# VFD terminology

E

#### engineer

hi,

what does the reference mean in VFD terminology? as i know, it's the external command the VFD is getting in the remote mode, something between 4-20mA.

R

#### Rob

Target Speed (a bit like "Setpoint")

D

#### driveguy

The "reference" is what the drive "refers" to for a particular input. In the drive world, usually this is means a speed or torque reference i.e. the setpoint that the ramp/PID's should attempt to maintain at etc. You mention remote and 4-20mA as a reference, while this is true you can also have a WIDE variety of places a reference can come from such as: analog inputs (Voltage or Current), communication bus (e.g. Ethernet), an internal preset (which may be digitally selected somehow), or even a local setpoint from a keypad right on the drive etc.

I also note you use the word "command" remember that a reference is a command, i.e. just because you are commanding the drive to do something doesn't mean it can't be overridden by something else... there may be other logic that is not allowing the reference to be followed like you think it should.