Monday, May 07, 2012

Field Instrumentation

Field Instrumentation refers to the sensors and actuators that are directly interfaced to the plant or equipment. They generate the analog and digital signals that will be monitored by the Remote Station. Signals are also conditioned to make sure they are compatible with the inputs/outputs of the RTU or PLC at the Remote Station.
Field Instrumentation refers to the devices that are connected to the equipment or machines being controlled and monitored by the SCADA system. These are sensors for monitoring certain parameters; and actuators for controlling certain modules of the system.These instruments convert physical parameters (i.e., fluid flow, velocity, fluid level, etc.) to electrical signals (i.e., voltage or current) readable by the Remote Station equipment. Outputs can either be in analog (continuous range) or in digital (discrete values). Some of the industry standard analog outputs of these sensors are 0 to 5 volts, 0 to 10 volts, 4 to 20 mA and 0 to 20 mA. The voltage outputs are used when the sensors are installed near the controllers (RTU or PLC). The current outputs are used when the sensors are located far from the controllers.
Digital outputs are used to differentiate the discrete status of the equipment. Usually, <1> is used to mean EQUIPMENT ON and <0> for EQUIPMENT OFF status. This may also mean <1> for FULL or <0> for EMPTY.
Actuators are used to turn on or turn off certain equipment. Likewise, digital and analog inputs are used for control. For example, digital inputs can be used to turn on and off modules on equipment. While analog inputs are used to control the speed of a motor or the position of a motorized valve.

The Remote Station

The Remote Station is installed at the remote plant or equipment being monitored and controlled by the central host computer. This can be a Remote Terminal Unit (RTU) or a Programmable Logic Controller (PLC). Field instrumentation connected to the plant or equipment being monitored and controlled are interfaced to the Remote Station to allow process manipulation at a remote site. It is also used to gather data from the equipment and transfer them to the central SCADA system. The Remote Station may either be an RTU (Remote Terminal Unit) or a PLC (Programmable Logic Controller). It may also be a single board or modular unit. 
The RTU (Remote Terminal Unit) is a ruggedized computer with very good radio interfacing. It is used in situations where communications are more difficult. One disadvantage of the RTU is its poor programmability. However, modern RTUs are now offering good programmability comparable to PLCs. The PLC (Programmable Logic Controller) is a small industrial computer usually found in factories. Its main use is to replace the relay logic of a plant or process. Today, the PLC is being used in SCADA systems to due its very good programmability. Earlier PLC’s have no serial communication ports for interfacing to radio for transferring of data. Nowadays, PLC's have extensive communication features and a wide support for popular radio units being used for SCADA system. In the near future we are seeing the merging of the RTUs and the PLC’s. Micrologic is offering an inexpensive RTU for SCADA system wherein the PLC may be an overkill solution. It is a microcontroller-based RTU and can be interfaced to radio modems for transmitting of data to the CMS.
Remote Terminal Unit (RTU)
Programmable Logic Controller
Programmable Logic Controller (PLC)

The Communications Network

The Communications Network is the medium for transferring information from one location to another. This can be via telephone line, radio or cable. The Communication Network refers to the communication equipment needed to transfer data to and from different sites. The medium used can either be cable, telephone or radio. The use of cable is usually implemented in a factory. This is not practical for systems covering large geographical areas because of the high cost of the cables, conduits and the extensive labor in installing them. The use of telephone lines (i.e., leased or dial-up) is a cheaper solution for systems with large coverage. The leased line is used for systems requiring on-line connection with the remote stations. This is expensive since one telephone line will be needed per site. Besides leased lines are more expensive than ordinary telephone line. Dial-up lines can be used on systems requiring updates at regular intervals (e.g., hourly updates). Here ordinary telephone lines can be used. The host can dial a particular number of a remote site to get the readings and send commands. Remote sites are usually not accessible by telephone lines. The use of radio offers an economical solution. Radio modems are used to connect the remote sites to the host. An on-line operation can also be implemented on the radio system. For locations wherein a direct radio link cannot be established, a radio repeater is used to link these sites.

