to choose from. What
type do I need and what should be abandoned? (68KB)
So your application calls for a thermocouple. This is just
the beginning - you are faced with too many choices. Here is
a brief account of which one fits which application and
which ones can be struck from the list for ever. |
| 33 |
Trouble shooting on Extrusion Temperature Control Equipment
(691KB)
This is a big topic. It deals first with how to know your
machine, how it behaves well and how it can go wrong. The
control techniques described here represent the results of
continuous development and refinement as control equipment
manufacturers have lived with and cooperated with extruder
manufacturers and users. ers. |
| 34 |
Trends in Temperature Control Equipment; Components, Wiring,
Operator Interfaces, Configuration, Operation, Support.
(31KB)
Components, Wiring, Operator Interfaces, Configuration,
Operation, Support. Walk around a few process plants
and you will see some 20 years of evolution. Starting from
the tried and true using
discrete Instruments all the way
up to
SCADA (Supervisory Control and
Data Acquisition) systems with color monitors and operator
interfaces, rich in control, protection and data analysis
capability. |
| 35 |
Checking your Heat Process on a Budget (162KB)
Your Test Instruments: Buy two, make two yourself
You are
visiting the job site and suddenly you hear
"Oh boy am I glad you're here, we have
trouble". You didn't expect this and you have to make
do with what test equipment you can find there; even make up
what else needed to check the controls on the process.
Here's how to make the best of it. |
| 36 |
Misfits between Man and Technology: (26KB)
Are you being set up for a Human-Error Verdict? Too often an
inquiry or inquest concludes “Human Error” and somebody is
named. An instinctive reaction is to search for a person to
blame when the finger should rightly be pointing to the
unrealistic complex actions expected from that person. All
too often the answer lies in neglect of the
Human Factor in the design of equipment,
documentation and procedures. Here are some reminders from
my earlier columns in Process Heating Magazine that point to
misfits and complexity between man and technology.
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| 37 |
The Human Factor by Kim Vicente
(49KB)
This book is about the misfits between man and technology
and the wide range of activities where neglect of the
Human Factor
brings trouble, from minor irritations to massive fatal
accidents. The field of industrial control is just one of
the many fields where you can apply the lessons from this
book. |
| 38 |
Temperature Controller Surveys.
(91KB)
Some industry magazines, typically once a year, will run an
issue containing a round-up and comparison of temperature
controllers from the well known manufacturers. It will be in
tabular form, taking in all the common features and
technologies that the compilers can think of. There will
always be advanced features that call for a deeper and more
detailed search and which cannot be fitted into the compact
tables. Here are some of them. |
| 39 |
Temperature Controller Technical Support.
(63KB)
A major Factor in choosing your supplier. Now that we have
high tech, reliable and versatile controls, some problems
have gone away; but now we are facing complexity and how to
match equipment to the process. Here is where you will need
fast access to experienced and articulate people on your
supplier’s help line regardless of your location.
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| 40 |
Raw Heat to Refined Heat.
(232KB)
Here you can look at the whole range of energy sources from
coal to the most refined and effective form of electrical
energy. The price per unit of energy becomes meaningless in
light of the miracles it can perform when highly refined. |
| 41 |
Gigawatts of Raw Power Trickling Down.
(764KB)
What stage of refinement do you want? You can start with a
massive volume of water with a lot of head giving you 15 000
Mw at +/- 450 kV dc. From here there is a never-ending
hierarchy of applicable heat down to a few milliwatts of
needle sharp laser eye surgery. Then finer yet to process
silicon chips.
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| 42 |
Nickel/Chrome and Comparable Heaters Unmatched variety and versatility.(617KB)
There is no limit to the ways in which you can deliver resistance heating to the material in your process. Chances are you will be looking for a heater that incorporates one or other of the many nickel/chrome alloy wires and ribbons.
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| 43 |
Infrared Thermometers. Point and Shoot hand-held models
(107KB)
When you have to measure the temperature of the untouchable, and have ruled out using the thermocouple and the RTD, your best choice is usually one of the many infrared thermometers. (These are also known as optical pyrometers.) The sensing technology is the same for hand-held as for fixed-position units that monitor continuously. Here we are looking at point-and-shoot, hand-held designs that usually look like a hair-dryer or a stick that clips in your pocket.
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| 44 |
Thermocouples - A Thousand Shapes and Sizes. Which one is for you?
(112KB)
Every different application of thermocouples demands that you choose a shape, size and material to match the process. That’s all this column deals with. Matters of temperature, environment, thermocouple alloys and construction materials are largely outside this month’s topic and are for another day. For want of a better approach we will look at your choices, in ascending order of size and mass, with corresponding increases in robustness and response time
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| 45 |
Help-Lines for Users of Process Heating Controls
(10KB)
Do your homework and construct a meaningful query. This is for: Managers and operators of process plants for whom control is just one among their many jobs.
Maintenance technicians under pressure to bring a process back on line.
Specifiers, designers and builders of process equipment.
The overloaded customer-support desks of equipment suppliers.
You are your worst enemy if you:
1.will not or cannot take time to read manuals and on-line FAQs
2.ask vague or incomplete questions that cannot yield an answer.
3.make your help-line person deliver a seminar on your technology before he can talk to you
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| 46 |
Traps and Colour Confusion in Thermocouple Wiring. Revisit
(273KB)
It is some six years since I wrote about the inaccuracies and instabilities caused by misuse of thermocouple extension cable on temperature control systems. In 1989, the International Electrotechnical Commission (IEC) published IEC 584-3. This world-wide standard could replace the jungle of different cable colour codes and do away with the consequent problems. The IEC colours and those used in different countries are shown here for the most common types of thermocouples. Yet even now, some 18 years on, the standard is virtually invisible in North America.
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| 47 |
Good Controller – Bad Control. What's going on?
(20KB)
For all the adjusting and tuning, the controller cannot do the job. Look at the process. Some examples.
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