Force Mapping from Modified Load Cell

I am having some trouble finishing a program that we have been asked to write. Basically, the program is connected to a piece of hardware we fabricated. The hardware (attached below) is basically a wheel with four spokes. Each spoke has a strain gage attached to it on either side. These are connected as two full-bridge circuits. I have been able to get the force output for each of the full-bridges as the maximum value. We have now been asked to create a map of the forces to show where the most force is being placed (assuming uneven distribution). My vision is that it would use colors to show where the forces are, similar to a temperature map. What would I use to go about doing this?
Attachments:
Force Measurement v1.vi ‏106 KB
Modified Load Cell.png ‏267 KB

Look at the Intensity Graph. That will plot data as a range of colors. You will need to do some math to determine the value distributions from your set of strain gauge readings. You may also need to do some geometry/masking to set the force to zero where there is no material.
Lynn

Similar Messages

Read from both load cell and accelerometer

Hi,
I'm trying to collect data from both load cell (which doesn't need excitation) and accelerometer (which needs 4 mA excitation). As you can see below, I wrote a simple program to collect data from both devices. However, my program provides 4 mA of excitation to all channels, one of which shouldn't receive any current. How can I selectively provide the excitation to specific channels?
Any suggestions?
Solved!
Go to Solution.
Attachments:
readfromtwodevices.vi ‏47 KB

Good morning jeongho20000,
Both aeastat and falkpl have provided excellent solutions for this. I also wanted to mention a good KnowledgeBase article found at ni.com by searching for "daqmx channel same task" in the internal search bar. This helps to outline both solutions. After searching, you can then select multiple entries, but the best that I found was the 3rd choice, titled: Using Different Types of DAQmx Global Channels in the Same Task.
You can download from the article the attached example VI titled Multiple Channels Created.vi, and modify the block diagram to fit your needs. Wiring the Task Out to the Task In of two DAQmxCreateChannel VIs is the programmatic equivalent of adding multiple Global Virtual Channels created in Measurement and Automation Explorer (MAX) to a common Task in MAX. Either method works, it is only a user preference. Feel free to reply if you need further clarification/explanation.
Best,
Message Edited by cyclone2k9 on 04-06-2010 11:08 AM
Message Edited by cyclone2k9 on 04-06-2010 11:09 AM
Adam
Academic Product Manager
National Intruments

Shaker control with output from load cell

Hi
I am using a (analog output) shaker to generate sinusoidal forces at different frequency and of different magnitude. I am also using a load cell (analog input) to sense these forces . The max force generated by shaker decreases as I increase the frequency of vibration. Whereas, the experiment requires the force to be constant when the frequency is changing. I plan to use the max force obtained from the load cell data, as the process parameter, to modify the amplitude of input wave which excites the shaker. I seek help in this regard. I am using PCI6221 and SCC68.
Thanks in advance.
RSD

Sorry, I have been extremely busy the last couple of days (months?). I still haven't had much time to ponder the problem, but one thought comes to mind, at what frequencies are you running this and what is the load cell, and its supporting electronics, frequency response. You mention that the amplitude decreases as the frequency increases, but that you increase the gain of the driver amplifier. It (the system) is most likely non-linear in its response, so how much you increase the gain will vary. The nonlinearity of the response is one of the reasons there is so much published about control systems, PID controllers, etc.
Putnam
Certified LabVIEW Developer
Senior Test Engineer
Currently using LV 6.1-LabVIEW 2012, RT8.5
LabVIEW Champion