Central Monitoring Station

The Central Monitoring Station (CMS) refers to the location of the master or host computer. Several workstation may be configured on the CMS, if necessary. It uses a Man Machine Interface (MMI) program to monitor various types data needed for the operation. The following is a sample configuration of a SCADA system for water distribution.
The Central Monitoring Station (CMS) is the master unit of the SCADA system. It is in charge of collecting information gathered by the remote stations and of generating necessary action for any event detected. The CMS can have a single computer configuration or it can be networked to workstations to allow sharing of information from the SCADA system.
A Man-Machine Interface (MMI) program will be running on the CMS computer. A mimic diagram of the whole plant or process can be displayed onscreen for easier identification with the real system. Each I/O point of the remote units can be displayed with corresponding graphical representation and the present I/O reading. The flow reading can be displayed on a graphical representation of a flowmeter. A reservoir can be displayed with the corresponding fluid contents depending on the actual tank level.
Set-up parameters such as trip values, limits, etc. are entered on this program and downloaded to the corresponding remote units for updating of their operating parameters.
The MMI program can also create a separate window for alarms. The alarm window can display the alarm tag name, description, value, trip point value, time, date and other pertinent information. All alarms will be saved on a separate file for later review.
A trending of required points can be programmed on the system. Trending graphs can be viewed or printed at a later time. Generation of management reports can also be scheduled on for a specific time of day, on a periodic basis, upon operator request, or event initiated alarms.
Access to the program is permitted only to qualified operators. Each user is given a password and a privilege level to access only particular areas of the program.. All actions taken by the users are logged on a file for later review.
Central Monitoring Station
Central Monitoring Station (CMS)

The Life of a Christian is not one that is devoid of Storms. Rather, it is one that cannot be sunk by any Storm.

Saturday, May 05, 2012



When I purchased my Samsung Solar netbook, I uninstalled the trial Microsoft office that came with it and installed the full version of Office 2003 onto the netbook. Last week Monday, a friend sent me an Excel document ending with .xlsx extension. It failed to open on my netbook, telling me "the file is not in a recognizable format". Instantly I googled for the cause and solution and I decided to share my findings with you today.

As a fact, if you installed Microsoft Excel 2003 on your PC, you will not be able to open a Microsoft Excel file created with Microsoft Office 2007. Excel documents created with Office 2003 ends with .xls while those created with Office 2007 ends with .xlsx.

If you would like to open, edit, and save workbooks that were created in the newer versions Excel with Excel 2003, you either install Microsoft compatibility pack or use a free online document conversion service.

In this post, I am sharing with you how to use zamzar.com, a free online file converter which I use to convert .xlsx files to .xls files.

STEPS


  •  Go to www.zamzar.com on your PC
  •  Use the "Browse" button to select the file you want to convert
  •  Choose the format you want to convert to. In this instance, you choose "xls" as seen in the picture below:


zamzar online converter



  • Enter your email address and click convert.
  • After some minutes, check your email inbox and you should receive an email from zamzar.com
  • Click the download link in the email to download the converted file.


You should now be able to open the file with your Microsoft Excel 2003.

That's all.

I hope it helps.

In my future posts,I will share with you how to install the Microsoft compatability pack, so you can  be opening .xlsx files with your Excel 2003 without converting the documents online. Just SUBSCRIBE to my blog for you not to miss this.

Cheers!

I have been making money online at fiverr.com for a while now but recently I noticed that the site no longer opens on my PC, though opens on my Blackberry. If you are facing similar problem, worry no more as am sharing with you in this post, how to fix the problem.

It is still not clear to me if it is fiverr that blocks some IP or if it is some Internet Service Providers that are blocking www.fiverr.com on their servers. Which ever way, you can unblock www.fiverr.com and keep making money on the website.

Solutions

1. If you are using network A to browse and fiverr no longer opens, try browsing with other networks. If you want to keep browsing with network A for reasons best known to you, try the second solution below.

2. Unblock fiverr.com with the help of softwares that hide your IP and ensure anonymous browsing. There are loads of them out there including the Your-Freedom SoftwareUltrasurfFreeGateHotspotshield etc. As at the time of publishing this, I use the free version of theHotspotShield software on my PC to access fiverr.com.

Proxy sites like ninjacloak and VPN softwares will also work for you. If you own a Blackberry phone, you can easily access your fiverr account without using any other software or proxy. I use my Blackberry a lot just to log in to my account to prevent suspension because if you fail to log in to fiverr.com after some weeks, your account might be suspended.

I hope this helps.



