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AQ: Home automation concept

The concept of home automation on a global scale is a good concept. How to implement such a technology on a global scale is an interesting problem, or I should say issues to be resolved. Before global approval can be accomplished the product of home automation may need a strategy that starts with a look at companies that have succeeded in getting global approval of their products.

If we look at what companies that have the most products distributed around the world we see that Intel is one of these companies. What’s interesting is that this company has used automation in their Fabs for decades. This automation has allowed them to produce their products faster and cheaper than the rest of the industry. The company continues to invest in automation and the ability to evolve with technology and management. We have many companies that compete on the world stage; I don’t think many of these companies distribute as much product. So to compete at a level to make home automation accepted and to accomplish global acceptance the industry and the factories have to evolve to compete. That mission by the automation can be accomplished by adapting a strategy that updates their automation in their factories, stop using products that were used and developed in the 1970s (another way of saying COTS) and progress to current and new systems. A ten years old Factory may be considered obsolete if the equipment inside is as old as the factory.

Now for cost, when I thank of PLC or commercial controllers I see a COTS product that may be using obsolete parts that are not in production any more or old boards. So I see higher cost for manufacturing, a reduction in reliability. Now many procurement people evaluate risk in such a way that may rate older boards lower in risk for the short term, not a good evaluation for the long term. The cost is a function of how much product can be produced at the lowest cost and how efficient and competitive the company that produces the product. So time is money. The responsibility for cost is the company and the ability to produce a competitive product, not the government.

Now into control systems and safety, if the automation system is used in the house safety has to be a major consideration. I know at Intel Fabs if you violate any safety rule you won’t be working at that company long. To address safety the product must conform to the appropriate standards. Safety should be a selling point for home automation. Automation engineers should get and remember safety is one of the main considerations for an engineer. If someone gets hurt or killed because of a safety issue the first person looked at is the engineer.

Now 30% energy saving in my book is not enough, 35 to 40 percent should be a goal. Now solar cells have improved but the most efficient in the south west US. The Sterling engines are 1960 designs and use rare gases such as helium which may not be a renewable resource, Wind generators need space and are electromechanical so reliability and maintenance needs improving.

Now on to the interface standards, most modern factories that produce processors use the Generic equipment Manufacture standard, good deal works. As far as what and when to uses a standard interface, on BOX produced by one company may use RE-422 where another company may use RS 485 so the system engineer should resolve these issues before detailed design starts. Check with IEEE. Or you may be able to find the spec at every spec.com this is a good place to look for some of the specs needed.

So I conclude, many issues exist, and when broken down home automation is viable and needs a concerted effort and commitment from at least the companies and management that produce products for automation and a different model for manufacturing and growing the home systems.
Home automation with a focus on energy savings as a goal is a good thing. We have a lot of work to ma

AQ: Signal processing and communications theory

Coming from a signal processing and communications theory background, but with some experience in power design, I can’t resist the urge to chime in with a few remarks.

There are many engineering methods to deal with sources of interference, including noise from switching converters, and spread spectrum techniques are simply one more tool that may be applied to achieve a desired level of performance.

Spread spectrum techniques will indeed allow a quasi-peak EMC test to be passed when it might otherwise be failed. Is this an appropriate application for this technique?

The quasi-peak detector was developed with the intention to provide a benchmark for determining the psycho-acoustic “annoyance” of an interference on analog communications systems (more specifically, predominantly narrow band AM type communication systems). Spread spectrum techniques resulting in a reduced QP detector reading will almost undoubtedly reduce the annoyance the interference would have otherwise presented to the listener. Thus the intent was to reduce the degree of objectionable interference and the application of spread spectrum meets that goal. This doesn’t seem at all like “cheating” to me; the proper intent of the regulatory limit is still being met.

On the other hand, as earlier posters have pointed out, the application of spectrum spreading does nothing to reduce the total power of the interference but simply spreads it over a wider bandwidth. Spreading the noise over a wider bandwidth provides two potential benefits. The most obvious benefit occurs if the victim of the interference is inherently narrowband. Spreading the spectrum of the interference beyond the victim bandwidth provides an inherent improvement in signal to noise ratio. A second, perhaps less obvious, benefit is that the interference becomes more noise like in its statistics. Noise like interference is less objectionable to the human ear than impulsive noise but it should also be recognized that it is less objectionable to many digital transmission systems too.

