VFD Speed Commands

[ibanez243]

I am having trouble understaning speed setpoints to Variable drives. In Rslogix 5000 a computation is being done and then sent to the drives. For a power flex 70 the computation is the setpoint/32767 and for a powerflex 700 it is setpoint/15124. those computation are then distributed to the last byte of the output. Where do these numbers 32767 and 15124 come from and why are they different from model to model.
Thanks

 

[Roy Matson]

The numbers refer to the binary resolution. One Drive requires more bits to give full speed. I don't have access to the manuals, hopefully someone else will respond with a clearer answer.
Roy

 

[danny.michael]

For the PowerFlex 700 drive, the speed reference is 0-32767 representing either 0-Max Frequency or 0-Max Speed. The default is 0-Max Frequency and the default for Max Frequency is 130 Hz. So 0-15124 represents 0-60 Hz assuming the default parameters for Max Frequency and speed reference have not been changed.

I usually bring those parameters in and do the math so the reference will always represent the maximum speed I want even if the drive parameters are changed.

Not sure about the PF70. Haven't worked with one of those in a while.

 

[Roy Matson]

The numbers refer to the binary resolution. One Drive requires more bits to give full speed. I don't have access to the manuals, hopefully someone else will respond with a clearer answer.
Roy

There you go, thanks Danny

 

[blamb]

How are the drives connected to the PLC? Are the speed commands being sent to the drives using a communications protocol (modbus, devicenet, etc) or are you using an analog output module (current / voltage)?

 

[ibanez243]

I am connected using DeviceNet. I understand it now. thanks guys. .