Controlling Linear Actuator via Load Cell

Hello,
I need to control the position of a linear actuator based on the force feedback from a load cell (rated up to 100 ft/lbs) connected to the tip of the linear actuator. What I want to be able to do is to set a force and have the linear actuator (driven by a stepper motor) move until it is within 0.1 ft/lb of the force setpoint. Once within 0.1 ft/lb of the setpoint, I would like to hold and control to the setpoint based on a user configured hold time.
I have the following hardware:
PXI-1033 chassis
PXI-7340 Motion controller card
UMI-7764 Terminal Block
P7000 Drive
Omega Engineering Load Cell model number LC201-100
Omega CCT-80 Load Cell Signal Conditioner
Omega FAR-1 Power Supply
I have the + output of the CCT-80 connected to the Analog Input (AIN1) and the - output connected to the Analog Input Ground (AIGND). This output signal is -10V to +10V (verified by DMM)
I have the ADC range set to -10 to +10
I'm reading the ADC as fast as possible (get about 700 samples/second) and this just isn't fast enough to control to the precision that I need. Also, it seems like there is a substantial amount of noise on this line.
Does anyone have any recommendations on improving the speed of the ADC read, or how to reduce the noise on the line?
If my requirement of holding to 0.1ft/lb is too strict for this hardware (7340 motion card) is there something else that I should try?
If I'm missing any other info that is needed to help me out, let me know and I'll update this post.
Thanks!

Hello AMac,
I have a setup similar to yours with a load cell attached to a linear stage. I want to use position control of the stage to apply a set load on the load cell (position-based explicit force control). Do you have a example VI I could look at if yours was successful?
Thanks,
Kyle

Applying 5 kN external force on a load cell - Force readings to start from 0 kN

I am recording readings from an Omega Load Cell using DAQmx (Continuous bridge example) . A pre-tension force of 5 KN is applied on the load cell. Is there any way of forcing the applied pre-load force to drop to zero so the readings to start from zero?
Thanks!

The way you worded your question in somewhat ambiguous.
You really do not want to remove the physical preload force, do you?
I think what you want to do is to change the readings to account for the preload. That can be done fairly easily if you have complete control over the applied loads and know when there is no additonal load on the cell. In the weighing (scale and balance measurements of force or mass) this process is called taring. The tare is the weight or force without the external load. At the grocery store they adjust for the weight of the container before they add your food.
Add a Tare state to your state machine. When the user presses the Tare button on the front panel, the program takes a reading from the load cell (or several readings to be averaged). That reading is the tare force. Place it on a shift register. Then subtract the tare force from the readings taken while the desired measurements are happening.
If the maximum load is close to the load cell limit, the termperature of the load cell varies, or there are impact loads involved, then this simple taring approach may not be good enough. That is not because of any inherent problem with the method, but due to the things that can cause a load cell to drift or change baseline outputs.
Lynn

Closed loop velocity control based on load cell force

Hello,
My application is for a drill, that drills into rocks of various densities for the purpose of collecting rock core samples.
My setup has 2 motors which get controlled, one spins the drill bit at a constant velocity, the other moves the drill mechanism along a Z axis.
For efficient cutting, it is desired to apply a constant force between the drill bit and the rock. I have a load cell which measures the force being exerted by the drill bit on the rock surface, and this force can be adjusted by changing the velocity of the Z axis. So I would like to employ closed loop control to adjust the Z axis velocity to maintain a constant force on the rock.
Platform: cRIO 9073, with NI 9505 & 9215 Modules, Labview 2010 Full with RT and FPGA modules.
The load cell is by Transducer Techniques, and I use their TMO-1 module to condition the signal, the output of which is attached to an input of the 9215 module, where 0-100 lbs equates to 0-8VDC.
The motors and encoders for the Drill and Z axis are connected directly to the 9505 modules.
Right now I am using a modified version the example found in ...\examples\CompactRIO\Module Specific\NI 9505\Velocity Control (closed loop)\Velocity Control (closed loop) - NI 9505.lvproj to accomplish velocity control of the motors.
My questions are:
1) Do I have the appropriate NI hardware/software for this task?
2) With my current hardware setup, what would be an appropriate way to control my Z axis velocity rate based on Analog feedback from the load cell?
3) Development time is a critical factor, so are there any toolkits etc that are easy to get started with that would drastically decrease my development time, or do I already have everything I need?
Thank you for your time
-MK Hokie

