Are DRO displays specific to the type of scale you have?

Mr.Miz

Mr.Miz

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I've been afraid to ask this question, because I'm sure it displays(pun intended) my ignorance but I've been searching for the answer here for a couple of days and I can't find a clear answer. My searching has lead me to more confusion. So here is the background and hopefully this will give someone with experience enough info to set me straight.
I bought a used Kent KTM-3vk Mill (late 80's I believe) with a DRO knowing the DRO display unit didn't work. After some attempts at testing capacitors and other parts on the display I was unable to bring it back to life. So now I'm in the market for a new DRO display. I have less then zero experience with DRO's and my shopping has lead me to the following display:
What's got me really confused is I can't tell if the displays only work with certain types of scales? the Amazon details say " Linear Scale Magnetic Scale Rotary Encoder" so at first I though that meant only Magnetic scales, but then after looking at scales. Glass scales are listed and Linear Glass Scales, and some don't even say glass just Linear Scales. Then to make matters even more confusing I found a post on here:
www.hobby-machinist.com

Swapping Magnetic and Glass Scales

My small lathe makes it difficult to fit a glass scale on the cross slide. Therefore I was hoping to use a magnetic scale on the cross slide because of its much smaller size. I contacted DRO Pros ( an American agent for Electronica Magnetic scales) and they told me I couldn't use an Electronica...
www.hobby-machinist.com www.hobby-machinist.com
Which basically says they have both magnetic and glass scales working on one DRO Display just by changing the plug from the scale. I would have no problem changing the plug on my scales as I seem to have had to change plugs on just about every use machine I've ever bought (and some new ones just to get things the way I want). However I can't say the I completely understand what wires doing what so I'm sure it would result in a lot of research to mate the cables correct. But I wanted to make sure before I buy, that I shouldn't just get a kit that includes the scales:

3 Axis DRO RPM Kits, 3Axis Digital Readout Display, 3pcs Linear Scale Optical Sensor Glass Scale Ruler, 50mm~1100mm (2inch~43inch) Lathe Milling Bridgeport Drill - - Amazon.com

3 Axis DRO RPM Kits, 3Axis Digital Readout Display, 3pcs Linear Scale Optical Sensor Glass Scale Ruler, 50mm~1100mm (2inch~43inch) Lathe Milling Bridgeport Drill - - Amazon.com
www.amazon.com
Ultimately this is 100% a hobbyist tool so ever penny I put in I am very unlikely to get back. It does happen occasionally but very rarely, but I would really prefer to put the extra coin to materials rather than achieving that "oh so perfect setup".

Thanks for any reply's and your kindness and consideration of my ignorance. Oh also if somebody already clearly detailed this out, post that link because either I'm using words that don't make sense or the Googlizer just hates me.
 
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I've had zero success using old scales with a Chinese head, or Chinese scales on an old head. But I didn't try very hard. I've found the Chinese stuff is generally interchangeable, at least with glass scales, but you have to watch the pin assignments on the DB connectors.

Why don't you buy a head first, and give a shot at making it work. If it doesn't, you can get the matching scales from the vendor later on. eBay is full of them.
 
The DRO displays are not scale type specific, but rather are scale output specific. And unfortunately the scale output that a particular display is expecting is not normally published in the spec's.

Many older DROs used a 1 volt peak to peak sine wave analog output from the scales and fed this to the display box, which then interpreted that output into a digital representation.

Most modern DRO scales output a 5 volt digital quadrature signal, and thus the display is just a simple counter.
 
RandyWilson said:
I've had zero success using old scales with a Chinese head, or Chinese scales on an old head. But I didn't try very hard. I've found the Chinese stuff is generally interchangeable, at least with glass scales, but you have to watch the pin assignments on the DB connectors.

Why don't you buy a head first, and give a shot at making it work. If it doesn't, you can get the matching scales from the vendor later on. eBay is full of them.
Click to expand...
I think that is probably the path I'm headed toward. I just have about 15 browser windows open and a head full of not understanding.
 
