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Mitutoyo DRO Fault

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Brian H16/11/2019 15:44:18
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1288 forum posts
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I have a Tom Senior Major milling machine with 2 axis DRO. One of the scales is not working but If I swap the inputs for X & Y then I get a reading which indicates to me that one of the amplifiers is not working.

However, operating the metric/inch button shows that the display is changing.

Can anyone suggest what might be wrong?

Brian

Brian Wood16/11/2019 18:04:09
2008 forum posts
37 photos

Brian,

I am a bit confused in my interpretation of your testing analysis. I am just a simple soul really!

If you take the X channel for example, does that give a different reading [as it should] when the X position is changed? And then, with the X input transferred to Y channel, do you still get another series of results that change as one expects? If so, the scale and reader are both good as well as the display.

Taking the same two tests but now using the Y channel instead. if the scale or reader are faulty then the same fault condition will be seen on either test.

I think you will be able to establish by these means whether a scale or reader are at fault and which one or whether the fault lies in one of the amplifiers in the readout

Spare ;parts like scale and/or readers may still be available from Mitutoyo. The display module too perhaps, but that is likely to be expensive.

Regards Brian

Brian H16/11/2019 18:53:59
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Thanks for the reply Brian and sorry if I confused you.

This DRO uses a separate amplifier for each channel, with it's own connection to the scale, i.e. the parts fastened to the milling machine tables.

The X axis shows no change, just a series of zeros . The Y axis works as expected.

I tried swapping the connections to the amplifiers and this confirmed that the scales were working so the fault must lie with the X axis amplifier.

I tried swapping the amplifiers and this confirms that the X axis amplifier is not working, but some of it is! If I press the metric inch button then the number of displayed digits alters on both displays.

Brian

Ian P16/11/2019 19:41:17
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2248 forum posts
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'Amplifier' is not a term that is normally used to denote part of a DRO system so interpreting your fault description is all the more confusing.

To clarify, There are two scales with their reader heads they are usually electronically identical to each other and only become X and Y when fastened to slides etc. The same applies to the readout/display unit which again usually has identical electronic channels but just labeled X and Y on the panel.

If you connect the lead from ONE scale and try it in both the display inputs do both displays work correctly?

Let us know and we can move on.

Ian P

Brian H16/11/2019 19:56:13
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1288 forum posts
99 photos

Thanks Ian, I used the term 'amplifier' because that's what Mitutoyo calls them but sorry if it's confusing.

Yes, If I connect one of the leads to the display input, then only one of the displays shows a reading that changes with moving the table. If I connect the other lead to the display input then same result, leading me to believe that both scales are fine but one of the display inputs is not. By the way, the scales are glass.

Brian

Ian P16/11/2019 20:50:28
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2248 forum posts
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I am not familiar with Mitutoyo DROs but I understand now that one channel of your display unit is not working (it lights up but does not change readings with a good scale connected to it. If I understand you also said you can switch units on that channel but it just remains at zero. Most likely then the fault is (electrically) near the input connector and the counting and display part of the signal chain is OK.

From an electronic engineers point of view having a fault on one channel of a two channel system helps significantly in diagnosing the fault, It could be as simple as a dodgy connector pin, or that the voltage supply that powers the scale is not present. It might be worth measuring and comparing the voltage on the same pins of both connector. I would expect one pin on each connector to have 5 volts as that is commonly used for optical scales.

Ian P

Michael Gilligan16/11/2019 22:27:23
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14244 forum posts
627 photos
Posted by Brian H on 16/11/2019 19:56:13:

.

Thanks Ian, I used the term 'amplifier' because that's what Mitutoyo calls them […]

.

Intrigued by that revelation, I found this document: **LINK**

https://www.mitutoyo.com/wp-content/uploads/2016/08/H-section.pdf

 

Which incidentally includes this gem, on page H-15

*1: The exact value is 0.0048828125μm since the 20μm signal is divided by 4096.

Humbling, is it not ?

MichaelG.

.

Edit: If all else fails, it might be worth trying here

https://www.gtprecision.co.uk/digital-readout-systems.php

 

Edited By Michael Gilligan on 16/11/2019 22:31:00

Ian P16/11/2019 22:46:10
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All the Mitutoyo resolution measurements are shown in the form of 0.0(and whatever) with the suffix um. (I dont know the ascii code for the micro symbol).

Is the suffix irrelevant, or should it just be 'm'?

I find it hard to believe that the resolution of some models is a 1000th of a micron

Ian P

Les Jones 117/11/2019 09:03:59
2097 forum posts
144 photos

In your first post I got the impression that each scale connected directly to the DRO (The unit with with the displays for the 2 or 3 axis's and the buttons for setting zero points etc.) I interpreted your use of the word amplifier as the internal circuits on the DRO that convert the signals from the scales to the logic levels that connect to the internal micro controller. I am assuming the scales are glass quadrature scales with 2 or possibly 3 output signals that are either sine wave or square wave. Are you now saying that the output of each scale goes via an "amplifier" before feeding the inputs on the DRO. Can you clarify how things are connected together with a block diagram.

Les.

Brian H17/11/2019 10:16:02
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1288 forum posts
99 photos

Hello again Les & thanks for the message.

I thought that a couple of pictures might be appropriate here.

The first one is the back of the display unit (which is 2 axis) and the 2nd one is of one of the amplifier units. There are 2 inputs on the back of each one and the difference is the resolution of the scale.

