# RPM METER GOES CRAZY



## riversidedan (Jun 15, 2022)

so I got one of those $20 digital RPM meters   for the table mill  hooked it up per instru. and it will not hold a steady reading and jumps all over the place!  >>>>>>>>>>  have any experience with those??


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## Aukai (Jun 15, 2022)

Is there a sensitivity adjustment(gain)?


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## markba633csi (Jun 15, 2022)

I have heard those things can pick up electrical noise from nearby motor wiring.  Does it flip around with nothing else on nearby? 
(including fluorescent lights)
How are you powering it?
-Mark


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## riversidedan (Jun 15, 2022)

markba633csi said:


> I have heard those things can pick up electrical noise from nearby motor wiring.  Does it flip around with nothing else on nearby?
> (including fluorescent lights)
> How are you powering it?
> -Mark


yes fluorescent light above, ac/dc conversion  to 12V


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## riversidedan (Jun 15, 2022)

Aukai said:


> Is there a sensitivity adjustment(gain)?


no sir.............magnetic pulse from a small magnet attached to metal draw bar`


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## chip maker (Jun 16, 2022)

Did you install the magnet in the proper direction? Also maybe try changing the air gap between the magnet and pickup I know I had this problem because the directions said one thing but found I needed less gap.


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## markba633csi (Jun 16, 2022)

It may be noise from the power supply or a grounding/shielding problem
Can you post pictures of the hardware?


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## riversidedan (Jun 16, 2022)

chip maker said:


> Did you install the magnet in the proper direction? Also maybe try changing the air gap between the magnet and pickup I know I had this problem because the directions said one thing but found I needed less gap.


the directions said 10 mm distance so I tried diffrent locations, no change as of yet


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## wachuko (Jun 16, 2022)

It might just be a bad unit... I had to replace one of mine because it came faulty from the factory...


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## riversidedan (Jun 16, 2022)

markba633csi said:


> It may be noise from the power supply or a grounding/shielding problem
> Can you post pictures of the hardware?


it could be that just not sure yet, will post wiring pix


riversidedan said:


> the directions said 10 mm distance so I tried diffrent locations, no change as of yet


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## Suzuki4evr (Jun 16, 2022)

I have the same problem, but could not figure out the problem yet,but the florescent light above could be a new problem to look at,thanks @markba633csi


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## markba633csi (Jun 16, 2022)

Try powering the unit from a 9V battery- see if that makes any difference
Once you can eliminate the power supply from suspicion you can move on and check other things
It's always possible the unit is just bad from the factory


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## mksj (Jun 16, 2022)

Detection range for the typical tachometer NPN sensor is 2-3 mm. The hall sensor is polarity specific, take a magnet and run it across the face sensor and see if the LED lights up/pulses as the magnet goes by. In one direct it will work, the other it will be weak or won't work. Try the 9V battery. It helps people assist you if you provide specifics as the the device you are having a problem with (i.e. link or model number) and pictures of the install). Sometimes it can be something simple like zip tying a low voltage control wire to an AC wire, or electrical noise. I have not found the need to use shielding on the sender cable and a few times I did it made things worse with VFD drives, but every situation is different.
Hall proximity model: NJK-5002D
Appearance: M12mm cylinder.
Detection range: 2-3mm
Proximity output current: 200mA
Detected objects: magnet
Response frequency: 100HZ


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## RandyWilson (Jun 16, 2022)

I have had three of these on my machines. Two were flaky as you say.  The third is rock solid. All three use the same sensor. The difference is the head. The two that didn't work well are the same; four wire hookup, larger case, display shows 0000 at 0rpm. The one that works very well is a smaller case, three wire hookup (unit and sensor share ground) and displays a single 0 when at 0rpm.


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