Generate PWM signal with 6602 utilizing load cell feedback

Hi Everyone,
I am new to LabVIEW so I apologize if this question is elementary but I really need some help with the coding. First of all, I need to generate 8 independent PWM signals to control 8 separate linear acuators using the NI 6602 board. I have each actuator wired to their own COUNTER OUT pins and ground on the SCB-68 that is connected to the 6602. The specs for the actuators state that it will take an input of "RC input range of 1.00 to 2.00msec pulse widths @ 55Hz. Bandwidth=.44to160Hz. Period from 6-23 msec". How can I code for these PWM signals given the specs from the manufacturer?
In the end I need to be able to not only control these actuators based upon duty cycle, but based upon the load each actuator is applying. Each actuator has a load cell in series measuring the tensile force through the load cell (the actuators will be pulling on strings). Each load cell is wired to a NI 9237 in a NI 9074 block that is connected via USB to the same computer. So first comes first, how can I code for the load cell output to be brought into the LabVIEW environment?
My last question is pulling this all together. How can I code so that I can input a specified load into LabVIEW and then based upon the value the load cell is reading, the duty cycle of the PWM will be adjusted until the the desired load is achieved?
Thanks in advance for any help! Also, I know that this is quite a complex questions so if you can even point me in the direction of resources that would be helpful, I would greatly appreciate that too!
Thanks,
Ryan

Hello Ryan,
Here's a tutorial on generating PWM with LabVIEW:
http://zone.ni.com/devzone/cda/tut/p/id/2991
How are the load cells outputting the data? Is it an analog signal? If so, you can read that in using an analog input task, and run that in parallel with the PWM task. Then you can modify the frequency and duty cycle inputs that you're giving you the DAQmx write inside the PWM code based on the analog input. By putting the DAQmx read and the DAQmx write in the same for loop, you can read from one and modify the other at the same time.
Here's a tutorial that shows a lot of useful information for using DAQmx within LabVIEW:
http://zone.ni.com/devzone/cda/tut/p/id/2835#toc6
If you're interested in getting better at LabVIEW in general, NI has some learning materials available here:
http://www.ni.com/academic/students/learnlabview/
Let me know if you have any further questions once you've gone through those first two tutorial links.
Colden

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HI Aamruth,
I atached a project, where you can see how to do it. I hope this helps.
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PWM.seproj ‏29 KB

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Eh..sorry. I do not know what happened, but it seems like my questions is gone in my previous post.
Let me recap, I'm new to NI Components and LabView.
I wanted to measure 8 PWM Signal generated from a controller (200Hz, Max 4A, 24Vdc).
WIth NI engineer's suggestion, I bought cRIO 9073 and NI 9423 for this purpose.
I have created a VI for this purpose. It seems to be working at first, but later on, the value read by the NI 9423 becomes unstable even though the out put signal from the controller was stable.
The value read by 9423 just goes up and down with an increasing PWM signal from my controller.
below is the setting for the 9423.
Thanks.

DAC voltage capped when operating in torque mode with load cell feedback

Hi, i'm doing a tension control on a cable driven system using servo motor. I had connected a load cell as analogue feedback for cable tension into the labview programme suggested in http://www.ni.com/pdf/manuals/371242c.pdf (Figure 13-3. Torque Control Using Analog Feedback Using LabVIEW)
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I can't see anything special with your settings, so I currently don't have a clear understanding, why the output voltage is limited.
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Servohydraulic control with load cell feedback

Hello,
We are planning to build a tie rod fatigue test system with Labview and NI PCI-7344 4-Axis Motion Control Board. We have two linear servohydraulic actuators for applying linear force to tie rod and a servo motor for steering wheel movement. Tie rod must be vibrated by linear servo hydraulic actuators with constant force (+/- 50N , compression and tension direction) as 20 Hz while the steering turns (this is for road simulation) .
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Best Regards
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Steward,
I think you should be able to use the analog feedback feature of the 7344 to accomplish your task. Please refer to this link where you can find an attachment that explains the details of using analog feedback.
I don't think that you will need any onboard programming for the control task but depending on your security needs you might want to use it for emergency stop actions (e. g. when something goes wrong and the speed or the force become too high).
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National Instruments Germany

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I'm trying to use the example
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Error -200077 occurred at DAQmx
Perform Shunt Calibration (Bridge).vi:1 Possible reason(s):
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Property:
AI.Bridge.ShuntCal.GainAdjust
You Have Requested: -61.980405e3
Valid Values Begin with: 500.0e-3
Valid Values End with: 1.500000
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How to "see" the calculations being
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2)
What the correct shunt element
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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!!!

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Thank you for your quick response.
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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.
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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.
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Here is the code that I am using:
ManchConversion6723();//produces SendIt array of series of 1s/0s
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When I arrive at the DAQmxCfgSampClkTiming line, I receive an error stating:
DAQmx Error: Measurements: Requested value is not a supported value for this property.
PropertyAQmx_SampTimingType
You Have Requested: DAQmx_Val_SampClk
You Can Select: DAQmx_Val_OnDemand
Task Name: _unnamedTask<0>
Status Code: -200077
I believe the problem stems from the source variable of the function. I am simply tring to send the data out at the 20KHz rate.
Any help would be greatly appreciated. Thanks in advance!
Solved!
Go to Solution.

Nevermind. Seems as though the PCI-6723 does not contain correlated DIO channels. In other words, sample clocks can not be tied to the DIO channels to allow for digital waveform generation. According to the AO Series User Manual, this applies to NI 6731/6733 Only. The error was trying to tell me that only a single transmit or receive channel was allowed.
For this reason, I will just stick with my PCI-6224 card.
Sorry for the confusion.

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
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Insulation Resistance
500
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200
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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.
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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.
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RSE terminal configuration
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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
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Generate PWM signal with 6602 utilizing load cell feedback

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