System Architecture of ABB Redundant CPU.

The Following System Architecture illustrates a physical connection of two redundant

 CPU(ABB PM-573 ETH) where data visual is provided by ABB HMI. The data transfer is using ethernet cable.This particular HMI has a facility of SWAP IP Configuration as well which connects to other CPU if one of them Fails to provide data, between both the CPU data is synchronized via the cross cable and the Coupler connected together with the CPU provides data updation to LAN where the HMI updates the data from.The Following IP provided is just for illustration,other IP can also be used. 

Three Phase Electric Arc Furnace - An Introduction

EAFs produce steel by melting scrap using a threephase electrical supply as the electrical energy input.The fundamental problem in the EAF industry is the production of steel at a specified quality at the lowest cost possible. The three-phase electrical input serves as the main energy input in the electric arc furnace. The electrical energy input needs to be controlled with the aim of achieving the lowest possible production cost. Each phase of the three-phase electrical input supplies power to one of the three electrodes that is mounted above the furnace bath through the roof. The furnace roof is closed when power is supplied to the system. The furnace operation is based on heat transfer into the bath from arcs drawn between the tips of the electrodes to the metallic charge. Thus, electrical energy is converted into heat which is transmitted to the charge through the electrodes. Constant melting
causes the arc length to change and results in a change in the electric energy input if control is not supplied to the system. Two variables are mainly used to control the electrical energy input, i.e. arc impedance and arc current. Both these variables are controlled via an electrode position controller which moves the electrodes in a vertical position to adjust the arc current or arc impedance according to specified reference values.

What makes up the electromagnetic spectrum?

The electromagnetic spectrum is a family of waves that travel through space by way of the production of electric and magnetic fields. Changing electric fields are set up by the oscillation of charged particles and these changing electric fields induce changing magnetic fields in the surrounding space. Changing magnetic fields then set up more changing electric fields and so on. The net result is that the wave energy travels across space.All electromagnetic waves travel at the same speed through the same medium or substance but they have a variety of frequencies which provide a corresponding variety of wavelengths. If the original charged particle vibrates rapidly, the frequency of the wave is high. Because there are many oscillations per second, the corresponding wavelength is short. Conversely, if the original charged particle vibrates slowly, the frequency of the wave is low and the corresponding wavelength is long.The whole range of frequencies and wavelengths is called the electromagnetic spectrum and different parts of the spectrum are given different names. These parts of the spectrum have different properties and, consequently, they have different uses. Therefore, it can be seen that there is the need for the coexistence of all kinds of radio services, which use the electromagnetic spectrum to convey information, with technical processes and products emitting electromagnetic energy as an undesirable by-product. Furthermore, the problems of EMC are not limited to interference with radio services because electronic equipment of all kinds is becoming more susceptible to malfunctions caused by external interference. This is particularly relevant in the case of electronic equipment that is required to continue running for economic or safety reasons. Banking systems and aircraft computers are two notable examples.

Booster

A pneumatic relay that is used to reduce the time lag in pneumatic circuits by reproducing pneumatic signals with high-volume and or high-pressure output. These units may act as volume boosters or as amplifiers. A 1:2 booster will take a 3 to 15 psig input signal and output a 6 to 30 psig signal. It has also been shown that a booster may improve the performance of a control valve by replacing a positioner. It can provide the same stroking speed and can isolate the controller from the large capacitive load of the actuator.  

