millivolt data logger

Is it possible to read the mV output of a load cell that has a 10vdc excitation voltage with the arduino? If possible I would like to make a 4 channel load cell data logger. The load cells that I want to monitor and log are 2mV/V wired to a summing board which is then wired to a amplifier/indicator. I just want to read the output of each load cell like you would with a voltmeter, but I want to be able to record the mV readings a couple times a second to help diagnose load cell/binding issues.

I was looking at a few of the load cell amplifiers, like the HX711, I liked the resolution that it offers and that they are readily available in breakout board form and they are relatively cheap through sparkfun and various other places online. I thought maybe I could wire only the output from the load cell into the amplifier but after a google search I found out that due to the excitation voltage I would fry it if I did that.

The standard Arduino ADC has 1024 steps. If the reference voltage is 5V, the resolution is about 5 mV per step, which is unlikely to be very useful with strain gauges.

You can use a lower reference voltage, like the 1.1 V reference for about 1 mV/step, but then the input voltage range is limited to 0 - 1.1V.

If the gauges are in Wheatstone bridge configuration, the center taps are at an offset of 1/2 the bridge supply voltage, which must be considered.

yes, they are wheatstone bridge configuration.

http://yourduino.com/sunshop//index.php?l=product_detail&p=453

So does this mean that the hx711 load cell amplifier boards will work? For only 5 dollars I will give it a try.

drummin89:
Is it possible to read the mV output of a load cell that has a 10vdc excitation voltage with the arduino?

HX711 boards have their own regulated excitation voltage (4.2volt).
The chip can NOT measure load cells powered with 10volt.
You should power the load cells from the excitation voltage of the HX711 board.
Leo..

I just want to read the millivolt values. The load cells are powered and monitored by an industrial load cell controller, which supplies 10v excitation.

I was also looking at the LTC2400 which is available as a breakout board but they are a little on the pricey side.

The INA125 (if powered by >=12volt) can be used to amplify the signal of a "10volt" load cell.
That amplified signal can be connected (via a 1:1 voltage divider) to an Arduino analogue input.
Not sure if the 10-bit resolution of the Arduino is a problem (for your monitoring/logging).
Leo..

could the INA125 be paired up with a higher resolution ADC that communicates to the arduino via SPI, I2C, etc?

Yes. An ADS11115 breakout board (Adafruit) would probably be ok.
Leo..