[thegasguy]

Does anyone know if the oil pressure sender that is used to feed a Grand Rapids EIS can also drive an additional analogue gauge?
I can't have the EIS on at start - up as it doesn't like the voltage surges and I would like to see the oil pressure rise as the engine fires up.
Also, it's not always convenient to switch pages in flight. - I can configure it to be on page one, but a small supplementary gauge would be nicer.
I don't know what the sender outputs, it's a single wire I think; the oil feed to it is a very small plastic tube.
ContinentalC90

[Shoestring Flyer]

It is usually not possible to split a signal from any sender.

[riverrock]

Don't know about C90 but I think Lycoming's oil pressure sensor is essentially just a variable resistor. If you tried to add a second gauge in parallel, you'd be essentially measuring the resistance of the other gauge as much as resistance of the pressure sensor. Therefore you can only have one.
Been a long time since I tried basic circuitry but something like this:

Code: Select all-ve ground               +ve
|                        |
|-----------gauge 2------|
|            |           |
|            |           |
|--RESISTOR---           |
|            |           |
|            |           |
|-----------gauge 1------|
|                        |


[thegasguy]

That's disappointing. I can see that two gauges in parallel wouldn't read correctly. It would be like resistors in parallel, r1xr2/r1+r2 I think.
The EIS resistance is negligible I imagine, as it's a digital device.
That probably makes it worse; no - I give up, I might have that backwards. I can't remember enough about electronics after 35 years out of it to make a rational argument.
Here's an idea; what about a second sender, which is connected to the same oil line through a "T", feeding a second, analogue gauge?
As I remember it, fluid pressure is constant throughout a hydraulic system so it should read true.
I do have room on the firewall.

[cockney steve]

Yes, you could put a "Tee" in the "small plastic pipe" and happily drive a purely mechanical gauge via small-bore (nylon? ) piping.....but remember you are introducing an extra potential failure-point in a somewhat vital area. (having said that, I cannot remember a failure of an oil-gauge or even work-hardened copper connecting pipe.)

[garethep]

Something like this should do the job.

http://www.demon-tweeks.co.uk/performan ... re-t-piece

[thegasguy]

Garethep; thanks for that link. Further over on that page is a 'remote T kit' which would be perfect. It replaces the nylon pipe with braided metal hose and has the second outlet all in one unit.
Now all I need to find out is what thread a C 90 14F oil pressure sender tapping has so as I can order the correct one.
I think the extra risk introduced is outweighed by the ability to keep a weather eye on the pressure at all times.

[garethep]

Glad to be of use!

[Ben Twings]

The GRT EIS is a sturdy bit of kit and designed to be on during engine start. Have you tried that or just being cautious?
Another alternative is to just to have an additional oil pressure warning switch connected to an annunciator light on the panel. The switch is designed to open at about 15-20 psi.

[carlmeek]

Agreed, I have my Dynon Skyview on during start, but all other avionics off.

[thegasguy]

I have had the EIS on during engine start - I did today by mistake !
It doesn't like it and freezes up- all I have to do is the old off- and - on trick to get it back.
This is despite a fly back diode being fitted recently.
Having looked closely today, I found that the sender is actually in a "T" piece already. It's twinned with a oil pressure switch that brings on the warning light on the panel.
I do want an actual gauge, so I may take that out to fit a feed pipe to a small gauge I can squeeze in somewhere.
Or fit another "T" ?, and have it as well.
Seems a bit poor to have a Christmas tree of T 's - maybe not.

[Rob L]

Now all I need to find out is what thread a C 90 14F oil pressure sender tapping has so as I can order the correct one.

1/8 NPTF in the crank case.

[DarrenL]

Just for info, we have a T with a second sender - one for the ECU and one for a dial - and it works just fine. Gave us all sorts of problems with minor oil leaks to begin with though (not C90).