6-Chan Load Cell Conditioning- Which NI Products?

We are building a machine with 6 strain gage based load cells. We need simple signal conditioning, including power supply, between the 6 load cells and our data acquisition system. What are the NI products we need to buy?

Sure. For simple signal conditioning, go to www.omega.com (Omega Engineering)and take a look at the following Bridge Conditioning Modules:
DMD-460 Series
BCM-1 Series
OM2 Series
All of these devices provide some/all of the capability you require. Omega Engineering has an extensive line of products to support accurate, economical, and easy pressure, force, and strain measurement. (No I do not work for Omega Engineering; however, I have used their products over the last 20 years and have always been satisfied with the results). Omega will also send a complete reference set of their current catalog in "paper form"(about 70 lbs) upon request. These catalogs have technical instructions and application notes that rival those found at NI

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How to load Cell Text (~8000 bytes) in HFM from a Flat File using FDMEE?

Hi,
There are numerous posts on OTN describing how to load cell text using the Create Memo API. However, we are struggling to know how do we use FDMEE to load Cell text which is about 8000 bytes from a flat file?
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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

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

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

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

"connecting a load cell to scb-100"

I have an scb-100 and want to know if it is possible to connect a load cell to it and if so, how.

It is probably possible, but you have to have some additional circuitry in order to use the load cell. Typically, load cells are comprised of strain gauges which require some kind of Wheatstone bridge completion. Additionally, most strain gauges need excitation. If you can provide the bridge completion and excitation, then you could simply read the output of the strain gauge by connecting the output + and - to your SCB-100. However, setting up this external circuitry can be a little complicated. So, the recommended setup is to use some signal conditioning. National Instruments provides a couple of options regarding signal conditioning for load cells. Below is a link to a tutorial that discusses how to measure a load cell and what hardware is recommended for
that. I hope this information helps.
Tutorial

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

Data acquisition from switching 500lbs load cell to 100lbs load cell

I am using 500lbs load cell, and acquiring data by inputing 2volts from 2345 signal conditioning board, and sensor output is connected to SCC-AI03 pin 3 and 4 , and configure this load cell to a channel using NI MAX, data neighborhood, traditional NI-DAQ virtual channel, the physical quantity is voltage set at range -10 to 10, and sensor also set at voltage with no scaling, but, I couldn't get any signal when 100lbs load cell is use, the difference of this 100 lbs load cell is the rated output is at 2.958mV/V, while the 500lbs rated at 1.8295mV/V , how should I do this?
Thanks.

Hi,
At this point, it is difficult to determine exactly what is happening to your acquisition. Could you please provide some additional information by answering the following questions:
What voltage are you reading with the 500 lb load cell?
Would it be possible to connect your load cells to a DMM and see what voltage reading you receive? If so, what do you see?
What is specifically happening when you connect the 100 lb load cell?
I also noticed that you are using the Traditional NI-DAQ (Legacy) driver. I recommend upgrading to the NI-DAQmx driver. Here are a couple of links with more information about DAQmx:
Advantages of NI-DAQmx:
Transition from Traditional NI-DAQ to NI-DAQmx:
Learn 10 Functions in NI-DAQmx and Solve 80% of Data Acquisition Applications:
Regards,
Hal L.

How to load binding conditionally

Hi All,
I have a page where I have two set of attributes. If condition=="A" then I need two set of attributes.
Though I display only one set of attributes the second set of attributes are used to set the read-only property of the attributes which are in the first set.
When I say a set that means all those attributes are from the same iterator.
If condition=="B" then I don't need second set of attributes. That means all the attributes from second iterator are not required.
Even I set render=false for the attributes from second iterator those bindings are available.
That means even after setting render=false for second set attributes if I display an output text with #{bindings.secondSet.Attr1}
then I can see the value. That means those bindings are loaded unnecessarily.
I don't want to load those attributes unnecessarily.
I tried with <c:if> condition also. But attribute bindings are loading from the page definition.
In pageDefinition How can we set some condition to load bindings conditionally...?
Please help.
Thanks
Abhilash