However, from an information theoretic perspective the nature of the interference doesn’t matter, but rather only the signal to noise ratio matters. Many modern communication systems employ wide bandwidths. Furthermore they employ powerful adaptive modulation and coding schemes that will effectively de-correlate interference sources (makes the effect noise like); these receivers don’t care whether the interference is narrow band or wide band in terms of bit error rate (BER) and they will be effected largely the same by a given amount of interference power (in theory identically the same, but implementation limitations still provide some gap to the theoretical limits).

It is worth noting however that while spectrum spreading techniques do not reduce the interference power they don’t make it any worse either. Thus these techniques may (I would argue legitimately as per above) help with passing a test which specified the CISPR Quasi-Peak detector and should not make the performance on a test specifying the newer CISPR RMS+Average test any worse.

It should always be an engineering goal to keep interference to a reasonable minimum and I would agree that it is aesthetically most satisfying (and often cheapest and most simple) to achieve this objective by somehow reducing the interference at source (this is a wide definition covering aspects of SMPS design from topology selection to PCB layout and beyond). However, the objective to control noise at the source shouldn’t eliminate alternative methods from consideration in any given application.

There will always be the question of how good is good enough and it is the job of various regulatory bodies to define these requirements and to do so robustly enough such that the compliance tests can’t be “gamed”.

AQ: Single Phase Input DC Drive

Armature voltage-controlled DC drives are constant torque drives, capable of rated motor torque at any speed up to rated motor base speed. Fully controlled rectifier circuits are built with SCRs. The SCRs rectify the supply voltage (changing the voltage from AC to DC) as well as controlling the output DC voltage level. In this circuit, silicon controlled rectifiers S1 & S3 are triggered into conduction on the positive half of the input waveform & S2 & S4 on the negative half. Freewheeling diode D (also called a suppressor diode) is connected across the armature to provide a path for release of energy stored in the armature when the applied voltage drops to zero. A separate diode bridge rectifier is used to convert the alternating current to a constant direct current required for the field circuit.

Single-phase controlled bridge rectifiers are commonly used in the smaller-horsepower DC drives. The terminal diagram shows the input & output power & control terminations available for use with the drive. Features include:

  • Speed or torque control
  • Tachometer input
  • Fused input
  • Speed or current monitoring (0-10 V DC or 4-20 mA)

AQ: What if

Many years ago we used to call this the “what ifs?”. Part of the design phase is when we model what we think the system is meant to do. Just as important is how the system is meant to react when things are not going well, the abnormal situations or what ifs?

Your client will tell you how their machine or process works, well he will describe how he thinks it works. This is OK as a starting point but we need to consider the scenarios of “what If” something goes wrong? Scenarios is also a good word as scenarios paint a situation that can be described to the customer for his comment.

For example on a compressor control project what if the lube oil pump fails on the compressor, how do we alarm this to the Operator, should we trip the compressor or do we start the back-up oil pump (if there is one). As you look at the system you can pick out various components and generate likely scenarios that you can discuss with the client. Using this approach gives more of a real world feel to your client meetings that are likely to generate a deeper insight into how the system is meant to work.

All scenarios do not have to be centered around abnormal situations but can also relate to things that need to be considered as part of normal operation. For example we might look at how a duty/standby pump system works? One scenario might relate to duty pump failure but another scenario might consider rotating the duty and standby pumps to even out wear and tear? You might also have manual mode and auto mode scenarios to consider?

What you have to remember is that most clients are not control systems experts. They might and probably will struggle with flow charts or any other pseudo code expression type formats that describe how you think the client’s system is meant to work? You have to tailor your approach to match your audience and that is also very important when you produce your documentation, you do not want to lose valuable information just because the client doesn’t fully understand what you are trying to tell him? Also make sure that you spend time with your client. Walk the client through your design, do this face to face as much as possible and do it more than once! Getting feedback on a regular basis helps to eliminate the dreaded word “REWORK”! Also taking this partnership approach builds a good relationship with your client.

For the machine builders your client might be in your own company? Remember same company or not they are your client and your success in no small way depends on your relationship with them.

Add the modes of operation and abnormal situations to your system model and develop the methods of how you will flag these situations to the Operator and Maintenance Engineer. Alarm Management is dealt with by EEMUA 191. If you do nothing else then read this document it will help you to set up alarm workshops, alarm reviews, alarm prioritization and rationalization and how to develop an effective alarm management structure for your system.

