sampling rate

[zura]

We use Cacti to monitor traffic. We use Netflow version 5. we just changed our router from Cisco to Juniper and got one problem. Juniper doesn't send every packet. It can send every packet from 100 or 1000. Is there a way to set sampling rate to 100 or 1000 like you can do in PRTG? I looked for the solution in the internet but couldn't find a solution.
I would be very grateful if someone could help me. thanks in advance.