VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics


Go Back   VAF Forums > Main > RV General Discussion/News
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 03-11-2018, 12:33 PM
N333M's Avatar
N333M N333M is offline
 
Join Date: Apr 2017
Location: central Il
Posts: 48
Default how do you determine..and fuel levels

How do you determine if you have resistive float senders, or capacitive senders in your tanks?

I am beginning to calibrate the fuel levels in my RV9A for a GRT EIS system, which I didnt build, with a bit of difficulty.
On my attempt yesterday, I filled the right tank one gallon at a time, noting the reading on the EIS after each. The empty reading was 4.2 It began to change on the 4th gallon.
Then, it stopped changing at the 7th gallon, and read 5.7 each gallon there after. this isnt going to work..
Don
__________________
D. Gherardini
Central Illinois
RV9A slider 0-320 carbed
Kitfox IV (SOLD)
Luscombe 8A (for sale)
Reply With Quote
  #2  
Old 03-11-2018, 12:44 PM
Ron B. Ron B. is offline
 
Join Date: Nov 2007
Location: Yarmouth, Nova Scotia
Posts: 2,202
Default

Resistive usually are just a flat thin metal plate on the outside of the tank and capacitive are usually 1/2" thick and plastic with epoxy filled center. The gauges normally do not read right to the top and if the sensor was not installed all the way to the bottom it might not read down to one gallon.
__________________
Thanks Ron
RV-10 SOLD
RV-14 Flying
Reply With Quote
  #3  
Old 03-11-2018, 12:54 PM
Mike S's Avatar
Mike S Mike S is online now
Senior Curmudgeon
 
Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 14,081
Default

Restive senders have only one wire, airframe is used as ground to complete the circuit.

Capacitive units that I have seen will have two wires, sometimes coax, and use a converter box.
__________________
Mike Starkey
VAF 909

Rv-10, N210LM.

Flying as of 12/4/2010

Phase 1 done, 2/4/2011

Sold after 240+ wonderful hours of flight.

"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
Reply With Quote
  #4  
Old 03-11-2018, 01:15 PM
N333M's Avatar
N333M N333M is offline
 
Join Date: Apr 2017
Location: central Il
Posts: 48
Default

OK, As far as I know, I have but one wire.
But..I didnt trace it to the tank.
The craft had the standard Vans 2 1/4 round fuel gauges in it. they seemed to work ok in the 75 hours I flew it before I started the GRT upgrade..
IF I understand this GRT EIS fuel level calibration correctly, They recommend using the reading for full tanks as the level where the float sender stops changing..and the empty reading as the level it stops when going empty..in my case, it seems that I will have an empty reading at 3 gallons, and a full reading at 7. hmm..as I said, thats not going to work for a 16 gallon tank.
I went thru the math several times on the GRT worksheet.
Im scratching my head. If the sender output stopped increasing after the 7th gallon added...I guess it could be faulty..hard to believe it would only have a 3 to 7 gallon range of motion. (if its a float)
aircraft was level sitting in the hanger.
__________________
D. Gherardini
Central Illinois
RV9A slider 0-320 carbed
Kitfox IV (SOLD)
Luscombe 8A (for sale)
Reply With Quote
  #5  
Old 03-11-2018, 01:23 PM
Mike S's Avatar
Mike S Mike S is online now
Senior Curmudgeon
 
Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 14,081
Default

Quote:
Originally Posted by N333M View Post
The craft had the standard Vans 2 1/4 round fuel gauges in it. they seemed to work ok in the 75 hours I flew it before I started the GRT upgrade..

If the senders were working correctly before switching from Vans gauges to the GRT----------my money is on the calibration process of the GRT.

I remember this being a royal pain in the backside, but sorry, I do not remember the actual process step-by-step.

There are two different parameters you need to get right, offset and scale factor.

http://grtavionics.com/media/User-Ma...th-figures.pdf
__________________
Mike Starkey
VAF 909

Rv-10, N210LM.

Flying as of 12/4/2010

Phase 1 done, 2/4/2011

Sold after 240+ wonderful hours of flight.