Choked Flow

Also known as CRITICAL FLOW. This condition exists when at a fixed upstream pressure the flow cannot be further increased by lowering the downstream pressure. This condition can occur in gas, steam, or liquid services. Fluids flow through a valve because of a difference in pressure between the inlet (Pl) and outlet (P2) of the valve. This pressure difference (Delta-P) or pressure drop isessential to moving the fluid. Flow is proportional to the square root of the pressure drop. Which means that the higher the pressure drop is the more fluid can be moved through the valve. If the inlet pressure to a valve remains constant, then the differential pressure can only be increased by lowering the outlet pressure. For gases and steam, which are compressible fluids, the maximum velocity of the fluid through the valve is limited by the velocity of the propagation of a pressure wave which travels at the speed of sound in the fluid. If the pressure drop is sufficiently high, the velocity in the flow stream at the VENA CONTRACTA will reach the velocity of sound. Further decrease in the outlet pressure will not be felt upstream because the pressure wave can only travel at sonic velocity and the signal will never translate upstream. Choked Flow can also occur in liquids but only if the fluid is in a FLASHING or CAVITATING condition. The vapor bubbles block or choke the flow and prevent the valve from passing more flow by lowering the outlet pressure to increase the pres-sure drop. A good Rule Of Thumb on Gases and Steam service is that if the pressure drop across the valve equals or exceeds one half the absolute inlet pressure, then there is a good chance for a choked flow condition. 

Example: 

P1 100 psig 
P2 25 psig 
_________ 
Delta P = 75 

P1 (ABS) = 100 + 14.7 or 114.7 1/2 of 114.7 = 57.35 
Actual pressure drop = 75 
Choked Flow is probable. 

The style of valve (that is whether it is a HIGH RECOVERY or a LOW RECOVERY style) will also have an effect on the point at which a choked flow condition will occur.  

Positioners and Valve -Troubleshooting

1. Start with the fail mode of the valve.  A: If the valve fails closed and is leaking...  Disconnect the positioners or controller input.  If the valve has a hand wheel, check to see that it is backed out.  Check to see if the bench range is correct.  Check to see if there is trash in, or damage to, the valve seat.  2. Next check the positioners.  3. Next check the controller.

Do not rely on the control room to generate signals. Generate your own with equipment that you know is properly calibrated. Do not assume anything. 

Remember that control valves only do what you tell them to. Many control valve problems turn out to be a problem somewhere else.

Tips & Tricks

1. If you are dealing with a corrosive fluid, choose the valve body and trim material to match the pump casing and impeller. 

2. Velocity is the key to handling abrasive materials. Normal city water velocity is about 7 to 10 F.P.S. (clean liquid). If you have a fluid that is abrasive, keep the velocity as low as possible - without having the particles drop out of suspension. 

3. Always sense pressure where you want to control it. Many control valves and pressure regulators do not function properly simply because they are sensing pressure at one point and being asked to control it somewhere else. 

4. Velocity is the key to handling noise. Noise is energy. When dealing with high pressure drop situations try always to keep the velocities below 0.3 mach. on the inlet pipe, valve body, and outlet pipe. 

5. If you use a transducer in a control loop, specify a positioner on the valve. Otherwise the transducer will rob the actuator of available thrust, and the valve will leak when it is supposed to shut off. 

6. In cavitating fluids - even if the control valve has cavitation trim in it - be sure to allow a straight run of downstream pipe after the valve. If there is a pipe "T"or elbow immediately downstream, the flow will choke out and back up into the valve. 

7. If you use a control valve with a bellows seal in it, try to size the valve so that its normal throttling position is near the bellows "at rest" position. This will minimize wear on the bellows. 

8. Don't use a valve below 10% of flow if at all possible. Even though a valve may have good rangeability, if the valve is used in an abrasive or erosive service (steam), it will not hold up unless it has hardened trim. 

9. If a PLC is being used to control the valves in a system, specify the valves with a linear flow characteristic. 

10. If a control valve is started up and fails to respond - or goes to full open or full closed and stays there - check the controller and reverse the controller's action.

Seat Leakages Classifications

Control valves are designed to throttle. However, this is not a perfect world, and control valves are also usually expected to provide some type of shut-off capability. A control valve's ability to shut off has to do with many factors. The type of valves for instance. A double-seated control valve will usually have very poor shut-off capability. The guiding, seat material, actuator thrust, pressure drop, and the type of fluid can all play a part in how well a particular control valve shuts off.