1. Your hardware and software look appropriate assuming the motors are compatible with the 9505s. You didn't mention the NI SoftMotion module in your software list which is something you will need.
2. There are a few ways of doing this. One method would be to have a force PID loop that would attempt to maintain a force setpoint by directly outputting values to your torque loop. In this case, the drill would essentially move as fast as it could while maintaining the force setpoint. Another option is to have the force loop output a velocity setpoint. You would then have a velocity PID loop that outputs torque values to the torque loop. By adding this additional velocity loop you could have control over your maximum and minimum velocities. There are likely other alternatives as well, but these are the first two that come to mind.
3. Unfortunately there are no shipping examples that close the loop on force feedback. My advice would be to start with the NI 9505 shipping example and adapt it to your needs. There are quite a few things you will want to change though. Do you know if you will need to use the trajectory generator to move the drill into position before starting the force control?
Assuming you don't need any trajectory generation, you can scrap the entire RT portion of the NI 9505 example and just create the necessary FPGA code. On the FPGA, you won't need the Spline or Synchronization code either because this information would no longer be coming from RT. You could take these out and replace the position loop with a force loop and possibly a velocity loop and your FPGA program would basically be finished. In fact the only real motion IP that you will need is for the encoders (assuming you want velocity control) and PID. Then you would need to create an RT VI that allows you to send down enable, disable, PID gains, and setpoints.
If you do need trajectory generation, you would want to keep most of the example code the way that it is, but then program in a 'Force Mode' that utilizes the force and velocity controly as described above. You could think of it as having two different routines programmed side by side.
Regards,
Burt S

Dynamic force control using linear servo actuator + load cell

Hello,
I am designing a test fixture which will allow us to test the performance of actuators we install in our products. I need to apply a constant load to the actuator while it is extending/retracting. I would like to be able to use a linear servo actuator and a load cell on the same axis as the UUT to provide and monitor the load. The actuator under test does not travel at high speeds, its max speed is approximately 1in./sec.
I need to be able to maintain a constant load while the actuator is moving. Therefore I'll need some kind of closed loop system to maintain a velocity such that the load being reported from the load cell is equal to the expected load as the actuator is moving.
I am trying to figure out how to best implement this in a cost effective and time-saving way. I have not purchased any hardware at the moment so am open to suggestions. We do have LabView 2009 with all the toolkits. Would it be best to implement this using a motion controller card or would I be able to get good results using a standard DAQ?
Message Edited by fnaeem on 02-05-2010 05:58 PM

As you have stated correctly, you will need a deterministic closed loop system to accomplish this task. The most cost efficient while reliable solution for this purpose is a motion control board like the PCI-7352. This board provides quadrature encoder inputs for positioning tasks and analog inputs for any other type of control. Torque/force control is a very typical task for this board and it provides a simple API and useful configuration tools.
If cost savings are a primary goal, you could also use a PCI-7342, but for your application I would recommend the PCI-7352, as the PCI-7342 provides only 12-bit ADCs, while the PCI-7352 provides 16-bit ADCs, resulting in a much better resolution of your force feedback signal.
I hope that helps,
Jochen Klier
National Instruments

Question on Measuring Lift Force for MAV Ornithopter for Student Project using Load Cell

