Zenith Aircraft Builders and Flyers
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Cruzer GRT Fuel Sender Calibration frustrations
Hi, All;
Received my AW cert the end of June, then prep for OSH, and upon return we've had 28 or more days of over 105 deg temps. Frustrating to get stuff done when you're stumbling all over from heat exhaustion!
Anyway, I've started calibrating my fuel senders. Std Zenith supplied VDO senders. I have a GRT Sport EX EFIS and model 2004 EIS. Fuel senders wired to the analog inputs of the EIS as per GRT direction. The GRT wiring diagrams say to use 470ohm resistors in the excitation voltage line.
After filling one tank to the brim (1 gal increments), recording the values and doing the math, I end up with a scaling factor of 672 and an offset of 1343. Also, I was getting some odd readings over the two days of calibrating, so I wrote GRT.
They said that the Zenith senders have a lower range of resistance. Like 0-70 or 80 ohms, whereas the EIS is expecting values in the 30-250 range. They suggest swapping out the 470 ohm resistors with 220-270 ohm. Just whining, I really don't want to be crawling under the panel trying to find where I put the resistors and replacing them.
Have other GRT users had similar issues? Did you change the resistors or do something else as a workaround. I *think* that my readings will work, but may have a smaller tolerance band. I want to get this part done so I can do a first taxi. Having a hip replaced in October, so won't even be able to contort myself to get in the cockpit until (?) 2024 or so... Thanks for any suggestions or experiences.
Replies to This Discussion
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Permalink Reply by Peter Eiberger on
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I ended up swapping out the Zenith (VW?) senders for some Stewart Warner senders with a wider resistance range to get a more accurate calibration on mine.
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Permalink Reply by Bob Simmons on
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If you can't compensate sufficiently using Fuel Scale Data, your only choices are likely going to be changing the senders or changing/adding resistors. You can add a resistor in series rather than changing out the pull up resistor in parallel, but figuring out the correct value might be difficult. And at that point, you may as well just swap out the pull up resistor. If done to plan, it should be on the DSUB connector on the back of the EIS.
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Permalink Reply by Carl Orton on
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Interesting, but I don’t understand. I ignorantly assumed the purpose of the resistor was to limit the excitation voltage. If GRT is saying use 220 ohms instead of 470, isn’t that less excitation voltage? So if I add a resistor in series, isn’t that increasing the resistance? Not looking for EE 101, I just don’t understand the oddities of resistance. Other than more ohms equals greater resistance.
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Permalink Reply by Michael radtke on
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hi carl,
i remember you from your sonex days. the vdo’s more prone to leak and corrode .
did you side mount or top mount?
vans sells the stewart warner guages . same bolt pattern as the vdo’s. better quality..
hope you get it sorted out.
good luck with you hip. my knees are going out.
cheers
michael.
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