 Synchronous Generator Construction

A DC current is applied to the rotor winding, which then produces a rotor magnetic field. The rotor is then turned by a prime mover (eg. Steam, water etc.) producing a rotating magnetic field. This rotating magnetic field induces a 3-phase set of voltages within the stator windings of the generator.
“Field windings” applies to the windings that produce the main magnetic field in a machine, and
“armature windings” applies to the windings where the main voltage is induced. For synchronous
machines, the field windings are on the rotor, so the terms “rotor windings” and “field windings” are used
interchangeably.
Generally a synchronous generator must have at least 2 components:
  •  Rotor Windings or Field Windings
  •  Salient Pole
  • Non Salient Pole
  • Stator Windings or Armature Windings
The rotor of a synchronous generator is a large electromagnet and the magnetic poles on the rotor can either be salient or non salient construction. Non-salient pole rotors are normally used for rotors with 2 or 4 poles rotor, while salient pole rotors are used for 4 or more poles rotor.
A dc current must be supplied to the field circuit on the rotor. Since the rotor is rotating, a special
arrangement is required to get the dc power to its field windings. The common ways are:
Salient Rotor of a Synchronous Machine
Non-Salient Pole Synchronous Machie
Non- Salient Rotor Synchronous Machine



  •  supply the dc power from an external dc source to the rotor by means of slip rings and brushes.
  •  Supply the dc power from a special dc power source mounted directly on the shaft of the synchronous generator.
A dc current must be supplied to the field circuit on the rotor. Since the rotor is rotating, a special
arrangement is required to get the dc power to its field windings. The common ways are:
  1.  supply the dc power from an external dc source to the rotor by means of slip rings and brushes.
  2.  Supply the dc power from a special dc power source mounted directly on the shaft of the synchronous generator.
Slip rings are metal rings completely encircling the shaft of a machine but insulated from it. One end of the dc rotor winding is tied to each of the 2 slip rings on the shaft of the synchronous machine, and a stationary brush rides on each slip ring.
A “brush” is a block of graphitelike carbon compound that conducts electricity freely but has very low friction, hence it doesn’t wear down the slip ring. If the positive end of a dc voltage source is connected
to one brush and the negative end is connected to the other, then the same dc voltage will be applied to the field winding at all times regardless of the angular position or speed of the rotor.
Some problems with slip rings and brushes:
  • They increase the amount of maintenance required on the machine, since the brushes must be checked for wear regularly.
  •  Brush voltage drop can be the cause of significant power losses on machines with larger field currents.
Small synchronous machines – use slip rings and brushes.
Larger machines – brushless exciters are used to supply the dc field current.
A brushless exciter is a small ac generator with its field circuit mounted on the stator and its armature circuit mounted on the rotor shaft. The 3-phase output of the exciter generator is rectified to direct current by a 3-phase rectifier circuit also mounted on the shaft of the generator, and is then fed to the main dc field circuit. By controlling the small dc field current of the exciter generator (located on the stator), we can adjust the field current on the main machine without slip rings and brushes. Since no mechanical contacts occur between the rotor and stator, a brushless exciter requires less maintenance.

The Equivalent Circuit of a Synchronous Generator

The voltage EA is the internal generated voltage produced in one phase of a synchronous generator. If the machine is not connected to a load (no armature current flowing), the terminal voltage will be equivalent to the voltage induced at the stator coils. This is due to the fact that there are no current flow in the stator coils hence no losses. When there is a load connected to the generator, there will be differences between EA and Vφ. These differences are due to:
  1. Distortion of the air gap magnetic field by the current flowing in the stator called armature reaction. 
  2. Self inductance of the armature coil
  3.  Resistance of the armature coils
  4. The effect of salient pole rotor shapes.
We will explore factors a, b, and c and derive a machine model from them. The effect of salient pole rotor shape will be ignored, and all machines in this chapter are assumed to have nonsalient or cylindrical rotors.

Armature Reaction

When the rotor is spun, a voltage EA is induced in the stator windings. If a load is attached to the
terminals of the generator, a current flows. But a 3-phase stator current flow will produce a magnetic field of its own. This stator magnetic field will distorts the original rotor magnetic field, changing the resulting phase voltage. This effect is called armature reaction because the armature (stator) current affects the magnetic field, which produced it in the first place.
Refer to the diagrams below, showing a two-pole rotor spinning inside a 3-phase stator.

Equivalent Circuit of a Synchronous Machine
Equivalent Circuit of a Synchronous Machine


.....to be continued.....





Handling anger is an important topic. Christian counselors report that 50 percent of people who come in for counseling have problems dealing with anger. Anger can shatter communication and tear apart relationships, and it ruins both the joy and health of many. Sadly, people tend to justify their anger instead of accepting responsibility for it. Everyone struggles, to varying degrees, with anger. Thankfully, God’s Word contains principles regarding how to handle anger in a godly manner, and how to overcome sinful anger.