There are actually six different seat leakage classifications as defined by ANSI/FCI 70-2-1976. But for the most part you will be concerned with just two of them: CLASS IV and CLASS VI. CLASS IV is also known as METAL TO METAL. It is the kind of leakage rate you can expect from a valve with a metal plug and metal seat. CLASS VI is known as a SOFT SEAT classification. SOFT SEAT VALVES are those where either the plug or seat or both are made from some kind of composition material such as Teflon.

Valve Leakage Classifications

Class I. Identical to Class II, III, and IV in construction and design intent, but no actual shop test is made.

Class II. Intended for double-port or balanced singe-port valves with a metal piston ring seal and metal-to-metal seats. Air or water at 45 to 60 psig is the test fluid. Allowable leakage is 0.5% of the rated full open capacity.

Class III. Intended for the same types of valves as in Class II. Allowable leakage is limited to 0.1% of rated valve capacity.

Class IV. Intended for single-port and balanced single-port valves with extra-tight piston seals and metal-to-metal seats. Leakage rate is limited to 0.01% of rated valve capacity.

Class V. Intended for the same types of valves as Class IV. The test fluid is water at 100 psig or operating pressure. Leakage allowed is limited to 5 X 10 ml per minute per inch of orifice diameter per psi differential.

Class VI. Intended for resilient-seating valves. The test fluid is air or nitrogen. Pressure is the lesser of 50 psig or operating pressure. The leakage limit depends on valve size and ranges from 0.15 to 6.75 ml per minute for valve sizes 1 through 8 inches.

Nominal Port Diameter (Inches)  1 1.5 2 2.5 3 4 6 8 10 12 Allowable Leakage (ml Per Minute)  (*Bubbles Per Minute)  0.15 1 0.30 2 0.45 3 0.60 4 0.90 6 1.70 11 4.00 27 6.75 45 9.00 63 11.5 81

*Bubbles per minute as tabulated are a suggested alternative based on a suitable calibrated measuring device, in this case a 0.25-inch O.D. X 0.032-inch wall tube submerged in water to a depth of from 1/8 to 1/4 inch. The tube end shall be cut square and smooth with no chamfers or burrs. The tube axis shall be perpendicular to the surface of the water. Other measuring devices may be constructed and the number of bubbles per minute may differ from those shown as long as they correctly indicate the flow in milliliters per minute.

Control Valve Flow Characteristic

Trim design will affect how the valve capacity changes as the valve moves through its complete travel. Because of the variation in trim design, many valves are not linear in nature. THE RELATIONSHIP BETWEEN VALVE CAPACITY AND VALVE TRAVEL IS KNOWN AS THE FLOW CHARACTERISTIC OF THE VALVE. Valve trims are specially designed, or characterized, in order to meet the large variety of control application needs. This is necessary because most control loops have some inherent nonlinearities, which you can compensate for when selecting control valve trim.

The percent of full flow through the valve is plotted against valve stem position. The curves shown are typical of those available from valve manufacturers. These curves are based on CONSTANT PRESSURE DROP across the valve and are called INHERENT FLOW CHARACTERISTICS.

The quick-opening characteristic provides large changes in flow for very small changes in lift. It usually has too high a valve gain for use in modulating control. So it is limited to on-off service, such as sequential operation in either batch or semi-continuous processes.

The majority of control applications are valves with linear, equal-percentage, or modified-flow characteristics.

Linear - flow capacity increases linearly with valve travel. Equal percentage - flow capacity increases exponentially with valve trim travel; equal increments of valve travel produce equal percentage changes in the existing Cv. A modified parabolic characteristic is approximately midway between linear and equal-percentage characteristics. It provides fine throttling at low flow capacity and approximately linear characteristics at higher flow capacity.

