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blood pressure monitor

ello  and Good day Everyone!

This is  my frist message to the discussion board,  i am  a new memeber to this forum!

Currently  i am working on my final year project to design a oscillometric blood pressure monitor!

Oscillometric follows the principle of reading the cuff pressure  from the cuff.  I am currently using a pressure sensor- SX015DN, this particular  pressure sensor gives a differential output  based on the pressure it reads  from the cuff., Out put from the pressure sensor is basically in milli volts. What i have done is , im passing the output from the  pressure sensor to the instrumentation amplifier( AD622) to amplifie the signal . Further i  have to pass on the analog out of amplifier to the  I/O board  of the dspace card. It is simple project  BUT ,my PROBLEM  is  im basically loosing the signal from the  output from the pressure sensor.  Noise is  overiding the output from the pressure sensor.  Issue is that pressure sensor gives differential output in milli volts and the milli volt signal is LOST by the time  it reaches the input of the amplifier AD622.

I am working on this project since ages now, its just that i am stuck and dunno  steps i should take so that i dont loose  my signal and also eliminate the noise!

I would APPRECIATE ANY SUGGESTION regarding the same.
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Message 1 of 12
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Please provide more Information on your hardware setup:

I would guess you have some EMC/gounding/shielding problems

I assume a Honeywell SX01DN Sensor (that was the onlyone I could find that far..)

In princible the differential output is good. What type of cable are you using? How is the shielding realised? How the powersupply?

Does your AD-Card (Type?) provide differential inputs?

Take a look at the AD622 datasheet, there you find some hints on how to use the reference output to connect to the AD input. ( star-ground-topology)

 

Message Edited by Henrik Volkers on 08-02-2006 02:10 PM

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


Message 2 of 12
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Hi Henrik, Thanks for ur suggestion!
 
I would surely agree with u..i feel there is grounding or shielding problem! I can ACE any software application, i must confess i am not the best guy for hardware. I am not able to exactly fingure out the problem.
 
 
 
 
following is the attachment of the datasheet for sx15DN! The differential output at max pressure applied is 40mV.
 
Currently what i have done is i have built my circuit on a Bread board. I have got my 12V power supply from a direct DC source to the AD622 amplifier.  I have used a 5V voltage regulator to supply DC for the sensor.i have have also used 10microfarad bypass capacitors.
 
According to the pin diagram of the sensor(DIFFERENTIAL GAGE) : Pin1-Ground, Pin2+Vout, Pin3-+Vsupply, Pin4-  -Vout.
 
I have directly used a none shielded or normal copper wire and connected
 Pin2 of sensor- pin 3 of AD622, pin4 of sensor- pin2 of AD622.
 
i have grounded the refrence pin6 of AD622 and pin7 and pin 4 are positive and negative  DC supplies! I have added resistor between pin1 and pin 8 to get a gain of around 200 V/V.
 
guys please let me know your suggestion and steps i should take to resolve the issue.
 thanks once again...
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Message 3 of 12
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@pbs wrote:
[...]
Currently what i have done is i have built my circuit on a Bread board. I have got my 12V power supply from a direct DC source to the AD622 amplifier.  I have used a 5V voltage regulator to supply DC for the sensor.i have have also used 10microfarad bypass capacitors.
 
According to the pin diagram of the sensor(DIFFERENTIAL GAGE) : Pin1-Ground, Pin2+Vout, Pin3-+Vsupply, Pin4-  -Vout.
 
I have directly used a none shielded or normal copper wire and connected
 Pin2 of sensor- pin 3 of AD622, pin4 of sensor- pin2 of AD622.
 
i have grounded the refrence pin6 of AD622 and pin7 and pin 4 are positive and negative  DC supplies! I have added resistor between pin1 and pin 8 to get a gain of around 200 V/V.
 
guys please let me know your suggestion and steps i should take to resolve the issue.
 thanks once again...


Take the shematic in figure 16 of the 622 datasheet as a guide. As a first breadboad test use bipolar power supply ! 

If you use +/- 5V you can also drive your sensor (bridge)  with 10V, Use 100nF AND 100pf (ceramic) parallel and as short as possible to the IA to buffer Vs and Vd to grnd,  

Use at least twistet cable pairs, better two shielded twistet pairs to your sensor. both shields grounded,  one for the power, second for signal. (or use cat5 cable that is flying around everywhere today, but look out which pairs are twistet)

   

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


Message 4 of 12
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What's about your AD-Card? Spec? Diff. input? 

 

PS: you can rate good answers 😉

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


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Message 5 of 12
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Personally, I would construct this on copper clad and with a full metal enclosure around it. Skip the power supplies and go to battery powered operation.
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~
"It’s the questions that drive us.”
~~~~~~~~~~~~~~~~~~~~~~~~~~
Message 6 of 12
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I just stumbled over an old but +++++  app. note (AN 43)  from Jim Williams (Linear) about bridge circuits ...  with a nice digg into history (Lord Kelvin,..,Mr. Hewlett (HP))

 http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1154,C1009,C1026,P1213,D4134

always worth a look!  Browse the app. notes to find an learn more about analog circuitry.

 

Message Edited by Henrik Volkers on 08-03-2006 02:06 PM

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


Message 7 of 12
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Hi Henrik,

Sorry bout the late reply!

The A/D card is basically a Dsapce card which i am using with controldesk 1.1 and matlab being used for analysis of the captured blood pressure waveform.

Let me know if u come across or have any more material for noise elimination and ground practise.

I am still tring to work out and eliminate noise! Project is easy..its just once sensor and a amplifier..things should work out...i am plannin to change sensor to mpx5050 gp..it gives out put in volts rather than milli volts. issue is i tried every place in melbourne but coudnt find any.

I wil keep u posted. I also NEED more feedback from other guys in forum pls!

cheers

priyank

 

Message Edited by pbs on 08-03-2006 09:03 AM

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Message 8 of 12
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Have you tried to get a FREE SAMPLE of the MPX from freescale?? 
 
Again, a spec or more details on your AD-Card (Type, configuration) will help a lot.
 
 
 
Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


Message 9 of 12
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Hi there,

Appologise for the late reply, was busy wid preparations for the test.

I am using dspace card- ds1102 to capture the waveform.

Basically ds1102 is stand alone controller board with various I/O units such as A/D, D/A conversion, digital I/O, PWM generation, incremental encoder interface and a harware interupt.

The purpose of the A/D converter is to provide read access for four parallel A/D converters.

Input voltgae supply range is +- 10 volts.

The resolution of the 1st 2 channels is 16 bits, whereas chaneel 3 and 4 provide 12 bit.

The conversion time of channels 1 and 2 is about 4micro second and of channel 3 and 4 is 1.25 micro seconds.

Henrik i am now going through the notes which u had recommended me.( Application notes of the linear technology). Lets see i will have to be quick to figure out something. WIth the mpx5050gp i wanna buyt them but the most unfortunate thing is none of the suppliers in australia stock them, so i am in a bit of fix due to that. I am tring to contact some friends in US and Uk to see if they can courier it to me.

Wish me luck. Will keep u posted.

cheers

priyank- <<I CAN DO IT, I WILL DO IT CAUSE I WANNA DO IT>>>>>

 

Message Edited by pbs on 08-07-2006 07:38 AM

Message Edited by pbs on 08-07-2006 07:39 AM

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