UMA tachmeter question

[JurgenRoeland]

Hi all,

My electrical skills are pretty close to non-existent, so please be gentle with the responses. Thank God for VPX and Dynon.

I am installing a T1A9-1 UMA tachometer and have a few questions related to the installation. I searched and read through other tachometer topics but couldn’t find answers specific to my situation.

The UMA tachometer sensor has a long wire that terminates in a signal wire, a power wire, a ground wire, and a shield wire.

The manual describes the sensor installation in combination with the UMA analog RPM gauge. However, I do not have that analog instrument and plan to use only the Dynon SkyView HDX to display RPM.

The UMA tachometer accepts any DC voltage between 5 and 24 V. I assume that, depending on the input voltage supplied to the sensor, this determines whether the standard RPM input Left (pin 32) or the low-voltage RPM Left input (pin 34) on the Dynon EMS is used.

The EMS 37-pin connector does not provide any 12 V sensor power pins (only 5 V). Therefore, I assume that if I want to power the tachometer with 12 V and use the standard RPM input (pin 32), I need to supply power from a dedicated VPX output directly to the tachometer.

Is this assumption correct?

I cannot find any documentation specifying a circuit breaker or maximum current draw for the UMA tachometer. What value should I configure in the VPX for this power wire?

Can the shield ground and the tachometer ground be spliced together and then connected to the aircraft ground block?

Wondering how others have wired the power pin and what pin was used on the EMS.

Thanks in advance for shedding some light on this.

Jurgen

 

[benapilot]

I used a slightly different UMA sender, the T1A3 (installs where the RPM cable was) so I'm not confident the wiring will be the same, but I don't see why it wouldn't.

Power wire, 20AWG to a 3A circuit breaker (or 12v VPX output in your case)
Ground wire to the main ground block (I don't remember if I had a shielded wire or not. I'm sure you know, only ground the shield on one end)
Signal wire to pin 32 (White/Green. Standard RPM Left Input).

Do you have this drawing? https://umainstruments.com/wp-content/uploads/2021/04/mag-pickup-wires.pdf
You'll need to specify how many pulses/rev in the EMS sensor setup to get the correct RPM (depending on 4 or 6 cyl)

Hope this helps and good luck!

Edit: on my installation I had to provide my own wiring to the sensor so I didn’t use shielded wire. On yours, I would recommend checking to see if the shield is grounded to the sensor. If so, leave the other end unshielded. If the shield is not grounded to the sensor, then splice into the ground wire as close to the ground block as you can.