Do you have the right VFD for Your Application

Choosing the right variable frequency drive for an application involves several important considerations. For example, based on acceleration requirements, sensorless vector control may be more suitable than volts-per-hertz (V/f) control. While V/f control is effective in dragging logs up a slope, it’s not appropriate for dockside hoists that position 12-ton shipping containers to within inches.

What is your load type: constant or variable torque?

To get a constant-torque load, the torque is independent of speed (ignoring momentary shock loads). Examples consist of conveyors and hoists. To get a variable-torque load, torque varies as a function of speed. Examples consist of fans and pumps. This main distinction underlies each choice you will make concerning the kind of drive.

What are your acceleration requirements?

Does it matter how fast your load accelerates up to speed? For a fan, probably not. For a centrifuge, almost certainly. In the latter case, you may want to select sensorless vector control, rather than volts-per-hertz (V/f) control. While the V/f approach is effective for many applications, it doesn’t allow a motor to develop near-full torque at near-zero speeds (unlike sensorless vector control). V/f control can be appropriate for dragging logs up a slope, but not for a dockside hoist that needs to position a 12-ton shipping container to within inches.
Controlled deceleration presents its own challenges.

Throughout decelerations, the motor acts as a generator. The resulting power must go someplace, and is usually dissipated as heat inside a braking resistor. Controlled-deceleration capability is really a great answer for constant-torque loads, altering loads, or perhaps unbalanced loads.

What is your speed range?

Although a conveyor belt may operate consistently at 60 Hz, for an unspooling module on a printing line, the motor needs to deliver torque as effectively at 0.5 Hz as 60 Hz. This is another application where garden-variety V/f control won’t do the job. Sensorless vector control will (and most VFDs these days include it). Keep in mind, however, that not all offerings are created equal. Be sure to double check specifications against your requirements.

How do I select the proper size VFD?

For most applications, select a VFD that has an output current rating that equals or exceeds the nameplate current rating of the motor. Do not just select the VFD based on the motor Hp rating, as this can result in a VFD that is too small. Some severe applications, such as punch presses, vibratory conveyors, mixers, etc, may require oversizing the VFD in order to handle the peak current demands of the load. Please contact AC Tech's Application Engineering Department for more information.

VFDs have a wide variety of programmable functions. Not all manufacturers call these functions by the same name. Research is required to properly utilize a VFD to its best performance. We are fortunate to live in an age where a great wealth of information is available on the Internet. Utilizing manufacturers’ websites and educational information, plus a little time, can make most any controls person an expert in VFD selection.

How Do VFDs Save Energy and Money

VFDs are developed to supply variable speed manage. They preserve the optimal speed needed for an application to improve production and save power. Low- and medium-voltage drives steadily accelerate and decelerate motors and pumps, assisting shield mechanical elements and extend their life, whilst decreasing inrush currents, which assists save power. VFDs are utilized inside a broad selection of industries and applications?aincluding HVAC, water and wastewater, and oil and gas.

VFDs are a critical component of motor speed control. They improve efficiency, reduce wear on mechanical components and improve system performance. Fundamentally, they are used to control the frequency and voltage supply to the motor and match the application’s speed requirements.

All VFDs are going to take 3 phase AC power and convert that 3 phase power to DC power inside the drive and pulse it out in a simulated AC wave form to the motor.  The motor still thinks it has AC power but the DC power conversion now lets us control the speed of the motor without harming it.  Now we are in control to save energy and money.

Variable frequency drives are widely used in many areas such as fan, pump, compressor, elevator, tower crane, CNC, paper making machine and more. There are many benefits of applying frequency inverter:

    Saving energy: when your production don't need the motor to run at full speed, then you can use a variable frequency drive to adjust the motor running speed, so energy can be saved during the process.

    Improving the control accuracy: in variable torque or tension control applications, the production needs variable toruqe or tension, such as paper-making industry, textile industry and etc. By using a frequency inverter, it can help users to control the torque or tension accurately according to the application requirements. Therefore, the production efficiency can be greatly reduced.

