Author Topic: Capacitive DRO bars - problems  (Read 842 times)

Offline Trevorc

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Capacitive DRO bars - problems
« on: January 07, 2019, 07:05:50 PM »
I have previously used the capacitive dro for each of the 3 axes on my milling machine. These were powered by their own batteries and once i had given them some protection from oil and swarf etc they worked fine but a bit inconvenient to move protection to take the reading!! So i took advantage of Santa’s generosity by updrading to similar ones that can be connected by a Mini B USB connector to a remote reader which can be mains powered via a switching adaptor supplied with the kit. The out put of this adaptor is 6v dc at 1 amp. This adaptor powers both the remote read out and the 3 dros.
Tried to use them in anger today and found major problem. When the mill a c motor is dwitched off the dro readings reset to zero :ShakeHead:
I presume that switching off the motor causes a voltage spike back onto the mains supply.
Has anybody else experienced this problem, if so what is the solution??
I feel,a bit like 2 steps forward and 3 back!!
Thanks for your help.
Trevorc

Offline Firebird

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Re: Capacitive DRO bars - problems
« Reply #1 on: January 07, 2019, 07:29:54 PM »
Hi Trevor

I have the blue tooth system for my DRO's and have battled with the problem you describe on my X1 mill. I have recently fitted the same thing on my Myford lathe and experienced the same problem, readouts jumping all over the place. Eventually I solved the problem by doing away with the power supplies and used a 9 volt (PP3) battery. They work perfectly now.

Cheers

Rich
« Last Edit: January 07, 2019, 07:38:21 PM by Firebird »

Offline bent

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Re: Capacitive DRO bars - problems
« Reply #2 on: January 07, 2019, 07:41:29 PM »
Using a surge protector might help.  My problem was a bit worse - the garage fridge on the same circuit would reset the darn things, never mind the mill motor (and surge protector wouldn't ride over the fridge compressor start cycle).  So I have a choice when milling - keep the beer cold or the DRO readouts constant.  Tough choice.

Offline Lew Hartswick

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Re: Capacitive DRO bars - problems
« Reply #3 on: January 08, 2019, 01:21:20 PM »
Sounds like you need a different power supply with better filtering.  "wall worts" just don't have room for big capacitors.
   ...lew...

Offline Don1966

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Re: Capacitive DRO bars - problems
« Reply #4 on: January 08, 2019, 02:28:34 PM »
Try using a switching power supply this should remove the line spikes. This power supply rectifies the line voltage and switches it at a  10 to 15 kilohertz signal then rectifies it again to a clean DC voltage. If you still have problems with the switching power supply you need to check your cable shielding for proper grounding.

Don

Offline Trevorc

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Re: Capacitive DRO bars - problems
« Reply #5 on: January 10, 2019, 06:48:58 PM »
Thanks you all for your advice and help. I would rather spend time making engines than rewiring workshop power suppy so will probably have to go down the route of using battery power. I find it really frustrating that a device intended to be usedin the workshop cannot tolerate the environment it will most probably experience. Have spoken to supplier who says it is not a problem with the product!! I beg to differ. It is like designing a car without suspension and then telling those that complain  about the rough ride “ it worked alright in the laboratory”. I am just sad that we dont make many of the items of tooling we need for our hobby anymore and instead have to rely upon imports from questionable sources- where possible i try to choose “ made in UK/EU” if possible!
Trevorc

Offline ddmckee54

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Re: Capacitive DRO bars - problems
« Reply #6 on: January 10, 2019, 08:21:50 PM »
I don't think a surge protector would work.  A surge protector is designed to fail in a certain manner when it encounters a massive power surge.  What we a talking about, while more than the affected equipment can handle, is just a spike that is riding on top of the incoming AC power.  The surge protector wouldn't even notice it, we need to filter out that spike.

In my 30 years of industrial controls design I've encountered this problem a few times.  There are small DIN rail mounted filters that are used to protect equipment that is sensitive to this sort of thing, they might work.  Here in the states both the Isolatrol and Sola brands come to mind, and I've used them both. (Google AC power filters)

For a "temporary", and portable, solution you could mount the filter and a receptacle in a small box.  Wire the input of the filter to a plug and the output from the filter to the receptacle.  You might even be able to find a filter that has already done this for you.  If the spike is big enough though the filter might not work.

Another trick that I have used when I'm desperate and can't think of anything else, or nothing else works, is to use a computer UPS - Un-interruptable Power Supply.  The UPS will effectively disconnect the incoming mains power from the outgoing mains power.  Any electrical noise, your spike for instance, will not be transmitted through the UPS.  This used to be an expensive option, but a UPS is "cheap as chips" anymore.  Since you don't need to power your device for more than a few seconds at most, you wouldn't need more than the minimum UPS capacity.

Don
« Last Edit: January 10, 2019, 09:17:19 PM by ddmckee54 »

Offline Admiral_dk

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Re: Capacitive DRO bars - problems
« Reply #7 on: January 10, 2019, 10:34:07 PM »
I hope the cheap UPS'es are a LOT better than some 20 years back ....
At Aarhus Universitet where I worked back then, we had a cheap UPS in each X-felt (?) - one on each floor, that all routers and switches where hooked up to. This worked fine for a year or two, until we where hit (near miss) by thunder - next the mains power partly disappeared and the UPS'es took over in most of the buildings and fried ALL the communications gear without exception  :zap:  :Mad:  :cussing:  I did some tests afterwards and discovered that under certain conditions the cheap UPS'es started up making 400Vac. for some 5 minutes before they decreased it down to the correct 230Vac. we have here in Europe  :hammerbash:

Needles to say that the guy that had bought them in the first place decided to have a meeting with all the responsible participants on all kinds of network on campus and they agreed to only buy certified UPS'es after that - especially considering that a 48 port Cisco switch is $10K a pop and we had at least a few hundred of them being toast after that single event.

Offline Don1966

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Re: Capacitive DRO bars - problems
« Reply #8 on: January 22, 2019, 10:37:46 PM »
There is a difference between a true UPS and a backup supply which a lot of stores call a UPS. So make sure it is a true UPS because you will pay a lot more money for it. A true UPS runs on battery consistently and the batteries are maintained by the power supply. A backup supply does not it only runs on battery after power fails so know the difference.

Regards Don

Offline RJH

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Re: Capacitive DRO bars - problems
« Reply #9 on: January 23, 2019, 01:17:04 AM »
Try to put Ferrite beads on the power and scale leads. I had this problem on a Shumatech DRO 550, it did help a lot. You can get a handful off E-Bay.