Anger is not always sin. There is a type of anger of which the Bible approves, often called “righteous indignation.” God is angry (Psalm 7:11; Mark 3:5), and believers are commanded to be angry (Ephesians 4:26). Two Greek words are used in the New Testament for our English word “anger.” One means “passion, energy” and the other means “agitated, boiling.” Biblically, anger is God-given energy intended to help us solve problems. Examples of biblical anger include Paul’s confronting Peter because of his wrong example in Galatians 2:11-14, David’s being upset over hearing Nathan the prophet sharing an injustice (2 Samuel 12), and Jesus’ anger over how some of the Jews had defiled worship at God’s temple in Jerusalem (John 2:13-18). Notice that none of these examples of anger involved self-defense, but a defense of others or of a principle.

Anger turns to sin when it is selfishly motivated (James 1:20), when God’s goal is distorted (1 Corinthians 10:31), or when anger is allowed to linger (Ephesians 4:26-27). Instead of using the energy generated by anger to attack the problem at hand, it is the person who is attacked. Ephesians 4:15-19 says we are to speak the truth in love and use our words to build others up, not allow rotten or destructive words to pour from our lips. Unfortunately, this poisonous speech is a common characteristic of fallen man (Romans 3:13-14). Anger becomes sin when it is allowed to boil over without restraint, resulting in a scenario in which hurt is multiplied (Proverbs 29:11), leaving devastation in its wake, often with irreparable consequences. Anger also becomes sin when the angry one refuses to be pacified, holds a grudge, or keeps it all inside (Ephesians 4:26-27). This can cause depression and irritability over little things, often things unrelated to the underlying problem.

We can handle anger biblically by recognizing and admitting our selfish anger and/or our wrong handling of anger as sin (Proverbs 28:13; 1 John 1:9). This confession should be both to God and to those who have been hurt by our anger. We should not minimize the sin by excusing it or blame-shifting.

We can handle anger biblically by seeing God in the trial. This is especially important when people have done something to offend us. James 1:2-4, Romans 8:28-29, and Genesis 50:20 all point to the fact that God is sovereign and in complete control over every circumstance and person that enters our path. Nothing happens to us that He does not cause or allow. And as these verses share, God is a good God (Psalm 145:8, 9, 17) who allows all things in our lives for our good and the good of others. Reflecting on this truth until it moves from our heads to our hearts will alter how we react to those who hurt us.

We can handle anger biblically by making room for God’s wrath. This is especially important in cases of injustice, when “evil” men abuse “innocent” people. Genesis 50:19 and Romans 12:19 both tell us to not play God. God is righteous and just, and we can trust Him who knows all and sees all to act justly (Genesis 18:25).

We can handle anger biblically by returning good for evil (Genesis 50:21; Romans 12:21). This is key to converting our anger into love. As our actions flow from our hearts, so also our hearts can be altered by our actions (Matthew 5:43-48). That is, we can change our feelings toward another by changing how we choose to act toward that person.

We can handle anger biblically by communicating to solve the problem. There are four basic rules of communication shared in Ephesians 4:15, 25-32:

  1.  Be honest and speak (Ephesians 4:15, 25). People cannot read our minds. We must speak the truth in love.
  2. Stay current (Ephesians 4:26-27). We must not allow what is bothering us to build up until we lose control. Dealing with and sharing what is bothering us before it gets to that point is important. 
  3.  Attack the problem, not the person (Ephesians 4:29, 31). Along this line, we must remember the importance of keeping the volume of our voices low (Proverbs 15:1).
  4.  Act, not react (Ephesians 4:31-32). Because of our fallen nature, our first impulse is often a sinful one (v. 31). The time spent in “counting to ten” should be used to reflect upon the godly way to respond (v. 32) and to remind ourselves how anger is to be used to solve problems and not create bigger ones.

Finally, we must act to solve our part of the problem (Romans 12:18). We cannot control how others act or respond, but we can make the changes that need to be made on our part. Overcoming a temper is not accomplished overnight. But through prayer, Bible study, and reliance upon God’s Holy Spirit, ungodly anger can be overcome. Just as we may have allowed anger to become entrenched in our lives by habitual practice, we must also practice responding correctly until it becomes a habit itself.

Thursday, May 03, 2012

SCADA What is SCADA



SCADA (Supervisory Control And Data Acquisition) system refers to the combination of telemetry and data acquisition. It consists of collecting information, transferring it back to a central site, carrying out necessary analysis and control, and then displaying this data on a number of operator screens.The SCADA system is used to monitor and control a plant or equipment. Control may be automatic or can be initiated by operator commands.

What is telemetry



Telemetry is usually associated with SCADA systems. It is a technique used in transmitting and receiving information or data over a medium. The information can be measurements, such as voltage, speed or flow. These data are transmitted to another location through a medium such as cable, telephone or radio. Information may come from multiple locations. A way of addressing these different sites is incorporated in the system.