    Reducing the maintenance cost of your equipments: when your production control system is without a frequency inverter, the motor will start instantly with large current which is harmful to your mechanical equipments. A frequency inverter which is developed with motor soft-start function can prevent this phenomena, so the equipment wear will be reduced and the equipment maintenance cost will be decreased also.

How much can you save using a VFD?

In these centrifugal pool pumps, (according to energy conservation experts) energy consumption is proportional to the cube of the flow rate. In plain English that means that even small reductions in speed and flow can result in significant energy savings. In pool applications, significant energy and cost savings can be achieved by reducing the operating speed when the filters are clean, or when the pool is experiencing off-peak loads.

How great are the savings?

A motor running at 50% of full speed capacity has a motor torque of 25% of full speed. In addition, electricity required to operate the motor at 50% of full speed is 12.5% of the amount of electricity required if the motor was running at 100% full speed capacity. Thus, reducing motor speed can significantly reduce the electrical energy consumption.

Plenty of applications which will save a lot of power by installing a VFD (Main, secondary air, exhaust/flue gas extractor fan, cooling pumps for certain, motors utilized for automatic adjustment of parameters). Anyway, in case from the plant/motor is utilized for energy balance regulation when the load is most likely to increase/decrease much more often, you are able to set up a VFD for saving energies. In case your plant is operating below nominal speed a lengthy time, the power saving using the motor is really a minor issue for you personally. The large loss will come from other points like electrical energy consumption, motor efficiency, upkeep and so on. Fitting a VFD for such motor won't assist as well a lot.

How to Select PLC for Motion Control

Almost every modern industry uses programmable logic controllers, commonly known as PLCs. These compact electronic devices enable much of the automation that is prevalent in today’s manufacturing processes. PLCs are utilized to get a myriad of purposes in company and business, such as every thing from climate manage systems to complex item assembly and packaging processes.

Buyers unfamiliar with PLCs and their benefits may feel overwhelmed as they begin the process of selecting and purchasing Delta PLC for their business or industry. This guide will offer a short overview from the history and function of PLCs, such as the programming specifications and a few important elements to help keep in thoughts whilst buying for PLCs.

The factors to consider when choosing a PLC:
I/O
Servos
Size of Memory
Communications
Compatibility to HMI
Format
Speed

Format of PLC

You can go away using the format of Little PLC Omron simply because the count of I/O is much less than one hundred and also you don't have servos or analog to compete with; although, from a view of studying point and becoming that Medium Format of PLCs would be the business function horse you'll make use of a Medium Format PLC having a genuine of back-plain.

Speed of PLC

The speed of PLC uses to be a main concern when planning controls but does not truly affect to controls now. Nowadays PLCs are rapid enough for the majority applications with full programs scan times usually less than 4 msec. This is the scan time needed for the PLC to seem at the service and program all the Inputs/Outputs. The Cycle Time is 4 seconds so the majorities PLCs today are glowing when think this requirement of time.

Size matters - Sizing a PLC is crucial towards the achievement of one's project. As well little and also you might max out your I/O on modifications and additions. As well big and also you might blow your spending budget. Be sure you leave space for expansion but do not break the bank.

Count up your:

Discrete input points
Discrete output points
Analog input points
Analog output points

Communications. ALWAYS have a port available on the PLC to communicate with it from your laptop without disconnecting other devices.  With modern PLCs with multiple communications methods, there is no reason for this to happen.

        Will you need remote I/O?  This can reduce installation time and troubleshooting in the long term.
        Will you system utilize an HMI?  How will you communicate with it?
        Will you have a way to remotely monitor it from either the office across the plant or across the country?  It is becoming a standard practice.  Personally I like Ethernet but there are many options.

