Need help to configure a two-channel acquisition using NI5154

[LCHEN5154]

Hello NI experts:

 I am configuring a high speed digitizer NI5154 for data acquisition. I have two channels of data need to be measured. Actually only the waveforms in channel 1 need to be captured and channel 0 is used for counting digital pulses.

My goal is like this: After started, the digitizer should count the digital pulses in channel 0 for some time untill a start trigger arrived in channel PFI_0. After received the start trigger in channel PFI_0 the digitizer should switch to channel 1 and start to captured waveforms and save them to disk.  After a well defined time the digitier stop the acquisition in channel 1 and then switch to channel 0 and repeat as cycles.

my questions are: What the best way to count the digital pulses in channel 0 ? The only way I know is set the reference trigger source to channel 0 and then get the "Records Done" number from the property node.  After the acquisition initialized the digitizer will waiting for the start trigger in channel PFI_0, No pulses in channel 0 will be counted. If I let the pulses in channel 0 not counted in the first cycle, in the end of each cycle how should I switch from channel 1 to channel 0 and saitch back after receiving the start trigger? It seems like I have to configure the trigger system repeatly.

[Efrain_G]

Dear LCHEN5154,

Unfortunately, there are certain limitations for what you are trying to do. You cannot set a separate triggering scheme for both channels since there is only one time base in the 5154 board. There are two options that we can try at this point. You can try to acquire on both channels and then do post processing in software. However, since you will be sampling at high rates this might not be possible. The easiest option for you would be to use a second board that can do the counting and then send a trigger to your scope board.

Efrain G.

National Instruments

[LCHEN5154]

Hello Efrain:

 Could you please explain a bit more about your second option?

 what's the second board I can use for easy counting job? 

thanks.

LIXIN

[Efrain_G]

Yeah, no problem LIXIN.

So basically you can set another DAQ board to do a counting task. This task will continue until you receive your PFI signal. This PFI signal can be used to both stop your counting and begin your waveform acquisition on your scope. You will need a retriggerable mode in your system so that you can repeat the process.

Regarding the signal with the digital edges you want to count. Can you tell me how does that signal look? Duty cycle, frequency, voltage range, etc. The cleaner this signal is, the easier it will be to count its edges.

Good luck with your application!

[LCHEN5154]

Thanks  Efrain.

The digital signal is simply  a TTL signal from a discriminator.  The highest rate may reach up to 30kHz-50kHz.

The width can be reduced to about tens of ns.

[Efrain_G]

Your frequency range is fine. You should be able to use a DAQ board with two counters so that you can count at those frequencies. However, I am a little bit worried about your pulse width. For instance, our NI X series boards can only detect a minimum pulse width of 10 ns in their counters.  

[Efrain_G]

Something to point out is that in order to do a multi-record acquisition in you NI 5154 you need to know how many records are you planning to acquire in advance. Please take a look at the niScope EX Multi Record example in LabVIEW. In this example, you set how many records you want to have. Every record begins when you receive a trigger. The trigger is rearmed in between records. 

[Efrain_G]

As far as your counter task, you should take a look at the DAQmx Count Digital Events Pause Trigger example in LabVIEW. In this example, you use a digital pause trigger to pause your counting task. This trigger can be easily changed to an analog level instead of digital.

Regards,

[LCHEN5154]

Thanks. Efrain.

Your information is very helpful.

I have a question concerning the NI5154 digitizer operation temperature.

As I read from the manual that the NI5154 should operate in a environment with temperature between 0-55 Celsius degrees. I just like to know what's the temperature of the NI5154 in my computer so I checked the device temperature using the niScope property node. This is a temperature measured by the onboard sensor and it shows that my NI5154's temperature is 53.5 Celsius degrees when the digitizer is not heavyly been used for a long time and the room temperature is about 25 Celsius degrees.

So I am a bit worried because I have to use the digitizer in a higher temperature environment, probably around 32 Celsius degrees, and during the running of experiments the digitizer will be heavyly busy for a week or so. Should I worry about this and what's the safe range of the device temperature as read from the niScope property node?

I am serious because we don't want to damage the hardware during the run.

[Efrain_G]

The temperature returned by the onboard sensor in your board is very reliable, so it is a good thing that you are trying to do something about it. You don't want to overheat your device.

First of all could you tell me if you are using a PCI or PXI form factor? If your device has not been used for a while, there's a chance that your device might have dust obstructing ventilation paths. Is your fan working properly? Are you keeping your device away from any heat source? Do you have any objects obstructing airflow?

When we write specifications for our devices we obviously go below the actual capabilities of the device to prevent any liability problems and to ensure safety. This means that it is up to you to run your device close to the limits specified. However, National Instruments will NEVER recommend you to do that because the risk of accidents is multiplied when operating above specifications.