Pt100 Wheatstone bridge arduino

abukharmeh

Hello,

i need help designing a Wheatstone bridge for pt100 temperature sensor
firstly i need recommendation for a good amplifier to amplify the output of my Wheatstone bridge, if a one that has (i2c or spi) control then that would be plus.
and secondly, any though about replacing the other 3 resistor of the Wheatstone bridge by (spi or i2c) controlled potentiometer, i am thinking about that to over come calibration problem
that might show up due to environment temperature change or other changes that might affect the performance of the circuit.
finally, any thought about general improvement that can be added to the bridge circuit to make it more accurate

Thanks

Beau Schwabe

Looks like Linear Technology has a chip that will do what you want providing 3-wire SPI communication ...

http://cds.linear.com/docs/en/design-note/dn237f.pdf

abukharmeh

Well, i know that there is ready made chips for that purpose, but i am designing the bridge as course work and i should use Wheatstone bridge and improve it performance , hence the suggestion of i2c controlled potentiometer

Beau Schwabe

Any digital potentiometer that you find is not going to have the accuracy you need.

Another option is the LTC2412 .... http://www.linear.com/product/LTC2412http://www.linear.com/product/LTC2412

evanh

Industrially, it's certainly not typical of Wheatstone's being used for PT100 temperature measuring. What you see in those generic ADC datasheets is the regular solution. I wouldn't even know where the Wheatstone balancing resisters are meant to be mechanically located for a PT100 circuit.

Wheatstone bridges are heavily used in weigh scales though. There the whole bridge is integral to the load-cell sensing element. All four wires to the four corners of the bridge run back along a shielded cable to the electronics.

abukharmeh

Thanks all for help,
if anybody interested in the topic, i found this great pdf from TI
http://www.ti.com/lit/an/slyt442/slyt442.pdf

dre

Hi,
Might I suggest the INA125 for the instrumentation amplifier.

cheers, David

Beau Schwabe

Wheatstone's are actually used more often than you think ... it's a form of differential signaling designed to minimize noise. While not a true differential, a whetstone provides one leg as a reference, while the other leg is your signal. The idea is that over a distance any noise that may enter a leg, does so to both legs and becomes common mode which can mathematically be removed .... or in the case of a instrumentation Amplifier the two legs can be subtracted from one another resulting in the removal of any common mode signal. The reason you use an instrumentation Amplifier over a standard Op-Amp is because with an instrumentation amplifier, the loading on the input pins is balanced, where as with an Op-Amp the loading is uneven which negates any common mode signal rejection.