Missile Works/CP Tech. Altimeter Sensor

Missile Works/CP Tech. Altimeter Sensor

Post by Craig Frase » Wed, 23 Dec 1998 04:00:00



Can anyone tell me the pressure sensor this altimeter uses? TIA
 
 
 

Missile Works/CP Tech. Altimeter Sensor

Post by Jeff Taylo » Thu, 24 Dec 1998 04:00:00


Quote:

> Can anyone tell me the pressure sensor this altimeter uses? TIA

 From the picture on the Missileworks web page, it looks like a Motorola
4115.

JT

 
 
 

Missile Works/CP Tech. Altimeter Sensor

Post by Craig Frase » Thu, 24 Dec 1998 04:00:00


Yes, it sure does, and that's what I'm hoping. Would drastically reduce my
cost if I tried a "kit" and could use my spare. But could be the 5000 series
too.
Quote:


> > Can anyone tell me the pressure sensor this altimeter uses? TIA

>  From the picture on the Missileworks web page, it looks like a Motorola
> 4115.

> JT

 
 
 

Missile Works/CP Tech. Altimeter Sensor

Post by Christopher Co » Fri, 25 Dec 1998 04:00:00


From what I understand, Motorola parts are noisy. It is the reason you do
not see them implemented on many of the commercial units.

Christopher Cox

 
 
 

Missile Works/CP Tech. Altimeter Sensor

Post by Konrad Hambri » Wed, 30 Dec 1998 04:00:00



Quote:

>From what I understand, Motorola parts are noisy. It is the reason you do
>not see them implemented on many of the commercial units.

>Christopher Cox

Christopher --

Do you have more info ?

The Motorola 4100 looks pretty clean
on a silly scope and at 8-bits, there
is no noise at all ;-)

-- kjh
--
------------------------------------------------------------

1111 Seacoast Dr.  Unit 41   |  home:   (619) 423-4451     |
Imperial Beach, CA   91932   |                             |

 
 
 

Missile Works/CP Tech. Altimeter Sensor

Post by Craig Frase » Wed, 30 Dec 1998 04:00:00


I thought it was just because of their high price. Mine work OK, and give
very consistent static readings, if that means anything.
Quote:

> From what I understand, Motorola parts are noisy. It is the reason you do
> not see them implemented on many of the commercial units.

> Christopher Cox

 
 
 

Missile Works/CP Tech. Altimeter Sensor

Post by Christopher Co » Wed, 30 Dec 1998 04:00:00


Quote:
> I thought it was just because of their high price. Mine work OK, and give
> very consistent static readings, if that means anything.

How many bits? 12, 14, 16? The noise, I am told, started to show up when
using a 14 bit or better converter.

Christopher Cox

 
 
 

Missile Works/CP Tech. Altimeter Sensor

Post by Konrad Hambri » Thu, 31 Dec 1998 04:00:00



Quote:

>> I thought it was just because of their high price. Mine work OK, and give
>> very consistent static readings, if that means anything.

>How many bits? 12, 14, 16? The noise, I am told, started to show up when
>using a 14 bit or better converter.

>Christopher Cox

Christopher --

I imagine so.  The Motorola MPX4100A Xducer has an abs pressure
range of around 12 psi ( 20 --> 105 KPa == 85 KPa ).

At 14 bits, assuming 4.5 volt output range and a 5-volt supply,
1-binary unit would be ( 1-Orville == 1-binary unit and at 14-bits,
there are 16384 Orvilles full scale ;-)

      Pressure / Volt    = 85 KPA / 4.5 Volts
                         = 18.8889 KPa / Volt

      Volts / Orville    = 4.5 / 16384
                         = 0.002747 Volt / Orville

      Pressure / Orville = 0.005188 KPa / Orville

The Altitude for a pressure difference of 0.005188 KPa at sealevel
is:

   palt -crv 101.325k
   Press      = 29.9213 inHg
   BasePress  = 29.9213 inHg
   PressRatio = 1.0000
   Altitude   = 0 ft

   palt -crv 101.3198k               # sub 0.005188 KPa from 101.325 KPa
   Press      = 29.9198 inHg
   BasePress  = 29.9213 inHg
   PressRatio = 0.9999
   Altitude   = 1 ft

A difference of 1-foot.

