Generate dc voltage from user input using PCI 6221 card ?

[Nhanna Marie]

Hello I am new to LabView. I have looked at several post in regards to Voltage generation however I am still confused about which Example would be best for my specifications.

At the end of the day I would like to have a VI that allows users to input shear rates which would be used to establish a rotational speed, and from the rotational speed generate a velocity.

I am using the PC 6221 Card with LabView 8.2.

I am considering using SVXMPL_Baseband FRF (DAQmx AI and AO), is this the appropriate example to use ?

[AustinMcElroy]

Analog output is the best way to easily produce a AC/DC voltage level.  You can use a Digital pulse train, duty cycle, and filters to do it also, but that is much more complicated.  Are you planning to drive a motor?  If so, you will need to look into a motor driving circuit that will allow the voltage from the AO port to drive a high current load like a motor. 

[Nhanna Marie]

Is SVXMPL_Baseband FRF (DAQmx AI and AO) a good example to start off with ?

Or should I look for an example that contains a motor driving circuit as well ?

[Matt_A]

Hello Nhanna,

There are a number of ways to meet the specifications you have listed. The best way to proceed will depend a great deal on your design decisions. The answers to the following questions should provide some insight into how you could proceed:

1. How do you plan on converting the user input into a physical phenomenon? As a previous user asked, do you plan on driving a motor? What are your drive strength requirements?

2. Do you have any LabVIEW Modules or Toolkits? The example you referred to in your post comes from the LabVIEW Sound and Vibration Toolkit, so I would assume that you have that particular add-on. However, the LabVIEW Order Analysis Toolkit has some additional functionality that deals specifically with rotational speed for machine condition monitoring. More information about this Toolkit can be found here.

3. Do you have any National Instruments Motion Control products? We provide several different products for motion control of all different types. You can find more information about Motion Control on our website here. This page includes a Motion Control Interactive Tutorial and a thorough description of Motion Control hardware and software.

I hope this information is helpful. The more details you can submit, the better information we can provide. Let me know if there's anything else I can do.

[Nhanna Marie]

Hey Matt,

I managed to get a copy of the code that was previously used within the lab to I would like to know if you might be able to help me translate it so that it is written in code from version 8.2. Please let me know if this is possible.

[Nhanna Marie]

I apologize I just realized that I didn't answer your questions.

1. How do you plan on converting the user input into a physical phenomenon? As a previous user asked, do you plan on driving a motor? What are your drive strength requirements?

Yes we plan on running a motor. The voltage needed to run the motor is 0V - 6V.

2. Do you have any LabVIEW Modules or Toolkits? The example you referred to in your post comes from the LabVIEW Sound and Vibration Toolkit, so I would assume that you have that particular add-on. However, the LabVIEW Order Analysis Toolkit has some additional functionality that deals specifically with rotational speed for machine condition monitoring. More information about this Toolkit can be found here.

From the LabView tutorial on Hardware - Chapter 4 in 8.2 manual, do you believe that it would be possible to actually start off with the DAQmx example and than build around that example. We were able to get the example to actually run with our machine.

3. Do you have any National Instruments Motion Control products? We provide several different products for motion control of all different types. You can find more information about Motion Control on our website here. This page includes a Motion Control Interactive Tutorial and a thorough description of Motion Control hardware and software.

At this point in time our professor has stated that we do not need Motion control products however she is open to the idea for future endeavors.

I hope this information is helpful. The more details you can submit, the better information we can provide. Let me know if there's anything else I can do.

As I continue to work on this code I have come across some additional questions

• If the DAQmx isn't showing that there is a custom option for scale units how can we create that option, or why would it not allow such
• What is the difference between task / channel in and data

Thank you for all your help this far. I definitely appreciate it.

I have also attached the code that I was referring to in the previous message.

Message Edited by Nhanna Marie on 02-27-2007 01:07 PM

[Matt_A]

Hello Nhanna,

Your options for converting VIs to LabVIEW 8.2 will depend on which version of LabVIEW was used to write the programs. Do you know when the program was originally written and what version of LabVIEW was used?

Basing your development on an example program is actually a really good way to get started because it provides you with a framework of basic functionality to build on. It is also helpful, because you know that the program works and you can experiment from there. Finally, it gives a place to return to if you begin to experience problems; you will not have to entirely rewrite your program if you have problems because you know that you have the working example as a base.  Some good examples of Data Acquisition (DAQ) programming can be found in the NI Example Finder. This utility can be found by going to the Help menu in LabVIEW and selecting Find Examples... This will open the NI Example Finder window. In the NI Example Finder you can find applicable examples by browsing to Hardware Input and Output>>DAQmx>>Analog Generation>>Voltage. Specifically, I would recommend that you examine Cont Gen Voltage Wfm-Int Clk.vi; this program demonstrates how to continuously generate an analog signal. Once you are able to generate your signal, you will only need to process your user input into signals that can control the generation. This is where the LabVIEW Toolkits and Modules come into play.

In regards to your additional questions:

• If the DAQmx isn't showing that there is a custom option for scale units how can we create that option, or why would it not allow such

You should be able to create a custom scale in the Measurement & Automation Explorer or using the DAQ Assistant in LabVIEW. For more information about custom scales, I would recommend that you examine this document.

• What is the difference between task / channel in and data

Data is the signal information that you want to send out of your device. It could have several representations, but is generally an Array of data points, a Waveform data type or a Dynamic data type. For more information about data types you can download a presentation here. To find more details about tasks and channels, there is a document online here.

[Nhanna Marie]

Hey Matt,

I actually was able to generate a voltage. However when I generate the voltage using DAQ Assistant and I test it seems like the voltage is still running even after the stop test button is pushed. I don't understand if it is a lack of programming since the only express in the block diagram is the DAQ Asst Express or something that I am over looking.

[Joe_H]

An output will stay at the voltage or setting until  you change it. That means if you do not the card to out out the voltage when you hit your stop button then you have to tell it to stop putting out the voltage.

[Nhanna Marie]

So Jhoskins,

I need to put on the outside a stop. For the DAQ assistant with A0 can I just put a stop feeding into the left hand side stop slot on the express ?