Brand - I'll be unpopular when I say this, but a PLC is a PLC when it comes to most capabilities.All of the major players such as Allen Bradley, Automation Direct, Mitsubishi,Omron, and Siemens have small, medium, and large scale PLCs. Always consider when brands the end user already is using. Things will always go smoother if the maintenance personel are already familiar with the brand of PLC you choose. Also try to choose a brand that will have good local  support for the end user if you are not in the area.

Conclusion

Whether buyers are looking for a replacement PLC for an existing system or are interested in automating a new process, they will likely be able to find PLCs that are appropriate for their needs on Fasttobuy. Fasttobuy’s user-friendly policies and search options allow buyers to enjoy a secure and profitable shopping experience. With their new PLCs, buyers will be able to implement time saving automation technologies for their business or industry.

The Brief Introduction of DC Servo Motor

What is the meaning of servo?

In modern usage the term servo or servo-mechanism is restricted to a feedback control system in which the controlled variable is mechanical position or time derivatives of position such as velocity and acceleration.

A servo is a device, electrical, mechanical or electro mechanical, that upon receipt of a stimulus or input, will employ feedback for velocity and/or position control, creating a closed loop.

A feedback system is a control system which tends to maintain a prescribed relationship between a controlled quantity and a reference quantity by comparing their functions and using the difference as a means of control

There are mainly two types of servo-motors

1)AC Servo motor
2)DC Servo-motor

AC servo-motors are generally preferred for low-power use. And for high-power use DC servo motors are preferred because they operate more efficiently than comparable to AC servo motors.

Unlike large industrial motors, dc servomotors are not used for continuous energy conversion. The basic operating principle is same as other electromagnetic motors.

Construction:

1.It has construction as same as dc motor. It is consist of stator and rotor and controlling parts.2.It has feedback generator for generating feedback for controlling the speed & torque.
3.It has two ports one for dc supply and other for controlled dc supply.
Field Controlled DC Servo Motor Theory:

The figure below illustrates the schematic diagram for a field controlled DC servo motor. In this arrangement the field of DC motor is excited be the amplified error signal and armature winding is energized by a constant current source.

The field is controlled below the knee point of magnetizing saturation curve. At that portion of the curve the mmf linearly varies with excitation current. That means torque developed in the DC motor is directly proportional to the field current below the knee point of magnetizing saturation curve.

Armature Controlled DC Servo Motor Theory:

The figure below shows the schematic diagram for an armature controlled DC servo motor. Here the armature is energized by amplified error signal and field is excited by a constant current source.

The field is operated at well beyond the knee point of magnetizing saturation curve. In this portion of the curve, for huge change in magnetizing current, there is very small change in mmf in the motor field. This makes the servo motor is less sensitive to change in field current. Actually for armature controlled DC servo motor, we do not want that, the motor should response to any change ofPerformance Specifications:

DC servomotors share many performance specifications that are applicable to all types of?DC motors. To properly size a motor, these specifications must be matched according to the load requirements of the application.

Shaft speed (RPM) defines the speed at which the shaft rotates, expressed in rotations per minute (RPM). Typically, the speed provided by the manufacturer is the no-load speed of the output shaft, or the speed at which the motor's output torque is zero.

Terminal voltage refers to the design voltage of the DC motor. Essentially the voltage determines the speed of a DC motor,and speed is controlled by raising or lowering the voltage supplied to the motor.

Torque is the rotational force generated by the motor shaft.The torque required for the motor is determined by the speed-torquecharacteristics of thevarious loads experienced in the targetapplication.

Starting torque - The torque required when starting the motor,which istypically higher than the continuous torque.
Continuous torque - The output torque capability of the motor under constant running conditions.

