topic Re: post processing using NI6225 in LabVIEW

post processing using NI6225

Clint Eastwood — Thu, 01 Dec 2005 14:51:20 GMT

I have 12 NI6225 DAQ Boards (~960 chs). I want to set up LV8 to read Ch1 on all 12 boards ( SW trigger) then Ch2 on all 12 boards, then Ch3 etc. I need to store ALL this data then process it ( post process?) after acquiring all 900 chs. Any suggestions or examples ? In post processing how does LV distinguish between the raw data from Ch1 board 0 and ch 2 board 0 or even ch1 board 1 ?

Make my day and answer this question.

Thanks,

Clint E.

Re: post processing using NI6225

Ryan_V[DE] — Fri, 02 Dec 2005 18:12:22 GMT

Clint,

In order to do this, you will need 12 individual tasks. Since you have 12 of these, I'm assuming that you have them inside of a PXI chassis. The attached example is for 2 devices, but you can extend it to more by repeating the bottom half of the code. You should physically locate the master device (the one with the reference clock being exported) in slot 2 of your PXI chassis (the source of the star timing). In this code, all other devices are synchronized with the master device reference clock. Whenever the master's Start Task VI is called, this will assert the AI Start Trigger signal on the master device, and all other devices will use that as a digital trigger to begin their acquisitions. Please make sure that all other devices execute their Start Task before the master does (Merge Errors VI would be helpful). This process will result in each of your devices acquiring samples at the exact same time. The output of each analog read will output an array of waveforms, with each waveform corresponding to the samples acquired on a single channel of that device. To specify the order with which the channels are scanned, order them that way in the physical channel control. For instance Dev1/ai1,Dev2/ai3, Dev1/ai5 will acquire one sample from channel 1, channel 3, and channel 5, then repeat. Please let me know if this is not what you were asking, or if you have any additional questions.

Hope this helps,

Message Edited by Voltage Viper on 12-02-2005 12:13 PM

Re: post processing using NI6225

Clint Eastwood — Mon, 05 Dec 2005 12:15:00 GMT

Ryan,

Could you save this in LV7.1 ?? I don't have LV8 yet.

If I understand this, when I SW Trigger on slot 2 a PF0 channel all the other boards are triggered simutaneously ? I assume its unique to the AI vi because what if I wanted to trigger each board individually ? You are correct, I do have them in a PXI Chassis.

Clint

Re: post processing using NI6225

Clint Eastwood — Mon, 05 Dec 2005 15:09:02 GMT

Ryan,

Another question. With these (12) Ni6225 I'll have 900+ channels. If a ch is above a certain threshold I plan on making it light up green and visible ( using property nodes). Can you set up say 500 property nodes without clicking on each LED and say Create>Property node? For example 500 will be displayed and green. The other 400 will be greyed out. If I have to do a property node for each LED it will create a tedious task.

Clint

Re: post processing using NI6225

Ryan_V[DE] — Mon, 05 Dec 2005 15:18:32 GMT

Clint,

Here is the VI in 7.1. You are correct in that a software trigger will simultaneously start all boards. Perhaps when you see the VI, this will make a little more sense. Basically, tasks for the other cards are set up to wait on a digital trigger from the device in slot 2. Whenever your application sends a software trigger to that device, it asserts a certain digital line (ai/StartTrigger) which triggers the other cards in your PXI chassis. I have also attached another VI which is used in this applicaion. It should already be on your computer, used in the shipping examples, but LabVIEW usually has trouble finiding it. Please let me know if you have any more questions.

Regards,

Re: post processing using NI6225

Ryan_V[DE] — Mon, 05 Dec 2005 15:22:08 GMT

Clint,

I would build a loop which reads the data, makes a decision (greater than threshold?), and then adds the result of that decision into a boolean array. Then, instead of individual booleans, you could just have an array of them and wire your data array directly to it. Does this sound like an option?

Re: post processing using NI6225

Ryan_V[DE] — Mon, 05 Dec 2005 15:23:35 GMT

Oops,

Here they are.

