Hardware suggestion for continous data Acquisation from 4 Load cells

[aash_9us]

Hi! My name is Aashish and I am working as a graduate assistant in California State University, Fresno, CA.

I am working on a project in which I want to collect real time data(weight) from 4 load cells (MLP-150-C) mounted on to a conveyor belt. So, I want to measure the weight of whatever stuff keeps falling on the conveyor belt. I will be dispaying the real time data in terms of pounds(lb) in Labview(8.6.1) and then will be continously saving that data in excel or some other form.

I have SG-2345 signal conditioning box and four SCC-SG24 modules too.

I want to know whats the best suited data acquisition hardware for such application?

Just to mention, I am a beginner in Labview so I am looking for something easy to work on or in which I can utilize the existing example VIs or can use them after a little bit of modification and get very precise output too.

Moreover, that would be a field application so I have to use it on a laptop and I guess USB is the only solution for such application. Thank you.

Regards,

Aashish Kharb

[EEsRULEtheWORLD]

Hi, Aashish.

It seems as if you have most of the hardware necessary for your system.  You're also going to need an M series data acquisition device.  The USB M series data acquisition devices will vary in cost based on maximum sampling rate, isolation and other features of interest.  In order to supply a 10V excitation from your M series, choose a USB M series that provides analog output channels with a voltage range that can reach +10V (USB 6211, for example).

I hope you're having a great day!

[aash_9us]

What do you say about 9237 module with compactDAQ chassis?

[EEsRULEtheWORLD]

Hello Aashish,

The NI-9237 with the Compact DAQ chassis would be a great solution for your load cell application.  Just make sure you check the specifications document here to make sure that it will work with your specific load cells.  This card offers great resolution and should be pretty easy to get started with.  If you already have LabVIEW or another supported Application Development Enviroment (ADE), you can download our DAQmx driver here and get started programming a simulated 9237.  Also, make sure that you download the patch for the DAQmx 9.0 driver.  It can be found here and includes some bug fixes for the 9237. This would allow you to start learning how to program the device even before you receive it.

[aash_9us]

I have few questions:

1. While configuring the whole system should I select strain or voltage as the analog signal being acquired in MAX?
2. How can I convert that acquired signal to pounds? 
3. Is there any VI in labview 8.5.1 by which I can average the signal from all the four load cells and display as a single reading?

[EEsRULEtheWORLD]

Hi, Aashish.

1)  Check out this link for configuring your system. Follow the NI-DAQmx 7.0 or later solution section.  This leads you to select Custom Voltage with Excitation.  This type of task will apply an excitation to the sensor and read a voltage on the output.  You can create a custom scale to convert the voltage reading into force by using the scaling factor provided by the specifications sheet for your load cells.

2)  The custom scale can be used to convert the voltage reading into into pounds.  The maximum and minimum input limits are in the units of the scale used.  For example, when using a Custom Voltage with Excitation task with a scale that converts Volts to pounds, the units of the minimum and maximum input limits are in pounds.

Note:  If you want the voltage to be expressed in units of strain, refer to the DAQmx Help and use the index tab to search for "strain."  Select the "bridge configurations."  Depending on the configuration that you use in your system, you can determine the strain reading according to the equations given in this Help document.

3)   The NI community has some example files that are uploaded by customers and NI employees.  A particular VI that I found to be useful in your application can be found here.  

[BuddyHaun]

Be careful if you choose the USB 6211. It may not be able to supply enough current depending upon the resistance of the bridge in your load cells.