are there any PC cards which have sample and hold capability

[ALD]

Are there any PC A/D cards which have sample and hold capabilities up to a 10 Khz sampling rate which we are interested in for modal testing of engine structures. Also if this type of card is available what would be the maximum input channel count of this card. We would be interested in the highest count available up to 64 channels.

A second question: We currently have a 64 channel PCI 6071 capable of 1.25 MS/s throughput. If we are using all 64 channels what would be the interchannel delay between the first and last recorded channel and at what frequency would we have to be sampling to even be able to see the affect of the interchannel delay of this specific card.

This issue has been debated wi
th in our group and your insight would be appreciated as you are the experts in this field.

[Michael_S.]

Hello,

Your best option for true simultaneous sampling at rates up to 102.4KHz on every channel would be to use a set of PXI 4472 boards which are 24-bit DSA boards with 8 channels each. Your system would require 8 boards which can be easily synchronized together to give you a high quality 64 channel acquisition system.

On the other hand, the PCI-6071 with a sampling rate of 1.25 MS/s will yeild the following results. The max sampling rate for all the channels will be (1.25MS/s)/(64 channels) = about 19.5kS/s. The delay between channel 0 and channel 63 will be the aggregate delay between the channel readings. The interchannel delay is 1/(1.25MS/s) = .8 microseconds. So the delay between channel 0 and 63 = .8*(63) = 50.4 micro seconds.

The syste
m with 4472 DSA boards would yeild delay on the order of a few nanoseconds.

Hope this helps with your project.

[ALD]

Michael,

Thanks for your answer. I do have one more question. Will the interchannel delay be constant over different sampling rates and with different counts of active channels? If so then do agree that a phase correction routine could be written to correct for the interchannel delay.

Regards,

Aaron

[omarp]

Dear Sir,

Thank you for using NI Developer Zone.

National Instruments has a product line designed specifically for acquisition of dynamic signals, it is called DSA - Dynamic Signal Analyzers. In according to the description of your application the card that best fits your needs is the NI-4472 that is available in PCI and PXI format. This card is able to acquire 8 channels simultaneously, as opposed to the regular DAQ cards that have a single A/D converter and a multiplexer. The NI-4472 has 8 Delta-Sigma A/D converters one per channel, what results in a better performance than having a single A/D converter in combination with a sample and hold and a multiplexer. To Acquire 64 channels you would have to have 8 boards and synchronize all 64 channels. The Synchronization process is very simple and with a couple of software calls we can synchronize as many as 112 channels for simultaneous acquisition at 102.4K samples per second per channel.

Regarding your second question, the PCI-6071 will sample between channels in a single scan at the maximum sample rate of the board (1.25 MS/s) but the
scan rate, i.e. the rate in which the same channel is sampled is defined by the user. Being that said, we can conclude that the interchannel delay will be the inverse of the 1.25 MS/s clock, or 0.8 micro seconds.
For a 1 KHz sine waveform, this represent a phase delay of 0.288 degrees between consecutive channels. For a channel list of 64 channels each one having the same 1 kHz sine waveform, the phase delay between the first and the last waveform will be 18.432 degrees.

I really recommend the NI-4472 as a very good solution for your application, besides that the combination of the NI-4472 with LabVIEW and the sound and vibration toolset will give you a tremendous tool to solve not only your immediate need but also provide you a system that will be easily modified and adapted for future needs.

If you need more info, feel free to contact me and I can give you more details about this product.
Call 1 800 IEEE488 and ask to speak with the Computer Based Instruments (CBI) support team.

Best Regards.

Omar De Andrade
Applications Engineer - Computer Based Instruments
http://www.ni.com/support/