When valves are installed with a pump, pipes, fittings, and other process equipment, the pressure drop across the valve will vary as the plug moves through its travel. When the actual flow in a system is plotted against valve opening, the curve is called the INSTALLED FLOW CHARACTERISTIC.                                                                  Inherrent Flow Characteristics For Common Valve Trim Designs

Direct and Reverse Acting Controller

Controllers can be set up in either direct or reverse modes. It was stated that 99% of the positioners are direct acting, and it follows that if a balance is to be maintained in the control loop that 99% of the controllers will be reverse acting. If the control valve and its controller are not in balance, the control valve will either go to the wide-open position and stay there, or it will stay closed and act as though it is not responding. This situation can normally be corrected by reversing the action of the controller.

Direct-Acting Controller

Setpoint Increases Output Increases Increase in Setpoint  = Increase in Output Setpoint Decreases Output Decreases Decrease  in  Setpoint =  Decrease  in  Output

Reverse-Acting Controller

Setpoint Increases Output Decreases Increase in Setpoint  = Decrease in Output Setpoint Decreases Output Increases Decrease  in  Setpoint =  Increase  in  Output

Two of the more common control valve uses are for pressure control. In both instances, the controllers are reverse acting. Most pressure-reducing valves will be fail-closed and most back-pressure control valves will be fail-open. If the pressure-reducing valve were fail-open or the back-pressure valve fail-closed, then the controllers would have been direct acting.

Direct and Reverse Action Positioners

The key to working with control valves and controllers is to remember that there must always be a balance maintained in the system. "Direct" and "reverse" are kind of like "positive" and "negative" in that where you find one you will usually find the other.

While control valve bodies and control valve actuators can be described as being direct acting or reverse acting, thinking about such things when working through a system problem only adds to the confusion. Therefore, it is always best to consider the FAIL SAFE mode of the valve and simply let the control valve be what it may be.

Positioners, 99% of the time, will usually mimic the input signal from the controller. That is, they will be DIRECT ACTING.

Direct-Acting Positioner

Input Increases Output Increases Increasing Signal from Controller  = Increasing Output from Positioner Input Decreases Output Decreases Decreasing Signal From                     Controller =  Decreasing  Output From Positioner

Another reason the direct-acting pneumatic positioner is so popular is that it can be by-passed and the control valve will respond to the input signal from the controller as though the positioner were in the control loop. If a positioner malfunction occurs or if the positioner causes the control valve to become unstable, it can be easily by-passed. Many control valves in the field are operating with a by-passed positioner.

Reverse-acting positioners are sometimes used on control valves, but their appearance is rare. Occasionally one will be found in a split-ranging sequence.

Reverse-Acting Positioner

Input Increases Output Decreases Increasing Signal from Controller  = Decreasing Output from Positioner Input Decreases Output Increases                       Decreasing Signal From           Controller =  Increasing  Output From Positioner

Positioners - Working

There are different types of Positioner but they have similar working operation .The positioner is mechanically connected to the stem of the valve. This stem position is compared with the position called for by the instrument controller, i.e. by the instrument output air signal. A separate air supply is brought into the positioner for positioning the valve at exactly the point called for by the controller.

Reason to use Positioners

1. Increase control system resolution: i.e. fine control.

2. Allow use of characteristic cams.

3. Minimize packing friction effects: i.e. high-temperature packing.

4. Negate flow-induced reactions to higher pressure drops.

5. Increase speed of response to a change in process.

           6. Allow split ranging.

           7. Overcome seating friction in rotary valves.

           8. Allow distances between controller and control valve.

           9. Allow wide range of flow variation: i.e. operate at less than 10% travel under              

              normal conditions.

          10. Allow increased usage of 4-20 mA electronic signal.

          11. Increase fast venting (unloading) capability.

          12. Permit use of piston actuators.

          13. Facilitate operation when the higher number in the bench-set range is greater than           

                15 psig: i.e. 10-30 psig, 6-30 psig, etc.