I guess you can't do that if you have the two iterators on one page.
The only thing you can do is to split the use case so that you have different pages for the condition (with different sets of iterators).
By the way, why is it so bad that the two sets are loaded? about how much variables we are talking?
Timo

I recently bought a KoboGlo ereader. Several days ago I bought an ebook from Booktopia. However I was unable to download the ebook onto my new ereader. I was told that I needed to load Adobe DRM which I did. When I contacted Booktopia they told me that wh

I recently bought a KoboGlo ereader. Several days ago I bought an ebook from Booktopia. However I was unable to download the ebook onto my new ereader. I was told that I needed to load Adobe DRM which I did. When I contacted Booktopia they told me that when I authorised my Adobe DRM I should have "select 'Booktopia' next to Vendor ID, and then log in using your Booktopia account details ie email address [email protected] and your Booktopia password as the password."
I erased my Adobe DRM software from my computer and reloaded it but I seem to be unable to convince your software that I want to start over... it keeps telling me that I am using an ID and password that was used to authorise another computer!
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A frustrated customer!
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[email protected]

In order to make your posts easier to read I suggest that you not type in all caps.
The operating system on your Gateway system is Windows based, as are all of the applications that you had installed. Your iMac uses the Mac OS X operating system. The applications on your external hard drive that you pulled from the Gateway system will not directly run on your iMac. One option is to purchase Mac OS X versions of the software where possible, or your can install Window's on your iMac and have the capability to use both Mac OS X and Windows.
Since you are a new Mac user it may be best to go back to your place of purchase and spend some time learning about your options for transferring your data and options. According to the Stamps.Com website, they apparently don't make a Mac OS X version of the software, but they supposedly allow you to print directly using the Mac's web browser. Microsoft sells a Mac OS X version of their Office suite which you can view at http://www.microsoft.com/mac/products.
Here's some more information that helps people like you who are converting from Window's to the the Mac OS X environment. There is some learning to do, but like me, I think you'll like it once you have everything configured correctly.
http://www.apple.com/support/switch101/

9237 with full-bridge load cell: load cell_null_off_shuntcal.vi throws error 200077

Hi,
I'm trying to use the example
load_cell_null_off_shuntcal.vi with a full-bridge load cell (Honeywell
Model 31, unamplified). I am using LabView 8.6, cDAQ-9172 and NI9237. The
load cell is connected to pins 2,3,6 and 7.
The inputs for the VI front panel
are: internal excitation10V; mV/V 2.1492 (calibration sheet); max weight 10
lbs; bridge resistance 350 ohms (Honeywell specs); 9237 internal shunt
resistance 100 kohms; shunt location R4 (default setting). I have selected
"Do offset null" and "Do shunt cal".
This is the error I receive:
Error -200077 occurred at DAQmx
Perform Shunt Calibration (Bridge).vi:1 Possible reason(s):
Measurements: Requested value is not
a supported value for this property.
Property:
AI.Bridge.ShuntCal.GainAdjust
You Have Requested: -61.980405e3
Valid Values Begin with: 500.0e-3
Valid Values End with: 1.500000
If the "Do shunt cal"
green button is not selected, there is no error. I understand that the Gain
adjust value should be approx 1, whereas the one I get is much larger. The subVI DAQmx PerformShuntCalibration
(bridge).vi contains a "Call library function node" which I don't
know how to interrogate.
Has anyone else had experience
with this error? Do you have any advice on:
1)
How to "see" the calculations being
perfomed inside the "call library function node"?
2)
What the correct shunt element
location for a full bridge load cell is? (although changing this location does
not eliminate the error, I can't find this info).
3)
Anything I may be doing wrong with
my inputs to cause this error?
Thanks,
Claire.
Solved!
Go to Solution.

