Step Response using PCI 4551

[NarayananK]

Hi,

Well i generated a square waveform of 5 Khz and acquired the same at 25 KS/s using PCI 4551.

However, the acquired square waveform has a ringing tone at the transient i.e. not able to acquire the square wave accurately.

Is is due to the low pass filter in the PCI 4551 card?

If so is there any method to avoid the same using traditional daq?

Please help me asap.

Thanking in advance

Naru

[Tica]

Hi Naru,

My assumption is that it is either a function of the filter or the fact of generating so much slower than you are acquiring.

Can you post a picture of the waveform that you are acquiring?

Thanks,

Tica T

Applications Engineer

National Instruments

[dsb@NI]

A square wave is not a band-limited signal (i.e. a perfect square wave has high-frequency content at the odd harmonics of the fundamental frequency of the square wave). Anti-aliasing and anti-imaging filters in DSA hardware are put in place to eliminate out of band energy on the input and output channels, respectively. This low-pass filtering in the hardware prevents high-frequency components from being incorrectly identified. The hardware anti-aliasing and anti-imaging filters cannot be disabled in Traditional DAQ nor in DAQmx. You can use your DSA device to measure the frequency response and then use signal processing techniques to extract the impulse and then step response. Or you can use MIO hardware (such as M series) to generate a sharper (unfiltered) square wave for your step response measurements.