Hey everyone!
I am new to these forums so bare with me, please. I am part of a senior design student group working on making a micro aerial vehicle ornithopter (generates lift by flapping its wings) similar to this Design.
We are using this load cell connected to an AD620 Op-Amp circuit that basically has two input wires from the load cell coming into the op-amp with a gain of 100 (there is an Rg resistor with 500 ohms in the circuit). The load cell and op-amp circuit are both powered correctly with 10 V and +-15 V, respectively. There are two output wires coming out of the circuit. One comes out of the 6th terminal of the op-amp, and one is connected to ground. If we turn on everything and test the output of the circuit with a multimeter there is little if no fluctuation in the output voltage, which is about .25 V with zero load. If we add precise weights and form a linear graph of the output voltage vs. weight, we can find that there is about .0045 volts/gram relationship.
Here comes the part we we are having trouble. It seems as though the circuit it working correctly, but when we try and hook it up to our USB-6221 DAQ Board though the ai0 (or any analog input) and confirm a LabVIEW program to read the output, we get a ton of noise along with a weird looking graph.
Here is a picture of the front panel that shows the output we are getting http://img130.imageshack.us/i/frontpanelg.jpg/
Basically, I would have though we could get a straight line that continuely increases or decreases depending on the load on the load cell. Why would it graph a ton of vertical lines? I would think it would be just one data point per time value?
Here is the simpler block diagram just to test the output: http://img26.imageshack.us/i/blockdiagramsmall.jpg/
Here is the main block diagram that we were going to use to convert to force, etc. but its not working (no need for while loop?): http://img15.imageshack.us/i/blockdiagrambig.jpg/
The properties of the DAQ Assistant VI is as follows:
input range: -10 to 10 v
RSE terminal configuration
acquisition mode: n samples and not sure how many samples we want to read or how fast. we had 1k hz and 100 samples and the image above is basically what we got it the program runs continuously.
I don't know what else I can tell you, except that if anyone helps me you would be like a godsend to our group. It would be very much appreciated
Thanks!!!

As I am unable to look at youor images (the corporate filter here is blocking the url) I can't see what you are describing. I will say that a multimeter will not show fast transitions that will show up in a LabVIEW/DAQ application, so using a meter usually doesn't tell you that much about signal "cleanness". How long are the wires from the op amp/load cell to the DAQ? How long are the wires, and what type (shielded, twisted pairs, untwisted pairs, etc.) from the load cell to the op amp. The output levels of the load cell are usually quite low, so the possibility of also picking up "environmental" electrical noise is very high, and this will be amplified as well. Since the output of the op amp is higher, the noise introduced between it and the input to the DAQ is less of an issue, but there as well. So making sure that signal wires are properly shielded and grounded is important, and there are long papers describing this for low level analog signals. Since the load cells desired output will probably vary relatively slowly (a few Hz) it may also be helpful to put a simple low pass filter before the DAQ.
You should insert the images into your post, as jpg, or png (you have jpg images) Not bmp! (this is for others that might read your post, yours are jpg which should be ok). Generally most of us won't or can't go to links, corporate network filters and corporate policies frown on it, too much maleware lurking at the end of unknown URL's
Putnam
Certified LabVIEW Developer
Senior Test Engineer
Currently using LV 6.1-LabVIEW 2012, RT8.5
LabVIEW Champion

Data acquisition from a 250N Load cell

Hi ,
I am very new at using the Labview.I am using Labview 6i(PCI 6052E).The load cell(250N) is connected to a pump.The pump has 2 bags.One of them is filled with water and the other is empty.I want to load the bag which is empty from the bag filled with water using the pump.The load cell is connected to the bag which is filled with water.I am trying to aquire a volatge signal continously from a load cell and display it on a chart.
My program has no errors and I am able to run the progam.But it is not aquiring any signal.Could u please help me out.Attached is my code for the same .
-Manasa

Hi Manasa,
Make sure you are handling your errors in your code. You can do this by wiring your error clusters through your VI and then terminate them in a General Error Handler VI. If you are doing this, make sure that your device works in Measurement & Automation Explorer (MAX). Do this by opening a test panel and verifying that you can get a known voltage (like a battery) to read correctly. If you can successfully get a voltage in MAX, try running one of the example programs. You can find them at Help » Find Examples..., then browse to hardware input and output. If you can get an example program that is similar to what you are trying to do to work, try comparing your code to the example.
Please post back if you have any questions. Have a great weekend!
Ryan D.
District Sales Manager for Boston & Northern New England
National Instruments

Is it possible to condition a load cell signal with a 1520 SCXI and then use it as the primary analog feedback for a 735X motion control board?

