Have you had problems operating a DRO in cold temperatures?

Niwot · Feb 4, 2020

I have an old Teledyne Gurley Patfinder 50/ Pointfinder DRO on a Bridgeport, and it has worked flawlessly for decades. This is the first time I have operated the mill in cold temps (ambient temp above freezing, but only by a few degrees ~35°F), and there is some serious skipping during use.

At first, this only happened on the x-axis, so I cleaned the glass scale and all was good. In hindsight, this could be due to the fact that the scale and encoder were warmed up while I serviced it. The issue actually appears on both axes.

Just for fun, I zeroed out the x-axis, and left it on overnight, and it jumped 57" (it was probably below freezing in the shop that night).

Has anybody else experienced something like this?

Thanks.

dkmc · Feb 4, 2020

I have 2 similar Pathfinders on Bridgeport mills as well. Never any problems. You might be getting condensation or 'fog' on the glass surface that's causing the errors. Might try an 'anti-fog' glass cleaner, but I'd guess the vapor goes away when you warm up the scales. Maybe hang light bulbs near the scales to keep them warmed up?

Niwot · Feb 4, 2020

I may try and preform an experiment, and see if a space heater placed proximate the scales solves the problem.

Scottl · Feb 4, 2020

Is there room to place a rod heater near the scales?

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guest · Feb 4, 2020

The old LCD's can act funny at cold temps. Response time slows way down, they will even freeze.

I have a height gage that got cold enough it wouldn't display, it was fine after it warmed back up.

dkmc · Feb 4, 2020

Niwot said:
I may try and preform an experiment, and see if a space heater placed proximate the scales solves the problem.

I was thinking minimal power use, so like a 40 watt incandescent light bulb 4-5 inches away. But I think a space heater with more BTU's should completely solve the problem.

guest said:
The old LCD's can act funny at cold temps. Response time slows way down, they will even freeze.

I have a height gage that got cold enough it wouldn't display, it was fine after it warmed back up.

These DRO's are from the late '70's or early '80's and are LED displays.

Niwot · Feb 4, 2020

Scottl said:
Is there room to place a rod heater near the scales?

I would imagine so. Definitely more economical than a space heater if it works. I wonder how long in advance I would need to turn on the rod heater to ensure smooth operation?

Also, I am assuming it is an issue in the scales at the moment, but I suppose it could also be an issue with the encoder or with the DRO electronics.

Niwot · Feb 4, 2020

dkmc said:
I was thinking minimal power use, so like a 40 watt incandescent light bulb 4-5 inches away. But I think a space heater with more BTU's should completely solve the problem.

The space heater is definitely for proof of concept only! That would be rather expensive to run continuously.

Clive603 · Feb 4, 2020

Have experience with a different make but similar technology.

The glass scale Heidenhain 2" / 50 mm travel probes of 80's (ish) vintage that I used to use in the lab had a fairly restricted operating temperature range. Maybe 10°C to 40°C, possibly less. Over 30 years since I last looked at the data sheet so I'm probably out a bit but that sounds about right.

Working in an air conditioned lab temperature was never an issue for me but there must have been a good reason for the spec. As I recall matters the scale and reader design was such that changes from thermal expansion and contraction were well compensated so accuracy ought to have held up over a much wider range.

Clive

dkmc · Feb 4, 2020

Niwot said:
I would imagine so. Definitely more economical than a space heater if it works. I wonder how long in advance I would need to turn on the rod heater to ensure smooth operation?

Also, I am assuming it is an issue in the scales at the moment, but I suppose it could also be an issue with the encoder or with the DRO electronics.

The scale is the encoder. Linear not rotary. The power supply in the Orange box does generate some heat, so leaving it on may help keep things inside warm and dry. I know of one shop that has (had?) about 8 of these units on BP mills and they were always on 24/7 for years.

