Matt's RV-8 Project



Matt Dralle's RV-8 Project
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Date:  4-17-2010
Number of Hours:  3.00
Manual Reference:  
Brief Description:  Bias Resistors For Westach Hall-Effect RPM Sensors

Instead of taking the RPM signal off the P-Leads on the Mags, I opted to use these sweet hall-effect sensors from Westach. I have described them before in other log entries. After the first engine start, I noticed that I wasn't getting any RPM indication on the EIS-4000. After a lot of troubleshooting and extra work that wasn't necessary, I finally figured out that the problem was that the sensors are open-collector transistor outputs similar to the FloScan 201B fuel flow transducers. This means that you have to bias the output with a resistor to get any signal. I experimented with a few values and found that a 47k ohm resistor to +12v seemed to work well.

A couple interesting things about using the hall-effect sensors:

1) Just turning the prop by hand does NOT cause enough magnetic impulse to trigger them. Turning the prop with the starter doesn't really seem to either. It wasn't until the engine actually started that I realized that they were finally working.

2) The other cool thing about the hall-effect sensors is that they will read RPM whether the mag is grounded or not! When you use the P-Lead to read RPM, when you ground the mag with the mag-switch, there is no RPM reading. That's enough reason to use the Westach sensors right there, in my opinion.
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47k Ohm Resistors Added

47k Ohm Resistors Added

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Connectors Re-sealed With Heat Shrink

Connectors Re-sealed With Heat Shrink

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