Some ratings of dc servo-motor available:

Shaft Speed:

Less than 1,610 rpm
1,610 to 3,187 rpm
3,187 to 4,700 rpm
4,700 to 7,090 rpm
7,090 rpm and up

Terminal Voltage:

Less than 20 VDC
20 to 50 VDC
50 to 100 VDC
100 to 180 VDC
180 VDC and up

Continuous Current: 

Less than 1 amps
1 to 4 amps 4 to 8 amps
8 to 17 amps
17 amps and up

Continuous Torque:
Less than 0.45 Nm
0.45 Nm to 1.70 Nm
1.70 Nm to 5 Nm
5 Nm to 17 Nm
17 Nm and up

Continuous Output Power:

Less than 0.4 HP
0.4 to 1 HP 1 to 2 HP
2 to 6 HP
6 HP and up

Advantages:

• High output power relative to motor size and weight.Encoder determines accuracy and resolution.
• High efficiency. It can approach 90% at light loads.High torque to inertia ratio.It can rapidly accelerate loads.
• Has "reserve" power. 2-3 times continuous power for short periods.
• Has "reserve" torque. 5-10 times rated torque for short periods.
• Motor stays cool. Current draw proportional to load.
• Usable high speed torque.
• Maintains rated torque to 90% of NL RPM
• Audibly quiet at high speeds.Resonance and vibration free operation.

Disadvantages:

• Requires "tuning" to stabilize feedback loop.Motor "runs away" when something breaks. Safety circuits are required.
• Complex. Requires encoder.Brush wear out limits life to 2,000 hrs. Service is then required.
• Peak torque is limited to a 1% duty cycle.Motor can be damaged by sustained overload.
• Bewildering choice of motors, encoders, and servo-drives.
• Power supply current 10 times average to use peak torque. 
• Motor develops peak power at higher speeds. Gearing often required.
• Poor motor cooling. Ventilated motors are easily contaminated.

Applications:

DC servomotors finds its applications in various domain. Some of them are given below:

• For very high voltage power systems, dc motors are preferred because they operate more efficiently than comparable ac servomotor.
• It has also find its application in inkjet printers and RC helicopters.
• To drive conveyors used in Industrial manufacturing and assembling units to pass an object from one assembly station to another.
•  It is also used in solar tracking system.DC servomotors are widely used in robots, toy cars and other position controlled devices.
• Widely used in radars, computers, robots, machine tools tracking system, process controllers etc.

Fasttobuy co.,ltd is a professional and experienced company which specializes in producing and researching,located in changzhou city,jiangsu province, china. Our main products are stepper motors and drivers,servo motor and drivers,gear motor and other automatic device, applied widely in printing equipment, engraving machine textile machine, computer external application equipment, medical instruments, stage light equipment, robot, CNC machine and other automatic controlling system.  Exported to United States, Canada, Germany, United Kingdom, France, Switzerland, Italy, Russia, Korea and so on more than ten countries and regions in the world.

Variable Frequency Drive Sizing

Have anyone done much vfd sizing for motors? I know you have to take torque and and horsepower into consideration alot. It appears most of the vfds I have seen tend to have larger conductors feeding it than one would calculate for a motor load without a vfd. Maybe its because the vfd is more oversized, or they used 150% NEC 2008 430.6(C). from the motor tables unlike only 125% sizing for conductors to the motor. If you want to buy VFD, you can go to our offical website: Fasttobuy.com. We provide We carry various VFD manufacturers from Mitsubishi to Delta VFD to provide you with a brand you know and trust. We supply both single-phase and three-phase drives in various voltages to help meet the specifications of your current system.

Any one have an instance where they had to size the vfd? Was the feed to the vfd allowed to be smaller than it would be for the motors itself? How did you size it? 

When a single VFD is utilized to manage numerous motors, VFD sizing and choice turn out to be much more complicated unless all the motors are began simultaneously. With numerous motors connected to 1 VFD, adding the horsepower of every to acquire a total load and choosing the VFD accordingly might not be adequate based on operating circumstances.

1 of much more motors cannot be began up whilst 1 or much more motors are currently operating unless the chosen drive is sufficiently oversized. To illustrate this point, think about the following instance with 3 460 VAC motors connected to 1 VFD.

