Signal Conditioning

cancel
Showing results for 
Search instead for 
Did you mean: 

Measuring a freq. sweep with the SCXI-1126, data enters PC with a 100 ms delay

We have build a system that has a drive unit that is driving a wheel. We measure the speed of this wheel with a puls sensor on this wheel. This puls is connected to a SCXI-1126 module which is connected to a daq board in multiplexed mode.
Also on this wheel a frequency meter with a can interface is connected.
When we know read out very fast the analog board and the latest can messages, we see that there is a delay between the can values and the analog values from the SCXI 1126. In fact the SCXI results are 100ms later then the can results. Is there a delay on the SCXI-1126? Also the edges when changing the frequency into a sweep are not that charp with the SCXI-1126. (We use a 12V puls signa
l, 50%DC and 1 Hz filtering)
0 Kudos
Message 1 of 3
(2,823 Views)
There is a delay from the SCXI-1126. Let�s examine why. The SCXI-1126 has a threshold voltage that the user can set. Using this threshold value, the module will take many samples of the input signal and then determine the frequency of the signal. Then this frequency which is represented by a an 8-bit number is converted to an analog voltage which is then multiplexed onto channel 0 or your DAQ board where it is then converted back to a 12 or 16-bit value and then read by software.

You may be able to change your filtering from 1Hz to 40Hz or faster to see improvements in the delay. Follow the guidelines on page A-2 of the SCXI-1126 User Manual. Here is the link: http://digital.ni.com/manuals.nsf/websearch/1FF17019174F7CA086256CED005C957B?OpenDocument&node=132
100_US

Regards,
Bill B
Applications Engineer
National Instruments
0 Kudos
Message 2 of 3
(2,823 Views)
Dear,

If I set the filter to 1Hz we stil have a delay of 100-200 ms. Is this acceptabel or is this to high? How much is many samples?

Regards,

Kurt Hensen
0 Kudos
Message 3 of 3
(2,823 Views)