Load Cell Measurements using HX711 amplifier in labview

[daviscav22]

Hi, 

I've been working on making all the electronics for a universal testing machine in labview. I'm basically going to use labview to control the motor on the machine and also take the data simultaneously (loading and displacement). We are using an HX711 amplifier for the load cell and I'm using a NI-DAQ6003 board to control everything. We plan to find the displacement by keeping track of the ticks on the encoder in the motor. 

I'm a little lost because I'm unsure of how to take the measurements from the amplifier and encoder. I don't know what the output is exactly from them and can't seem to find anything that explicitly says what it outputs. If I knew what it output and its relationship to the load cell's current loading, I would be able to set up the VI to do the math and everything. At least, this was my idea. 

If anyone knows anything about this or has done this before, I'm very open to hearing any advice. 

[Maxwell.B]

I'm a little unsure of exactly what your question is. If you are reading the information from the encoder and load cell into the 6003, the input on that device will correspond to the channel you are reading the data on in LabVIEW. If your question is knowing what the outputs are on the encoder and load cell, that's going to be described in their respective manuals or spec sheets.

[daviscav22]

I suppose my question is more like: How will the 6003 interpret the outputs from the amplifier and the encoder? The amplifier has two leads that are both required to take the data so what do those two leads supply to the module and how can i interpret those readings as a loading? 

For the encoder, what exactly are the ticks? Is there a tick for every change from high to low? If this is the case, then I would set up my VI to count the number of changes from the input so I know when there is a transition from high to low, and this would mean I see a tick and each tick corresponds to certain amount of linear displacement.

[Maxwell.B]

The 6003 is going to be reading a voltage into it from those and you have to set up your task to read in the "format" of the voltage being sent in. Your encoder is going to be sending a pulse train that is then interpreted by an encoder read task in LabVIEW. Here's an article that talks about the signal that comes out of an encoder:

Encoder Measurements: How-To Guide

http://www.ni.com/tutorial/7109/en/

You're going to have to consult your encoder's manual or spec sheet to determine what the distance between edges is, which will be necessary to get a interpret the data.

A load cell is also reading a voltage, but it's going to be a continuous signal that is proportional to the force applied. 

I recommend looking at the examples included with LabVIEW for a starting point on reading each of these sources. Those are always my go-to.

[daviscav22]

So after some more research, the HX711 is actually a 24 bit ADC. How can Interpret those bits coming out of the ADC as a voltage? 

Thanks for the advice on the encoder, that helps a lot!

[Maxwell.B]

You'e welcome!

It sounds like you'll need to have a digital input task in order to read what's coming out of the ADC. The analog voltage has already been converted to a digital signal, so you can read it in that way.