View Full Version : RFD rotor tach question
04-23-2006, 07:27 PM
I can't seem to get a meaningful reading out of the rotor tach I purchased from Rotor Flight Dynamics. On the ground during prerotation it doesn't budge from 0, and in flight it bounces around between 0 and 400. The sensor is mounted close up against the ring gear with less than a millimeter gap.
I'm beginning to wonder if I don't have the leads hooked up correctly to the display. The instructions weren't very clear on which wire goes to which terminal (a picture would be worth a thousands words here), so could someone relate how they got theirs working properly?
Attached is a picture of my setup.
04-23-2006, 07:54 PM
Several questions to ask.
Is it possible that the sensor is accidentally rotated 90 deg such that the sensitive axis is perpendicular to the gear tooth rather than parallel to it?
If the sensor is a Hall effect unit, the gear must be ferrous (steel). Are you possibly using an aluminum alloy gear?
Crimp connectors sometimes do not engage the copper wire properly. You might consider checking the instrument loop with an Ohm meter test on a high resistance scale to keep the current low.
04-23-2006, 09:29 PM
Iven. Here's Red Lion's tech sheet for the DT-8 Tach. Might find help here:
04-24-2006, 07:25 AM
I have been selling the Digital rotor tach mfg by Red Lion for at least 10 years and never had any trouble with an indication.
I use the Red Lion "sender" instead of the automotive unit. I have found the gap to be not all that critical and there are no orientation issues with the sender.
04-24-2006, 07:27 AM
OOOPs I meant to add that you do have to set the switches in the back of the unit so it will properly count the teeth of the Wunderlich ring gear. I send mine out set, I thought Ernie did as well.
04-24-2006, 08:47 AM
Even a millimeter is too much. If you're using the Plymouth ignition pickup as supplied by RFD, swing it in toward the gear until it grinds on the teeth somewhere in the gear's rotation (usually the gear is sightly out-of-round). Then tap it back until the the contact JUST stops. You may even leave the sender's mounting screw slighlty slack and just let the gear push the sender away, then tighten the screw. The air gap is measured in molecules, not millimeters.
Check with Ernie about the setting of the switches on the back.
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