My system
PXI 1052 chassis
PXI 8196 RT controller
Flexmotion 7356 motion controller
Flexmotion 7354 motion controller
6259 M series DAQ
1520 SCXI
1520 SCXI
1314 SCXI frount mounting terminal block
DSM strain gage load cells
Exlar SR Brushless PM motors
Kollmorgen servo star CD series 5 drives
My objective:
I want to measure the force on the load cells with the 1520 SCXI (i.e. excite the load cell then amplify and condition its output) then I want to use this analog (force) signal as the primary feedback for my motion control system (7356 and 7354 motion controller connected to my drives and motors).
The problem:
The motion controller boards (7356 and 7354) can be configured for force feedback control via analog feedback from a load cell. However the boards implicitly expect the load cell signal to be amplified and conditioned with and external signal conditioner rather then using an NI SCXI module. Currently I’m am reading the SCXI signals via the 6259 M seriers DAQ and consequentially have no way to route the signal into the 735X boards for force feedback control. I can use softmotion to control the motors but then I loose the fast PID update rates possible with the 735X boards.
The question:
Is it possible to condition a load cell signal with a 1520 SCXI and then use it as the primary analog feedback for a 735X motion control board?
Thanks
Patrick Aubin
Ph.D Candidate
University of Washington &
VA MedicalCenter of Excellence for
Limb Loss Prevention and Prosthetic Engineering

Hi GG,
Thank you for your feedback.
>create your own external circuitry to amplify the signal.>
True a few op-amps could amplify and filter the signal externally but the performance of such an amateur built system will never match the accuracy and functionality of the 1520 SCXI. That’s why we spent the $2500 for the professional version.
>One thing that you could do is to use a UMI with your motion controller and then wire your signal from your SCXI to the UMI.>
As I understand it the UMI is basically a break out connectivity interface for third party drives. After conditioning and amplifying the analog force signal with the SCXI module the analog signal isn’t available to wire into a UMI. To my knowledge the conditioned signal of the SCXI resides only in the PXI backplane (i.e. there is no physical access to the conditioned analog signal). Can you explain how the UMI could be help here.
Again thanks for your input GG.
Patrick

VI to measure Load Cell

Hello everyone,
So I'm extremely new at this and really need some help. I need to create a VI that is going to be able to read the force using a load cell.
if anyone can help me I am willing to pay for your time, I don't have much time to learn on my own so I need the help of someone.
I have a power supply load cell and DAQ
please email me if your willing to help me and make some money
Power Supply: http://www.testequipmentdepot.com/bk-precision/power-supplies/1786a.htm?gclid=COahppSjtbUCFQuqnQodmF...
Load cell: http://www.omegadyne.com/ppt/prod.html?ref=LC401&flag=1
DAQ: NI USB-6008
[email protected]

Hi,
If you need to acquire voltage from your load cell with a USB-6008, you can run the attached VI.
Regards,
Attachments:
Voltage.vi ‏34 KB

Custom scale for load cell

Hi
I am using a load cell to monitor an impact force. The load cell has a fixture attached to it which results in a non zero output. I am using a custom scale to convert the output from the load cell in volts to force to Newtons.
I am creating a custom scale and applying it to the task. I then want to be able to programmitically tare (zero) the load cell output before testing. However, my code does not work. There are no errors, but the gradient and intercept controls within the while loop do not function. Can anyone tell me why? I am aware that this could be done mathematically but I do not understand why the property node method does not work.
I am using labview 2010 with the latest version of daqmx (9.17 I think). My hardware is the USB-6211 card.
Many thanks.
John
Attachments:
custom_scale.png ‏53 KB

Hi John,
Thank you for a good description of the problem you are facing, as I understand it you have set up a custom scale but it doesn't seem to be functioning as you expected.
I have looked into this for you and have found a few examples which may help with the development of your application, I have also linked some articles for you.
The custom scale will need to be created entirely before the task is created, so any modifications can only be done before acquisition begins.
I hope this information is useful, and if you have any further queries please go ahead and post them and I will look into it for you.
Thanks
Stephanie L
Applications Engineer
National Instruments UK and Ireland

