Pressure transducers

[Ryan]

I'm trying to learn about pressure transducers and I've learned a tiny
bit on the web, but not found it as fruitful as I had hoped. (Or I just
don't understand what to look for.)

Do they permit air to pass through them, or only into them, like a
pressure tank?

Is their output linear with pressure throughout its rated range? If the
transducer is good from 0-30 psi, then does the output range from
something like 0 to 30 volts? When their max rated pressure is reached
and then exceeded, does the output stop changing? Is it accurate to say
the transducer is saturated?

Would the power supply in this example need to be 30 volts? Does the
supply need to be steady? If the supply fluctuates, does that throw off
the measurement? If the supply is noisy DC, does this throw off the
measurement?

It seems like they are always zero to X psi rating. Can the same
transducer measure vaccuum too? If I want to guage -20 psi up to 40
psi, can this be done with a single transducer? If not, is there a such
thing as using two transducers to measure this range and to install one
of them backwards?

Thank you.

 

[Ralph Mowery]

I'm trying to learn about pressure transducers and I've learned a tiny
bit on the web, but not found it as fruitful as I had hoped. (Or I just
don't understand what to look for.)

Do they permit air to pass through them, or only into them, like a
pressure tank?

Is their output linear with pressure throughout its rated range? If the
transducer is good from 0-30 psi, then does the output range from
something like 0 to 30 volts? When their max rated pressure is reached
and then exceeded, does the output stop changing? Is it accurate to say
the transducer is saturated?

Would the power supply in this example need to be 30 volts? Does the
supply need to be steady? If the supply fluctuates, does that throw off
the measurement? If the supply is noisy DC, does this throw off the
measurement?

It seems like they are always zero to X psi rating. Can the same
transducer measure vaccuum too? If I want to guage -20 psi up to 40
psi, can this be done with a single transducer? If not, is there a such
thing as using two transducers to measure this range and to install one
of them backwards?

Thank you.

Go here and look around.

http://www.emersonprocess.com/rosemount/products/pressure/m3051.html

The pressure transducer usually just has air to pass into them.
The output can be made almost any way. As you did not state what you wanted
to do, the output in many cases is a 4 to 20 miliamp circuit.
The output will saturate when the maximum range is exceeded. They may
overrange a small percentage. That is if the rated output is for 20 psi
then it may go to 21 psi.
There are transducers that can be ranged from negative presure (gauge) to a
positive pressure.
BTW you can not get -20 psi. Around 14.7 psig is as low as you can get.
That would be zero pressure absolute.

 

[John Popelish]

I'm trying to learn about pressure transducers and I've learned a tiny
bit on the web, but not found it as fruitful as I had hoped. (Or I just
don't understand what to look for.)

Do they permit air to pass through them, or only into them, like a
pressure tank?

Into or onto them. Some are made like a plug that fits in a pipe
threaded hole. Some measure the difference between atmospheric
pressure and applied pressure, some measure absolute pressure (have a
vacuum on the back of the sensing diaphragm). Some have two ports, so
they can measure the difference of two arbitrary pressures.

Is their output linear with pressure throughout its rated range?

Some are linearized, some produce an output directly from a strain gauge.

If the
transducer is good from 0-30 psi, then does the output range from
something like 0 to 30 volts?

There are many types.

When their max rated pressure is reached
and then exceeded, does the output stop changing?

Most have some over range with reduced accuracy (or some sort of
saturation) that doesn't damage the sensor.

Is it accurate to say
the transducer is saturated?

When additional pressure produces no additional output change, it is
saturated.

Would the power supply in this example need to be 30 volts?

There are many types that operate from a wide range of supply
voltages. Some regulate the current when a voltage is applied
(current loop operated transmitter).

Does the supply need to be steady?

Some do, some don't.

If the supply fluctuates, does that throw off
the measurement?

See above.

If the supply is noisy DC, does this throw off the
measurement?

There is always at least a little bleed through from the supply. How
much is a specification (power supply rejection).

It seems like they are always zero to X psi rating.

It may seem like that, but it is not the case, especially for the two
port types.

Can the same transducer measure vaccuum too?

Some can. The absolute pressure types certainly can. A perfect
vacuum is just their zero scale point.

If I want to guage -20 psi up to 40
psi, can this be done with a single transducer?

With the right one, sure.

If not, is there a such
thing as using two transducers to measure this range and to install one
of them backwards?

Not the best way to do it, but possible.

 

[Brian]

I'm trying to learn about pressure transducers and I've learned a tiny bit
on the web, but not found it as fruitful as I had hoped. (Or I just don't
understand what to look for.)

Do they permit air to pass through them, or only into them, like a
pressure tank?

Is their output linear with pressure throughout its rated range? If the
transducer is good from 0-30 psi, then does the output range from
something like 0 to 30 volts? When their max rated pressure is reached
and then exceeded, does the output stop changing? Is it accurate to say
the transducer is saturated?

Would the power supply in this example need to be 30 volts? Does the
supply need to be steady? If the supply fluctuates, does that throw off
the measurement? If the supply is noisy DC, does this throw off the
measurement?

It seems like they are always zero to X psi rating. Can the same
transducer measure vaccuum too? If I want to guage -20 psi up to 40 psi,
can this be done with a single transducer? If not, is there a such thing
as using two transducers to measure this range and to install one of them
backwards?

Thank you.

Have a look at
http://users.pandora.be/educypedia/electronics/sensorspres.htm
Brian