Hi Claire,
You have to physically connect the SC terminals to one arm of the bridge (normally R3). The terminal is not provided for connecting external resistors.
See example
C:\Program Files\National Instruments\LabVIEW 8.6\examples\DAQmx\Analog In\Measure Strain.llb\Cont Acq Strain Samples (with Calibration) - NI 9237.vi
"A VI inside a Class is worth hundreds in the bush"
യവന്‍ പുലിയാണു കേട്ടാ!!!

9237 + full-bridge load cell: load cell_null_off_shuntcal.vi - error 200077

I'm trying to use
load_cell_null_off_shuntcal.vi with load cell (Honeywell Model 31,
unamplified). I am using LabView 8.6, cDAQ-9172 and NI9237. Inputs:
internal excitation10V; mV/V 2.1492 (calib. sheet); max weight 10 lbs; bridge
resistance 350 ohms (Honeywell specs); 9237 internal shunt resistance 100
kohms; shunt location R4 (default setting). Have selected "Do offset
null" and "Do shunt cal".
Error -200077 occurred at DAQmx
Perform Shunt Calibration
(Bridge).vi:1 Possible reason(s):
Measurements: Requested value is not
a supported value for
this property.
Property:
AI.Bridge.ShuntCal.GainAdjust
You Have Requested: -61.980405e3
Valid Values Begin with: 500.0e-3
Valid Values End with: 1.500000
If "Do shunt cal" green
button not selected, no error. Gain adjust should be approx 1. subVI
DAQmx PerformShuntCalibration (bridge).vi contains "Call library function
node" which is locked (?).
Any ideas?
What is the correct shunt element
location for a full bridge load cell? Changing this location does not eliminate
error.
Solved!
Go to Solution.

Hello CFJ,
The problem is most likely in your external connections of the NI 9237 and the load cell. As referenced in the NI 9237 Operating Instructions and Specifications, page 9, the SC+ and SC- pins should be connected across the resistor specified in the DAQmx Perform Shunt Calibration (Bridge).vi (in the case of a full bridge it would be R3).
Let me know if you are still having issues with your calibration.
Message Edited by Dan_K on 01-22-2009 04:31 PM
Regards,
Dan King

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

PASCO Load Cell and NI DAQ Interfacing

Hi everyone,
I have a PASCO Load Cell PS-2200 and I am trying to interface it with an NI-9201 AI (in conjunction with a NI-cDAQ 9172). Instead of attaching wires to the cell's pinout, I stripped a PS2 connector and rearranged the wires to match the pinout of the sensor (which are the strain gauge input, strain gauge output, the excitation voltage of 4.2 and the ground). I connected the strain gauge signal to a channel of the NI 9201 and I am using an external power source to provide voltage to the cell. My VI is trivial and consists of an input DAQ and Lowpass filter.
The problem is that the input signal is obviously not right, it looks periodic for one. The filtered signal appears stable at first but slowly increases over time. And the signal does not respond to applied stresses.
I would really appreciate any help on this. I am a ME sophomore and have little experience with LabVIEW.
Thank you.

Thank you Jignesh and Dave,
Jignesh, I do not have a scope I can measure the ouput with. And no, the cell does not respond to variable loads. Also, please find attached the snapshots you had asked for. The front panel snapshot shows the cell's reponse when under no load
Dave, the module I am using has a 16 bit resolution and within a +/- 10 full inut range, don't we have enough resolution to acquire the smallest change?
Also, from the pinout of the load sensor, the pin for the excitation terminal and the positive strain gaugw output are adjacent. They are not the same terminal. We took every possible precaution to make sure that the terminals of the PS2 connector did not touch during soldering.
Thank you for your help again.
Attachments:
block diagram.jpg ‏159 KB
front panel.jpg ‏390 KB

6-Chan Load Cell Conditioning- Which NI Products?

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