DRO readouts freezing when adding second scale

Hi all 🙂

I’m just setting up a DRO on my X1 milling machine and have finally got the second scale mounted … and whilst the DRO readout worked perfectly with the first scale, as soon as I added the second scale the readouts of both axes freeze / jitters by +/- 5um when the axes are moved.

If I unplug either of the linear scales the other one works just fine, which rules out an issue with either scale.

The DRO is by Vevor:

**LINK**

and the scales are by Warco:

**LINK**

Can anyone offer a suggestion as to what might be going wrong?

I’ve tried adding a ground wire from the DRO to the machine but it made no difference …

Many thanks for your help 🙂

David

Edited By David Hogg on 10/04/2022 13:12:27

Hi, David. FYI, you have accidently linked twice to the same site (Vevor).

Bill

Sounds like a power supply issue. Enough power to drive one readout properly but when the second one is added it can't supply either the voltage or current needed to run both.

As the scales work OK individually at least we can rule out socket pin out incompatibility. Unfortunately not all the 9 pin D connectors have the same layout.

Clive

Wild guessing:

• An earth loop. Unlikely I feel, but try dismounting the second-scale from the machine and laying it on an insulator to see if the two scales work OK. If they do, suspect hum from the machine being injected via the two mountings. Connecting the two mountings together so they are both at the same earth potential might fix it. (Note to electricians: earth loops degrade low voltage signals, electronics not electrical safety.)
• Scale and Read-out are incompatible. In the past DROs and scales had to be carefully matched because Tom, Dick and Harry all had different rules. I've read modern Chinese Glass Scales are mostly to the same standard, but I don't know if scales bought from Warco are good with a Vevor DRO. That they work at all is a very good sign, so I wonder if it's something silly like the DRO being set to 3.3V whilst the scale expects 5V. 3.3V might be enough to run one scale correctly, but two causes misbehaviour. Does the scale and DRO manuals say anything about signal and pin requirements, and do the DRO settings allow them to be changed to match the scale?

Dave

Thanks for the quick replies!

Sorry, here’s the correct link for the DRO scales:

**LINK**

I will check when I’m back home but I did look at the specs for the DRO and the scales before I connected them together, and the pin-outs and voltages all looked the same.

Thanks again and will report back 🙂

David

Are both scales the same resolution?

Howard - they’re both identical scales. The third one I’ll be fitting on the Z axis is the same brand but longer.

Thanks 🙂

David

Have you tried reversing the scale connections, x to y, y tox?

David - yes I’ve now tried all 3 scales on all 3 inputs, and on their own they all work fine.

I’ve done some more experimenting, and strangely, the 250mm scale that’s destined for the Z-axis works perfectly no matter what — whether it’s plugged in on its own, or whether one or more other scales are also plugged in, it always works. It was bought from the same page on the Warco website as the two 200mm scales, so the only difference should be the length … but something is obviously different otherwise it would also suffer the same freezing / jittery readout issue.

I’ve tried a few things including:

• Removing all the scales from the machine and laying them on wooden blocks — no difference.
• Checking the resolution setting of the DRO — 5um for each axis, the same as the linear scales
• Checking the pin outs for the DRO and scales — all match, with the same voltages
• Plugging each of the scales in on their own, in different sockets, and they always work flawlessly when they’re the only scale connected. As soon as a second or third scale is connected, neither of them work — unless one of them is the 250mm scale, which always works.
• Connecting a ground lead from the 4mm ground socket on the back of the DRO (marked PE?), and touching this to the suspect scale which is having reading issues … no difference.
• I’ve looked through the manuals of both the DRO and scales, and there aren’t any significant user-changeable options on the DRO such as changing the output voltage on the 9-pin connector, or changing the reading frequency, etc.

Also, on one of the reviews for the DRO someone said they got their scales from Warco and it worked fine, which is why I bought my scales there too…

One thing I did notice that may or may not be relevant, is that sometimes (not always), when you move one of the scales, the readout for one of the other connected scales (not the 250mm one though), jitters slightly as well. It’s as if there’s some cross-coupling interference between the two, which I imagine there shouldn’t be …

I’m at a bit of a loss what to try next, although I will be emailing the manufacturers of the DRO and scale tomorrow to see what they say.

Thanks for for your help!

David 🙂

Edited By David Hogg on 10/04/2022 20:08:10

Ship it all back to Warco!

The scales were from Warco but the screen was direct from Vevor … and although I’m not quite sure which is at fault, my money is on the DRO given that all the scales work fine on their own.

Have asked Vevor if I can send it back for a refund …

Cheers!

David

Can you get Warco to check the scales for you? Or better still someone local to check the scales with their readout although you is need to be sure they don’t melds up someone’s readouts.

Warco someone might do a cheap compatible box/ you could buy to test the scales?

Both Warco and Vevor sell Scales and DRO packaged together, and if David had bought one of them this malfunction would clearly be a fault.

But as far as I can see Warco don't claim their scales are Vevor compatible, and Vevor don't claim their DRO works with Warco Scales. (Warco do mention Easson.)

Both could be in working order, but not together, like refueling a petrol car with diesel.

However, David's symptoms suggest the Vevor DRO is faulty: it very nearly works properly, suggesting the scales are compatible and measuring correctly. I doubt there will be any quibble if he sends the DRO back, just saying it only works on 1 axis.

Dave

I'm very pleased (and relieved) to say that Warco's DRO arrived today and all 3 scales work perfectly with it!

https://www.warco.co.uk/digital-readouts-scales-dro/303110-warco-digital-readout-dro-display-counters.html

Moral of the story ... don't buy cheap Chinese-made junk! Buy more expensive Chinese-made ... equipment ... that at least has a known manufacturer's sticker on it!  The Warco DRO also feels more sturdy as the housing is metal too ...

I've not kept the packaging of the Vevor DRO so I'm not sure if they'll take it back now ... but I've asked the question.

Now to get the Z-axis scale and the additional quill readout mounted!

Thanks again for your help everyone, it's so appreciated,

David

Edited By David Hogg on 13/04/2022 20:21:36

Hi everyone,

So Vevor have refunded me £30 of the £51 total cost as I guess it was too long since I bought it … anyone want a slightly suspect cheap DRO for parts? 😆

Cheers!

David

Hi David

As a retire electronics design engineer I wouldn't mind checking it out to see if the unit has a fault or is not correctly designed.

CS

Hi David,

look in your inbox please?

Roger

Thanks for your messages! Clive was first so I will offer it to him first 🙂

David