Powerflex 40 stumped me! 1

[pooslinger]

I have a AB powerflex 40 VFD that is running a belt. The Operator controls the speed of this belt with a dial that inputs a analog 0-10v into the analog input of the drive. The drive is terminated with the factory jumper at the "stop" input, and the start input is run thru an auxilary contact from the motor starter that is between the drive and the motor. No other digital inputs are used. This thing drops to 5htz randomaly with out a fault. And then comes back to the desired speed just as randomaly as it went out. My analog is good and I have 24v at the start input. Has anybody experenced this and can tell me what the heck is going on?

 

[itsmoked]

The first thing I though as I read your post was 0-10V.. Yuck. Fairly easy for noise to pollute that form of input.

5Hz is about 3/4V variation.
You could have a dirty pot.
The pot could be under-rated.
The pot could be coarsely wound and be vibrating between winds.
If you aren't using a pot you could be having a ground loop problem.
Or a strong local radio source could be imposing a voltage onto the control wires when say, a hand radio is transmitting.

Are the 0-10V lines properly twisted?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[ozmosis]

As a quick test, do you have a keypad on your PF40 VFD? If yes and there is a facility to operate the drive from the keypad, do that. If the drive still drops to 5Hz, then you know it is something other than the AIN.

 

[jraef]

Also, 5Hz is a very typical default speed for a VFD to go to on "loss of input signal", often programmed as the "Jog" speed. On some drives, that is the default programming so if you did not change it, that may explain why this is happening. For instance if you have a bad wiper on the pot or a circuit with intermittent conductivity, it might be defaulting to that Jog speed because it was not reprogrammed otherwise.

 

[pooslinger]

Thanks for your help. It was a odd analog converter that was between the Operators hand held control box and the VFD. Who ever designed this should be shunned.

 

[LionelHutz]

^- I like this answer. However, I'm not sure it applies to a 0-10V input because a loss of signal will produce 0V input and the drive doesn't know if it's being given a minimum speed signal or if it's lost it's signal. Now, with 4-20mA it for sure knows the signal is lost because a bad connection gives a 0mA input while the minimum speed signal would be 4mA.

I'd be more likely to say the drive is set to a minimum operating speed of 5hz and that the analog is being lost giving a 0V input which tells it to run at 5hz.

 

[pooslinger]

That wasen't the case. The minium speed of the unit was 0 tz. 0v = 0 Htz. This unit was a tempory portable processing machine brought in by a outside contractor. If it was owned by this plant, it would of been 4-20mA. Thanks for the tip!