Substitute for MPX100AP pressure transducer

[spatial]

I'm looking for a subsitute for the Motorola MPX100AP pressure transducer for use in a Digipress 96 controller for vacuum bagging (see http://frederic.brame.free.fr/electron/electron.htm) I've found a reference (http://www.d8apro.com/heath3.htm) that suggests that the MPX2100AP will be an acceptable substitute, but I'm wondering how close these two parts actually are. Any ideas?

Paul

[william541]

Paul,

Freescale kind of has you over a barrel on this one. The older Motorola MPX100A sensors were not temperature compensated and had an deltaV/deltaP output of 0.6mV/KPa.

The MPX2100A and MPX2050 are temperature compensated, but the outputs are 0.4mV/KPa (MPX2100A) and 0.8mV/KPa (MPX2050).

Sorry, not drop in replacement. If your machine has a way to trim or calibrate the pressure reading, then one of the two sensors may work for you.

-Bill-

[Acetronics]

:)
Hi, paul

Just two resistors to modify to correct the amplifier gain ( R8 and R9 ) ...

Alain

[spatial]

Alain,

I should have expected a francophone to know what I was talking about ;)
Thanks for the info's, that definitely gives me some hope! what values do you suggest for R8 and R9?

It's interesting try to make sense of the doc's as my french is very limited and the babblefish translations leave a lot to be desired :confused: At least I understand enough to build the unit.

Paul

[Acetronics]

Hi, Paul

Just modify R8 to be 1020 k Ohms ( two resistors in series ) - or a small 47k cermet pot plus 1M resistor.

Other solution ( the best ! ) is to parallel R14 with 200k 1% . ( giving 66.666667 k )

Alain

[spatial]

Hi Alain,

merci!! just recieved notification that the MPX2100AP I'd ordered has shipped so your information was fortutious ;)

Paul

[spatial]

ok, i'm a bit stuck here.... I've got the digipress 96 unit built and "working", done a dodgy translation of french -> english for the UI and all seems good, however I obviously have missed something vital in the substition ov mpx2100 for mpx100. I'm unable to zero the pressure reading and have a "depression" reading of 200millbars with the trimpot set to minimum - from what i understand I need to get this setting to be 0 millibars. The voltage to the dac should be 1.76V for an atmospheric pressure of 1013mb, but I'm getting 2.15V @ 1019.8mb so Ive clearly got something messed up with the gain compensation.

the schematic can be found at: http://frederic.brame.free.fr/electron/digiprs/sch-digi.gif

I've paralleled r14 with a 200k 1% metal resistor to 66.67K, but this gives the above readings. I'm obviously going to have to alter the gain to get things working correctly. Unfortunately I'm still pretty much at "follow the instructions" syage so I'm a little lost as: a) how to calculate what the gain should be and b) how then set the gain of the opamp to suit.

any advice and/or explations would be really appreciated :)

cheers
Paul

[Acetronics]

:D
Hi, Spatial

I couldn't do your translation 'cause impossible to find anymore the link to the project ( i didn't save it ...)

I must apppologize ... the 200 k resistor was to parallell to R9, instead of R 14 ... that way, it doesn't trouble Zeroing the device ...

so, just move it, and everything will go well.

For the beauty of electronics, you can parallell a 200 k on R 10 also ... this will improve ( a small bit !!! ) the linearity.

in the time looking for, I found another vacuum regulator ... but with a PIC processor ...

Alain

[spatial]

Hey Alain

just got back from reading up on op amps :) so i can understand now that the change in r14 increases gain by x1.5 to compensate for x1.5 decrease in output of MPX2100 vs MPX100... I'd realised looking at the schematic that the offset was the culprit so I was about to ask a revised question re: that, but you have already answered my new question. time to plug in the soldering iron again :)

i agree that it's working well and the offset is the only problem now :0

what is the new pic based vacuum regulator you have found?

cheers
Paul

[Acetronics]

Just edited my message ... reload it ...

Alain

[Acetronics]

Hi, Paul

The PIC vacuum regulator is here :

http://www.teaser.fr/~osegouin/aeromode/picapress.phtml

but, you must ask for programming the device ...