Thanks for all help

Brian

p1190974.jpg

p1190975.jpg

Stuart Bridger17/11/2019 10:31:38
362 forum posts
23 photos

Having the modular amplifiers should help in diagnosing the location of the fault.
I suspect that you should be able to just swap the ampliifiers between slots.

So take one scale input (you know these are good) plug into each amplifier in turn. Then swap the amplifier modules between slots ans see if the fault stays with the slot or moves with the amplifier.

While you are at it, it would be worth reseating the connectors from the back panel to the PCB and also give the edge connector a clean

Les Jones 117/11/2019 10:36:36
2097 forum posts
144 photos

My understanding is that you have swapped over the two cable connections at the top right and this proved that both scales work on one of the inputs but neither works on the other input. You should now be able to prove it the fault is one of the "amplifiers" or deeper inside the DRO by swapping the positions of the "amplifiers" in the DRO. So does it always fail with the top position (For example.) or does it always fail with the "amplifier" that WAS in the top position (For example.) ?

Les.

Brian H17/11/2019 11:10:00
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1288 forum posts
99 photos

I have swapped over the plugs and find that the display that previously worked, now doesn't and the one that previously didn't work, now does.

I then swapped the actual amplifiers with similar results so to me, that would indicate a fault with some part of the amplifier but not a total failure because switching from metric to inches results in the correct number of digits and even the decimal point changes position correctly. There is a switch on the back of the unit that changes from 'Normal' to 'Diameter' and when switched to 'Diameter', both displays show a small 'D' at top left.

Hope that helps

Brian

Edited By Brian H on 17/11/2019 11:16:30

SillyOldDuffer17/11/2019 14:13:20
4843 forum posts
1018 photos
Posted by Brian H on 17/11/2019 11:10:00:

I have swapped over the plugs and find that the display that previously worked, now doesn't and the one that previously didn't work, now does.

...

Hope that helps

Maybe. It suggests a cable or connector fault to me rather than electronic trouble.

No disrespect but the style and condition of the unit hint that it's been round the Sun a good few times since it was new! The problem may be dirt, corrosion or ageing of a joint that wasn't quite perfect on day one.

As the plugs and cables are proper armoured industrial gear, I think it unlikely anything has given way internally inside them, though dry-joints are always possible. Solder joints in electronics should be shiny silver, never grey and crystalline looking. Any crystalline joints should be remelted with a dab of fresh solder. A bad case might need to be de-soldered so the metal underneath can be cleaned before the joint can be remade properly.

Rather more likely is dirt and corrosion on the male and female parts of connectors causing intermittent or broken connections. Sometimes it's enough to recover metal to metal contact just by removing and replacing plugs a few times but I'd clean the whole lot carefully with q-tips and switch cleaner. Not just the panel connectors but the metal innards of the plastic plugs and sockets on the board as well, plus the board's gold-plated contacts on the other side.

Although the electronics are in a proper box, it's also possible that decades of dirt or a barely visible whisker of swarf has managed to bridge a track on the board. Again, a gentle polish of both sides of the board with switch cleaner might clear it.

Dave

Dave Halford17/11/2019 14:57:40
489 forum posts
4 photos

Brian,

Given you now say swapping the plugs swaps the fault proves the display unit is good.

That leaves you with a broken wire or a dead bulb or led in the scale or SOD's suggestion a dirty plug.

If this machine is new to you it's possible someone has stressed the lead during transport or removal, if you have had it some time then the lead is probably fine.

You can normally remove the end of a scale and slide the read head out. If the scale or head is gunged up with oil, then it may only need a simple clean with meths. The head has a lens that focus's the light ( visible or IR) onto the reader so both the lens and the reader must be clean as well as the glass scale.

Dave

Les Jones 117/11/2019 16:02:59
2097 forum posts
144 photos

Your description " with similar results " is not clear. If you have proved that one of the "amplifiers" does not work in either position with either scales then that "amplifier" is faulty. Conversely I assume the other "amplifier" works in either position with either scale. I don't think the fact that the display will change between metric and imperial indicates anything about the "amplifiers" Even if you had a schematic of the amplifier I don't think we could talk you through diagnosing and fixing the fault on the faulty "amplifier".

Les.

Dave Halford17/11/2019 16:19:59
489 forum posts
4 photos
Posted by Les Jones 1 on 17/11/2019 16:02:59:

Your description " with similar results " is not clear. If you have proved that one of the "amplifiers" does not work in either position with either scales then that "amplifier" is faulty. Conversely I assume the other "amplifier" works in either position with either scale. I don't think the fact that the display will change between metric and imperial indicates anything about the "amplifiers" Even if you had a schematic of the amplifier I don't think we could talk you through diagnosing and fixing the fault on the faulty "amplifier".

Les.

Les,

I think this from the OP

I have swapped over the plugs and find that the display that previously worked, now doesn't and the one that previously didn't work, now does.

Proves both amp cards and the display box are working

Dave.

Stuart Bridger17/11/2019 16:29:07
362 forum posts
23 photos

We are struggling with some lack of clarity from the OP. We just need to know whether the fault lies with scale/cable, amplifier module or display/chassis. Simple swapping of components, should isolate this easily.

Brian H17/11/2019 19:04:15
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1288 forum posts
99 photos

Ah well, all this swapping of plugs and amplifiers has resulted in the one that WAS working, now isn't!

Brian

Ian P17/11/2019 19:37:58
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2248 forum posts
90 photos
Posted by Brian H on 17/11/2019 19:04:15:

Ah well, all this swapping of plugs and amplifiers has resulted in the one that WAS working, now isn't!

Brian

That really clarifies things.

The 'one' what?

Ian P

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