Tachometer sender going backwards

[CaptTom]

I'm not sure how else to say this. Never seen it before.

I just bought two new Faria tachometer senders for a mechanical sensor on my diesels. Starboard side works great; more RPMs put out more pulses, and I can calibrate it on my Noland RS11 engine monitor using their setup software.

Did the same thing on the port side. New sender, new wires, hooked up to the RS11 and ran the config software.

The higher I rev the engine, the lower the number. No matter what PPM (pulse per minute) setting I choose, the resulting RPM number is lower at higher RPMs.

I tried switching the wires, port for starboard, and the problem followed the wires. So it's not the RS11. Somehow, the new sender appears to be sending more pulses at lower RPM than higher.

It's a two-wire system, both wires are intact from the sender to RS11. So it's not a bad ground.

I'm out of ideas. How can a sender put out fewer pulses per minute at higher RPM?

[JPA Cate]

Try re-configuring it using the one that works correctly's software. If no joy, get onto their tech support.

Ann

[CaptTom]

Originally Posted by Ann T. Cate

Try re-configuring it using the one that works correctly's software. If no joy, get onto their tech support.

They both go into the RS11 converter. I swapped the wires to connect the port (problem) one to the starboard (working) input. The problem followed. So it's not the firmware.

I also put the drive tang (pin) into an electric drill to take the engine and all mechanical connections out of the equation. No change.

It's down to the sender itself, or somehow the wiring, which I just installed and verified every inch of - no breaks, sharp bends or kinks. There's only one pair of heat-shrink butt connectors and they look good. It only registers pulses - incorrectly - when the sender is being rotated (by the engine or drilal) so I doubt it's something wrong with the wiring. I swapped positive and negative just to rule that out. No change.

At this point I guess it's tech support, not sure if I want to talk to the sender or the NMEA data converter manufacturer. I'm leaning toward the sender, since the converter works fine on both inputs, but only from the "good" sender.

[CaptTom]

OK, maybe some day this will spare someone a half-day of troubleshooting.

Be kind, it's not easy to admit how stupid I was...

Now remember, I spent half the day disconnecting and reconnecting wires, removing and re-mounting sensors and senders, resetting and restarting electronics, and running the engines again and again.

Before I gave up, one more thought came to me...

I turned off the engine room lights.

Yup. That did it. Both tachs settled right in where they belong, perfectly in sync and moving in the right direction.

Last year I had replaced my power-hog 12V incandescent Edision-base bulbs with florescents. They are SO much more efficient, cooler and give off more light. I was real proud of myself.

At least now I have no phone calls to make tomorrow. And my next job was waxing, so I'm not THAT heartbroken about not getting to it.

[donradcliffe]

Don't blame yourself too much--the electronics should be rugged enough to not be buggered by the noise from a fluoro.

[a64pilot]

Wow, I would have thought they would be hardened better that that, that's just not that much EMI

[JPA Cate]

Capt. Tom,

Glad you got it solved.

A.

[landonshaw]

Good work in figuring out the source of the problem.

[Sailor g]

Wow, I agree they shouldn't mess with it that much. It's a good bit of info to have for the future. Thanks for sharing.