Yaskawa Drive Fault

[The Plc Kid]

I have a yaskawa drive that faults every half hour with a pg error as described on page 58 of the manual here http://www.yaskawa.com/site/dmsearch.nsf/sitesearch?openagent&query=(676vg3)

It says to check PG cable with this fault?

Does anyone know what PG is? Is it just a yaskawa thing or industry standard?

Does anyone know what may cause this fault? Line voltages look fine?

The drive is a varispeed-676VG3

 

[just_lionel]

PG is Pulse Generator.

 

[panic mode]

what is the error code?
LF = your motor wiring has loose contact
S_E = wrong torque limit, servo load way too large or PG signal problem

PG (pulse generator) is what ever sends pulse train to amplifier (probably PLC high speed output).
you want any high speed signals shielded, wiring length kept short (few feet, not few miles),
routed away from sources of noise (any power switching device - specially the fast ones like
power supplies, VFD or servo drives etc.)

S_E could indicate things like:
- loose wiring in PG circuit (could be also internal to components such as PLC or drive),
- improper or missing shielding of the PG signals (don't strip more than 2" of shield, sink to ground only one end etc.)
- poor routing of the PG signals (drive picking up noise)
etc.

 

[leitmotif]

How are the motor conductors and sensor conductors run? All in the same conduit and or cable assembly? Laid in cabe tray together? Are sensor cable(s) run with a separation from any power conductors? What is distance from VFD to motor?

Is sensor grounded internally or is it completely isolated from ground?
Is it firmly mounted to not vibrate or flex with shaft rotation?

Dan Bentler

 

[The Plc Kid]

The error is Pg cable fault. It is about 15 feet from the motor to the drive.

Has a sturdy 3 point mount to the motor.

I just never knew pg stood for encoder.

 

[LadderLogic]

I just never knew pg stood for encoder.

You may encounter all kinds of strange things when dealing with English manuals translated from Japanese. I have already used to follow Yaskawa's idea to call homing 'origin search'.

Not that it is incorrect - actually it is very precise term. But it seemed unusual at the beginning. Same is here: an encoder (in most cases) generates pulses - so why not call it a 'pulse generator'?

 

[leitmotif]

Kid
OK sounds like encoder is not jiggling around so that may be OK

Check to see that your encoder cable or wiring is not in close proximity to any power wiring ie if in cable tray separated by six inches or more.

Check to ensure shield is grounded at only one end. Lift shield and check to ground you should get infinity - if not you may have a ground loop problem.

Hmmm faults every half hour or so. LONG SHOT is there something else that is starting at the same time it faults? I hate these they can be hard to find - much easier when they break and stay broke.

How old is encoder is it heating up - indicating bad bearing etc?

Check to ensure all conductors from encoder are properly terminated.

Does it reset right away or do you have to wait for a while?

Dan Bentler

 

[keithkyll]

Put a 'scope on the encoder pulses. Is it an optical encoder?
1) Weak LED'S (need to get in to encoder to monitor analog signals - need datasheet).
2) Dirty wheel (oil film). Clean with Isopropyl Alcohol.
3) Weak pulses. Should be 5 volts. 3 volts or less will cause intermittent problems.
4) Weak power supply feeding encoder.
5) VFD has intermittent input electronics.

Can you speed up the motor temporarily? This might expose a weakness making it easier to troubleshoot.

 

[TheStarr]

Never worked on Yaskawa drives, but have dealt with Motoman Robots and Amps. One thing I have found is that they are very sensetive to overheating due to dirty fan filters or dirt coating the internal components.

We get all kinds of strange faults when the filters are not kept extra clean. Once a year, or so, we even open up the boxes and vacuum/compressed air clean out the internal components.

 

[The Plc Kid]

It has not done it today so far so i am waiting for it to rear it's head again.

Dan should the shield be grounded to the encoder housing or in the cabinet? I will have to try and find a data sheet on the encoder to see if it shows but i will lift in the cabinet and take a measurement to ground.

This is a winder app so i can run the drive at a higher speed with no product but that one will be hard to shut down as it is the big money maker running right now.

Thanks for the ideas guy's

 

[leitmotif]

It has not done it today so far so i am waiting for it to rear it's head again.

Dan should the shield be grounded to the encoder housing or in the cabinet? I will have to try and find a data sheet on the encoder to see if it shows but i will lift in the cabinet and take a measurement to ground.

This is a winder app so i can run the drive at a higher speed with no product but that one will be hard to shut down as it is the big money maker running right now.

Thanks for the ideas guy's

Kid

The rule is to ground only one end of a shield to prevent ground loops.

As to which end
I am not POSITIVE if it makes a difference which end you ground at provided shield is adequately bled to ground.

The common practice is to ground at the receiver end (sensor would be transmitter end).

My guess is this has come about as a result that that is the only end that has conductors left to be terminated - at sensor end they are already terminated so no one messes with them especially if the unit is encapsulated.

Dan Bentler

 

[keithkyll]

Think of it like this, and you'll never wire it wrong:
The shield is a resistor. The outside surface is bombarded with RF. RF is at it's maximum potential at the floating end, and zero volts at the grounded end.
Ground both ends, and RF is at it's maximum potential in the middle of the cable.

 

[The Plc Kid]

So i want max potential at the drive/encoder end and not at the drive itself?

Correct?

 

[keithkyll]

Correct.

 

[TheStarr]

The true reason to only ground one end is to avoid "ground loops".

This is where a current is passed along the shield because it is connected at both ends and is therefore a complete circuit between two different sections of the machine that may have different potentials.

The magnetic field induced from the current flowing through the ground loop could cause more interference then using no shield at all.

Actually, having it grounded at only one end is WORSE for blocking RF, but the negative impact of potential ground loops is a bigger risk, so we only ground one end.

Here is a good explanation: http://www.epanorama.net/documents/groundloop/cable_shielding.html