OT: 24v Noise

I've been having some wierd problems, with a unidrive servo, that keeps pointing back to noise on the control wires. I've isolated the lines, from anything, AC, and I'm still having problems. What do you guys reccomend for suppressing noise, on a 24VDC system.....

-Mur

I would look and make sure all shield wires are gounded to the same point
(no ground loops), check and make sure you don't have a flaky 24 volt power supply If you can isoltae the servo drive control wires from the rest of the circuit and power it from a seperate supply see if the noise still exists (trying to isolate noise thru crosstalk). If no noise then place on original power supply one by one hook up and power all other 24 volt devices and try to run what you can (attempting to isolate the noise source) Another possibility is the 24 volt supply is getting noise thru switch action Ie electro mechanical relays if all else fails try to add shielding (conduit, metal raceway etc)
edit almost forgot I would try a different drive and motor to make sure its not generated from either component

Does your servo have a 0-10 volt input, and is that where the noise is manifesting itself?
Add a .1uF monolythic ceramic cap across the 10 volt input screws at the servo.
Make sure control wire shield is grounded at the servo, and floating at the source (PLC Analog output card). Noise is RF. With one end of the cox floating, you have maximum RF signal at the float end, and zero RF at the grounded end.
Try running the control cable through a ferrite core (donut). At low frequencies, you will need 2 or 3 loops.

Return lines have resistance. During a solenoid or stepper motor event, the voltage can be a few volts above ground for several milliseconds on the return line. If this is the case, increase the diameter of the wire. Make sure nothing else is 'sharing' this 24VDC return wire on it's way back to the 24DC supply.

For grounds, establish one point as the 'zero-voltage' point. From here, understand that all metal has resistance. Noise will take the shortest path to the 'zero-point'. Is the shield or return of your control wires in this path?

I've also seen poor neutral bonds cause some intereting noise issues one way to test that is to do a neutral to ground voltage check there should be no voltage do this on the 120 volt supply and the 24 volt supply. Also check and make sure all connections are tight.

mordred said:

I would look and make sure all shield wires are gounded to the same point
(no ground loops), check and make sure you don't have a flaky 24 volt power supply If you can isoltae the servo drive control wires from the rest of the circuit and power it from a seperate supply see if the noise still exists (trying to isolate noise thru crosstalk). If no noise then place on original power supply one by one hook up and power all other 24 volt devices and try to run what you can (attempting to isolate the noise source) Another possibility is the 24 volt supply is getting noise thru switch action Ie electro mechanical relays if all else fails try to add shielding (conduit, metal raceway etc)
edit almost forgot I would try a different drive and motor to make sure its not generated from either component

Click to expand...

I do have the 24 Volts seperate from the rest of the system.... I'm using the supply from the Unidrive, for all it's inputs, and using relays, to send the discrete command signals. I did find one input, that was firing, when a relay closed, even though the supply was open through a switch, to shut off that function.... I solved this, by grounding the input, when the switch is in the off position. But I recently started having problems with noise on a wire for a prox switch causing problems when the prox was off (getting a false true signal for a cancel) In many of the panels, we do have 110VAC, but in the one, the only AC is the 480 to power the drive. I have also made sure that the 24V is not routed near AC as much as possible.

Thanks for the help,

-MUR

Sorry Kieth, I guess I should have been more specific....

I am using discrete signals to command a program in a Control Techniques Unidrive (positions and speeds are updated through the network). I am using the 24V supply from the drive, and have kept it seperate from the other 24V systems in the cabinet (relays or sensors start or stop movement. To be honest, I have never had a problem with false true signals on a 24V system... Lower votages perhaps. I didn't know, if a cap or a resistor between each of the inputs and ground would be best. I also didn't ground the common to the cabinet at all, as I have had problems with ground noise before on lower volt systems, would this be recommended first perhaps?

Thanks

-Mur

mordred said:

I've also seen poor neutral bonds cause some intereting noise issues one way to test that is to do a neutral to ground voltage check there should be no voltage do this on the 120 volt supply and the 24 volt supply. Also check and make sure all connections are tight.

Click to expand...

The 24V supply is from the drive, and I have checked it, and it seems solid.... the unidrive appears to only need a couple of volts to turn on, though, which seems to be causing problems.

-Mur

Brijm,

I did not sleep at a Holiday Inn last night. So here goes what might be nothing.

Does your 480 system have a solid ground wye connected neutral? If it doesn't, and if you have exhausted all the "cheap" options maybe you should look at getting a "drive isolation transformer". These transformers have wye connected secondarys that you can ground. Some servo drives make a lot of noise. The noise wants to go back to where it came from (secondary winding on the transformer). If you have one of those floating delta systems the noise can't get back to the source so it goes where ever. Possibly in your case the controls.

I have resolved similar problems on a servo controller by using "quench-arc" surge suppressors. My servo controller had very high speed inputs that would detect even extremely short duration noise spikes and consider them to be true inputs for things like the Home Prox and registration sensors. I can't recall the specific part number we used but it was largely successful.

Daft question but they are the ones that some times work, is the earth screw in the drive connected to earth (ground) If not it may be worth a try