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interiorpainter
01-28-2010, 11:34 AM
Whats the gender of a dro. It might explain something.
This is the second dro that has the numbers running like a slotmachine. The first one did this when it was just sitting there. This one only with the machine running.
They are the caliper type without the prongs.
Brandless used for the quill so they stay clean all the time. No loose screws or connections because i have soldered a penlight to the circuitboard. It drains a sr44 to quick to bother.
The previous one was not soldered so i think i did not fry the circuit.
These cheap things die so quickly that i take them from somewhere i do not really need it and stick them on with tape.
It took more time to install this thing than the time it ran.

The unit is sitting on a gearhead dovetail benchmill using single phase 220v (Europe) stuck on the front of the head.
Could it be because of the Eddycurrents these things start to act up after a while.
I think the best OT answer is buy a Sino but dislike the idea this shop is getting more of my money this way since they haven't got a clue.
Is this just bad luck or is there a scientific explanation.
Why the need of a dro? The leadscews do not make sense.
Hope I did Thanks.

JTToner
01-28-2010, 11:45 AM
I can't help you with your problem, but I can tell you that I'm running Chinese DROs on my mill and lathe. Both are working fine and one of them is a Sino.
Johnny

EVguru
01-28-2010, 12:22 PM
They use a capacitive detection system and can be sensitive to moisture and dirt, particularly metallic particles.

Here's some good gen from the Shumatech site;

http://www.shumatech.com/support/ChineseScalesExperience.pdf

interiorpainter
01-28-2010, 02:50 PM
The unit that died on me earlier looks like the ones from Shumatec in every detail but I am certain that they are not because I live in Europe.
I think that the grease that is discribed in the article is used to glue the shims to speed up assembly.
I disassembled the dro and lost some parts and tore one lead of the circuitboard along the way:mad: and found no debris.
Wiped the surface with my dumb, stuck and soldered everything together.
It works again with the up and down button missing but i did not use that anyway. I am a hack when working on these annoying items.
Annoying like why does it always start up in inch. I live in Europe remember.
Pressing zero it likes to go to 0.03:cool: I'll be the judge on that.
For quick and dirty it works which is what I am payed for.
If wiping with my dumb solved the problem it is way to sensitive for my use and expect it to act up soon.
Normally a short circuit by a chip will make the digits illegible. Puzzled!
Sino when I run out of these tools.

Black_Moons
01-28-2010, 04:28 PM
try replacing the battery. Unlike more expensive electronics I find calipers just 'go nuts' when thier battery dies. LCD doesnt fadeout, 'low battery' symbol doesnt appear, it just goes nuts and can't remember 0 anymore for more then a few seconds (causing the readout to jump at random)

interiorpainter
01-28-2010, 05:19 PM
Yes that is so true about the batteries but it is working fine right now with the same battery.
Earlier someone posted a link to a personal study about batteryconsumption of calipers. He came to the conclusion that some models use almost as much energie when shut off to store point zero. Also that it pays to get quality batteries. Cheaper ones last me a week hence the soldering the AA.
At some point i learned the hard way not to buy models equipped with auto shutoff. ALL of the auto shutoff functions failed after a few months draining the batteries. Thank God the remaining have an off button.
One of them blinking more than half a year and working fine;)
Just looked for a listing of Sino. 700 euros for 3 axis:eek: No way!

The Artful Bodger
01-28-2010, 05:32 PM
You soldered a battery to it? I guess you used some bits of wire to connect? The device was designed to be all enclosed in that tiny case and those lengths of wire may be picking up mains hum (or something) and spooking the electrics. Perhaps you can try soldering a very small capacitor across where you connected to the board.

loose nut
01-28-2010, 07:37 PM
To much humidity can bugger them up too.

JoeLee
01-28-2010, 07:49 PM
Stray RF or strong magnetic fields can cause them to count all over.
Being in close proximity to tv or radio transmitting towers or high voltage power lines. Ground loops can also cause rf feedback or poor grounding.