At the edge of the troposphere, 11,000 meters ( 36089 ft ), the
pressure of the US Standard atmosphere would be:

   palt -k 11000m
   22.6061 KPa

The altitude difference for a change of 0.005188 KPa at 11000 m is:

   palt -crv 22.6061k
   Press      = 6.6756 inHg
   BasePress  = 29.9213 inHg
   PressRatio = 0.2231
   Altitude   = 36089 ft

   palt -crv 22.6113k               # add 0.005188 KPa to 22.6061 KPa
   Press      = 6.6771 inHg
   BasePress  = 29.9213 inHg
   PressRatio = 0.2232
   Altitude   = 36084 ft

A difference of 5-feet.

Noise, pressure and temperature hysteresis, sensitivity variation
with temperature, voltage supply noise, actual pressure variation
in the altimeter bay and especially the natural variation of the
US Standard Atmosphere far exceed this level of precision
( by orders of magnitude ).

Maybe the problem lay elsewhere ?

What was the user trying to accomplish with the pressure xducer ?

-- kjh
--
------------------------------------------------------------

1111 Seacoast Dr.  Unit 41   |  home:   (619) 423-4451     |
Imperial Beach, CA   91932   |                             |

 
 
 

Missile Works/CP Tech. Altimeter Sensor

Post by Christopher Co » Thu, 31 Dec 1998 04:00:00


Quote:
> Noise, pressure and temperature hysteresis, sensitivity variation
> with temperature, voltage supply noise, actual pressure variation
> in the altimeter bay and especially the natural variation of the
> US Standard Atmosphere far exceed this level of precision
> ( by orders of magnitude ).

> Maybe the problem lay elsewhere ?

Nope, general noise problem went away when dropping the Motorola part.

Quote:
> What was the user trying to accomplish with the pressure xducer ?

Measure to the foot.

The philosophy is very much like the one taken to receive very weak radio
signals, every part helps. With radio, every dB in the chain counts even
though a single dBi by itself is hardly worth the labor. I am told the
Motorola parts have a poor noise floor, part replacement with a less costly
part with a better measured noise floor seems logical.

Christopher Cox

 
 
 

Missile Works/CP Tech. Altimeter Sensor

Post by Konrad Hambri » Fri, 01 Jan 1999 04:00:00



Quote:

>> Noise, pressure and temperature hysteresis, sensitivity variation
>> with temperature, voltage supply noise, actual pressure variation
>> in the altimeter bay and especially the natural variation of the
>> US Standard Atmosphere far exceed this level of precision
>> ( by orders of magnitude ).

>> Maybe the problem lay elsewhere ?

>Nope, general noise problem went away when dropping the Motorola part.

>> What was the user trying to accomplish with the pressure xducer ?

>Measure to the foot.

>The philosophy is very much like the one taken to receive very weak radio
>signals, every part helps. With radio, every dB in the chain counts even
>though a single dBi by itself is hardly worth the labor. I am told the
>Motorola parts have a poor noise floor, part replacement with a less costly
>part with a better measured noise floor seems logical.

>Christopher Cox

Thanks a __lot__ Christopher.  

Now I gotta go measure the MPX4100 noise with an oscilloscope :-)

I'll let you know.  I have not been able to find any pub'd
specs on the MPX4100 signal-to-noise ratios as %FSS.

