Read every 0.1 seconds, but the counter is not fixed

[陳米拉]

Dear all

I use python write an ci counter read code

my input frequency is fixed at 20Khz and i use while loop to get counter every 0.1 sec

but the conter is not fixed number

There will be a two-digit jump 

for example 1421 →1421 →1423 →1421 →1428 →1425 →1426 →1421 ........

how can i get fix counter ？

CT = 0
while (tCT >0):
tCT = NI.read() //NI is function task.ci_channels.add_ci_count_edges_chan('Dev1/ctr0').ci_count_edges_term = 'PFI0'
print(str(thCT-CT))
CT = tCT
time.sleep(0.1)

thanks all

[santo_13]

I think it's not a problem with the counter but with the execution of the Python program, your python program does not execute "exactly" at 100ms intervals.

Software execution times are not guaranteed by OS and hence the difference is counter readback values are the variation in OS execution time of your loop.

Edit - counters being an HW are the most precise you can get given the reference clock is the best you can get