What is data acquisition



Data acquisition refers to the method used to access and control information or data from the equipment being controlled and monitored. The data accessed are then forwarded onto a telemetry system ready for transfer to the different sites. They can be analog and digital information gathered by sensors, such as flowmeter, ammeter, etc. It can also be data to control equipment such as actuators, relays, valves, motors, etc.

What are the differences between SCADA and DCS



Similar to the SCADA systems are the Distributed Control Systems (DCS). The DCS is usually used in factories and located within a more confined area. It uses a high-speed communications medium, such as local area network (LAN). A significant amount of closed loop control is present on the systemThe SCADA system covers larger.geographical areas. It may rely on a variety of communication links such as radio and telephone. Closed loop control is not a high priority in this system.

Components of SCADA System



Components of a SCADA System A SCADA system are composed of the following:
  1.  Field Instrumentation
  2.  Remote Stations 
  3.  Communications Network
  4.  Central Monitoring Station
Field Instrumentation refers to the sensors and actuators that are directly interfaced to the plant or equipment. They generate the analog and digital signals that will be monitored by the Remote Station. Signals are also conditioned to make sure they are compatible with the inputs/outputs of the RTU or PLC at the Remote Station. The Remote Station is installed at the remote plant or equipment being monitored and controlled by the central host computer. This can be a Remote Terminal Unit (RTU) or a Programmable Logic Controller (PLC). The Communications Network is the medium for transferring information from one location to another. This can be via telephone line, radio or cable.
The Central Monitoring Station (CMS) refers to the location of the master or host computer. Several workstation may be configured on the CMS, if necessary. It uses a Man Machine Interface (MMI) program to monitor various types data needed for the operation. The following is a sample configuration of a SCADA system for water distribution.

Wednesday, May 02, 2012

It has been said that a parable is an earthly story with a heavenly meaning. The Lord Jesus frequently used parables as a means of illustrating profound, divine truths. Stories such as these are easily remembered, the characters bold, and the symbolism rich in meaning. Parables were a common form of teaching in Judaism. Before a certain point in His ministry, Jesus had employed many graphic analogies using common things that would be familiar to everyone (salt, bread, sheep, etc.) and their meaning was fairly clear in the context of His teaching. Parables required more explanation, and at one point in His ministry, Jesus began to teach using parables exclusively.

The question is why Jesus would let most people wonder about the meaning of His parables. The first instance of this is in His telling the parable of the seed and the soils. Before He interpreted this parable, He drew His disciples away from the crowd. They said to Him, "Why do You speak to them in parables?" Jesus answered them, "To you it has been granted to know the mysteries of the kingdom of heaven, but to them it has not been granted. For whoever has, to him more shall be given, and he will have an abundance; but whoever does not have, even what he has shall be taken away from him. Therefore I speak to them in parables; because while seeing they do not see, and while hearing they do not hear, nor do they understand. In their case the prophecy of Isaiah is being fulfilled, which says,

‘Hearing you will hear and shall not understand, And seeing you will see and not perceive; For the hearts of this people have grown dull. Their ears are hard of hearing, And their eyes they have closed, Lest they should see with their eyes and hear with their ears, Lest they should understand with their hearts and turn, So that I should heal them.’ But blessed are your eyes, because they see; and your ears, because they hear. For truly I say to you that many prophets and righteous men desired to see what you see, and did not see it, and to hear what you hear, and did not hear it" (Matthew 13:10-17).

From this point on in Jesus’ ministry, when He spoke in parables, He explained them only to His disciples. But those who had continually rejected His message were left in their spiritual blindness to wonder as to His meaning. He made a clear distinction between those who had been given “ears to hear” and those who persisted in unbelief—ever hearing, but never actually perceiving and “always learning but never able to acknowledge the truth” (2 Timothy 3:7). The disciples had been given the gift of spiritual discernment by which things of the spirit were made clear to them. Because they accepted truth from Jesus, they were given more and more truth. The same is true today of believers who have been given the gift of the Holy Spirit who guides us into all truth (John 16:13). He has opened our eyes to the light of truth and our ears to the sweet words of eternal life.

Our Lord Jesus understood that truth is not sweet music to all ears. Simply put, there are those who have neither interest nor regard in the deep things of God. So why, then, did He speak in parables? To those with a genuine hunger for God, the parable is both an effective and memorable vehicle for the conveyance of divine truths. Our Lord’s parables contain great volumes of truth in very few words—and His parables, rich in imagery, are not easily forgotten. So, then, the parable is a blessing to those with willing ears. But to those with dull hearts and ears that are slow to hear, the parable is also an instrument of both judgment and mercy.
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