AQ: DC Drives Basic Operation Principles

DC drives vary the speed of DC motors with greater efficiency & speed regulation than resistor control circuits. Since the speed of a DC motor is directly proportional to armature voltage & inversely proportional to field current, either armature voltage or field current can be used to control speed. To change the direction of rotation of a DC motor, either the armature polarity can be reversed, or the field polarity can be reversed.

DC drive diagram

The block diagram of a DC drive system made up of a DC motor & an electronic drive controller. The shunt motor is constructed with armature & field windings. A common classification of DC motors is by the type of field excitation winding. Shunt wound DC motors are the most commonly used type for adjustable-speed control. In most instances the shunt field winding is excited, as shown, with a constant-level voltage from the controller. The SCR (silicon controller rectifier), also known as thyristor, of the power conversion section converts the fixed-voltage alternating current (AC) of the power source to an adjustable-voltage, controlled direct current (DC) output which is applied to the armature of a DC motor. Speed control is achieved by regulating the armature voltage to the motor. Motor speed is directly proportional to the voltage applied to the armature.

The main function of a DC drive is to convert the fixed applied AC voltage into a variable rectified DC voltage.

SCR switching semiconductors provide a convenient method of accomplishing this. They provide a controllable power output by phase angle control. The firing angle, or point in time where the SCR is triggered into conduction, is synchronized with the phase rotation of the AC power source. The amount of rectified DC voltage is controlled by timing the input pulse current to the gate. Applying gate current near the beginning of the sine-wave cycle results in a higher aver age voltage applied to the motor armature. Gate current applied later in the cycle results in a lower average DC output voltage. The effect is similar to a very high speed switch, capable of being turned on & off at an infinite number of points within each half-cycle. This occurs at a rate of 60 times a second on a 60-Hz line, to deliver a precise amount of power to the motor.

AQ: System operation

Our PSA unit (meaning Pressure Swing Adsorption) uses 5 adsorption vessels. The process itself is a batch process, but in order to run in a continuous process plant, each of the 5 vessels can complete all the adsorption process but at the same time, each of them is in a different status of the sequence (i.e. gas in, gas out, adsorption, pressurizing, depressurizing, cleaning, etc). The sequence is mainly controlled by time and pressure condition in each step of the sequence, by managing several valves (I think 5 by vessel, but I’m not sure right now).

Panel operator experienced some problems with valve 1 (gas entry) in vessel 2 because it should open but immediately it received the close command. Instruments technician check that orders coming from the DCS were OK, and also check the valves by injecting the open order, so, they and operation staff concluded that “the program has some kind of problem”.

Some time ago, I spent a lot of time studying the operation manual of this unit and the code written to control it and I wrote a document merging both knowledge. In page 9, I described a condition (an exclusive pressure difference between vessel and gas coming in the vessel) avoiding valve 1 opening during adsorption stage. I explained this condition to operation staff and they confirm that the values were right and that the excessive delta P really exist so, the decided to check back the valve 1 (already checked), discovering a problem (the stem moved, but the disk not).

Conclusion:
– If operation staff know properly the process, they know about this condition, but this could be solved with a properly designed HMI (i.e. including and alarm indicating “valve 1 closed by excessive deltaP”).
– The initial inspection of the valve didn’t show anything wrong, but stem and disk were disconnected.
– If we didn’t dig into the code, this problem, solved in less of an hour could take several hours.

AQ: How is frequency inverter saving energy?

This studies show that up to 80 percent of the energy from the power source to the industrial consumer can be lost. Energy conversion—converting energy into useful work via motors, heat exchangers, process heaters, pumps, motors, fans, compressors, and so forth—represents a large opportunity for energy savings in manufacturing. Industrial electric motor-driven systems represent the largest single category of electricity use in China.

The industrial sector consumes approximately one-third of the energy used in China (see Fig. 1).

Studies show that up to 80 percent of the energy from the power source to the industrial consumer is lost through the transition of raw material to the point of useful output—much of that at the point of conversion from electrical to mechanical output (see Fig. 2).

Rising energy costs, a sense of environmental responsibility, government regulation, and a need for energy reliability are driving efforts for energy efficiency in manufacturing.

