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VM1000 manifold pressure and CHT sensors

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sarg314(at)comcast.net
Guest

Posted: Sun Sep 09, 2007 2:34 pm Post subject: VM1000 manifold pressure and CHT sensors

I have a VM1000 that has sat in a box for 6 years.  VisionMicro (=JPI) 

tells me they have an inventory of VM1000 spare parts but are not going 

to maintain it any more. When those parts are gone, they're gone forever.



I finally got the VM1000 installed and powered up.  It was flaky until I 

reseated the 4 socketted DIP components in the main control box.  I 

attribute that to sitting unused for so long (and maybe cheap sockets).  

Seems to come up reliably now, but shows 2 problems. The CHT3 is 

consistently 15 - 20 deg. low and the manifold pressure is about 2.5 

inches low. It reads 27.3 when the barometric pressure is 30.00.  The 

M.P. sensor is a bellows type and can get stuck, so the tech at Vision 

Micro recommended I just run the engine a bit. Well, I'm a few months 

away from being able to do that and their inventory of spare parts is 

only getting smaller, so rather than wait, I hooked up a hose to it and 

actually blew into it gently.  I was able to make it change +- 1 inch, 

so I don't think I did it any violence. But it still returns to 27.3 in. 

when I leave it be.



There must be lots of people out there with experience with these 

things.  Should I spend the $250 to buy a new MP sensor now, or wait 

until the engine is actually running and hope that all the vibration and 

pressure swings will get the thing working, OR that Vision Micro will 

still have sensors on the shelf?



Since the CHT is a thermocouple, it is as likely that the failure is the 

amplifier circuit it is connected to as it is a bad thermocouple.  I 

don't know anything about the innards of these things.  What is the 

typical failure mode for a VM1000 temp. sensor?  Is it the sensor itself 

or the circuitry reading it?  All the other thermo probes seem OK.



Thanks,

--

Tom Sargent, RV-6A, electrical system

Vanremog(at)aol.com
Guest

Posted: Sun Sep 09, 2007 2:51 pm Post subject: VM1000 manifold pressure and CHT sensors

In a message dated 9/9/2007 3:36:20 P.M. Pacific Daylight Time,  sarg314(at)comcast.net writes:

  	  Quote: 	
		  Since    the CHT is a thermocouple, it is as likely that the failure is the    

amplifier circuit it is connected to as it is a bad thermocouple.  I    

don't know anything about the innards of these things.  What is the    

typical failure mode for a VM1000 temp. sensor?  Is it the sensor    itself 

or the circuitry reading it? 	


 

 ======================================

  

 Easy to swap the TC out with one of the others and see if the problem  moves with it.

  

 Regarding the MP sender, it seems a stretch to me that benign storage could  cause it to drift in this fashion to that degree.  I would try to find  someone else out there in RV builder land with another identical sender that you  could swap out to see if this is the culprit.  Either that or go thru all  of the printed troubleshooting tips that VM gives out to try  and pinpoint the problem (low voltage to the sender, wrong  output, high resistance at the connections, bum wire).

  

     

 N1GV (RV-6A, Flying 865hrs, O-360-A1A, C/S, Silicon  Valley) 





Make AOL Your Homepage.

  [quote][b]

sarg314(at)comcast.net
Guest

Posted: Sun Sep 09, 2007 3:12 pm Post subject: VM1000 manifold pressure and CHT sensors

Thanks, I guess I'll have to swap CHT sensors.  I don't like handling 

those things - I keep expecting that stiff T.C. wire to fatigue and break.



I was looking for a "trouble shooting" section in the manual, but mine 

doesn't have one.  I didn't get anything else with the unit and their 

web page has no downloads.  How did you get yours?



Vanremog(at)aol.com wrote:



 	  Quote: 	
		   Either that or go thru all of the printed troubleshooting tips that VM 

 gives out to try and pinpoint the problem (low voltage to the sender, 

 wrong output, high resistance at the connections, bum wire).

   

  

 *N1GV (RV-6A, Flying 865hrs, O-360-A1A, C/S, Silicon Valley)*

n5lp(at)warpdriveonline.c
Guest

Posted: Sun Sep 09, 2007 3:13 pm Post subject: VM1000 manifold pressure and CHT sensors

On Sep 9, 2007, at 4:33 PM, sarg314 wrote:



 	  Quote: 	
		   



 I have a VM1000 that has sat in a box for 6 years.  VisionMicro  

 (=JPI) tells me they have an inventory of VM1000 spare parts but  

 are not going to maintain it any more. When those parts are gone,  

 they're gone forever.



 I finally got the VM1000 installed and powered up.  It was flaky  

 until I reseated the 4 socketted DIP components in the main control  

 box.  I attribute that to sitting unused for so long (and maybe  

 cheap sockets).  Seems to come up reliably now, but shows 2  

 problems. The CHT3 is consistently 15 - 20 deg. low and the  

 manifold pressure is about 2.5 inches low. It reads 27.3 when the  

 barometric pressure is 30.00.