Two from the motors are rated at five HP having a complete load amp (FLA) rating of six.two amps. The third motor is rated at ten HP with an FLA of 14 amps. If all motors are accelerated, decelerated and run in unison-the sum from the connected motor FLA enables use of a 20 HP drive. But if it had been essential to accelerate and run the five HP motors and after that begin the ten HP, the sum from the FLA would need to be recalculated.

The FLA for every from the five HP motors could be utilized within the calculations, however the locked rotor amps (LRA) for the ten HP would need to be taken into account. The LRA will be the quantity of present drawn by a motor at startup.

Simply because the ten HP motor wouldn’t be accelerated from zero frequency and voltage to its operating situation, it would appear in the drive as a fixed voltage/frequency line starter and would need its complete LRA rating to rapidly accelerate towards the drive’s output frequency.

Therefore, the amp draw around the drive when the ten HP drive is coming on line could be the FLA of every from the five HP motors, plus the LRA of ten HP motor that is 86.five amps. The total amp figure to become utilized for VFD sizing is therefore six.two FLA + six.two FLA + 86.five LRA = 98.9 Amps. This amp load would need upsizing to a 75HP VFD having a minimum continuous output rating of 99 Amps, a 50% improve in VFD size.

Final Recommendation

With modern power electronics and advanced microprocessor technology, Delta's AC Motor Drives are able to efficiently control motor speed, improve machine automation and save energy. Taking advantage of our strong position in power electronics technology, Delta's VFD Series of AC motor Drives has evolved rapidly. Each Drive series is designed to meet specific application needs. Our AC Drives accurately control speed and torque, smoothly handle an increased load, and provide numerous custom control and configuration operating modes. Our AC Motor Drive product line provides a full range of motor control technologies and is used throughout a wide range of industries, to enhance and improve machine automation. 

This guide is intended to become of use for common application sizing and isn't intended to become a complete guide. You will find applications and loads that might need unique sizing and consideration. When you're sizing or specifying a VFD for any application it pays to become conservative and leave some buffer space within the FLA and overload ratings. This really is particularly accurate in case your load is difficult to begin or sees heavy loading throughout operation. When you have any concerns about your application or in sizing a brand new VFD contact and speak to 1 of our application specialists before buying.

What are the advantages and disadvantages of PLC

What is PLC?

Programmable Logic Controller (PLC) is a digital computer used for the automation of various electro-mechanical processes in industries. These controllers are specially designed to survive in harsh situations and shielded from heat, cold, dust, and moisture etc. PLC consists of a microprocessor which is programmed using the computer language.

The program is written on a computer and is downloaded to the PLC via cable. These loaded programs are stored in non – volatile memory of the PLC. During the transition of relay control panels to PLC, the hard wired relay logic was exchanged for the program fed by the user. A visual programming language known as the Ladder Logic was created to program the PLC.

The main difference from other computers is that PLCs are armored for severe conditions (dust, moisture, heat, cold, etc) and have the facility for extensive input/out put (I/O) arrangements.

Disadvantages of Programmable logic controller (PLC, programmable controller) control:

1. There's too much work required in connecting wires.
2. There's difficulty with changes or replacements.
3. It's always difficult to find errors; And require skillful work force.
4. When a problem occurs, hold-up time is indefinite, usually long.

Advantages of Programmable logic controller (PLC) control:

1. Rugged and designed to withstand vibrations, temperature, humidity, and noise.
2. Have interfacing for inputs and outputs already inside the controller.
3. PLCs are easily programmed and have an easily understood programming language.

PLCs Applications

How do you calculate the RPM of a 3 phase VFD motor

Variable frequency drives (VFDs) and electric motors are strange companions: The VFD is a static device, delicate, intolerant of wide variations in environmental conditions; extremely adjustable and controllable by microprocessors; capable of being monitored and controlled from remote locations; and a product of modern electronic engineering and precision—the beauty.

Calculating RPM for a three phase VFD is relatively simple… AC Three Phase Induction Motor RPM is determined by the formula:

    RPM = (120 * Frequency) / # of poles in the motor

Since the number of poles of a three phase induction motor is established when it is manufactured, the only way to change the speed of the motor is to change the Frequency.

