Pressure sensor!!

[Seagull]

Has anyone used any of Freescale pressure sensors before? I got a sample of (MPXV5050GP) that is used in the application note (AN1571). I am having a difficulty dealing with these sensors and I believe it is because of the mechanism of reading the pulse, i.e. the way I am putting it on my rest to read the pulse.

If you have used this sensor before please do advice me the right way to get best results and if you have not, I'll be happy to get any general advices that might help.

By the way, I am using the same amplification circuit that Freescale recommended but I can not get the results that is shown in figure 4/page 3 of the application note!!

Thanks.

[Seagull]

Sorry Moderator .. I thought of that before but all other forums are either for MCUs or for CodeWarrior, and I thought this might be good place because itis called "Forum Use, Policies, and General Questions ".. It might be worth to make specific forum for such topics .

[bigmac]

Hello Tom,

The categorization of this type of query does seem to pose a problem.  Perhaps a quick solution to the issue might be to alter the description for the forum "Other microcontrollers/microprocessors" to include "Other microcontrollers/microprocessors and sensors".]

Regards,

Mac

[J2MEJediMaster]

I'll look into this. I try to be flexible. After all, that's why I left it here. It didn't seem to be a good fit anywhere else...

[Seagull]

Here we go,, I got it work.. happy days .

I thought of explaining what I did so that might help others, I really searched a lot about this matter over the net and could not find any details.

What I did before was following the application note that Freescale has provided, which was useful in the electronics area, but it didn't mention any mechanical notes (unless if I missed something while reading).

The change that I did was to put the port of the pressure sensor into closed environment,, I used a cap of pipe, made hole in it and passed the pressure port in it. I used the same op-amp circuit that Freescale recommended and I got it work

So it is all about holding the pressure in small area, which is between my rest (to read the pulse) and the port of the pressure sensor, see figure 1

 

Figure 1

Doing this caused good signal to appear on the oscilloscope, see figure 2

Figure 2

You could see there is some sort of noise,, the application note has 2nd order high pass filter, I was surprised they don’t use band pass filter instead!!!!  Because we have two sources of noise, one is the instability of the hand (or the inflatable cuff too) which causes (low frequency) noise to appear (< 3 Hz) and the other high frequency noise is coming from the power source and any other components that would generate some ripple.

So the next step is to replace the high pass filter with band pass filter (passing 2-10 Hz) and the signal was far cleaner, see figure 3

Figure 3

So, here we go, the analogue bit seems better now and I can progress with my final year project now and start playing with the digital bits

SEAGULL

www.telsim.co.nr

Message Edited by Seagull on 2008-07-31 11:51 AM

[J2MEJediMaster]

Well, normally you're not supposed to ask technical questions here, and I make a point of moving them when it happens. However, I can't think of where this one would go in the regular Freescale forums, and since bigmac answered it, I'm going to leave it here.

However, having said that, in the future post any technical questions in the forums, please.

---Tom

[Seagull]

Cheers Mac for the information,, I'll keep trying to work it out and if I do so I'll post the solution here.

[Seagull]

I am using the same op-amp,,but I don't use the inflatable cuff because I am not concern the amplitude accuracy at this stage.. I assume using the inflatable cuff is like a mechanical amplification,, please correct me if am wrong.

All what I am after is to get the pulse reading on the oscilloscope, I thought it would be far easier when I read the datasheet of the sensor,, but it does not seems as easy as I thought!!

[bigmac]

Hello,

The operation of a pressure cuff would be similar to the diaphram of a microphone - a means of coupling the pulse signal to the pressure transducer.  A stethoscope might be another possibility to achieve the coupling.  Without a similar coupling arrangement, it may not be feasible to use the pressure sensor.

For measurement of heart rate, there may be other potential methods such as optical detection.  My understanding is that a LED and photodetector combination can be attached to a finger, with the LED projecting light through the finger to the photodetector.

Regards,

Mac

[bigmac]

Hello,

For blood pressure and heart rate monitoring, the application note assumes the use of an inflatable cuff.  You do not say whether this is what you are using to couple into the pressure sensor.

For the amplifier circuit, are you using the specified op amp type, or perhaps another type?  Your input bias voltage of about 0.86 volts will require that this be within the common mode input range for the device you are using.

Regards,

Mac

[mauricio2346]

Hello.

does anybody tried to sense airflow trough venturi tubes?

in this moment i have some MPX2010 gauge pressure sensors, one friend of mine has some differential sensors (same label) but he can't find those sensors.

anyway, i was wondering about using gauge sensors to sense airflow this way:

sense  each gauge pressures from the only pipe port of the sensor (unfortunately, it will sense some little vacuum related to atmospheric pressure -depends of air speed).   then (keeping in mind atmospheric pressure reading) compare both signals, and obtaining differential pressure, then airflow rate.

is it possible?

what do you think?

plus, i have one MPX2010D (stainless steel case, no ports).  what would be the applications for this sensor? (how to make readings)

greetings;

Mauricio

[railroadnut]

My apologies for posting here, but I did not see any other sensor questions listed elsewhere. We are intending to use an MPX5999D sensor to measure pressure in a closed system. The working fluid is mineral oil. Has anyone verified compatibility with fluids other than air? Will I need to make an isolation barrier between the oil and the air in the sensor?

Any feedback would be helpful.

Steve Green

Engineer

Crist Instrument Co

[mazzim]

Steve,

I have not used that specific sensor in oil. BUT,  I have used the MPX4250 in oil for over 12 years with no problems.  I even stressed it over it's maxim rating many, many times and it has survived.

I don't think you'll be able to use the your MPX5999D in a closed system without somehow exposing one of it's faces to atmoshperic pressure. Not easy.

Marco