Valve Positioners

A valve Positioner is a device used to increase or decrease the air pressure opertaing the actuator until the valve stem reaches the posion called for by the instrument controller............................................

                           

Positioners are generally mounted on the side or top of the actuator. They are connected mechanically to the valve stem so that stem position can be compared with the position dictated by the controller.

A positioner is a type of air relay which is used between the controller output and the valve diaphragm. The positioner acts to overcome hysteresis, packing box friction, and valve plug unbalance due to pressure drop. It assures exact positioning of the valve stem in accordance with the controller output.

Electromagnetic Flow Meter

The electro-magnetic flow meter is based on the principle of Faraday’s law of Induction.
To simplify the explanation, if one induces a magnetic field for example across a pipe
and a conductor is moved at right angles through the field, then a voltage proportional to
the velocity of the conductor will be induced. There are many other factors involved in
this law, which I feel would only serve to confuse the reader.

Electro-magnetic flow meters have been in existence for many years and their evolution
has been moving fairly slowly until recently. Many companies manufacture these meters,
but few have been successful in developing a meter that is accurate within very tight
tolerances.

Flow Measurement - A need and difiiculty

During the past number of years, we have seen the move by the dairy, food and beverage
industry, toward using poly bags and poly bags in boxes as a packaging medium. This
move has necessitated the development of machinery to accurately fill these bags.
Certain machines use a positive displacement cylinder that contains a predetermined
volume, while other machines use a predetermining counter device, which is interfaced
with a flow measurement device.

There are a number of flow measurement devices on the market today ranging from
positive displacement meters to electro-magnetic flow meters. Positive displacement
meters are very accurate meters but tend to be rather expensive and usually require a
great deal of maintenance. Today, many strides have been made in improving positive
displacement meters by incorporating pistons that can be CIP’d and the use of electronic
pulse transmitters in order to interface them with electronic counters. They still have
many applications for this type of device especially where very accurate measurement is
required with products that are non-conductive of electricity such as oils and certain types
of syrups.

Because of the expense of the positive displacement meters, many companies in the filler
industry decide to use what is known as a turbine meter. This meter works on the
principal of a turbine rotor, which spins as product is passed through it. As the blades of
the rotor spin, they pass a transducer, which senses that the blade has passed it and in turn
creates a pulse, which is then sent to a counting device. These pulses in turn are
converted into volumetric units such as litres, and gallons. Initially, these turbine devices
seemed to work pretty well but with the advent of acid sanitizers and high speed cleaning
systems many problems started to develop with the turbine meters. In addition, the acid
sanitizers start to corrode the rotor blades thus changing the number of pulses sent for a
given volume of product. Because of its nature, the turbine meter also requires that for
each different product a different factor (K-factor) be entered into the pre-determining
counter. When one combines all these problems, it is very difficult to accurately fill a
bag with a known volume of product on a consistent basis.

MBits Ethernet

Signals sent over all 10 Mbit/s media systems uses Manchester encoding. Manchester encoding combines data and clock into bit symbols, which provide a clock transition in the middle of each bit. 
A logical zero (0) is defined as a signal that is high for the first half of the bit period and low for the second half, i.e. a negative signal transition. A logical (1) is defined as a positive signal transition in the middle of the bit period. The signal transition makes it easy for a receiver to synchronise with the incoming signal and to extract data from it. A drawback is that the worst case signalling rate is
twice the data rate.A link test signal is transmitted when there is no data to send.

PLC- Determine the Sequence of Operation

We have to identify the equipment or the system to be controlled. The ultimate purpose of the
programmable controller will be to control an external system. The system to be controlled may be machine,equipment, or process to be controlled.The movement of the controlled system is monitored
in real time by the input devices. It gives a specified condition and sends a signal to the programmable
controller. The programmable controller outputs a signal to the external output devices which actually
controls the movement of the controlled system as specified and thus achieves the extended control action. In simple, one needs to determine the sequence of operation in steps form for onward development of flow chart by completely understanding the system detailed operation.