For Example: A four pole three phase VFD when operated at 60 Hz will be very close to 1800 RPM(synchronous speed). The rated full load speed will be less than synchronous speed by the value of “Slip”. A four pole three phase induction motor with a rated full load speed of 1750 has a slip rating of 2.7%. By formula:

    ((Synchronous Speed – Rated Full Load Speed) / (Synchronous Speed)) * 100% = Slip Rating
    ((1800 RPM -1750 RPM) / 1800 RPM) * 100% = (50 RPM / 1800 RPM) * 100%
    (50 RPM / 1800 RPM) * 100% = .027 * 100%
    .027 * 100% = 2.7%
    Slip Rating = 2.7%

When using this information and the above formulas the running speed of an AC three phase VFD can be calculated at any input frequency. So how fast will a four pole three phase Delta VFD run when operated at 45 Hz? The three phase VFD has a Full Load RPM rating on the nameplate of 1760 RPM.

    RPM = (Frequency * 120) / # of poles in the motor
    RPM = (45Hz * 120) / 4
    RPM = 1350

Next, we calculate the Slip Rating:

    ((Synchronous Speed – Rated Full Load Speed) / (Synchronous Speed)) * 100% = Slip Rating
    ((1800 RPM – 1760 RPM) / (1800 RPM)) * 100% = (40 RPM / 1800 RPM) * 100%
    (40 RPM / 1800 RPM) * 100% = .022 * 100%
    Slip Rating = 2.2%

Instead of using a percentage, we will convert the Slip Rating into how many RPMs actually slip using the following formula:

    RPM Slip = RPM * Slip Rating
    RPM Slip = (1350 * .022) = 27.7 RPM
    RPM Slip = 27.7 RPM

So full load RPM of this motor at 45 Hz will be calculated as such:

    Full Load RPM = RPM – RPM Slip
    Full Load RPM = 1350 RPM – 27.7 RPM
    Full Load RPM = 1322.3 RPM

When selecting a three phase motor, the number of poles is chosen to achieve the speed of rotation that you require. Here are two tables, one for a 50 Hz power supply and one for a 60 Hz power supply:

The formula is n = 60 x f /p where n = synchronous speed; f = supply frequency & p = pairs of poles per phase. The actual running speed is the synchronous speed minus the slip speed.

For a 50 Hz three phase supply:

2 poles or 1 pair of poles = 3,000 RPM (minus the slip speed = about 2,750 RPM or 6 -7% n)
4 poles or 2 pairs of poles = 1,500 RPM
6 poles or 3 pairs of poles = 1,000 RPM
8 poles or 4 pairs of poles = 750 RPM
10 poles or 5 pairs of poles = 600 RPM
12 poles or 6 pairs of poles = 500 RPM
16 poles or 8 pairs of poles = 375 RPM

For a 60 Hz three phase supply:

2 poles or 1 pair of poles = 3,600 RPM (minus the slip speed = about 2,750 RPM or 6 -7% n)
4 poles or 2 pairs of poles = 1,800 RPM
6 poles or 3 pairs of poles = 1,200 RPM
8 poles or 4 pairs of poles = 900 RPM
10 poles or 5 pairs of poles = 720 RPM
12 poles or 6 pairs of poles = 600 RPM
16 poles or 8 pairs of poles = 450 RPM

To figure out the amount of poles, you are able to study the information plate straight or calculate it in the RPM stated around the information plate or you are able to count the coils and divide by three (poles per phase) or by six (pairs of poles per phase). Exactly where the energy from the induction motor is continuous, the torque increases in the price that the speed decreases.

Using the advent of variable frequency drive (VFD), you are able to have any frequency / rated volts you want. I frequently see name plates with issues like 575VAC, 42.five Hz and so on. When these "specials" are produced I generally see six pole machines - but that might be just a manufacturer's preference.