PCI-7344 Servo Command Analog Ouput

[choijs]

Hi,
I am currently working on a project controlling several servos with PCI-7344.
Servo amplifiers are working with +/-10 V. But with the servo's direction command, the polarity of servo command decides the motor's rotation direction.
For an instance, with CCW direction, -10V means the maximum speed in reverse. and 0 means sero speed.
So the problem is how to configure DAC outputs to produce -10V and +10V for full speed and 0 for zero speed.

[KenSun]

Hi Choijs,

The DACs on the PCI-7344 are already configured to work in the mode you are describing when you are in servo mode.

When you specify a target position, and do a start motion, the controller will automatically output +10V which means maximum torque (acceleration) in one direction. And for a target position in the opposite direction, the controller will output -10V.

You should just configure the 7344 for servo control, and with proper external amplification, everything should work as you expect.

Ken Sun
Applications Engineer
National Instruments

[choijs]

Do you mean that a target postion 2000 will give as an output +10V and a target postion
-2000 will be an output -10V given the velocity as a maximum?

[KenSun]

Yes. Remeber, the output voltage is related to Acceleration and not velocity. So, at maximum constant velocity you should see output close to 0v. But during the ramp up and down you should see the maximum output.

[Cooper]

What if my drive is velocity only. I'm have trouble getting the thing to stop when a limit is made with out backing up after stopping. Plays havoc with wire tension that I'm winding.

[TCoupe]

I too need output voltage to be related to velocity. Can this be accomplished with the PCI-7344?

[Cooper]

You have to enable the secondary feedback to the same encoder as the primary feedback. I know it sound crazy but it works. I scared half the maintenance crew to death the first time I tried to run autotune. Then tune manually start with real low values like 1. One of the techs sent the attached file it helped. Oh I found a work around for my stopping problem I break the command line to my drive and have a 100k resistor shorting the command out that takes it to 0 volt and stoppes the motor. Of the hundred plus drive we have in this plant none use torque command. So much for Industry standard 🙂 Hope this help you.

[TCoupe]

Thanks for the info! I will give it a try and post if I have any more problems.

[Ben84170796]

Excuse me, I want to use the 7344 to output a stable positive voltage to a piezo controller, but according to what you said, the 7344 ouput voltage will only be more than zero in motor ramp up or ramp down period. How can I match the servo output voltage the fit my application?