Re: post processing using NI6225

Clint Eastwood — Mon, 05 Dec 2005 18:29:28 GMT

Thanks ! That may have saved me a lot of work. As far as the property node goes, I may still have to do trial and error on that one. I didn't quite understand your explaination.

Re: post processing using NI6225

Ryan_V[DE] — Mon, 05 Dec 2005 19:30:30 GMT

Clint,

I have attached an example which simulates a decision on 12 cards and 80 channels. I'm sure you could come up with something similar to build a 2 dimensional array with the result of your read operations. This array is displayed on a classic array indicator with small LEDs, no indices, and a transparent border. It appears to be a grid of booleans. After running once, you will notice there is a difference between "on," "off," and "disabled" states. Please let me know if you have any questions on this.

Hope this helps,

Re: post processing using NI6225

Clint Eastwood — Tue, 06 Dec 2005 11:23:36 GMT

Ryan,

Again, thanks a lot. Its up to me now. I was trying to save myself "calling" every LED ( 960 !!) and setting the property node for it. When I run the test certain LEDs will be lit based on a voltage level. If the LED is outside this group ( pattern) but is above the level ( a miswire) it will be lit red and greyed out to indicate its outside what is expected but has voltage on it. This is to show the operator something is wrong. I tried setting a property node for an array thinking it would be applied to each LED in the array. It wasn't the case. It applies the property node to the element "array". You've given me a great starting point.

Thanks

Re: post processing using NI6225

Philip_Courtois — Wed, 07 Dec 2005 20:48:48 GMT

Hi Clint Eastwood (!),

You can do almost anything in LabVIEW - but finding the most efficient way is what the art is. You CAN indeed access the properties of the element INSIDE the array. I have shown this in the attached "ChangingProperties.vi" as the first part. The problem with changing the properties of an element inside the array is that once you change one element, you change ALL elements. This is because the array simply stores the "type" information for one element and the difference between each element therefore only can be the value.

So what if you actually use 960 indicators in the front panel? Other than taking you a month to manually create the front panel, there is actually a way to access the properties of a certain indicator - without having to create 960 Property Nodes. In the "ChangingProperties.vi" I am accessing one of two indicators using only the name of the indicator to specify which indicator to access. You will then have to do the code that decides exactly which indicator you need to change.

Okay, the above two solutions both have issues in terms of development time, readability, maintainability and scalability. I definitely see the best solution in your case to be the use of two 2D-arrays on top of each other. One array (let's call it "Array 1") will show the actual value of the channels in numbers and the other array ("Array 2") will show different colors depending on the different states that you want. I chose to use a Color Box as the element in Array 2 to give you more than the two options (True/False) you would have had if you used a Boolean indicator instead. In the attached "MultiArrayColors.vi" I compare the values of each element in Array 1 with the specified Threshold value and colors (green or red) the Array 2 according to the result. I also compare with a second condition to color some of the elements a third color (blue).

The hardest part of the third solution is to color every part of Array 1 transparent. It is done fastest by coloring the element and the empty array shell transparent before you insert the element into the array shell. After that you just put Array 1 on top of Array 2 and use the "Reorder » Move To Back" option from the toolbar to make sure that Array 2 is places behind Array 1.

Let me know what you think, thanks.

Have fun - and more of it with LabVIEW 8!

Message Edited by Philip C. on 12-07-2005 02:49 PM

Re: post processing using NI6225

Clint Eastwood — Thu, 08 Dec 2005 11:19:08 GMT

Philip,

You're a "proven active veteran" so I'm sure this will work. Give me some time to try it. I'm a big advocate of LV. I tell everyone whatever they can do in CVI I can do in LV.

Clint

Re: post processing using NI6225

Clint Eastwood — Thu, 08 Dec 2005 17:55:14 GMT

Philip,

Can I customize the elements in the array you sent me ? Right now they're colored rectangles. Can I make them round and a specified radius? On that same note can you specify the radius size ?? I'm trying to overlay the digits into the rectangular array elements and without trial and error I don't know how big to make them so that one fits inside the other.

