Why do we use frequency inverters & PLCs together in a process ?

[phatcreators]

Why do we use frequency inverters & PLCs together in a process ?

What's the advantage & benefit of using frequency inverters whether servo or vector with PLCs ? Although PLCs are used to control the perimeters of the process or the entire process .

thanks in advance

 

[ALERTLINKS]

Freuency inverters, as indicated by its name converts mains frequency to required frequency. Ther are motors' whoes speed depnds upon frequency rather than voltage. So it is used to control speed of synchronus ac motors, PLC controls acordingly.

 

[phatcreators]

Freuency inverters, as indicated by its name converts mains frequency to required frequency. Ther are motors' whoes speed depnds upon frequency rather than voltage. So it is used to control speed of synchronus ac motors, PLC controls acordingly.

thanks for your reply

i mean to say , why not only VFDs controlling the motors ..... why PLC is also there ? What things are being controlled by PLC ?

 

[FvM]

I think, the answer depends on the processes you are considering. May be anything from a simple slurry pump on a farm up to a municipal water plant.

 

[ALERTLINKS]

What is a Variable Frequency Drive (VFD)? How Does a VFD Work?
See about VFD operator interface
Variable-frequency drive - Wikipedia, the free encyclopedia


PLC – VFD Comunication | Delta Automation Tips & Tricks

Most VFDs have digital, analog and communication interfaces you can use to exchange with an external controller. Digital signals will include for example Start, Stop, Rotation CW, Rotation CCW, Jog, Set Speed 1, Set Speed 2 (these Set Speeds are from the drives parameter set), drive status, alarms... Analog signals will include Speed Reference, Speed Feedback, motor current, voltage, DC bus voltage, RTD feedback...

Communication fieldbuses will give you both digital and analog signals, through Modbus, Profibus-DP, Ethernet/IP, ControlNet, and many others, depending on the manufacturer. And snce they allow multiple connections, you will save a lot on cabling, one cable from PLC to many drive nodes.

You have to check the protocol of VFD, then ask supplier of VFD to supply the related hardware and software. But ask your PLC supplier also.
The interface could be as simple as one wire for run, with a single preset speed in the drive... to analog signals for speed and/or torque control... to a comms bus as previously mentioned.
Of course, depending on the features of the drive, there may some digital interfaces available such as Allen-Bradley Remote I/O, DeviceNet or FieldBus. Depending on the application, you may still want an analog speed reference while using digital start/stop/status. For safety you will also want to use some sort of dry-contact Emergency stop.
Many VFDs are available with communication cards, so you may wish to communicate over Profibus, DeviceNet, etc. Without knowing more about your system and the type of PLC/VFD it would be difficult to provide a detailed solution.

PLC – VFD Example | Delta Automation Tips & Tricks