 |
Matronics Email Lists
Web Forum Interface to the Matronics Email Lists
|
| View previous topic :: View next topic |
| Author |
Message |
millner(at)me.com
Guest
|
 Posted: Sat May 12, 2012 10:16 am Post subject: connect 1-5 volt fuel level sender to legacy type fuel ga |
 |
|
>> What are the characteristics of the instrument?
The existing fuel level transmitter/probe is ~200 ohms at empty and less
than 10 ohms at full. I'll check current. The tank characteristic is
fairly nonlinear, which is reflected in the non-linearity of the gage
markings. The JPI gage works via a look-up table, so it should be OK...
I guess we could get fancy and linearize the legacy gage, but then the
analog gage would require remarking. Note that even though the existing
gage in marked non-linearly, it's not accurately so... the 1/4 full mark
is about 1/3 of the way up the scale, and actually represents about 1/3
full on the 30 gallon wing tank. But I've become accustomed to that
over time. 
Current full scale?
I will ascertain!~
>> It's pretty easy to craft an op-amp signal conditioner that will
apply the necessary gain and offset to spread the 1-5 volt signal over
the legacy instrument's scale.
So... would the old fuel gage continue in service as originally
constructed, sending a voltage to the op amp circuit which would be
'resisted' appropriately to fool the gage into thinking it's seeing the
resistance fuel level transmitter/probe? Or would we have to modify the
conformal coated (!) circuit board on the back of the gage that has
power, ground, light and fuel tank inputs?
>> These tend to be 'beefy' instruments of perhaps 10 ma full scale.
That's a relief... I was wondering how many Joules were being dissipated
inside the vapor space of the fuel tank.
>>The signal conditioner would have to be vetted for this much sink or
source current.
Heat sinks are us...
>> If you can get full scale current value for me along with the old
resistance sender's empty-full span I can sketch a circuit and propose
parts.
I'm on it! Mom's 89 and in the hospital (fell on her birthday last
week), so time's a little limited for visiting the airport. So if I
don't have numbers for a couple of weeks, it's NOT from lack of
interest, but rather competing priorities. Meeting with the geriatric
care RN on Tuesday to explore 'options' for where she lives, etc.
Moving will be challenging in many respects after 30 years in the same
house, if that comes to be necessary.
>> On way to do it in the airplane is hook a rheostat up to emulate the
old sender. Adjust the rheostat first for FULL indication, measure
voltage across the rheostat before disconnecting it to measure its
resistance. Repeat for 1/2 and empty.
Got it!
>> The only reason you need reading at 1/2 is to verify that the
instrument is reasonably linear.
It's not linear, but whether unreasonably so or not remains a topic of
speculation and debate.
Thanks for the action plan and assistance!
Paul
--
Please note my new email address!
millner(at)me.com
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
 |
nuckollsr
Joined: 24 Mar 2009
Posts: 95
Location: Medicine Lodge, KS
|
| Posted: Wed May 23, 2012 6:45 pm Post subject: Re: connect 1-5 volt fuel level sender to legacy type fue |
|
|
Paul, sorry to have let this dangle. Got distracted with graduation things last week and was away from the computer. Now my SMTP service seems broken on matronics so I'm using the web-access utility.
Your query prompts this idea. There's a joint-venture wig-wag controller project going on that will take a jump forward tomorrow when I get some boards stuffed and shipped. With a slight modification to the electronics, this same assembly could become a signal conditioner that would accept your fuel level data and drive it past a look-up table to output the the correct current for the gage. All issues of calibration and linearity can be washed out.
I'll pray over this some more and see what the hardware might look like. We may be able to find a byte-herder on the List who can do some code for you.
Bob . . .
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