Alain

[spatial]

ahhh cnc@net ;) looks good!

so is the change to the offset R11 is still needed??
and parallel r9 & r10 with 200K resistor

cheers
paul

[Acetronics]

;)

No more need to change R11 ...
Parallel R9 and R 10

Translation:

Consigne = Target pressure

Reste = time remaining

T mot = total motor running time

Ouvrir tube = open tube ( for zeroing )

Meteo = Zeroing pressure ( on your barometer )

Pression = pression in the bag

Taux de fuite = % of leakage ( from what acceptable )

Her we are ... now !!!

A question : are you interested in 1/5 car races ???

Alain

[spatial]

ooops better get the solder wick out (again) ;)

ok i haven't gone to far wrong with the translation by the sounds of it!

i haven't seen any 1/5th car racing... the closest i go to car racing is my fathers vintage cars - my parents spent six months last year driving thru europe in a 1934 lagonda rapier and spent quite a bit of time in france :)

cheers

Paul

[Acetronics]

"1934 lagonda rapier "

I found wonderful pics on the web ... THAT's a car !!!

it's really a way of life ...

Alain

[spatial]

for my parents car in action in france see:

http://www.grandprixdetours.com/engages2004/lagondarapier1934-2.jpg

i'm interested in the 1/5th scale car racing :)

paul

[Acetronics]

Ok, paul

a frien of mine is a modeller and a 1/5 tyre manufacturer, he'll go to Australia for the world contest.

Here is his mail : morbin.william@wanadoo.fr
his site : http://perso.wanadoo.fr/mes-avions-rc

"little" interesting things to watch ...

Alain

[spatial]

thanks again alain,

i've added the parallel 200K resistors at R8,9 and everything seems to be working, however I've had to make R11 750k to get it to zero :confused:

seems to be reading slightly over actual pressure - less than 10 millibars so i guess that is within spec :)

when/where are the world championships?

cheers
Paul

[Acetronics]

:confused:

I'm a bit surprised by the 750 k ...

you could verify the measure by placing a tube in the inlet, with 1.00 meter heigh of water ... pressure will have to raise by 100 mb or 101.3 kPa.

Championships are for summer 2006 ... you'd better ask more from William ( very kind guy )

Alain

[spatial]

i'm not sure how I should make the water tube setup! I'd imagine that simply attaching a tube and feeding water into the mpx2100 would damage/destroy the device.

After doing a bit of digging to fill in the gaps in my knowledge I see that increasing the value of r11 is increasing the trimming voltage being feed to pin 5 of the tl082. So it would seem that the gain being applied to the differential between pins 2 and 4 of the MPX2100 is too high?

I'll double check all the component values but I'm pretty sure they are correct.

cheers
Paul

[spatial]

I've been reading one of freescales app notes for the mpx2100ap and discovered something that sheds light on my problem.

One of the differences between the original MPX100 and the MPX2100 is the rated suppy voltage. The MPX100 has a typical supply voltage of 3v while the corresponding value for the MPX2100 is 10v. The supply voltage to the MPX unit on the digipress 96 is 5v.

According to the app note (AN1326) for the MPX2100 the difference between the typical supply voltage and the actual supply voltage effects the full scale span in a linear manner.

So the for the MPX2100 running at 5V: 5/10 * 40mV = 20mV

Assuming the same applies for the MPX100?

then: 5/3 * 60mV = 100mV

If my assumptions are correct, the required gain increase is 5 rather than 1.5.

cheers
Paul

[Acetronics]

Hi, Paul

You're right. Ididn't had a look to output vs. typ supply voltage.

MPX 100 output is also a function of supply voltage.

so, the 100k resistors R8 and R9 can be replaced by 20k 1% ...

regards

Alain

[spatial]

Alain

thanks for the confirmation. I'll make those substitutions tonight. better dash and buy some solder wick before the shops close :0

cheers
Paul

[spatial]

bingo!! r8 & r9 = 20K, r11 =330k, depression can be set to zero with trim pot p2 near center of travel. we have a winner!

Alain thanks so much for your help with this :)

cheers
Paul