-- kjh ( is not the net noise of a system the sum ( or product )
         of the noise of each part of the complete system, too ? )
--
------------------------------------------------------------

1111 Seacoast Dr.  Unit 41   |  home:   (619) 423-4451     |
Imperial Beach, CA   91932   |                             |

 
 
 

Missile Works/CP Tech. Altimeter Sensor

Post by Bob Kapl » Sat, 02 Jan 1999 04:00:00


Quote:



>>> Noise, pressure and temperature hysteresis, sensitivity variation
>>> with temperature, voltage supply noise, actual pressure variation
>>> in the altimeter bay and especially the natural variation of the
>>> US Standard Atmosphere far exceed this level of precision
>>> ( by orders of magnitude ).

>>> Maybe the problem lay elsewhere ?

>>Nope, general noise problem went away when dropping the Motorola part.

>>> What was the user trying to accomplish with the pressure xducer ?

>>Measure to the foot.

>>The philosophy is very much like the one taken to receive very weak radio
>>signals, every part helps. With radio, every dB in the chain counts even
>>though a single dBi by itself is hardly worth the labor. I am told the
>>Motorola parts have a poor noise floor, part replacement with a less costly
>>part with a better measured noise floor seems logical.

>>Christopher Cox

> Thanks a __lot__ Christopher.  

> Now I gotta go measure the MPX4100 noise with an oscilloscope :-)

I would think that linearity would be as critical or more so than noise. I
remember early CD players that used really crappy DACs that were relatively
noise free but VERY non linear. it became a very popular upgrade hack to
replace several components to improve the "pure perfect sound". One of these
days, I'm gonna get me that CAL Vacuum Tube Analog CD player (no funny face,
this is for real).

        Bob Kaplow      NAR # 18L       TRA # "Ctrl-Alt-Del"

Kaplow Klips:   http://members.aol.com/myhprcato/KaplowKlips.html
NIRA:           http://www.nira.chicago.il.us  NAR:    http://www.nar.org

 
 
 

Missile Works/CP Tech. Altimeter Sensor

Post by Konrad Hambri » Sat, 02 Jan 1999 04:00:00



Quote:




>>>> Noise, pressure and temperature hysteresis, sensitivity variation
>>>> with temperature, voltage supply noise, actual pressure variation
>>>> in the altimeter bay and especially the natural variation of the
>>>> US Standard Atmosphere far exceed this level of precision
>>>> ( by orders of magnitude ).

>>>> Maybe the problem lay elsewhere ?

>>>Nope, general noise problem went away when dropping the Motorola part.

>>>> What was the user trying to accomplish with the pressure xducer ?

>>>Measure to the foot.

>>>The philosophy is very much like the one taken to receive very weak radio
>>>signals, every part helps. With radio, every dB in the chain counts even
>>>though a single dBi by itself is hardly worth the labor. I am told the
>>>Motorola parts have a poor noise floor, part replacement with a less costly
>>>part with a better measured noise floor seems logical.

>>>Christopher Cox

>> Thanks a __lot__ Christopher.  

>> Now I gotta go measure the MPX4100 noise with an oscilloscope :-)

>I would think that linearity would be as critical or more so than noise. I
>remember early CD players that used really crappy DACs that were relatively
>noise free but VERY non linear. it became a very popular upgrade hack to
>replace several components to improve the "pure perfect sound". One of these
>days, I'm gonna get me that CAL Vacuum Tube Analog CD player (no funny face,
>this is for real).

Bob --

Linearity is one thing I did test for myself on the MPX4100A.

Motorola claims linearity is +|- 0.2% FSS.  Near as I can
tell the claim is true.  The output is straight as a stick
and very temperature independent.

The 4100A is "Compensated and Calibrated".  IOW, it is temp
stable and the output is very consistant from unit to unit.

-- kjh ( Ain't vacuum tubes great ? )

--
------------------------------------------------------------

1111 Seacoast Dr.  Unit 41   |  home:   (619) 423-4451     |
Imperial Beach, CA   91932   |                             |

 
 
 

Missile Works/CP Tech. Altimeter Sensor

Post by Marie Holyfiel » Mon, 04 Jan 1999 04:00:00


   Ok  So somebody tell me do they work?