JL.............

whitis
01-29-2010, 12:23 AM
Yes that is so true about the batteries but it is working fine right now with the same battery.
Earlier someone posted a link to a personal study about batteryconsumption of calipers. He came to the conclusion that some models use almost as much energie when shut off to store point zero. Also that it pays to get quality batteries. Cheaper ones last me a week hence the soldering the AA.
At some point i learned the hard way not to buy models equipped with auto shutoff. ALL of the auto shutoff functions failed after a few months draining the batteries. Thank God the remaining have an off button.
One of them blinking more than half a year and working fine;)
Just looked for a listing of Sino. 700 euros for 3 axis:eek: No way!

This type of calipers/scales are never off. Only the display and maybe the SPC output turn off. As incremental devices, they must continuously watch for movement to keep track of their position. Otherwise, you would have to reset the zero every time they were turned on.

As for auto off, most turn "on" when you move the scale. Vibration or electrical noise might wake it up.

I have a pair of the calipers that served me for many years without problems. Until I disassembled it. Had a hard time reassembling it such that it would behave correctly - and I know what I am doing. Reassembly was unusually touchy. Very sensitive to alignment and not because it is a measuring device. I would suggest you consider getting the cables from www.littlemachineshop.com #1990 or #3483 and use or modify those instead of opening up and modifying the device - though you may still need capacitors on the power supply lines if using external power. Shielding the cable reduces electrical noise but may increase battery drain somewhat.

First problem is the zebra strip. The zebra strip is a strip of rubber with closely spaced alternating conductive and insulating bands that connects the LCD to the printed circuit board. Nice thing about zebra strips is that they do not have to be aligned very precisely; however, the pads on the LCD must be well aligned above the pads on the printed circuit board. If your display is showing characters that don't look like digits or not showing digits, this is likely your problem. Note that the zebra strip may not work properly until the unit is fully assembled. Zebra strips are common on many devices with LCD displays.

Another issue dealt with how the PCB was bolted down. IIRC, I ended up not fully tightening the screws as fully tightening them caused problems, perhaps by bending the board slightly.

Now, I have a hard time getting the calipers to malfunction, even when I try. This includes passing the calipers through a TV degaussing coil exposing them to a 60hz field and running the coil around them from all sides. However, they will malfunction if I operate a small Tesla coil in their vicinity. The tesla coil makes a lot of electrical noise. Thus, they aren't susceptible to 60hz but are susceptible to higher frequency noise such as you might get from a VFD, DC motor control, stepper or servo driver, or other motor control. Shield your motor wires and try to avoid running them adjacent to your DRO wires.

As far as resistance to damage while soldering is concerned, it isn't entirely fair to compare the caliper/scales with the DRO display board. The scales need much finer detail. This means that the traces are narrower, the copper is thinner, and the via holes are smaller. So it is more susceptible to damage even though the board is probably made to a higher quality standard than the display board.

One very annoying flaw in many, but apparently not all, of these calipers is that the case (ground) is connected to the positive side of the battery, not the negative. This causes a number of problems. It is harder to design electronics to read the SPC output without draining the battery and without malfunctioning if the metal parts of the scale are grounded. It also means that if the SPC cable is grounded to the machine/DRO/computer on one end and short circuits or crud between the metal parts of the scale and ground (such as the metal parts of your machine tool) can cause malfunction or drain the battery without proper isolation. If you are having trouble with battery life, the problem could be at the DRO end. You may want to remove the batteries entirely and jumper the DRO to provide power if it has his option.

