Beginner at LabView, Load Cell Force Measurement?

[RedSeal]

I am a beginner at using NI products and I was wondering if anyone can help get me started with a simple load cell force measurement? Basically, what I want to do is acquire the signal from a load cell convert it to Newtons and display the waveform. The measurements will be continuous and will end when the user hits stop. Also, I would like to null the load cell before acquiring the signal. I am using LabView 7.0, PCI 6040E DAQ, SC2345 and SCC SG04 module on Win XP. Thanks for the help. Additionally, you can email me at losincontrol@hotmail.com. Thanks.

[Conseils]

Assuming that you are happy to use one of the built in data aquisition examples as a basis. Labview and NI-Daq are installed and the hardware fitted in the computer system.

Well a plan would be a good start so how's this: -


1.0.0) Your first task would be to prepare the system.
1.1.0) Read all the instructions.
1.2.0) Choose data channels.
1.2.1) Insert SCC SGC04 into appropriate channel
1.2.0) Make the physical connections.
1.2.1) Use screened cables to Load Cell
1.2.2) Route earth and 0v seperately
1.3.0) Determine data aquisition rates.
1.4.0) Check all connections.
1.4.1) Look for short circuits.
1.4.2) Use a multimeter to check for shorts!!!!
1.5.0) Connect SC2345 to P.C.
1.5.1) Ensure P.C. is off !!!!
1.5.2) Take care with 50 pin connectors they can
be damaged if inserted with excessive force
1.6.0) Check all connections (AGAIN)!!!!

2.0.0) Your next task is to check systems operation
2.1.0) Apply power to the P.C. (see 1.4.0)
2.2.0) Configure the Hardware
2.2.1) Open the 'MAX' application
2.2.2) Drill to 'Devices and Interfaces'
2.2.3) Select 'Device 1' (assuming 1 card)
2.2.4) Right click 'Device 1'
2.2.5) Select 'Properties'
2.2.4) Configure the hardware connected to
'Device 1' (see manuals)
2.3.0) Configure the Load Cell
2.3.1) Right click 'Device 1'
2.3.2) Open 'Test Panel'
2.3.3) Apply simulated load using resistor to
shunt (calibrate) simulate largest load.
2.3.4) Adjust / determine channel gain untill
the best range of the input cards A/D
convertor is used for max resolution.
2.3.0) Work out scale factor for the unit
now that you have maximum load and Volts
for the maxiumum load.
3.0.0) Your final task would be to modify the design.
That's the easy bit!!! Honest.
This is a Labview task and you can find
great examples in the on-line documentation.
Get familar with them as you will learn heaps
from the different implementations.

You can use MAX (Measurement And Automation Explorer) to handle channel configuration but I suggest you avoid this until you have a better feel around the software. Max is a great tool for debunking and isolating the area of issues from hardware or software.

Finally you don't say if your Load cell is used with any 'Load arm' or force is applied directly (compressive or tensile). There are conventions for representing tensile and compressive forces and the wiring or you Load Cell mean that you will have to check for 'sense'. These are things you need to know and consider. Aditional factoring is required for 'Load Arms'. It's not always possible to apply a test load to a Load Cell and can be dangerous, as often the test / calibration load would not be applied as the instrument was intended to be used. Here you are using a resitive unit rather than a piezeo device. Hence the 'Shunt' or Calibration resistor. This is a small resistor which is determined by the physical design of the load cell (mechanical, gauge selections and signal conditioning). It is placed in parallel with one 'Arm' of the load cell strain gauge. It is possible to purchase Load Cell simulators for both Strain and Piezo type Load Cells. In the case of a strain gauge type you can completely simulate the Load Cell with a resistor network wired appropriately (normally a wheatstone bridge but again can be dependadant on the design).

I think this raises more questions than you asked but then that's what a good plan should do.

Good Luck

[RedSeal]

Thanks for the help. Do you see any problems with using the load cell found at this site: http://www.smdsensors.com/detail_pgs/s400.htm
I will be using it measure the compressive force of an epidural needle. Thanks again.

[Conseils]

I note that the SCC SG04 has a 2.5v excitation voltage and the force unit indicated is recommended at 10v excitation.

There is a 10v excitation unit which is the SCC SG24.
Anyway with a lower excitation voltage you get less mV output for a force input which could mean that you loose ability to measure the desired force as it would be 4 times smaller than recommended.

The smallest force unit is 50lb force full scale. This is quite a lot for pressing a syringe isn't it? An alternative way of looking at this is that you don't get enough resolution in the measurement if you sensor range is too big.

I could have the wrong end of the stick for your application?

Best advice is to perform a simulation with some wieghts.

[yousif]

I am a beginner at using NI products and I was wondering if anyone can help get me started with a simple load cell force measurement? Basically, what I want to do is acquire the signal from a load cell convert it to Newtons and display the waveform. The measurements will be continuous and will end when the user hits stop. Also, I would like to null the load cell before acquiring the signal. I am using LabView 7.0, PCI 6040E DAQ, SC2345 and SCC SG04 module on Win XP. Thanks for the help. Additionally, you can email me at mohamedyosuif@hotmail.com. Thanks

[RavensFan]

Message 2 seems to be a very through instruction list on how to get started.  Have you tried following that?

After working with that, then post back if you run into any problems.

(PS:  Posting your e-mail address in a public forum is going to attract a lot of spam.)

[dineshmeena]

Hi,

I need to acquire a signal for Load cell, strain gauge and LVDT using usb 6211 for 16 channels and two channel is to acquire a signal for load cell and 4 channel is to acquire for LVDT and 10channel is to acquire for Strains and i need to convert the scales in to kN for load cell , in microstrains for strain gauge and in millimeter for LVDT how can i acquire a signal i need some model program to use it for and i was using signal conditioner of 0-10v, 4-20mA output signal, will you give some ideas to go on further and am i need to apply any formulas to convert the acquiring signal in terms of microstrain , kN and mm the load cell range is 200kN is anybody can help me i need to finish it in two days

Thank you in advance,

Regards,

Dinesh

[dineshmeena]

Hi everybody,

        Is there any conversion function for load cell like strain conversion.vi in labview for acquiring voltage signal? because i need to convert a load cell acquiring in terms of voltage in daq 6211 i need to convert in terms of kN or newton, if it is any pls msg me.

Regards

Dinesh