Load Cell Input UMI 7764

[Ned Mandingo]

Hi.  I have a UMI 7764 and I want to use it control a stepper motor and load cell input.  I am using a power supply connected to the analog input on the card to simulate a load cell.  However I can not find/read it in MAX.  I am able to control my stepper motor with no problems. 

Any input would be appreciated!  Thanks.

[Jochen]

Hi,

to read analog values with your motion control board, you need to use the Read ADC function in your programming environment. Are you using LabVIEW? Do you just want to read the load cell signal or do you want to control force? Which are your timing and accuracy requirements? Which NI-Motion controller are you using? the UMI-7764 is just a connector block.

Thanks and kind regards,

Jochen Klier

National Instruments

[Ned Mandingo]

I am using the UMI with a PCI 7342 motion controller.  I am using the load cell for feedback purposes mostly; creating a force vs. travel plot.  I do need the program to stop if the force nears the load cell rating (which I have been able to accomplish using a USB DAQ).  I am programming using the most recent LabVIEW.

Is there any way to set up a task or global virtual channel for my load cell using the UMI/PCI, or do I just have to use the ADC function?

Thanks.

[Jochen]

Ned,

thank you for this information. For this purpose the analog inputs on the 7342 are ok and as you have been able to accomplish the functionality by using a USB DAQ device, I don't think, that your timing requirements are extremely high.

Setting up tasks and global virtual channels refers to NI-DAQmx, which is the driver for NI data acquisition devices. The PCI-7342 is supported by NI-Motion, which comes with it's own API, so these terms are not valid here. In fact Read ADC is all you need, but as this is obviously a quite simple approach, the performance is also not very high. You shouldn't expect reading rates better than 200 Hz.

If you want to increase the safety aspect of your application, you also could think of moving the part of your code that monitors the force and stops the axis if a limit is exceeded, to an onboard program. Onboard programs don't run extremely fast, but they run independently from your host application, so even in a case when the PC is busy or even if it crashes, the onboard program still makes sure, that the axis stops at the force limit.

Please refer to the shipping examples if you are interested in onboard programming.

Regards,

Jochen

[Ned Mandingo]

Thanks for the info! The Read ADC function was the ticket!

[kdmart12]

Hey Jochen,

This thread sounds a lot like what I am trying to do. A couple questions for you: What are my options for reading analog values at higher rates? Also do you have any links to information about onboard programs and general information about using the NI-Motion API.

Thanks!

Kenny

(Also using a pci-7342 with a UMI-7764)

[cody_a]

Hi Kenny,

First off, you may notice that this forum thread is nearly 6 years old.  In the future, you'll typically have better luck getting responses by posting to a new thread on the motion forum.

To answer your questions:

1. The analog inputs on the NI 73xx motion controllers are not capable of being hardware timed, and therefore are limited to very slow sampling rates. This KB explains more.  You'll notice that AI sampling rates are slower when used with onboard programs since the onboard controller must share processor time with higher priority tasks.

2.  You can find more info about using onboard programs with 73xx motion controllers here.  Also, there are a lot of shipping examples that show how to use the NI-Motion API and onboard programs.  You can find all of those under Hardware Input and Output>>Motion Control>> NI 73xx in the Example Finder.