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Electronics Help

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Downwindtracker2

Super User
This is way outside my expertise, but my question should be fairly simple . I have a Mach Tach on my lathe which is giving erratic readings . Now that it's running ! The manual says VFD interference on the power, so they suggest common mode filter EH28-1.0-02-75M-X T0836R and two capacitors 0.1uf. Now, the question how do I do a simple board ? Or point me to a video. THX
 
Downwindtracker2 said:
This is way outside my expertise, but my question should be fairly simple . I have a Mach Tach on my lathe which is giving erratic readings . Now that it's running ! The manual says VFD interference on the power, so they suggest common mode filter EH28-1.0-02-75M-X T0836R and two capacitors 0.1uf. Now, the question how do I do a simple board ? Or point me to a video. THX
Click to expand...
Are you asking for a circuit diagram? Or a PCB board layout? Is this single phase power or three phase?
 
What sensor are you using? Are you using a gear tooth counter, hall effect, or infrared? The Machtak will use a variety of sensors, but for the tooth counter and the infrared, first thing I would do is clean the sensor. grease and dust will befuddle an infrared and any magnetic chips wil confusse a gear counter.
 
Looking at the MachTech documentation - that is a 5V device. It produces a 0-5v TTL signal.

docs: >>
4. Why would I need the VFD Filter? Sometimes machines that have a VFD or other
frequency drive motor controller create a noisy electrical environment. This is similar to static on
a radio when a power tool is operated but is conducted through the power wiring. The filter
removes the noise so that the MachTach can operate correctly. The noise can cause erratic
MachTach operation. You should not need an external filter as of V2.6 of the MachTach.
<<

The power input to the MachTech seems from the documentation to be driven from the same supply line as the VFD. Firstly I would isolate that supply using a simple 9v wall-wart. This will avoid most of the induced VFD noise.

The MachTech output should be a clean square wave. If the problem persists after fixing the power supply, borrow an oscilloscope and manually crank the lathe, then compare the signal with the lathe under power. If there is still noise on the TTL line, I would start by verifying that the cabling is shielded and grounded. Then as Ironman suggests, take a close look at the hardware for damage/interference.

Machine noise is the devil to diagnose.

This is the image from the documentation - no circuit board is needed. The filter would connect in line with the 9V supply. But as I mentioned if you use an independent 9V source, this filter is not needed.

1740949041007.png
 
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If any of the sensors uses a shield type cable, make sure that it has a good connection to a good ground.
 
I was just looking on how to put together a board. But cleaning the lens of the infrared sensor might have helped a little, still not enough to get a half of an idea of rpm. 280 to 410

I'm powering the transformer off a wall plug.

On the Mach Tach circuit board there is a female power receptacle. I really had no hope of finding a matching plug, but dug in the drawer anyway. Much to my great surprise I did find one ! I already had a 9volt battery plug . Together they gave me a steady rpm. A good bit lower than it had been reading . Thanks for the prodding. I guess I need a filter.
 
Arbutus said:
The power input to the MachTech seems from the documentation to be driven from the same supply line as the VFD. Firstly I would isolate that supply using a simple 9v wall-wart. This will avoid most of the induced VFD noise.
Click to expand...
Most wall warts are a switching power supply, you need a transformer wall wart, they are out there.

Glad you got the noise killed off
 
It's always better to filter the noise at the source rather than try and get rid of it on every device picking it up. There are entire books written on the subject.

Keep the Drive motor and VFD lines as far away as possible from the sensor pickup.

Way back when I was building my ELS I considered the concept of electrical noise and I designed a couple of TTL to differential modules. Never did use them. I can see if I still have the information somewhere. Not sure where...
 
I'm a bit late to the party.

Bad design like this unfortunately seems to be the rule instead of the exception.

Industrial type environment, that tach should have a differential input not a single ended TTL input. The cable shielding and grounding should also be spelled out.

I made a career (consulting) of fixing poor design for companies that were actually often established companies with teams of engineers that had enough knowledge to make something work on the bench but not in the real world.

Glad you got it working
 
jcdammeyer said:
It's always better to filter the noise at the source rather than try and get rid of it on every device picking it up.
Click to expand...

^^^ This!

If you do that and then add input filtering, you should be good.

As @Ironman suggested, find a transformer based Wall-Wart. They usually have better noise isolation and are usually also more efficient.

For simple stuff like that, you don't need a circuit board, just solder or couple all the component and circuit leads together in a bundle.

Batteries (like your 9V) are also great isolators provided no other common wiring exists (not even grounds).

Sounds to me like you have that tiger by the wee hairs.
 
Here's the prototype. Tested with just one index pulse. There's a second channel for an encoder that would create say 100 PPR. Finally found these in a plastic box that was holding up a piece of wood that brought the CNC machine mouse up to a less wrist bending position.

1740959218331.png

I'll see if I can dig out the drawings. Essentially this interfaces to an open collector type opto sensor or hall effect and translates it to RS485 differential. The other end returns the differential signal back to TTL. In this example it's wired to the ELS for 5V, Ground, Signal A and Signal B.
 
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