what is motion operated pot?

[unsaint32]

I am a newbie studying VFD. Can someone tell me what "MOP: Motor operated potentiometer is and how it is used? I did my share of looking up online but just cannot find the answer. Thanks.

 

[rdrast]

A classic MOP is exactly that, a potentiometer connected to a motor so it can be adjusted remotely via simple switches for increase and decrease. They inherently provide a ramp function, adjustable with the gearing reduction on the motor head.

In more recent times, the motor and the potentiometer have been eliminated, and electronic circuits are used to provide the same function. For the generic electronic ones, you have an analog output, and several digital inputs to raise or lower the output.

For electronic circuits, the output is generally a voltage, but could also be a current signal.

The advantage of an actual motor operated pot over most electronic versions, is that it can be actually placed in a circuit to affect it's operation; ie, it isn't limited to just providing a voltage (or current) output, it can actually be used as a variable resistor.

Mechanical MOP's generally hold their last setting when power is interrupted, electronic ones may or may not.

 

[unsaint32]

A classic MOP is exactly that, a potentiometer connected to a motor so it can be adjusted remotely via simple switches for increase and decrease. They inherently provide a ramp function, adjustable with the gearing reduction on the motor head.

In more recent times, the motor and the potentiometer have been eliminated, and electronic circuits are used to provide the same function. For the generic electronic ones, you have an analog output, and several digital inputs to raise or lower the output.

For electronic circuits, the output is generally a voltage, but could also be a current signal.

The advantage of an actual motor operated pot over most electronic versions, is that it can be actually placed in a circuit to affect it's operation; ie, it isn't limited to just providing a voltage (or current) output, it can actually be used as a variable resistor.

Mechanical MOP's generally hold their last setting when power is interrupted, electronic ones may or may not.

so, it's another AO source.
I still don't understand Powerflex 70 Parameter#11 MOP FREQUENCY: Value of the signal at MOP in Hz or RPM.

 

[rdrast]

That is just an electronic MOP built into the drive.

Rather then having a speed pot, you can have one or more sets of "Speed Increase" / "Speed Decrease" pushbuttons along a machine, and use the drive's MOP function to set it's speed (or torque, or whatever).

The MOP buttons can either be configured to only increase/decrease "X" amount each push, or linearly ramp up or down if they are held.

 

[unsaint32]

That is just an electronic MOP built into the drive.

Rather then having a speed pot, you can have one or more sets of "Speed Increase" / "Speed Decrease" pushbuttons along a machine, and use the drive's MOP function to set it's speed (or torque, or whatever).

The MOP buttons can either be configured to only increase/decrease "X" amount each push, or linearly ramp up or down if they are held.

Ok, so is it an AI to the drive, or is it an AO from the drive? If it is an AI to the drive, then why is the pot called "motor operated pot," when a pushbutton operates the pot? An,d are the pushbuttons the up and down arrows on the drive's keypads or HIM?

 

[JRW]

I hope this software diagram helps. Its internal in the drive
The mop raise and lower are digital inputs
R1050 to the right is the speed or whatever value out of the mop
Like RD said- you can parallel inputs and the operator can raise or lower line speed anywhere around the machine.
Having multiply speed pots around the machine would be difficult...right?
This is a Siemens diagram but it should help you understand-

 

[lostcontrol]

So, it is an AI.
Thanks anyway. It clears a lot of confusion.

NO, NO, NO.

As others have said, it is an internally generated speed references, that can be controlled via digital buttons rather than a dial.

Reason it would of been called Motorised Pot is that is replicates what a traditional motorised pot would of done.

 

[unsaint32]

NO, NO, NO.

As others have said, it is an internally generated speed references, that can be controlled via digital buttons rather than a dial.

Reason it would of been called Motorised Pot is that is replicates what a traditional motorised pot would of done.

Are the digital buttons (for the MOP) the the up down arrows on the HIM? Or are they external push buttons that can be wired to certain terminals on the drive?

 

[alan_505]

Are the digital buttons (for the MOP) the the up down arrows on the HIM? Or are they external push buttons that can be wired to certain terminals on the drive?

It depends on how the drive is configured.

 

[Lancie1]

Are the digital buttons (for the MOP) the the up down arrows on the HIM? Or are they external push buttons that can be wired to certain terminals on the drive?

There could be digitial external Up/Down buttons wired to Powerflex 70 programmable terminal blocks, or any SCANport DPI adapter can be used as a MOP control (including a HIM). Parameter 284 MOP Mask sets which adapters are enabled to issue MOP commands to the drive.

 

[DickDV]

Wow! This doesn't need to be that complicated. MOP is simply a way of providing speed control for a VFD or DC drive that uses two digital inputs, one to increase the speed setpoint and one to decrease it. That way you don't need any analog speed input. As mentioned, many VFD keypads have a form of MOP with two pushbuttons on the keypad, again, one for increase speed and one for decrease.

There are several handy uses for MOP control but, in my view, the two most important are: first, if you have several operator locations which need full control of speed, you can wire the increase and decrease speed pushbuttons in parallel for each operator station; second, if the VFD is controlled by a PLC, it avoids the need for an expensive analog output module, instead using two relay outputs for the speed control.

The term "Motor Operated Pot" may mean something to us oldtimers but it is largely useless for communicating function to today's crop of techies. That's why some VFD manufacturers have chosen to describe this type of speed control as "Floating Point" control or maybe other similar titles.