For a university research project, I am using a XTM-190M absolute pressure sensor with a millivolt output from Kulite Pressure Transducer Catalog (pressure sensor datasheet attached). This sensor utilizes a wheatstone bridge (standard four wire integration, red, black, white, green). I would like to amplify the signal to a voltage output, so I purchased the SparkFunHX711 load cell amplifier given it seems to work on the same principle with wheatstone bridge load cells.
I first tested the HX711 board with a mV output 10lb compression load cell (same four-wire setup) I had lying around in order to verify the board was working (load cell datasheet also attached). I was able to get it working fine with the HX711 board as per the instructions on the product page (exact example script used also attached). I was able to get clear rises in values from pressing on the load cell with my finger, and it settled back down to a consistent value after releasing.
However, upon integrating the XTM-190M pressure sensor with the same setup, pressing against the pressure and subjecting it to various kinds of loading did not generate any change in values, just a consistent stagnant value. I have verified with a multimeter that the sensor is being supplied with voltage and that there are no weird shorts going on.
I am not sure if this is an indication that this external party sensor is not compatible with the SparkFun HX711 board if I am simply missing something in my process. Regardless, I am confused because the pressure sensor in principle should work with the HX711 board in the same way as it does with a wheatstone bridge load cell. Help will be much appreciated so we can generate some really fantastic results with this neat SparkFun product!
DIW:
However, upon integrating the XTM-190M pressure sensor with the same setup, pressing against the pressure and subjecting it to various kinds of loading did not generate any change in values, just a consistent stagnant value. I have verified with a multimeter that the sensor is being supplied with voltage and that there are no weird shorts going on.
Are you just applying force with your hand or something? Your sensor is for fluid (gas & liquid) pressure. I also noticed your sensor has a maximum output of 75 mV which is pretty high.
I tried applying a force with my finger, as well as using a threaded cap with a hole and blowing on it with a sealed hose attachment. I did not get a signal for either. I suppose I thought some mechanical force on the diaphragm would generate a signal. I will hook it up to air pressure and a regulator and see if I can get a change in signal.
When you say the sensor has an output that is high, how would this affect (negatively or positively) the readings from the HX711?
brow:
I also noticed your sensor has a maximum output of 75 mV which is pretty high.
In regards to the 75 mV full scale output, would it be beneficial to adjust the gain? I could hook up the O+/O- from the pressure sensor to the B+/B- channel on the HX711 board instead of the A+/A-, giving me a gain of 32. According to the HX711 datasheet, a gain of 128 corresponds to a 20 mV output and a 64 gain for a 40 mV output, leading me to believe a gain of 32 would suitable for a 80 mV output (within the range of the pressure sensor 75 mV output). Does my thought process hold merit? If so, do I need to make any firmare changes to adjust the gain to 32, or is using the B+/B- channel sufficient?
If i want to apply +10V excitation voltage for the load cell that i am dealing with, at the same time i am using HX711 module that deal with 5V so how to solve that issue? knowing that higher excitation voltage provide more mv output from load cell