# wheatstone bridge drive by small current, issues?

I've got question about Wheatstone bridge. I've designed device which contain NCP1210 pressure sensor and works with 3.0V power supply. I've did calculations and now I've got some questions.

My device based on this eval board:

http://www.cdiweb.com/datasheets/ge_novasensor/CDI_Universal_Evaluation_Board.pdf

I read NCP1210 (I've got sensor with 0.025mbar resolution) values for 1.5mA current source. Typical output voltage value is 50mV (for 0.025mbar). Typical NCP1210 input impedance is ~4k.

So... with Ohm law:

U=RI

U=4000 Ohm * 0.0015 A=6V

I need ~6V to properly drive sensor wit 1.5mA. Furthermore voltage on resistor in current sink system has value of non-inverting input. So with this eval board I need at least 6V + 1.2V =7.2V to properly work with 1.5mA current source.

I've decided to use eval board ideas in my project. I use:

-> 1.6V Reference voltage

-> 3.0V power supply

With these values I calculate that I must use 8k resistor in current sink. With this resistor I should achieve current with value: 0.2mA.

And now my question: With this current (0.2mA) proportionally I can achieve ~6.6mV on NCP1210 output.I want to connect NCP1210 output to MCP6N11-100 instrumentation amplifier and I'm afraid that these values will be too small to reach good measurement.

Additionally I thought about build voltage doubler, but It will small battery-powered RF device and voltage doubler may take up too much space.

• This is the exact type of situation where instrumentation amplifiers shine. Why are you "afraid that these values will be too small to reach good measurement"? You can probably get away with a gain of just a few hundred depending on how much resolution you actually need. May 13, 2014 at 13:11