Energy is lost primarily in three areas:

  • Generation
  • Distribution
  • Conversion

The third area, energy conversion—converting energy into useful work via motors, heat exchangers, process heaters, pumps, motors, fans, compressors, and so forth—represents a large opportunity for energy savings in manufacturing.

Industrial electric motor-driven systems represent the largest single category of electricity use in the China—more than 65 percent of power demand in industry. Consequently, motor-driven systems offer the highest energy savings potential in the industrial segment.

Supporting this statistic, studies show that 97 to 99 percent of motor life cycle costs are expended on the energy that the motor uses. This fact alone should be a driving motivation for companies to perform a periodic energy consumption analysis on the motor systems they use in their facilities.

Inefficient and ineffective control methods in two areas waste motor systems’ energy:

  • Mechanical flow control (pumps, fans, compressors)
  • Energy recovery (regeneration of braking energy or inertial energy)

An inverter is an effective tool in conserving and recovering energy in motor systems.

What Is a frequency inverter? Why Use It?

A frequency inverter controls AC motor speed (see Fig. 3). The frequency inverter converts the fixed supply frequency (60 Hz) to a variable-frequency, variable-voltage output to enable precise motor speed control. Many frequency inverters even have the potential to return energy to the power grid through their regenerative capability.

A frequency inverter’s precise process and power factor control and energy optimization result in several advantages:

  • Lower energy consumption saves money
  • Decreased mechanical stress reduces maintenance costs and downtime
  • Reduced mechanical wear and precise control produces more accurate products.
  • Lower consumption lowers carbon emissions and helps reduce negative impact on the environment.
  • Lower consumption qualifies for tax incentives, utility rebates, and, with some companies, energy savings finance programs, which short

AQ: How to improve troubleshooting techniques?

The guy asked for suggestions on how to improve troubleshooting techniques. I mentioned this earlier as a “suggestion” for starters but the idea got lost in all the complaining and totally irrelevant responses like the one above.

Proper lay out of inputs and outputs and a “Troubleshooting guide” or flow chart. I have an Aris cablem modem and Netgear wireless router for internet If loose Internet service I can do three things.

A. Pick up the phone, call tech support and wait two days for someone to show up

B. Take them apart and ‘DIG INTO THE PROGRAMMING”

C. Read the instructions someone took the time to write. Before I can get an output identified by the LEDs, I have to have the correct inputs identified by the LEDs. It’s a waste of time tearing in the “programming” over a loose cable connection somewhere. Same for the wireless router and a bad LAN cable connection or network service issue on the computer. I’m already familiar with the proper LEDs for normal operation. When one goes out it gives me an idea where to start looking before even opening up the instructions which I’ve downloaded in PDFs for quick access to their “troubleshooting” guides. Maybe the service is off line – there is an LED for that. No TVs either, no service or common upstream cable connection problem, no-brainier. The first thing a Xfinity service tech does is go outside and look for a signal at the house customer jack. It’s either in his cable or my house. Once their cable had to be replaced. It mysteriously got damaged right after AT&T dug a big hole in my backyard to upgrade their Uverse service – go figure.

In order to get something to operate output wise, you need a certain amount of inputs to get it. If you don’t have a particular output, then look at the trouble shooing guide and see what inputs are required for it. If there are four direct sensor inputs required for a particular output, group them together.

Grouping internal interlocks together helps also when digging into a program like ladder logic instead of hopping through pages of diagrams or text to find everything it takes to get one output. It’s a common program development issues to throw in ideas as you program depending on where you are sequentially.

AQ: Non-regenerative & Regenerative DC Drives

Non-regenerative DC drives, also known as single-quadrant drives, rotate in one direction only & they have no inherent braking capabilities. Stopping the motor is done by removing voltage & allowing the motor to coast to a stop. Typically nonregenerative drives operate high friction loads such as mixers, where the load exerts a strong natural brake. In applications where supplemental quick braking and/or motor reversing is required, dynamic braking & forward & reverse circuitry, may be provided by external means.

Dynamic braking (DB) requires the addition of a DB contactor & DB resistors that dissipate the braking energy as heat. The addition of an electromechanical (magnetic) reversing contactor or manual switch permits the reversing of the controller polarity & therefore the direction of rotation of the motor armature. Field contactor reverse kits can also be installed to provide bidirectional rotation by reversing the polarity of the shunt field.

