P-Mag to AF2500 Tachometer Signal

[Canadian_JOY]

After using my good friend "Mr. Search" and reading through several contradictory posts from way back in history, I'm afraid I'm left scratching my head...

This is a net-new installation of an AF2500 (yeah, I know, it's been a very long build process!) in our aircraft, and a net-new installation of a Series 114 P-Mag, just back from the shop for their terrific flat-rate checkup and firmware update service.

What I can't figure out is how to wire up the tachometer signal from the P-Mag. I've seen posts that say "wire direct from P-Mag to AF2500 Analog Module", some posts saying to wire it that way but select 4-pulses-per-revolution instead of the default 2-pulses-per-revolution, and even one post from Rob Hickman which indicated using the raw P-Mag tach signal could result in damage to the AF2500 Analog Module.

Needless to say, I have no desire to damage our Analog Module, nor do I want a wonky tach that either doesnt work or doesn't read correctly. Because I want to be able to test the point at which the P-Mag internal generator stops producing power, I want to take the signal off the P-Mag since the impulse-coupled Slick mag will but grounded out during this test.

What does real-world experience say is the right way to hook up the P-Mag tach signal to the AF2500?

Thanks in advance for your helpful replies.

[Larco]

If I am understanding correctly? Use the 3 wire tack sensor which is screwed into the slick mag connected to the 2500. It will tell you RPM regardless with mag you have switched on or off. The sensor can be installed on either R or L side Slick mag. I did it this way with a single P mag installed on the right side and impulse slick on the left and it did the trick. Larry

[Canadian_JOY]

Originally Posted by LARCO

If I am understanding correctly? Use the 3 wire tack sensor which is screwed into the slick mag connected to the 2500. It will tell you RPM regardless with mag you have switched on or off. The sensor can be installed on either R or L side Slick mag. I did it this way with a single P mag installed on the right side and impulse slick on the left and it did the trick. Larry

Hmmm, now there's food for thought - thanks, Larry. I've seen additional posts here (not necessarily referring to the AF2500 but to other EMS equipment) which referred to the tach sensor not functioning with the magneto P-Lead grounded. Now that I think about it, if those other EMS units are sensing the flyback voltage on the P-lead, they absolutely would die when the P-lead is grounded. The inductive pickup provided by AFS won't have this problem since it is sensing the spinning parts of the magneto, rather than the P-lead voltage itself.

Yup, that might indeed be the best way to go. Thanks for waking up my addled thinking! My P-Mag tach signal will likely become a spare wire in the bundle coming through the firewall...