timer nanosecond 4462

[Rinku]

I am using NI PCI 4462 board. Using this I wish to carry out underwater acoustic signal acquisition.

I wanto determine the time interval between two input channel whenthey acquire signal of a particular frequency and amplitude.

I cannot use Tick Count(ms), this provide time in milliseconds.

I tried counting nos. of samples, tht provided a resolution of 4.8us ie 1/204.8k.

Is there any way, I could measure time diffrence b/w two channels, which has a resolution in nanoseconds.

Ravinder Singh

DCE

[Ima U]

Hi Ravinder,

The PCI 4462 is a Dynamic Signal Acquisition (DSA) board.  Each channel on NI DSA boards has it's own ADC which are simultaneously sampled.  With this method, all the channels are sampled exactly at the same time using sample-and-hold circuitry and an independent amplifier for each channel. The values are then multiplexed and sent to the ADC for conversion.  Since each channel is sampled from the same clock on the same rising edge, there will not be a measurable amount of interchannel delay.

I hope this helps.

[Rinku]

I understood that but thts the case when we use the clock on DAQ card, I want to use a computer clock, If i use that I will be able to measure the time difference between two channels.

I have a PCI card that gets attached to PCI slot in a motherboard, The labview applicaation I will develop will use DAQ features for acquiring signal from the channels.

If one channel detects a particular signal I will switch on the time (basically the CPU timer of the motherboard and CPU) and will then stop when the signal is reached on second channel.

Since my application is using hydrophones (underwater) time difference will be small and depend on arrangement of hydrophones. In that case If I have timer in nanoseconds then I can easily get time difference be it in nanoseconds or milliseconds.

The whole point of  my work lies in determining the time difference. Using this I will feed the time in some equation which will then provide me the location( bearing and angle) of acoustic soure

[balki]

Rinku,

I think what your trying to do is a standard beamforming application.  In your case, I wouldn't try to control the hardware signals independently as that invalidates the purpose of all the channels scanning simultaneously.  Rather, manipulate your data on the back end, since you know that all data samples taken from each channel were taken simultaneously, you can figure out when the sound wave reached each microphone from when that signal appears on each channel. 

You might reference the following case study:  http://sine.ni.com/cs/app/doc/p/id/cs-472

This discussion post also references a similiar question: http://forums.ni.com/ni/board/message?board.id=150&message.id=23&requireLogin=False