LabVIEW 7, MAC OS9

[Haibo]

I recently upgraded LabVIEW 5.1 on OS 8.6 to LabVIEW 7.0 on OS 9.2, and found AI operation slower than before for existing VIs. Specifically, I found AI Start.vi, which typically completes in 3-4ms, has significant jitter, causing it to complete in 6-10ms (or even longer) every now and then. Is this normal?

This poses a problem for a DAQ vi where an external TTL signal from a rotary encoder is used to repeatedly trigger AI Start and AI Read in a while loop. (100 date points are taken and averaged for every 0.1 degree rotation, which through the rotary encoder generates a TTL pulse) The TTL signal comes every 18ms, the jitter in AI START causes the AI READ to complete reading the 100 data points after the next TTL pulse has arrived. The AI START
/READ therefore has to wait for the next pulse, causing a syncchronization problem with the rotary encoder. This problem did not exist with LabVIEW 5.1 on OS 8.6.

Should I expect a degradation in DAQ speed with LabVIEW and OS upgrade? I have already drastically upgraded computer memory, and assigned 120MB to LabVIEW. Thanks! -Haibo

[Spencer S.]

Haibo,

To perform retriggerable analog input with a trigger signal whose frequency is close to the time it takes to reconfigure the operation in software, you may want to consider using your device's counters to achieve hardware retriggering. Below, I have included a link to an example program that demonstrates this procedure:

Retriggerable Analog Input with Two DAQ-STC Counters [link removed; example no longer available]

Spencer S.