Aetna Digital Synchs with the Analog Sometimes

[Vincentc]

I just installed one of the two Aetna digital tachs I bought for the broken flybridge tachs. At low idle the digital matches the helm OEM analog. Both indicate 450 rpm. However when I increased the throttle to 800 rpm on the analog, the FB digital shows 650 rpm.

The engines are 671ti's and the tach sender comes off of the Glendinning. I ran a shielded wire from the post on the helm tach up to the digital tach.

I have difficulty understanding how the tachs could match at one speed and one be 80% of the other at a differenct rpm.

I will call Aetna tomorrow, but wondered if anyone has any experience or ideas relating to this situation.

Regards,

 

[Vincentc]

I spoke to Jim at Aetna and he seemed very interested in helping, but could not identify a specific cause yet. He suggested some things for me to check to better identify the problem. First will be trying out my $30 photo tach.
Regards,

 

[the kuz]

Jim, when we repowered we switched to the Aetna digital tachs, and really like them. Only complaint is that they are a little hard to see in bright sunlight. I remember an initial adjustment/calibration at installation (something to do with how the pick up reads), but can't recall details. I know several others on the forum also have them. I have wondered about the accuracy/consistency of the Aetna tachs, so please continue to share what you learn.

Thanks Bob K

P.S. We sync the the engines with these tachs, and based on that I can say that our two read the same when the Port & Starboard are in sync.

 

[Vincentc]

I checked the FB digital and the Helm Analog with a $30 photo tach and discovered that the OEM Sun at the helm read high or low depending on RPM. The Aetna was consistently 75% of the photo tach. Aetna told me to change the dipp switches inside the tach and change from 4 to 3 Pulses Per Revolution. Moving the #1 switch from off to on brought the digital tach up to the correct range.

A 5 minute fix and another excuse to mess with the boat.