JimDawson said:
The DRO displays are not scale type specific, but rather are scale output specific. And unfortunately the scale output that a particular display is expecting is not normally published in the spec's.

Many older DROs used a 1 volt peak to peak sine wave analog output from the scales and fed this to the display box, which then interpreted that output into a digital representation.

Most modern DRO scales output a 5 volt digital quadrature signal, and thus the display is just a simple counter.
Click to expand...
Jim so do you think I could hook an Oscilloscope and power supply up to the scale to get the output of the scales? I can borrow a scope but since you were talking sine waves and the like my mind immediately went to hooking them up to a scope I'll fish around on them and see if I can get part numbers and look them up too I just wanted to think through testing them to make sure their isn't anything different or wrong with them as well.
 
Yes, it's an absolute minefield. Have a look here:


TouchDRO itself is an attractive option, but there's a wealth of info on scales in general there. Yuriy who created it is also a supporting commercial vendor here.
 
Mr.Miz said:
Jim so do you think I could hook an Oscilloscope and power supply up to the scale to get the output of the scales? I can borrow a scope but since you were talking sine waves and the like my mind immediately went to hooking them up to a scope I'll fish around on them and see if I can get part numbers and look them up too I just wanted to think through testing them to make sure their isn't anything different or wrong with them as well.
Click to expand...
Absolutely, that's the way I test them. But honestly I quickly run out of patients with trying to troubleshoot old scales and just toss them. I would rather buy new hardware that has documentation, the new hardware is very inexpensive compared to the old stuff. Frankly I am a real fan of magnetic scales and run them on all of my machines, using them both for encoder feedback to my CNC controllers and using them with DRO displays. Same scales for both.

Just identify the power input pins, then start probing the other pins to see what's going on, it will quickly become apparent if you have sine wave or digital output scales.
 
In general, newer DRO's that do not have a proprietary scale type/plug will run either glass or magnetic TTL scales interchangeably. There can be some issues with pin outs being different. As far as DRO Pros magnetic scales interchangeable with glass if I recall it was a pinout issue and not a signal issue with the Easson 12 (which I had, as welll as the 12B and EL700). I spoke to them about it and they were a bit vague on the issue, probably had to do more with wanting to go with their products. I have an Easson 12B and I run both glass and magnetic scales with no issues. If you have the model number and manual of the old DRO head/scales you should be able to see what type of plug and output signalling it used or you can do something per below:

How to Find Glass DRO Scale Pin Functions

Chinese Glass DRO Scales have become very inexpensive, and can be found on eBay, AliExpress, etc. for under $100/piece. Unfortunately many sellers are unable or unwilling to provide accurate documentation, so it's often up to the buyer to figure out what the pinout of the particular scales is...
www.touchdro.com

As others have mentioned, you will often find that the DRO packages with scales is not much more than the DRO head alone. If you want to go to an all magnetic scale system, you might look at purchasing a package from Machine DRO in the UK and you can specify the kit components as to scales, resolution and head unit. The ship by air and arrives in about 1 week.
www.machine-dro.co.uk

Easson ES-12C LCD digital readout package including 3 linear magnetic encoders

3 Axis Easson ES-12C LCD graphic digital readout package with three magnetic encoders. The encoders offer a very compact profile size and can be cut to length to custom fit the machine being installed. The package is suitable for mills up to Bridgeport 42" sized machines or 30" between centre...
www.machine-dro.co.uk www.machine-dro.co.uk
 
Just and update... the scales on the mill are Futaba PulseScales SMA55A Googling them now for manuals. Didn't come with any documentation it was purchased new for a music shop in the 80's and they had long since lost everything. To THE INTERWEBS... I go:

found them looks like 15v square wave.
 
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One additional note -

Both of theDROs that I have (Chinese, probably originally Sine, but rebranded to TAPC Tools and PM) allow you to set the scale resolution independently for each axis. The instructions that come with your DRO display head will most likely include the pertinent info.
 
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