	


What do you mean by when the pressure is 30.00, the altimeter  

setting?  What is your altitude? If your elevation is around 2,700  

feet the MP is probably correct.



Larry Pardue

Carlsbad, NM

khorton01(at)rogers.com
Guest

Posted: Sun Sep 09, 2007 3:35 pm Post subject: VM1000 manifold pressure and CHT sensors

On 9 Sep 2007, at 18:33, sarg314 wrote:



 	  Quote: 	
		   



 ... the manifold pressure is about 2.5 inches low. It reads 27.3  

 when the barometric pressure is 30.00.  The M.P. sensor is a  

 bellows type and can get stuck, so the tech at Vision Micro  

 recommended I just run the engine a bit. Well, I'm a few months  

 away from being able to do that and their inventory of spare parts  

 is only getting smaller, so rather than wait, I hooked up a hose to  

 it and actually blew into it gently.  I was able to make it change  

 +- 1 inch, so I don't think I did it any violence. But it still  

 returns to 27.3 in. when I leave it be.


	


What is the source of the barometric pressure you are using to  

compare the MP indication against?  Is it really the true barometric  

pressure, or is it possible that it is sea level corrected barometric  

pressure?  What is the elevation of your shop, roughly speaking?



Kevin Horton         RV-8 (finishing kit)

Ottawa, Canada

http://www.kilohotel.com/rv8

sarg314(at)comcast.net
Guest

Posted: Sun Sep 09, 2007 3:46 pm Post subject: VM1000 manifold pressure and CHT sensors

Larry:

    I am at 2200 ft. altitude.  The 30.00 is what I'd uses as the 

altimeter setting.  I didn't think 2200 ft would account for 2.7 in. of 

pressure difference, but I admit I was just guessing. 



Larry Pardue wrote:



 	  Quote: 	
		   What do you mean by when the pressure is 30.00, the altimeter  

 setting?  What is your altitude? If your elevation is around 2,700  

 feet the MP is probably correct.



 Larry Pardue

 Carlsbad, NM

n616tb(at)btsapps.com
Guest

Posted: Sun Sep 09, 2007 3:50 pm Post subject: VM1000 manifold pressure and CHT sensors

Tom,



Is this already all installed in your airplane?  I have an original VM1000

and if it wasn't installed I would drop it like a rock.  It would be a hard

decision because of what I spent for the system, but I would change mine out

even now if the sensors were compatible with something else.



I had a bad DPU resulting in no oil pressure reading.  I have been flying

with a mechanical oil pressure gauge installed under the dash for 10 months.

I finally got it taken care of but it took a lot including a flight to VM.

I would be very surprised if they had any spare parts at all.  In fact I

would be very surprised how much longer they will even have parts.



JPI bought them out but they are kind of like little orphans stuck in a

little hanger in Texas with little to no facilities.  My hangar at home is

better equipped than VM.



If it isn't installed, have you asked them about upgrading (actually

downgrading cost wise) to the VM1000c version?  I would steer completely

away from VM but since you have it they might swap you for a VM1000C latest

version.



Anyway, just my thoughts.  I am not happy with them and was very

un-impressed when I went to their facility.  It actually wasn't a facility

at all.



Tim



[quote] --

n5lp(at)warpdriveonline.c
Guest

Posted: Sun Sep 09, 2007 4:23 pm Post subject: VM1000 manifold pressure and CHT sensors

The rough rule of thumb for lower altitudes is one inch per  

thousand.  The altimeter setting is an entirely different thing than  

the true pressure.

Larry

On Sep 9, 2007, at 5:45 PM, sarg314 wrote:

 	  Quote: 	

 Larry:

    I am at 2200 ft. altitude.  The 30.00 is what I'd uses as the  

 altimeter setting.  I didn't think 2200 ft would account for 2.7  

 in. of pressure difference, but I admit I was just guessing.

 Larry Pardue wrote:

> What do you mean by when the pressure is 30.00, the altimeter   

> setting?  What is your altitude? If your elevation is around  

> 2,700  feet the MP is probably correct.

>

> Larry Pardue

> Carlsbad, NM

>

khorton01(at)rogers.com
Guest

Posted: Sun Sep 09, 2007 4:37 pm Post subject: VM1000 manifold pressure and CHT sensors

There is a big difference between altimeter setting and barometric  

pressure.  At sea level they would be the same thing.  If the  

altimeter setting is 29.92, that just means that the barometric  

pressure at that location is the same as the standard atmosphere  

pressure for that elevation.  The standard pressure for 2200 ft  

elevation is 27.62 " HG, so your MP gauge should read somewhere  

around that value, depending on whether the pressure of the day is  

higher or lower than a standard atmosphere.

The altimeter setting is just a way to adjust the altimeter to  

account for non standard pressure.  2200 ft elevation with an  

altimeter setting of 30.00 gives a pressure altitude of 2127 ft, and  

the standard pressure for that altitude is 27.69 inches of mercury.   

So, the MP indication should have been 27.7, which isn't a huge  

amount different from the 27.3 that you reported.  You might have a  

small error, but in my experience many MP gauges have errors of  

around 0.5". HG.

