Suggestions for building a load cell network

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changks
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Suggestions for building a load cell network

Postby changks » Thu Apr 02, 2015 8:58 am

Hi -

I need to get the weight readings of 48 samples at the same time. The maximum weight of each sample is ~4 kg (8 lbs). I think Phidgets board offers an ideal solution, because I don't need to wire amplifiers to each load cell. I have several questions before placing my order:

1. PhidgetSBC3 allows me to connect 8 load cells, so I need I/O 6 boards for this project. I am just wondering if you have any hubs to plug 48 load cells into one I/O board?

2. The website indicates that FC22 compression load cell (0-10 lbs) has been discontinued. Is that possible if you can order more 0-10 lbs load cells? The max. sample weight is ~8 lbs.

3. What is the major difference between ”Compression Load Cell” and “Micro Load Cell” in terms of their measuring accuracy, waterproof capability and installation?

4. What is the VDC required onboard for 8 load cells?

Thanks. Looking forward to using Phidget boards in our projects.


Michael

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mparadis
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Re: Suggestions for building a load cell network

Postby mparadis » Thu Apr 02, 2015 11:04 am

First, I think it's important to point out that only the following load cells can be plugged directly into the analog input on a PhidgetInterfaceKit or an SBC:

3121_0 - FC22 Compression Load Cell (0-25 lbs)
3122_0 - FC22 Compression Load Cell (0-50 lbs)
3123_0 - FC22 Compression Load Cell (0-100 lbs)

The rest of them need to be connected to the PhidgetBridge 4-Input, and then to the USB port of a computer or SBC.

1. We do not have any boards with more than 8 analog inputs.

2. We are no longer buying new stock of the FC22 series load cells due to low demand. You may be able to contact the manufacturer, Measurement Specialties for more stock.

3. The advantage of micro load cells is that their structural design allows you to measure force in only a single direction (shear force, but not compression or torsional force). As for accuracy, you can compare the specifications listed on the data sheets for the individual cells. Each one is different, but a large part of the resolution of the measurements depends on the measuring range of the load cell. Smaller ranges have higher resolutions.

As for waterproofing, neither of these types of sensors have official specifications, and we haven't tested them personally in wet applications. The micro load cells should be resistant to drips and splashes thanks to the silicone coating, but obviously the Phidget boards are not.

As for installation, the compression cell requires a bit of soldering since it needs to connect to a Phidget sensor cable. The load cells that connect to the PhidgetBridge are simply wired into the screw terminals.

4. You should be able to run 8 load cells directly from the Phidget board they're connected to; they use a very small current, which is why they usually need to be amplified.

changks
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Re: Suggestions for building a load cell network

Postby changks » Fri Apr 03, 2015 5:06 pm

Thanks a lot. Okay. We'll get some two SBC boards first for testing prototype and get the load cell from other manufactures. Please kindly help us on these questions we have.

1. Particular reasons why only some load cells can be connect directly to a SBC?
2. Recommended manufacturers for high precision load cell?
3. Requirements for load cell to work with a SBC?
4. Any example source code for using load cells on a SBC?

Best regards,
Michael

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burley
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Re: Suggestions for building a load cell network

Postby burley » Mon Apr 06, 2015 7:12 am

Load cells have a very small output. The ADCs on our traditional analog inputs do not have enough precision to be able to get useful measurements from them so you would need an instrumentation amplifier to get the output of the sensor into a readable range. The FC22 series have an amplifier built into them (hence why they are more expensive), the others do not.

The 1046 has been designed to work with the non-amplified load cells.

You can check someone like Vishay or Honeywell for very high precision load cells.

The only requirement for using a load cell with an SBC is that it has output in the range of 0-5V which is what the analog inputs accept. Or, you would need to plug a 1046 into the USB hub on the SBC. Example code for making it work depends on how you are doing it but it will either be the interface kit samples or the bridge samples. You can download them in a variety of languages from our programming page (link at the top of the website).
Brian Burley
403-282-7335 ext. 6003
support@phidgets.com

changks
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Re: Suggestions for building a load cell network

Postby changks » Thu Apr 16, 2015 9:27 am

Hi Brian:

Hi Brian:

Do you carry the wiring cable (4 wires, white/red/black/green) and screw/nut (M5x0.8) for the micro load cell (5 kg)?

If not, please indicate where we can get from the 3rd party?

Thanks.


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