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iGaging EZ View interferince
#1
I'm trying to fix my interferince problem with the EZ View scales. 

My lathe is 3 phase and I have a Hitachi VFD.

If I use the iGaging display head with internal batteries, there isn't any interferince from the running motor. Tried a wall power supply, but got interferince from it. I did have to electically isolate the scale from the lathe, so I 3D printed mounting blocks to prevent a ground loop.

OK, now I have a working baseline, on to the Touch DRO. 

Tried the Touch DRO and a wall power transformer, with the scale isolated from the lathe, and get interferince..
Swapped the transformer for a 7.2volt LiPo battery, and still got motor interferince. 

Next, I pulled the cable from the scale to measure what I could with a breakout on the end. 

The cable is not ground shielded, as expected. The metal plugs on both ends aren't connected to each other or ground.
With the cable plugged only  into the EZ View display, I measured 3.0 volts on vcc to ground, and 2.7 volts on D+ to ground. 
With only one end of the cable plugged into the Touch DRO, I measured 3.3 volts on vcc to ground and nothing on D+ to ground.
The vcc to ground differences are due to the EZ View being on batteries. 

OK, now my questions and confusion. 

1. If the EZ view works perfectly when on batteries with the scale isolated from the lathe, 
why doesn't the Touch DRO work on a battery with the same scale and on the same cable? 
2. The only difference I could find is that the EZ View shows voltage on the D+ to ground while the Touch DRO does not. How is that voltage being used? 

I haven't put a capacitor in the scale, since no capacitor works fine with the EZ View display. I don't understand how it would make a difference, any thoughts? 

TIA, 
Rick
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#2
Rick,
What kind of interference are you seeing? Resets, position jumps, or something else?
Did you build the adapter board or are you using one of the pre-made ones?
Regards
Yuriy
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#3
Yuriy,
Thanks for the quick reply. I bought the Touch DRO iGaging board from your store in late October. The interference I'm seeing is changes in the readings from tenths to whole inches, both up and down bounces. As long as the motor is off, it is stable. The VFD can be on, it jumps when I run the motor, not just starting it. The VFD is at the motor end of he lathe, I've moved the Touch DRO as far as possible to the other end, about 6 feet away, with no change.

Rick
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#4
Rick,
The circuit in the EZ-View head is different from TouchDRO. They might be using different value bypass capacitors, etc. and thus might be insensitive to your VFD's particular frequency. Moreover, iGaging display averages a LOT of values to get rid of the last digit flicker, so it could be simply masking the issue. Do you see any difference if you enable/disable digital filter in the app?
I have four VFDs in my garage (two Allen Bardy's and two Teco's) and don't see that much interference. Is the VFD grounded correctly? What is the carrier frequency?
Regards
Yuriy
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#5
Yuriy,
The TouchDRO digital filter is enabled, it has no effect. The VFD is a Hitachi WJ200-015SF with the carrier frequency set at 12kHz. It is grounded and wired into the power panel correctly, as the lathe motor and bed are also bonded and grounded.

I'm going to add a capacitor to the scale, and I'll post back what happens. BTW, I got the EZ-View scales from Taylor Tool Works on eBay in October when I ordered the TouchDRO from your store.

Rick
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