Modbus communication with a load cell

Hello..!
I'm a new user of LV and I try to communicate with a load cell by RS232 modbus.
After installed NI Modbus Library I created a master VI with labview 8.6 using these library, and I can obtain a communication with load cell , these value are added into 1 register U32Bit, and it's okay, if I press a load cell I can see the values go on.( from 0 to 65535) . Now I want to show on front panel the value in KG , as decimal point,, for a right interpretation of value for my customer, so I added a block array to unbundle than I convert a value with I32Bit ( -32768 to 32768 ) with an indicator, but I can't see any values..
I suppose I doing something of wrong ( conversion ), I read some KB, but I can't see a suitable solution..
Can someone give me a link or information to show me an example to convert this value..?
Thanks in advance for any helps..
Configuration of MAster VI:
Read holding register
Starting address 2012 ( query for obtain net value from the load cell)
quantity 1
Slave address: 1
RTU
9600
Com 3
parity none
Solved!
Go to Solution.

Hello Ravens,
I tried to use your good advices and finally I can communicate correctly with my trasducers showing on front panel the right value ( Kg). Has been a problem of conversion from output of register ( U16Bit as 0-65535 ) to I16bit ( -32765 to 32765).
Thanks very much for your help, and I hope to chat again for new challenge...
Have a nice WE
Julio
Attachments:
Comunicazione Modbus load cell.jpg ‏46 KB

NI 9219 with load cell

Hello,
I am using the NI 9219 with a Futek Load Cell whose specifications are as follows:
Name
Min
Typ
Max
Unit
Channel: 1
Compensated Temperature
60
160
F
Excitation
1
20
Vdc
Hysteresis
-.25
.25
% of R.O.
Input Resistance
744
Ohms nom.
Insulation Resistance
500
Mohms @ 50 Vdc
Nonlinearity
-.25
.25
% of R.O.
Nonrepeatability
-.05
.05
% of R.O.
Operating Temperature
-60
200
F
Output Resistance
700
Ohms nom.
Safe Overload
150
% of R.O.
Temperature Shift Span
-.01
.01
% of Load/F
Temperature Shift Zero
-.01
.01
% of R.O./F
Zero Balance
-1
1
% of R.O.
Capacity
500
lbs
Rated Output
2
mV/V nom.
Calibration Excitation
10
Vdc
I am getting a signal from my load cell which is great, but I was wondering how you can adjust the signal output to have minimal interference from noise, vibrations, etc. and how to program the load cell that it can be calibrated to zero (0) before any data is aquired?
Any help is greatly appreciated!
Thanks,
Yatsco

Hello Yatsco,
Thank you for using NI forums. One thing you will probably want to look into is using the filtering VI's in LabVIEW. A low-pass filter can help to eliminate any high frequency noise from your measurement. Also, take a look at the Field Wiring and Noise Considerations article for some more information on eliminating noise. Lastly, this community example shows how you could calculate the DC offset and compensate for it before measuring your signal. Please let me know if you have any additional questions concerning this application.
Regards,

Configuring Load Cell [ NEW ] Feild Point

Hi, I'm trying to set up some Data acquisition from a load cell through my FeildPoint AI-110. The Load Cell I have is rated to 500KG and has a Out put of 2.997 mV/V. I can connect the load cell to field point and display the voltage difference in Max, but I’m struggling to use this to get any kind of scaled reading to using in Labview.
Can any one help.
Many thanks

I think the attached should get you pretty close. The top section uses just the constants you posted and
assumes a constant excitation voltage of 12.25. The bottom section uses the actual, current excitation
voltage when the measurement is made. I think this second approach will probably give you better long
term results.
The bridge voltage is the voltage displayed in MAX.
Matt
Message Edited by Matthew Williams on 07-04-2007 08:48 AM
Attachments:
strain_example.vi ‏34 KB

Force Mapping from Modified Load Cell

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