All DC motors are DC generators as well. The term regenerative describes the ability of the drive under braking conditions to convert the generated energy of the motor into electrical energy, which is returned (or regenerated) to the AC power source. Regenerative DC drives operate in all four quadrants purely electronically, without the use of electromechanical switching contactors:

  • Quadrant I -Drive delivers forward torque, motor rotating forward (motoring mode of operation). This is the normal condition, providing power to a load similar to that of a motor starter.
  • Quadrant II -Drive delivers reverse torque, motor rotating forward (generating mode of operation). This is a regenerative condition, where the drive itself is absorbing power from a load, such as an overhauling load or deceleration.
  • Quadrant III -Drive delivers reverse torque, motor rotating reverse (motoring mode of opera tion). Basically the same as in quadrant I & similar to a reversing starter.
  • Quadrant IV -Drive delivers forward torque with motor rotating in reverse (generating mode of operation). This is the other regenerative condition, where again, the drive is absorbing power from the load in order to bring the motor towards zero speed.

A single-quadrant nonregenerative DC drive has one power bridge with six SCRs used to control the applied voltage level to the motor armature. The nonregenerative drive can run in only motoring mode, & would require physically switching armature or field leads to reverse the torque direction. A four-quadrant regenerative DC drive will have two complete sets of power bridges, with 12 con trolled SCRs connected in inverse parallel. One bridge controls forward torque, & the other controls reverse torque. During operation, only one set of bridges is active at a time. For straight motoring in the forward direction, the forward bridge would be in control of the power to the motor. For straight motoring in the reverse direction, the reverse bridge is in control.

Cranes & hoists use DC regenerative drives to hold back “overhauling loads” such as a raised weight, or a machine’s flywheel. Whenever the inertia of the motor load is greater than the motor rotor inertia, the load will be driving the motor & is called an over hauling load. Overhauling load results in generator action within the motor, which will cause the motor to send cur rent into the drive. Regenerative braking is summarized as follows:

  • During normal forward operation, the forward bridge acts as a rectifier, supplying power to the motor. During this period gate pulses are withheld from reverse bridge so that it’s inactive.
  • When motor speed is reduced, the control circuit withholds the pulses to the forward bridge & simultaneously applies pulses to reverse b

AQ: Machine tool

Ahh I see the words machine tool and shop floor; now I can see where you guys are coming from. The type of machines that you talk about were controlled by relay logic and then when technology arrived the electrical drawings were probably “converted” into ladder logic. The techs had lots to do because you cannot translate relay based systems into ladder logic 100% successfully as they behave differently.

The guys doing this work are just that programmers. They are probably NOT software engineers and are closer to the shop floor techs who are fiddling about with your machines.

I can and have designed many control systems for automotive type machines such as hobbing machines, milling and borers. Very easy code to write if you do not translate the relay logic directly but use the existing documentation as a reference. All of the systems that I did work really well. I did some similar type of machines in a pharmaceutical plant but that was after another company was kicked out after failing to make the machines work. I had to redesign the whole control philosophy as the machine tool world methods used were really a bad fit for the intended application.

But that is only one facet of the work that we Industrial Automation Engineers do. I work in many different industries where the demands for quality deigned, controlled and maintained systems is paramount. We go through proper project life cycles and we deal with the project from inception through design, build, test and commissioning. We even do the maintenance of the systems. We do not sit in Ivory Towers but do the work at the customer site no matter where that is on the planet.

Electrical engineers are tasked with doing all things electrical and we are tasked with all things control. Programming, that is writing the actual code is only one part of what we do and not necessarily the most time consuming part.

I am here in Kazakhstan at the sharp end of a multi-billion dollar project a long way from any ivory tower. I fix other engineers software too, why? Because the vendor may use offshore resources to code much of the systems that are installed at site. Kazakhstan has extreme Summers (up to 60degC) and Winters (down to -50degC), most of the people are friendly but English is not so prevalent. A long way from your shop floor environment. Far more dangerous too as the plant processes H2S or will when first Oil & Gas comes onshore.

Here I have supported technicians performing loop checks and other engineers doing logic tests. I can diagnose many loop problems without even looking in the code but just by looking at what is happening. I have found that if a loop doesn’t work then the techs approach us first as a one stop shop to give them an answer rather than actually trouble shooting the loop themselves.

I said to you guys before you need to get out and look at other industries and see what is going on in the rest of the world. Much of what I have seen would go a long way to improving your world too! Engineers like myself are far away from the “programmers” you have.