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advice on a simple pressure sensor?

A

amorphia

Jan 1, 1970
0
Hi all,

I'd much appreciate any advice on my search for a cheap and simple
pressure sensor. I need to make a device which can measure how hard a
baby is squeezing a tube, around 2cm thick. I figure the best way is to
use a silicon tube, just above atmospheric pressure, and connect it via
a pneumatic tube to a pressure sensor. So what I need is a pressure
sensor that does not have to be accurate in absolute terms, but needs
to be relatively sensitive, so it can measure changes in grip strength.
I reckon if it went up to 1000 kPa that would be more than enough.
Preferably it would come with an integrated USB interface and drivers
which provided an API. Alternatively, if you know a good one but it
just outputs a voltage, perhaps you could also recommend a good cheap
and cheerful USB A to D converter?

So far the best thing I've found is this, which you can combine with
a USB interface from the same supplier:
http://store.pasco.com/pascostore/showdetl.cfm?&DID=9&Product_ID=51374&Detail=1
But I think it will only interface using their proprietary software -
it's for classroom use, after all. But this gives you a basic idea of
what I'm after.

Other solutions to the basic problem also gratefully received!

Cheers,

Ben
 
C

CWatters

Jan 1, 1970
0
amorphia said:
Hi all,

I'd much appreciate any advice on my search for a cheap and simple
pressure sensor. I need to make a device which can measure how hard a
baby is squeezing a tube, around 2cm thick.

Presumably you will also need to correct for temperature - The baby's hand
will warm up the air in the tube causing the pressure to rise even if they
don't squeze it.
 
1000kPa is ~145PSI! It's going to be one strong baby?!

You're going to need a design but here's how I would go about it - I
would connect the silicon tube directly to the sensor and seal the open
end. Before use I would take a reading from the sensor without the baby
squeezing the tube and uses this as a baseline (this would remove
ambient conditions such as room temperature and altitiude), then get
the baby to squeeze and take a reading then subtract the baseline
reading from the measured reading. The trouble is babies are not always
the most cooperative and like the other poster mentioned the heat from
the hands would effect the readings if the tube was held too long. The
wall of the tubing would have to be pretty thin so as not to damp the
readings too much as I wouldn't think the baby will have a very strong
grip. I have a sensor (but is is just sensor with a voltage o/p -
nothing more) in mind but don't have the info to hand at the moment;
will try to dig the info out tomorrow.
 
Z

Zak

Jan 1, 1970
0
like the other poster mentioned the heat from
the hands would effect the readings if the tube was held too long.

Fill the tube with a liquid: less expansion.



Thomas
 
Zak said:
Fill the tube with a liquid: less expansion.

Sensor would need to be waterproof.

The sensor I was thinking of was the motorola MPX2200A (0-29PSI) or
similar (try googling for datasheet) - silicone tube would connect
directly to the port on the sensor.
 
A

Andy Baxter

Jan 1, 1970
0
amorphia said:
Hi all,

I'd much appreciate any advice on my search for a cheap and simple
pressure sensor. I need to make a device which can measure how hard a
baby is squeezing a tube, around 2cm thick. I figure the best way is to
use a silicon tube, just above atmospheric pressure, and connect it via
a pneumatic tube to a pressure sensor. So what I need is a pressure
sensor that does not have to be accurate in absolute terms, but needs
to be relatively sensitive, so it can measure changes in grip strength.
I reckon if it went up to 1000 kPa that would be more than enough.
Preferably it would come with an integrated USB interface and drivers
which provided an API. Alternatively, if you know a good one but it
just outputs a voltage, perhaps you could also recommend a good cheap
and cheerful USB A to D converter?

So far the best thing I've found is this, which you can combine with
a USB interface from the same supplier:
http://store.pasco.com/pascostore/showdetl.cfm?&DID=9&Product_ID=51374&Detail=1
But I think it will only interface using their proprietary software -
it's for classroom use, after all. But this gives you a basic idea of
what I'm after.

Other solutions to the basic problem also gratefully received!

Cheers,

Ben

http://www.maplin.co.uk/Module.aspx?ModuleNo=44202&doy=14m10D

have 'quantum tunnelling compound pills', which work as pressure sensors -
you could embed one or two in a piece of rubber and use that.

you could also try

http://www.rfmicrolink.com/

who sell a conductive rubber that changes conductivity when under pressure.
 
R

Rich, Under the Affluence

Jan 1, 1970
0
1000kPa is ~145PSI! It's going to be one strong baby?!

You're going to need a design but here's how I would go about it - I
would connect the silicon tube directly to the sensor and seal the open
end.

I seriously doubt if he'll get much of a reading at all from a silicon
tube.

Silicone, maybe.

Cheers!
Rich
 
B

Bob Eldred

Jan 1, 1970
0
amorphia said:
Hi all,

I'd much appreciate any advice on my search for a cheap and simple
pressure sensor. I need to make a device which can measure how hard a
baby is squeezing a tube, around 2cm thick. I figure the best way is to
use a silicon tube, just above atmospheric pressure, and connect it via
a pneumatic tube to a pressure sensor. So what I need is a pressure
sensor that does not have to be accurate in absolute terms, but needs
to be relatively sensitive, so it can measure changes in grip strength.
I reckon if it went up to 1000 kPa that would be more than enough.
Preferably it would come with an integrated USB interface and drivers
which provided an API. Alternatively, if you know a good one but it
just outputs a voltage, perhaps you could also recommend a good cheap
and cheerful USB A to D converter?

So far the best thing I've found is this, which you can combine with
a USB interface from the same supplier:
http://store.pasco.com/pascostore/showdetl.cfm?&DID=9&Product_ID=51374&Detail=1
But I think it will only interface using their proprietary software -
it's for classroom use, after all. But this gives you a basic idea of
what I'm after.

Other solutions to the basic problem also gratefully received!

Cheers,

Ben

--
Dr. Ben Kenward
Department of Psychology
Uppsala University, Sweden
http://www.benkenward.com

1000kPa??? That's about 10 Bar or 150 PSI. What baby is going to be able to
create that pressure squeezing on a tube? You're going to have to be about
100 times more sensitive than that, say 10kPa or 1.5 PSIG (gauge pressure)
to be effective. That's about 100cm of water. Get a cheap pressure gauge and
play around with it first before you try to instrument it.
Bob
 
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