How Variable Friquency Drive Work

The first stage of a VFD is the converter, which comprises six diodes, which are similar to check valves used in plumbing systems. These allow current to flow in only one direction; the direction shown by the arrow in the diode symbol. For example, whenever A-phase voltage (voltage is similar to pressure in plumbing systems) is more positive than B- or C-phase voltages, that diode opens and allows current to flow. When B phase becomes more positive than A phase, B-phase diode opens and A-phase diode closes. The same is true for the three diodes on the negative side of the bus. Thus, we get six current pulses as each diode opens and closes. This is called a 6-pulse VFD, which is the standard configuration for current VFDs. We can get rid of AC ripple on DC bus by adding a capacitor. A capacitor operates in a similar fashion to a reservoir or accumulator in a plumbing system. It absorbs AC ripple and delivers smooth DC voltage. The diode bridge converter that converts AC to DC is sometimes just referred to as a converter. The converter that converts DC back to AC is also a converter, but to distinguish it from the diode converter, it is usually referred to as an inverter. It has become common in the industry to refer to any DC-to-AC converter as an inverter. When we close one of the top switches in the inverter, that phase of the motor is connected to the positive DC bus and voltage on that phase becomes positive. When we close one of the bottom switches in the converter, that phase is connected to the negative DC bus and becomes negative. Thus, we can make any phase on the motor positive or negative at will and can thus generate any frequency that we want. So we can make any phase positive, negative or zero. Notice that, output from the VFD is a rectangular waveform. VFDs do not produce a sinusoidal output. This rectangular waveform would not be a good choice for a general-purpose distribution system, but is perfectly adequate for a motor. If we want to reduce motor frequency, we simply switch the inverter output transistors more slowly. But if we reduce frequency, we must also reduce voltage in order to maintain V/Hz ratio. Pulse width modulation (PWM) does this. Imagine, we could control the pressure in a water line by turning the valve on and off at high speed. While this would not be practical for plumbing systems, it works very well for VFDs. Notice that, during the first half-cycle, voltage is on half the time and off the rest. Thus, the average voltage is half of 480V, that is, 240V. By pulsing the output, we can achieve any average voltage on the output of the VFD.

3-Phase Induction Motors control Using PLC, VFD

Various automation processes in the industry need control of AC induction motors using AC drives. An electrical motor is an electromechanical device that converts electrical energy into mechanical energy. In case of 3-phase AC operation, the most-widely-used motor is the 3-phase induction motor as this type of motor does not require any starting device, being a self-starting motor.

 Delta’s AC motor drives are able to efficiently control motor speed, improve machine automation and save energy. Each drive in its variable frequency drive (VFD) series is designed to meet specific application needs. AC drives accurately control torque, smoothly handle increased load and provide numerous custom control and configuration operating modes. A VFD can be used to vary speed, direction and other parameters of a 3-phase motor.

We share some block diagram of system. We will study the same in our future post.

Testing of Mobile phone Speaker, Buzzer or Ringer

Speakers also known as earpiece is the device that allows the handset user to hear the other user during call conversations. While the Buzzer or a Ringer is the one that sends out the ringtone to be heared by the handset user.
Both Earpiece, buzzer or ringer are same speaker. It only varies the loudness of it sounds being produce.Ringer buzzer generates more loudness than the earpiece speaker.A speaker is a device that  converts electrical signal into sounds.
It is made by a magnetic wire winded into a coil and a metal piece of magnet.
below is an example oh how to test of a good and working speakers .

 Simply set the analog or digital multimeter to resistance scale or beep sound , and attach one probe to one the speakers terminal while tick tacking the other one unto it. A working speaker produce a crackling sounds with analog MM and the multi-tester pointer moves, while the a busted one will not and have no reading. Digital multimeter show a small resistance or give beep sound on either side connected.

 

Testing of Mobile Phone Microphone or Mouthpiece

Mobile phone microphone also known as mouthpiece is the one that intercepts the voice to transmit to other  mobile phone users. Without it or a defective one will result that the other user on a phone cannot hear the one with a defective microphone on its mobile phone handsets.
A microphone is made of an electrical magnetic wire shaped into a round coil with a magnet metal surrounds it,  the mechanical vibration  generated by it will then produce an electrical voltage signal.
Checking the microphone is also been so easy, Just set the analog or digital multimeter to resistance scale then attach both test probe to its terminal. A good sign of a working microphone tends to have a reading of about 1000 ohms and by changing the probe on mic terminal it shows open or 1 in digital multimeter.

Testing of Mobile Phone Battery Voltage

 

A  working battery voltage is approx. 3.7 volts DC,  below this voltage range the phone will not be power on. Checking the battery voltage by a digital multi-meter is so easy, just set  it to a DC range 20 volts then attach the both test probes to each corresponding polarity, Red probe to positive terminal, then black probe to negative battery terminal. Check the maximum battery voltage reading  3.7 volts. A battery voltage lower than 3.7 volts can power on the handsets but it shows Battery Low on a screen. A battery voltage lower than 2 to zero volts will hardly charge the phone and won't power up the phone.