Månadsvis arkiv: juli 2016
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. Delta PLC 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 PLCs 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:
Size of Memory
Compatibility to HMI
Format of PLC
You can go away using the format of Little PLC 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 PLC Omron 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.
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.
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
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.
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 yaskawa servo driver. 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 panasonic 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:
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
Less than 20 VDC
20 to 50 VDC
50 to 100 VDC
100 to 180 VDC
180 VDC and up
Less than 1 amps
1 to 4 amps 4 to 8 amps
8 to 17 amps
17 amps and up
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
- 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.
- 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.
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.
A Variable Frequency Drive (VFD), sometimes referred to as a Variable Speed Drive (VSD), is a piece of equipment that regulates the speed and rotational force of an electric motor. By controlling the speed at which your applications operate, your business can save on energy costs and significantly reduce the amount of energy being consumed.
A Delta VFD may enhance the user’s profitability by improving the process, which in turn produces a fast return on investment (ROI). Process improvements may come from better:
Monitoring quality; and
Let’s examine some motor equations to understand how this works.
The governing formula for the no-load (synchronous speed) of an alternating current (ac) motor in revolutions per minute (rpm) is as follows:
rpm = (ac frequency, or Hz) x (60 sec/min) / (No. of motor pole pairs)
Since rpm are in units of minutes (rev/min), and frequency is in units of seconds (cycles/sec), seconds are converted to minutes by multiplying by 60 seconds/minute. The equation can be rewritten as:
rpm = (Hz) x (60 sec/min) / (No. of motor poles/2)
If both the denominator and numerator of the above equation are then multiplied by 2 and written without units, the equation becomes:
rpm = (Hz) x (120) / (No. of motor poles)
This really is the simplest type of the equation. The much more poles the motor has, the slower the RPM. Conversely, the fewer poles the motor has, the quicker the RPM. Also, because the electrical frequency decreases, the motor?ˉs speed (rpm) will reduce, and, as frequency increases, the motor’s speed increases.
Because it’s simpler to let electronic devices alter the frequency from the voltage coming to a motor than it’s to alter the amount of poles within the motor, vfd110b23a have gained growing recognition within the HVACR business. Numerous refrigeration, air conditioning, and heat pump compressors these days can employ electronic VFDs to differ the frequency feeding their electric motors.
VFDs function by converting the motor’s ac input to direct present (dc). In the direct present, the VFD will produce a simulated ac signal at varying frequencies (see Figure 1 above). The microprocessor controlling the VFD turns on and off the waveforms?ˉ good or unfavorable half. A greater output voltage materializes in the energy device remaining on longer. Conversely, the shorter the energy device is on, the reduce the output voltage will probably be. The switch frequency will be the speed at which the energy device switches on and off. Much more heat is generated within the energy device because the switch frequency increases, but there’s now much more resolution and smoothness within the output waveform.
As talked about earlier, motor speed is straight proportional towards the electrical frequency utilized by the motor. Consequently, by varying the frequency towards the compressor?ˉs motor, the compressor’s motor speed (and, therefore, the compressor capacity) may be controlled.
Usually, the VFD also features a backlit liquid crystal show (LCD) that shows a number of motor operational parameters which are totally programmable by the user. Solid-state devices just like the silicon controlled rectifier, triac, and insulated gate bipolar junction transistor have permitted the variable-frequency drive to turn out to be the technique of option for AC motor speed manage.
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. Delta 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 PLC Omron 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.
Variable frequency drives (VFDs) and electric motors are strange companions: The Delta VFD Drive 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 YASKAWA 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.