Hello, I want to build a small SDOF structure and connect to it an accelerometer, a couple of strain gages and a couple of load cells for simple experiments. I want to see the data plotted in real time on a computer screen, and store it and export it to Excel. I don't know how to program, or much about electronics. I believe I will need a wheatstone bridge with an amplifier for the strain gages and the load cells. Can you help me figure out the equipment I need and if LabJack products can get the job done?
Would something like this work: Connect an analog accelerometer directly to a U6 DAQ, connect the gages and load cells to a wheatstone bridge with an amplifier, and then connect that bridge to the same U6 DAQ, and then use the LabJack software to view and store the data from the five sensors?
Thank you.
.png%3Fitok=PHGBxf6M "EEV Blog Reviews LabJack T7-Pro & Software Tools")
.jpg%3Fitok=B1YcuDFK)
.png%3Fitok=Ybt-OlgU "LabJack + JEDI One Can Create a Powerful Distributed DAQ Ecosystem")
In general this sounds like a typical application.
Accelerometer: Have you chosen one yet? If you use an ICP or IEPE, they require a special constant current excitation source that you will have to provide. Instead look for a sensor that runs of a normal voltage source (5 volts DC is ideal, but other voltages like 12 VDC are easy to provide). MEMS type sensors usually look good.
Measurement Specialties
http://www.meas-spec.com/
Omega (lots of sensors, but I'm not sure if they have any with easy voltage supply)
http://www.omega.com/
Analog Devices (they make the elements themselves, not packaged probes)
http://www.analog.com/en/
Strain Gages & Load Cells: You are correct that these are bridge circuits. A load cell already provides a complete bridge in most cases. For a strain gage, the ideal is to use a full bridge, but if you need to use a half or quarter bridge just add matching resistors or dummy gages to make a complete bridge. Then see the following:
http://forums.labjack.com/index.php?showtopic=4376
Sounds like you have about 5 signals. How fast do you want to scan these signals?
Thank you for being so helpful. I realize I asked this question in the U6 section, but seeing that the U3 is one third the price, please help me figure out if I can obtain the data I want with a U3 DAQ (I'm pretty sure 12-bit resolution would be enough for me, if that's their main difference). With the right equipment at hand, I can find someone to help me with details such as settings, etc.
I would like to get up to 1000 measurements per second, but I can probably do with 500/s; and I would configure my strain gages as full bridges.
1. Is the LJTIA the type of amplifier I would need? If so, would I need any other equipment other than a U3, a USB cable, a number of LJTIA's, the load cells/ gages with their wires and a computer?
2. Can each LJTIA deal with two separate load cells/strain gages? Would that mean I could connect up to 12 load cells to a U3, which would end up as 12 different channels per time stamp on a spreadsheet?
3. How many tri-axial accelerometers can a U3 deal with?
4. Does the LJStream UD download come free with the product?
Thanks again.
Normally with a number of bridge circuits, we would suggest the U6/T7 because of their built-in amp, but since you want to scan multiple channels at 500-1000 scans/second, you are likely going to need external amps anyway, so if the 12-bit resolution of the U3 is sufficient for you then the U3 + LJTIAs is a good consideration.
1. Yes, the LJTIA is a good solution. One thing not on your list that you might want is a CB15 terminal board. Also, you might want to use 1 LJTick-Vref-25 to provide excitation for all your bridge circuits, then you can just monitor the voltage of that 1 excitation source to get the real-time excitation value.
2. Yes, each LJTIA can handle 2 bridge circuits, and thus the U3-HV could handle 12 bridge circuits and the U3-LV could handle 16 bridge circuits (the LJTIA works best connected to low voltage analog inputs on the U3). Whether 1 LJTick-Vref-25 can excite 16 bridge circuits depends how much current each needs.
3. The U3-LV has 16 low voltage (0-2.4V or 0-3.6V) analog inputs. The U3-HV has 12 low voltage analog inputs and 4 high voltage (+/-10V or -10 to +20) analog inputs. If you want to measure higher voltage signals with the low voltage inputs, you can do so with a voltage divider of your own or the LJTick-Divider from us.
4. LJStreamUD is free and part of the main Windows installer.