The shumatech 350 DRO connects two 100K ohm resistors in series across the battery of the DROs. This puts a small, but significant, drain on the battery. In addtion when the 350 is off, the protection diodes on the ICs can put a larger drain on the battery. Just having an SPC cable connected to the scales/caliper can drain the battery (driving cable capacitance).
The 350 also shorts the batteries of the 2/3 scales together. However, the 350 has a jumper which allows you to power the scales externally. The scales will forget their position, however, when the 350 itself is turned off as they don't have power.
The shumatech does not use circuitry which can read the negative voltages from the scales; instead, it connects its own ground to the negative side of the battery. Which means that the shumatech "ground" itself must not be grounded anywhere. The 350 model readout also may have had some noise issues.

Do not apply external power to the scales from a DRO or other device without removing the batteries. Otherwise, you end up charging a non-rechargeable battery resulting in leakage and corrosion.

One should not substitute a manganese dioxide LR44 or equivalent battery for the silver oxide SR44 or equivalent (357, EPX76, etc.) battery. Some battery stores may treat them as interchangeable; they are not. The chemistry and discharge curves are very different. Some suppliers even ship calipers with the inferior LR44. Some calipers seem to stop working at 1.4V and others as low as 1.0V. The higher the voltage required, the less of a batteries rated capacity can actually be used.

If your caliper isn't picky about voltage, you may get a year with even a poor battery. If it is picky, it can make a difference between 2 months and 8 months. If it is picky, try an EPX76 or a 357/303H (not the one without the "H").

Estimate of battery life vs battery and cutoff voltage. Battery data sheets are pretty crappy, and batteries vary, so these are rough estimates. Data from energizer.


1.4V 1.3V 1.2V 1.1V 1.0V
SR44 (EPX76) 250days 300days 345days 416days 445days
SR44 (old 357) 241days 300days 354days 375days 387days
SR44 (357/303H) 267days 312days 354days 366days 375days
SR44 (357/303) 125days 229days 291days 354days 375days
LR44 (A76) 62days 166days 292days 333days 354days

Good battery: 8-14months, depending on caliper
Bad battery: 2-12 months, depending on caliper

Even a dirty finger print on the battery could conceivably drain it or cause contact problems.

The low voltage high impedance logic levels on the SPC cable also mean that you may have problems with noise pickup in the cable, either on the
the data/clock lines or power/ground.

Because they measure the difference in capacitance to buried traces at various points over the plastic part of the long scale, crud there could affect results.

Proper shielding of the scales can affect results; disassembly/reassembly can affect this. Those little pieces that look like brass shims ground the stationary to the sliding part.

If you damage the electronics in one of the scales, you can probably scavenge parts from one of the cheap calipers.

EDIT: fix typo LPX76 -> EPX76

interiorpainter
01-29-2010, 05:05 AM
The dro is soldered to the battery via a 4 inch lead. This lead can be shielded from the effect of the motor that is sitting 4 inches further. I suspect shielding the motor will affect cooling. The working space is painfully dry and kept reasonable clean with a shopvac and brush.
Scavenging and altering these tool make me loose track about what they originally were intended for and hope i got it right concerning the model.

So its either a cap or a diode to put in the circuit after isolation after reading the suggestions. Right after putting some aluminun ducttape over the leads.
Should help keeping the dust out as well.


Overlooking the difference between the sr and lr44 is easy to do.
Going even cheaper with Zn air hearing aid batteries did not even work at all.

My latest aquisitions are aluminum scales with the readout on lead. You can cut them to suit with a small hacksaw but are a bit floppy.
Nice big digits and to lithium 3v batteries in them. They should last long though the first set was doa.
It is not sitting close to something inductive and is not showing any of all the problems. Never saw a set like that in a US webshop. 60 euros for 24 inch and 99 euros for 40 inch. How will these hold up on a lathe. To cheap to try.
They are not listed on the website of this Dutch shop.
Some of these auto shutoff items like to idle between 0.01 and 0.02 and therefore never shut off draining the battery. Alas this is an auto shutoff again. I haven't seen any relation between price and quality for the brandless so far so lets hope for the best.

All these suggestions should keep me from using the last 2 dro's that are sitting on a shelf until much later. All these small expenditures add up really fast. Thank you for slowing it down.