Pressure gauge schematic

[Vincent Himpe]

I'm looking for a schematic of a pressure gauge that uses a load cell (
wheatstone bridge )

Gauge measures between 0 and 4500psi ( 300 bar ) I got the load cell

problem is signal conditioning. full scale is only 100mV. and i need to
amplify this to 2.25 volts ( so 0.5 millivolt is 1 psi. the gauge gives me
)

The opamp circuits i made all tend to drift and are sensitive to noise due
to the high gains involved . plus ther eis the problem of the common mode
voltage.

I know tere are special instrumentation amps available but those cost an
arm and a leg. Does anyone have a schematic on how to build this using
regular god opamps like op177 ?

 

[Ross Herbert]

On Sun, 29 Aug 2004 09:13:27 GMT, Vincent Himpe
<vincent_himpe@hotmail.com> wrote:

|I'm looking for a schematic of a pressure gauge that uses a load cell (
|wheatstone bridge )
|
|Gauge measures between 0 and 4500psi ( 300 bar ) I got the load cell
|
|problem is signal conditioning. full scale is only 100mV. and i need to
|amplify this to 2.25 volts ( so 0.5 millivolt is 1 psi. the gauge gives me
|)
|
|The opamp circuits i made all tend to drift and are sensitive to noise due
|to the high gains involved . plus ther eis the problem of the common mode
|voltage.
|
|I know tere are special instrumentation amps available but those cost an
|arm and a leg. Does anyone have a schematic on how to build this using
|regular god opamps like op177 ?
|


Possibly something like http://www.linear.com/pdf/lt1250.pdf

 

[Vincent Himpe]

Ross Herbert <rherber1SPAMEX@bigpond.net.au> wrote in
newsdb3j01bdc3l04vrhbj7amn4pamg9i6iqr@4ax.com:

On Sun, 29 Aug 2004 09:13:27 GMT, Vincent Himpe
vincent_himpe@hotmail.com> wrote:

|I'm looking for a schematic of a pressure gauge that uses a load cell
|( wheatstone bridge )
|
|Gauge measures between 0 and 4500psi ( 300 bar ) I got the load cell
|
|problem is signal conditioning. full scale is only 100mV. and i need
|to amplify this to 2.25 volts ( so 0.5 millivolt is 1 psi. the gauge
|gives me )
|
|The opamp circuits i made all tend to drift and are sensitive to noise
|due to the high gains involved . plus ther eis the problem of the
|common mode voltage.
|
|I know tere are special instrumentation amps available but those cost
|an arm and a leg. Does anyone have a schematic on how to build this
|using regular god opamps like op177 ?
|


Possibly something like http://www.linear.com/pdf/lt1250.pdf

Looks like what i need.
Except i dont have negative voltages and the gain resistor is not prsent
either. I'll feed the top and bottom of the bridge 2 known 'hard' reference
voltages ( coming from my A/D system ).

Output of the opamp goes to a 12 bit a/d convertor. Scaling and offset
happens in the cpu. I checked prices. Seems acceptable: 6$, drops to 3$ per
1000. and readily available.

Thanks. I see you responded to the oxygen thing too. Unfortunately they
won't sell to me. But i found a company that sells these things to
individuals.

 

Vincent Himpe <vincent_himpe@hotmail.com> wrote:

But i found a company that sells these things to
individuals.

Making your own dive computer? Make sure you sign off on all the
"life support" documentation from each and every one of your
vendors...

 

[Vincent Himpe]

William P.N. Smith wrote in news:qmo3j0hugj11g8ki0ok14etnt5qnf36iad@
4ax.com:

Vincent Himpe <vincent_himpe@hotmail.com> wrote:
But i found a company that sells these things to
individuals.

Making your own dive computer? Make sure you sign off on all the
"life support" documentation from each and every one of your
vendors...

nope. fully automatic nitrox/trimix blender and analysers

 

Vincent Himpe <vincent_himpe@hotmail.com> wrote:

William P.N. Smith wrote:
Making your own dive computer? Make sure you sign off on all the
"life support" documentation from each and every one of your
vendors...

nope. fully automatic nitrox/trimix blender and analysers

Yow! More power to you, but make sure your {business,life} insurance
is well paid up, and for a couple of orders of magnitude more than you
think you need! 8*}

 

[Ross Herbert]

On Sun, 29 Aug 2004 12:52:02 GMT, Vincent Himpe
<vincent_himpe@hotmail.com> wrote:

|Ross Herbert <rherber1SPAMEX@bigpond.net.au> wrote in
|newsdb3j01bdc3l04vrhbj7amn4pamg9i6iqr@4ax.com:
|
|> On Sun, 29 Aug 2004 09:13:27 GMT, Vincent Himpe
|> <vincent_himpe@hotmail.com> wrote:
|>
|>|I'm looking for a schematic of a pressure gauge that uses a load cell
|>|( wheatstone bridge )
|>|
|>|Gauge measures between 0 and 4500psi ( 300 bar ) I got the load cell
|>|
|>|problem is signal conditioning. full scale is only 100mV. and i need
|>|to amplify this to 2.25 volts ( so 0.5 millivolt is 1 psi. the gauge
|>|gives me )
|>|
|>|The opamp circuits i made all tend to drift and are sensitive to noise
|>|due to the high gains involved . plus ther eis the problem of the
|>|common mode voltage.
|>|
|>|I know tere are special instrumentation amps available but those cost
|>|an arm and a leg. Does anyone have a schematic on how to build this
|>|using regular god opamps like op177 ?
|>|
|>
|>
|> Possibly something like http://www.linear.com/pdf/lt1250.pdf
|>
|>
|
|Looks like what i need.
|Except i dont have negative voltages

You can generate your own negative voltage from the positive supply
using an inverter. eg.
http://www.linear.com/prod/datasheet.html?datasheet=179

|
|
|Thanks. I see you responded to the oxygen thing too. Unfortunately they
|won't sell to me. But i found a company that sells these things to
|individuals.

Wouldn't the companies concerned let you know who their distributors
were in your area? Anyway, it is fgood to see you found a source.