26-05-2012, 10:10 AM
Control Arrangements for an AFD
[attachment=23079]
1. Local Control
In the picture above, an AFD, motor and conveyor are operated from
the keypad on the front of the drive. Local control of the AFD means that
operation of the AFD is completed strictly through the keypad on the front of
the drive, or Local Control Panel (LCP). An operator monitors the readings
and controls the AFD by using this keypad. Even if the keypad, LCP is
remotely mounted away from the drive, maximum of 3m (10’), the control
arrangement inside the program of the AFD is still considered as LOCAL.
Anytime LOCAL is seen in the program, please think KEYPAD.
2. Remote Control
Other arrangements are possible including remote signals. If there is
a problem and the conveyor must be stopped immediately, it would be
difficult to run back to the AFD to stop it. Stop switches can be placed at key
positions to stop the AFD, AC motor and conveyor. It is important that the
AFD accept these stop signals as well as other remote signals. These
remote control signals come in Four Types:
1) Digital Inputs (DI) are 2-position (ON/OFF) signals sent into the AFD.
These commands tell the AFD to Start/Stop, go Forward/Reverse, Jog or No
Jog, etc. A DI requires 24Vdc which is supplied by a terminal on the drive.
2) Analog Inputs (AI) are proportional or modulating signals sent into the
AFD. These commands tell the AFD what the reference speed should be or
tell the AFD what a feedback signal is doing such as pressure.
3) Analog Outputs (AO) are modulating signals sent by the AFD to a device
such as a meter which could display speed or current.
4) Digital/Relay Outputs (DO/RO) are 2-position (ON/OFF) signals sent by
the AFD to a device such as a light to indicate an Alarm, or when the AFD
has reached a certain speed or to a relay to remove the mechanical brake.
Digital Outputs have power 24Vdc already attached and Relay Outputs do
not have power also known as “dry” contacts.
3. Multi-Motor Operation
The multi-motor arrangement is usually done because of strict cost
considerations. Not only must the AFD have the current capacity for all the
motors, but each individual motor must have overload protection. In the
picture above, one AFD operates 3 AC motors, which in turn operates the 3
conveyors together. They operate at the same speed or close to the same
speed.
When this arrangement is used some AFD features are restricted.
First the motors and conveyors must all run at the same speed. Another
restriction is that the AFD can not be tuned to a individual motor. Motor
Tuning is where the AFD is tuned or matched to an individual motor for
better performance and energy saving. The last restriction given here is that
the slip compensation should be set in the OFF position.
[attachment=23079]
1. Local Control
In the picture above, an AFD, motor and conveyor are operated from
the keypad on the front of the drive. Local control of the AFD means that
operation of the AFD is completed strictly through the keypad on the front of
the drive, or Local Control Panel (LCP). An operator monitors the readings
and controls the AFD by using this keypad. Even if the keypad, LCP is
remotely mounted away from the drive, maximum of 3m (10’), the control
arrangement inside the program of the AFD is still considered as LOCAL.
Anytime LOCAL is seen in the program, please think KEYPAD.
2. Remote Control
Other arrangements are possible including remote signals. If there is
a problem and the conveyor must be stopped immediately, it would be
difficult to run back to the AFD to stop it. Stop switches can be placed at key
positions to stop the AFD, AC motor and conveyor. It is important that the
AFD accept these stop signals as well as other remote signals. These
remote control signals come in Four Types:
1) Digital Inputs (DI) are 2-position (ON/OFF) signals sent into the AFD.
These commands tell the AFD to Start/Stop, go Forward/Reverse, Jog or No
Jog, etc. A DI requires 24Vdc which is supplied by a terminal on the drive.
2) Analog Inputs (AI) are proportional or modulating signals sent into the
AFD. These commands tell the AFD what the reference speed should be or
tell the AFD what a feedback signal is doing such as pressure.
3) Analog Outputs (AO) are modulating signals sent by the AFD to a device
such as a meter which could display speed or current.
4) Digital/Relay Outputs (DO/RO) are 2-position (ON/OFF) signals sent by
the AFD to a device such as a light to indicate an Alarm, or when the AFD
has reached a certain speed or to a relay to remove the mechanical brake.
Digital Outputs have power 24Vdc already attached and Relay Outputs do
not have power also known as “dry” contacts.
3. Multi-Motor Operation
The multi-motor arrangement is usually done because of strict cost
considerations. Not only must the AFD have the current capacity for all the
motors, but each individual motor must have overload protection. In the
picture above, one AFD operates 3 AC motors, which in turn operates the 3
conveyors together. They operate at the same speed or close to the same
speed.
When this arrangement is used some AFD features are restricted.
First the motors and conveyors must all run at the same speed. Another
restriction is that the AFD can not be tuned to a individual motor. Motor
Tuning is where the AFD is tuned or matched to an individual motor for
better performance and energy saving. The last restriction given here is that
the slip compensation should be set in the OFF position.