Kevin Horton

On 9 Sep 2007, at 19:45, sarg314 wrote:

 	  Quote: 	

 Larry:

    I am at 2200 ft. altitude.  The 30.00 is what I'd uses as the  

 altimeter setting.  I didn't think 2200 ft would account for 2.7  

 in. of pressure difference, but I admit I was just guessing.

 Larry Pardue wrote:

> What do you mean by when the pressure is 30.00, the altimeter   

> setting?  What is your altitude? If your elevation is around  

> 2,700  feet the MP is probably correct.

>

> Larry Pardue

> Carlsbad, NM

>

sarg314(at)comcast.net
Guest

Posted: Sun Sep 09, 2007 5:37 pm Post subject: VM1000 manifold pressure and CHT sensors

Kevin:

    That's awfully close.  I'd better check this before I "fix" the MP 

sensor.  I guess I was shooting from the hip on that one. 

Thanks.



Kevin Horton wrote:



 	  Quote: 	
		   



 There is a big difference between altimeter setting and barometric  

 pressure.  At sea level they would be the same thing.  If the  

 altimeter setting is 29.92, that just means that the barometric  

 pressure at that location is the same as the standard atmosphere  

 pressure for that elevation.  The standard pressure for 2200 ft  

 elevation is 27.62 " HG, so your MP gauge should read somewhere  

 around that value, depending on whether the pressure of the day is  

 higher or lower than a standard atmosphere.

sarg314(at)comcast.net
Guest

Posted: Sun Sep 09, 2007 5:42 pm Post subject: VM1000 manifold pressure and CHT sensors

Tim:

    Thanks for relating your recent experiences. I'm afraid I'm 

"married" to the thing at this point.  It's fully installed.  These 

things seemed to be the way to go 5 or 10 years ago, but I guess they 

are quite dated now.  The JPI buy out certainly doesn't help.



Advice to other builders who aren't as far along as I am:  Don't buy the 

expensive, complicated electronic stuff until you really have to in 

order to proceed.  This stuff changes fast and gets smarter and more 

cost effective as time goes on.  I bought the VM1000 because I was 

offered a good price just before a price hike was going to happen.  Of 

course, I didn't think it was going to take me this long to finish the 

plane at that time, but that's a different problem.



Tim Bryan wrote:



 	  Quote: 	
		  

Tom,



Is this already all installed in your airplane?  I have an original VM1000

and if it wasn't installed I would drop it like a rock.  It would be a hard

decision because of what I spent for the system, but I would change mine out

even now if the sensors were compatible with something else.

  



-- 
	


Tom Sargent

recapen(at)earthlink.net
Guest

Posted: Mon Sep 10, 2007 4:03 am Post subject: VM1000 manifold pressure and CHT sensors

I have one of the early ones too.  Initially Vision Microsystems was the best on the market and their service was pretty good too.  I had mine upgraded to the RS232 connectors and the DPU was initially set up for the wrong fuel pressure sender (but they shipped the correct sender).  I got a great deal when I bought it.  It was completely installed - waiting for the rest of the project to finish.



Since reading about their purchase by JPI (another can of worms itself) and their dropping of support for the first and second generation units, I've decided to remove it and install an AFS3400EM - it's now completely installed and I've been parting out the VMS1000 parts to keep existing units running.



Ralph Capen



--

Vanremog(at)aol.com
Guest

Posted: Mon Sep 10, 2007 7:29 am Post subject: VM1000 manifold pressure and CHT sensors

In a message dated 9/9/2007 4:13:59 P.M. Pacific Daylight Time,  sarg314(at)comcast.net writes:

  	  Quote: 	
		  Thanks,    I guess I'll have to swap CHT sensors.  I don't like handling 

those    things - I keep expecting that stiff T.C. wire to fatigue and break.



I    was looking for a "trouble shooting" section in the manual, but mine    

doesn't have one.  I didn't get anything else with the unit and their    

web page has no downloads.  How did you get  yours? 	


 

 ===========================================

  

 Tom-

  

 I have a sheet of troubleshooting info for each of the instrument systems  in hard copy.  I will happily fax it to you if you like.   

 N1GV (RV-6A, Flying 865hrs, O-360-A1A, C/S, Silicon  Valley) 





Make AOL Your Homepage.

  [quote][b]

n616tb(at)btsapps.com
Guest

Posted: Mon Sep 10, 2007 7:45 am Post subject: VM1000 manifold pressure and CHT sensors

Tom,



You are right it was once the one to have.  I understood Mooney was putting

them in there certified planes.  These were the reasons why I chose it.  Too

bad it had to go down hill from there.  Of course I purchased the UPS

slimline stack for my airplane also just before Garmin bought them out and

discontinued some of the product.  I noticed the MX20 is now discontinued

also.  It really sucked to have my stuff all discontinued even before my

airplane flew.  It still works great however and I am enjoying it but would

like to see some updates (never will happen).



Tim

Do Not Archive



[quote] --

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