Niwot · Feb 4, 2020

Sorry...I meant to say reader--not encoder. As in not sure if the issue is the glass scale (of the encoder) or the reader (of the encoder).

hobbyman · Feb 4, 2020

Years ago I ran a 3/4 inch plate shear with a digital readout and rotary encoder driven by the lead screw. It would be giving me crazy readings every winter morning and I would have to re-configure the readout. I asked my daughter who was taking instrumentation and controls. She looked at me like I was stupid and said, "Of course it would do that unless they used military spec'd electronics." So regular integrated circuits are not designed to operate at freezing temperatures..... At least that's what my daughter told me.

HWElecRepair · Feb 5, 2020

"milspec" for the most part, especially electronic components, are the cheapest things that money can buy.

Do you have a pinout the the scales on it? I would recommend leaving the unit off all night, and as soon as you turn it on, check the (most likely) 5vdc signal. My guess would be that it is low. Then check again after a few hours of it being on, and see if it has a stronger signal.

Jon

EmGo · Feb 5, 2020

dkmc said:
The scale is the encoder.

As I remember, when Bausch & Lomb came out with the first ones, they described how they worked. They aren't simple 'count the flashes' encoders. They measure displacement using moire fringe patterns of two gratings moving across each other, but I can't find an original description. This is an improvement on the original, still not real comprehensible to me, but

Moire optical transducer - Pitney-Bowes, Inc.

MrStretch · Feb 5, 2020

Also, extreme temperatures can expose faults in older circuitry like cold solder joints that might not be evident at room temp. Just about around freezing should be ok for lcd displays, but if you go really low they get kind of comical.

laminar-flow · Feb 5, 2020

I think I know what your problem is as I have had the same. The air space behind the push buttons gets lower pressure than ambient and makes the button always in contact. Try by warming up some buttons with a hair dryer and see what happens. It took me months to figure it out but one day I thought of this and went over to the DRO, I already had an idea of what button would have been causing the problem, and using a needle, vented the keypad just under the suspect button and it worked. Call me if you want.

Niwot · Feb 5, 2020

laminar-flow said:
I think I know what your problem is as I have had the same. The air space behind the push buttons gets lower pressure than ambient and makes the button always in contact. Try by warming up some buttons with a hair dryer and see what happens. It took me months to figure it out but one day I thought of this and went over to the DRO, I already had an idea of what button would have been causing the problem, and using a needle, vented the keypad just under the suspect button and it worked. Call me if you want.

That is clever!

I have the old school mechanical buttons that probably don't suffer from this issue. It seems there were multiple versions of the keypad in use. (pics lifted from the web)

75077-teledyne-gurley-8771-2-pathfinder-50a-x-y-axis-digital-readout_75077.jpg.jpg

Niwot · Feb 5, 2020

HWElecRepair said:
"milspec" for the most part, especially electronic components, are the cheapest things that money can buy.

Do you have a pinout the the scales on it? I would recommend leaving the unit off all night, and as soon as you turn it on, check the (most likely) 5vdc signal. My guess would be that it is low. Then check again after a few hours of it being on, and see if it has a stronger signal.

Jon

I have the original manuals, and will check this out if there is a pinout lurking around in there. Thanks for the suggestion!

I have a feeling that the control box is the culprit based on comments here and a conversation I just had with a knowledgeable gent.

laminar-flow · Feb 5, 2020

Yes, I had one of those older ones but now have the keypad type. Too bad they don't make them anymore.

Niwot · Feb 6, 2020

So yesterday it was a bit colder than when I had had the original DRO issues. The ambient temp was 16°F, and an IR thermometer let me know that the Bridgeport body was 25°F. However, I turned on the DRO 4 or so hours before use, and pointed a space heater towards the display unit/electronics about 2 hours before use. There was no skipping of any sort. This is a sample size of 1, so take it with a grain of salt, but I am definitely going to keep the unit on 24/7 from now on, and see if that alone solves the problem.

Time is always short with a toddler running around, so I have yet to even check if I have a pinout diagram, per HWElecRepair's suggestion.

Have you had problems operating a DRO in cold temperatures?

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