High Volume Transfer Lines

Generally, high-volume transfer lines are composed of several machining stations together with
mechanisms for part transferring and fi xturing. A high-volume transfer line consists of a transfer
mechanism, a number of machining stations, and fi xturing mechanisms for the machining stations.
A part is presented to each machining station by a transfer mechanism, and it is clamped by
a fixturing mechanism. A number of asynchronous machining stations are synchronized by part
flow. Each mechanism and machining station is simply called a station. Each station performs a
particular process necessary to the overall production of the part using simple and fast motions.
Each motion is called an operation and a sequence of operations is associated with each station.
In the transfer line,all machining stations are milling stations and the motions in each machining 
station are provided by two or three single axis sliding mechanisms.

CANopen Protocol- Baudrate and Pin Assignment

Baud rate                                     Bus Length

1Mbps-------------------------------------- 25m
750Kbps------------------------------------ 50m
500Kbps(Default)------------------------- 100m
250Kbps------------------------------------ 250m
125Kbps------------------------------------ 500m

Pin assignment for RJ45 for CAN bus wiring.


Pin No.                                      Signal Name                            Description

   1                                              CAN_H                                CAN_H bus line
   2                                              CAN_L                                CAN_L bus line
   3                                              CAN_GND                           Ground
   4                                                 ---                                     Reserved
   5                                                 ---                                     Reserved
   6                                                 ----                                    Reserved
   7                                              CAN_GND                           Ground
   8                                                 ---                                     Reserved

Types of Transmission - Comparison

ASYNCHRONOUS TRANSMISSION

1.Used for short bit sequences
2.Idle = No signal, negative voltage, 1
3.One Start bit, 7 or 8 data bits
4. One parity bit: Odd, Even, None
5.  Minimum Gap = Stop bits = 1, 1.5, or 2 bits
6. Efficiency = data bits/total bits

8N1 = 1 Start bit + 8 Data bits + 1 Stop bit + 1 parity bit (even 
though the parity is not being used by this site)
⇒ 8/(1+8+1+1) = 73%

7.  Faster clock: 7% ⇒ 56% off on 8th bit ⇒ Error
8.  Framing error ⇒ False start/end of a frame

SYNCHRONOUS TRANSMISSION


1. Used for longer bit sequences
2.  Requires clock transmission
Use codes with clock information (Manchester)
3.  Begining of block indicated by a preamble bit pattern called
“Syn”
4.  End of block indicated by postamble bit pattern
5. Character-oriented transmission: Data in 8-bit units
6. Bit-oriented transmission: Preamble = Flag
7. Efficiency: Data bits/(Preamble+Data+Postamble)
8. High-Level Data Link Control (HDLC) uses bit-oriented
synchronous transmission. 8 bit of overhead for 1000 data bits
⇒ 48/1048 = 4.6% overhead

IEC 61850

IEC 61850 is the international standard that defines the hardware and communication requirements
for all products. IEC 61850 is being applied increasingly within substation automation, T&D automation, and grid integration applications. This standard ensures interchangeability for the myriad
of devices which comprise power and energy, especially between all of the intelligent electronic devices (IEDs) from different manufacturers.IEC 61850-3 is the hardware standard of general requirements ensures environmental and EMI immunity of network devices used in substations. Another standard
for electronic power substations is IEEE 1613, detailing environmental and higher standard testing
requirements for communications networking devices.

Power and Energy.

Power & energy applications are becoming more and more critical as demands for
electricity continue to increase worldwide. Additionally, new challenges are arising due to
the limitations of our traditional power resources as we try to minimize the impact our
power usage has on the environment. To that end, renewable energies, such as wind and
solar power are playing more significant roles in modern electricity to generate electricity.
Furthermore, the modernization of legacy Transmission & Distribution (T&D) systems and
providing reliable T&D information for electric power management are becoming key goals for
today’s power and energy applications.