Re: post processing using NI6225

Philip_Courtois — Mon, 12 Dec 2005 04:06:36 GMT

Hi Clint,

Thanks for the nice words.

Your new requests will not be as easy to implement as the solution I already provided you. The "Color Box" control that I used in the array as the background, only comes in rectangle shape. You therefore can't use the "Color Box" as your round object, sorry.

If you REALLY need a round shaped color background, there's one other solution and that's to use a "Picture Ring" as the element in the 2D-array as the background. You can then insert three different images of round, colored shapes created in another application (for example Microsoft Paint). You can then choose different pictures in the "Picture Ring" by specifying the index number of the image you want to show. Since you are using images, the size of the round shape has to be specified in the application you use to create the image with. If you use my rectangle solution, you can easilly change the size of the elements by using the "Resize Objects" menu in the toolbar.

I hope you'll be able to get some good results...

Re: post processing using NI6225

Clint Eastwood — Tue, 13 Dec 2005 13:44:54 GMT

Ryan,

Does this allow for full BW ( 250 KHz) when each channel on each card is read ?

Re: post processing using NI6225

Ryan_V[DE] — Thu, 15 Dec 2005 16:45:38 GMT

Clint,

Actually, for our E and M series devices (but not S Series), we multiplex each channel into the ADC. The 250kS/s must be shared among all channels. If you are scanning 80 channels, your maximum rate for each channel will be approximately 3.125kS/s. Please note that even if you did have a DAQ card that could sample each channel at 250kS/s, you would have an aggreate data rate of around 500MB/s (250kS*2B/S*80channels*12cards), which exceeds the theoretical PCI bus bandwith of 127MB/s. What is the greatest frequency you need on each channel? Looks like you might have to wait for PCI Express.

Hope this helps,

Re: post processing using NI6225

Clint Eastwood — Thu, 15 Dec 2005 16:58:33 GMT

Ryan,

I'm putting the read each channel into a for next loop with the index associated with the proper channel and card. I want to concatenate the index to produce the proper output format which will correspond to the channel. I hope this way it will access each channel on an individual card at full BW.

Haven't tried it yet.

Re: post processing using NI6225

Ryan_V[DE] — Fri, 16 Dec 2005 22:17:51 GMT

Clint,

I'm not quite sure what you wish to accomplish here. Are you trying to sequentially read a finite amount of data off of each channel on your board? I think we may be confusing "bandwidths" here. Basically, your card has a fixed analog input bandwidth. The rate at which you can acquire a signal is determined by your sample clock. And since we have to obey Mr. Nyquist, it is up to you to make sure that there is no frequency content on your analog input signal higher than half of your sampling rate.

If your signals have information up to 125kHz, then you must sample at 250kS/s. In order to do this for sequential channels, and quickly, I would set up finite tasks for each channel that you plan to use, then "Verify" them all with the "DAQmx Control Task VI." Then, all you need to do is sequentially call the "DAQmx Read" for each of these tasks, with "number of samples" set to -1. This will automatically start the acquisition on the board on the specific channel for the task, and acquire the exact number of samples specified. I would use for loops with shift registers to accomplish all of this. And of course, in your case, repeat this 12 times.

Hope this helps,

Re: post processing using NI6225

Clint Eastwood — Wed, 04 Jan 2006 13:10:58 GMT

Ryan,

I'm working w another Engineer who called National to get a SR#. Is there any way you can take control of that SR# so we can discuss this over the phone ??

( SR# 749607)

Thanks

Re: post processing using NI6225

Ryan_V[DE] — Wed, 04 Jan 2006 22:51:59 GMT

Clint,

I've spoken with the Engineer who has been helping your colleague. I brought him up to speed on what we have discussed and you are certainly welcome to phone him regarding this issue. Alternatively, I would be more than happy to continue helping you here for the benefit of others.

Regards,
Ryan