RPM METER GOES CRAZY

[Suzuki4evr]

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

 

[markba633csi]

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

 

[mksj]

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

 

[RandyWilson]

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.