weibbridge to diff pair?

[xray]

Looking to build up a gain stage out of a load cell. Client has placed a load cell on an electric trailer brake to actuate increased torque on a big whirly gig, vertical blades wind mail. There is not enough output 3mv/V to see a voltage on the oscope? Can read some change with a digital voltage meter, input resistance 10M ohm. I was thinking to design a differential pair, BJT's, able to adjust the gain fairly easily with a turn of a pot and have all the components. The diff. pair will not have 10M ohm input, DC block, but am not seeing any reason not to go ahead. I will be placing this into an adc to create a digital controller. Any thoughts. Thank you for your consideration.

Cy Drollinger

 

[ScottyUK]

Any reason why an op-amp based circuit can't be used? You'll get better performance in just about every respect compared with a discrete approach.


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If we learn from our mistakes I'm getting a great education!

 

[bogeyman]

Better still use an instrumentation amp with its gain set around 1000, you only need one resistor to set its gain and maybe an r/c lowpass filter to clean up the signal a little.
With luck you can power it from the excitation voltage.

Lots are available from the usual semiconductor folks, i.e.Analog, National, Texas, Maxim and the like.

There are some devices specific to weighing applications with an in amp and a 20 bit convertor in one package.

 

[xray]

Thank you for the input. It is going to make the project completion easier by having a bit of reason pull me back. I selected the ADS1230 a complete front end ADC for a weighscale type application much like my current project. I have completed the design of the support circuitry for the chip, hooking up the input, and the embedded system, off the shelf.

Sincerely,

Cy Drollinger