"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
Reply With Quote
  #6  
Old 03-11-2018, 02:35 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 5,086
Default

First, check the wiring. You should have a wire from the regulated power (4.7 volts, I think) going to a resistor (470 ohms). The other side of the resistor is connected to both the EIS input for fuel level, and the center terminal on the float gauge. The other side of the gauge should be grounded locally.
Turn off the aircraft master switch (power off).
Disconnect the wire from the float gauge center terminal. Put an ohmmeter on the center terminal, and measure resistance to ground. It should be somewhere between 30 and 250 ohms.
If all this works, there are several ways to trouble shoot. My guess is on the wiring.
With the wire still disconnected, but not shorted to ground, turn the power on. Put the voltmeter on the disconnected wire and measure the voltage (other probe on a good ground). It should be 4.7 volts. If not, there's a wiring problem. With the same setup, carefully hold a 470 ohm resistor between the probes (while still in contact with the wire). You should see the voltage drop in half, to, 2.3 volts or so. If grossly off, you don't have a 470 ohm resistor on the other end. You'll need to find it and replace it.
Finally, if you suspect the sender:
Drain the fuel, then start adding it back into the tank. Measure the resistance each time you add fuel. You should see it smoothly go from about 250 ohms to about 30 ohms (probably stop changing as you get with 3 or 4 gallons of full). (I might have it backwards, 30 to 250? I forget.)
Reply With Quote
  #7  
Old 03-11-2018, 03:30 PM
clam clam is offline
 
Join Date: Oct 2005
Location: Lakeland, TN
Posts: 144
Default

... If the 470 ohm resistors were not installed, but presumably everything else in this system was installed correctly, would changing the fuel level still be reflected on the instrument fuel quantity readings? Ie, would you still see some indication change as fueled or refueled?
__________________
RV-8, building
Reply With Quote
  #8  
Old 03-11-2018, 04:23 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 5,086
Default

Quote:
Originally Posted by clam View Post
... If the 470 ohm resistors were not installed, but presumably everything else in this system was installed correctly, would changing the fuel level still be reflected on the instrument fuel quantity readings? Ie, would you still see some indication change as fueled or refueled?
Hard to say, maybe yes, maybe no. For ideal circuits the answer is no.
If there are no resistors but the 4.7 volt source is connected directly to the EIS and float gauge, it may or not not be able to supply enough current when the float is at 30 ohms, e.g., the voltage may sag.
If the 4.7 volt source is not connected, there may be some bias voltage from the input circuity of the EIS which will be a bit affected by the changing resistance of the fuel level detector. I'd expect pretty small changes.

What I was really looking for was the resistor being grossly off in value, or hooked to 12 volts by mistake, so that the voltage is going over the range the EIS is designed to accept.
Reply With Quote
  #9  
Old 03-11-2018, 06:37 PM
Mark Dickens's Avatar
Mark Dickens Mark Dickens is offline
 
Join Date: Apr 2012
Location: Collierville, TN (KFYE)
Posts: 892
Default

Bob, I was with clam most of the day today (and last weekend) wrestling with this, so I am also trying to figure it out. The GRT documentation or lack thereof does not help.

Our understanding, flawed as it probably is, is that there are two ways to connect the float based sensors in a scenario where you have a single HXR EFIS and a single EIS. Option one is to connect them directly to the EIS and then convey that info via serial port to the EFIS. Option two is to connect them directly to the EFIS via the aux ports. Option two is never mentioned in the HXR install manual...in fact, the word "fuel" is never mentioned in the HXR install manual, which I find curious. But we've heard that you can do a direct connect to the HXR...is that true? In either option, you'd need the 470 ohm resistor, right? And in option two, since there's no excitation current available from the HXR, would you have to get it from the EIS?
__________________
RV-8 #81077 Super Slow Build
Titan IOX-370, Dual P-Mags, AFP FM200A FI, Sensenich GA Prop
First Flight November 20, 2016 - Phase One Complete June 1, 2017
Reply With Quote
  #10  
Old 03-11-2018, 08:20 PM
N333M's Avatar
N333M N333M is offline
 
Join Date: Apr 2017
Location: central Il
Posts: 48
Default

YEs..the Blue 4.8 v excitation wire is tied to a resistor installed parallel to the signal wire from the sender. The video from GRT calls it a "resistor tree" you need to build. I did that, but I did NOT check to see what the voltage was after installation.
I will do that next.
__________________
D. Gherardini
Central Illinois
RV9A slider 0-320 carbed
Kitfox IV (SOLD)
Luscombe 8A (for sale)
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 08:50 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.