RVDT Replacement 2

[CUBOID88]

Hi all,

We have a unit in on which the RVDT is broken and Woodward MPC no longer manufacture the unit. Its a 26 VRMS 400 Hz single channel sensor that measures the angular position of the shaft on a throttle valve, that rotates through a range of 90 degrees. I've gone to nearly every OEM I can find to try and get a suitable replacement but none seem to do 26 VRMS sensors. I'm no electrical engineer so my knowledge on this is pretty limited. Could someone please help with suggestions of where to go?!

Thanks

 

[byrdj]

I'm not much on electronics, but I have damaged a few non OEM LVDTs by not properly matching transducer voltage.

I would think the 400hz would be the hardest to match. I noticed Kavlico and Moog offer 26v 400hz devices,I just googled
"26 vrms 400 hz rvdt" and got catologes from moog showing several designs specific for aviation

 

[VEBill]

26 VAC (400 Hz) is as common as dirt on aircraft systems.

A good reference (almost the bible on this field) is the 'Synchro / Resolver Conversion' handbook by DDC. It includes a few pages of info on RVDT.

"Since RVDT/LVDTs are not standardized in their characteristics, as are synchros and resolvers, the converters will have to be adjusted for input gain to accommodate the full scale voltage of the particular type transducer."

You could also check the input circuit card to see what flexibility it offers.

What is the application? The reason I ask is that using an RVDT as a throttle shaft position sensor (overkill), and your field (Aerospace), raises other issues about making such substitutions. You're probably already aware of such issues, but I think it's worth double-checking just to be safe.

 

[CUBOID88]

Thanks for the concern VE1BLL, but its actually an industrial application, so no need to worry! Byrdj, thanks for the info, been onto Kavlico already, their product doesnt really match our needs but Moog's unit might be worth looking at.

 

[Skogsgurra]

I have used automotive throttle sensors. There are both resistive and magnetic. Simplest possible interface with a 10 or 5 V supply and potentiometric output. Life concerns? No, not really.

I even used an inclinometer once for a temporary measurement. Taped it onto the arm and took three flexible wires to the computer interface. Simple, again.

http://gke.org/pub/files/Test with inclinometer and flux gate as position transducer.pdf

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[MacGyverS2000]

I have used automotive throttle sensors. There are both resistive and magnetic. Life concerns? No, not really.

I don't know about the magnetic ones, but the resistive ones definitely have lifetime issues. Once the resistive element gets a bit worn, the readings coming off of it will be quite erratic. Had to replaced the entire throttle body on my car because the 25 cent resistive throttle position sensor got a bit thin at idle position... car died anytime I came to a stop.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[Skogsgurra]

What age was that sensor? With 'no issues', I mean five - ten years. Not infinitive.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[CUBOID88]

VE1BLL, thanks for the "bible" info, it's really helpful. Just got a quote from Kavlico of in and around $15K for a new unit (from their Aero product line), you can see my frustration! Surely if 26VRMS 400HZ is common as dirt I should be able to come across one for cheaper than this right? We've certainly got new LVDT's in the past for about the $2K mark..

 

[VEBill]

If it's 400Hz and $15K, then perhaps you're being pulled into the aircraft parts market (where $15k will get you a bag of 200 washers and box with 200 Certificates of Conformance - ;-) ).

Given that it's for an industrial application, can you fix the old one?

 

[MacGyverS2000]

Gunnar,

5 years sounds about right...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[CUBOID88]

VE1BLL, your exactly right, that's one of Kavlico's Aircraft units, hence the price. And there's our problem, we don't have capability in house to repair them. Does anyone know of any places that repair RVDT's? I really didn't think that such a widely used type of sensor would pose such a problem...

 

[byrdj]

this is a long shot, but many years back I dealt with RDP and they were very helpful with an LVDT project design I had

http://www.rdpe.com/us/index.htm

 

[CUBOID88]

Thanks for all the input guys, just in case anyone else comes across this problem in the future, we received got a quote from Sensonics.co.uk to build a custom RVDT for us. No exact numbers yet, they indicated the 4 figure range but nowhere near the $15k mark. Finally some progress! I hope this doesn't count as promoting!

 

[VEBill]

Sensonics.co.uk ...the 4 figure range...

£9,500

 

[CUBOID88]

Is that reliable info?!..

 

[MacGyverS2000]

<chuckle> Currency conversion will get ya every time ;-)

Dan - Owner

http://www.Hi-TecDesigns.com

 

[VEBill]

No, I'm just imagining a "4 figure" UK price that slightly exceeds US$15k. Just pulling your leg.

Maybe...

 

[jraef]

Just thought it would be worth asking, but is your power supply system really 400Hz? Or is that just the spec on the RVDT because they hapened to chose one from the aircraft industry? 400Hz is fairly unusual for an industrial control application.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[CUBOID88]

Cheers for that VE1BLL, the sterling always comes back to bite anyone not from the land of said currency! Jraef, I see where your coming from but the unit is from an aeroderivative gas turbine so I'm assuming the engine will be running on aircraft supply, i.e. 400Hz..we only repair the components, not the engines!

 

[VEBill]

You could try Googling the exact part number (put it in "quotes" to limit the search to exact matches). This will bring up all the merchants dealing in used aircraft parts. Sort those into two lists: legitimate dealers and scammers (based on location, website). Then fill up the RFQ form for the larger dealers.

If you've already done this sort of process to access the Used Parts market, disregard and carry on.