O2 Monitoring system for ground coffee silos

Hi There,
We are a coffee capsule packing facility. I am after some advise on the best multi sensor (multi-head) system to monitor O2/CO2 in our Nitrogen flushed silos. We have 8 x 2 tonnes silos in total and degassing is expected to run for 2-4 hours as we produce Nitrogen on site at 99.9% purity. 
Anyone has experience with the described system? 

Many thanks in advance.

Kind regards,
Olesia

Hmmmmmmmmm this is a tricky one

My partner is at a coffee roaster............the Ministry of labour came in, and the CO2 detectors they were wearing on their person went off........but the actual CO2 meter did not, turns out that the process of roasting actually produces NO2...........long story short, you may not be able to get a meter that is going to work in the presence of that level of pure nitrogen.....

you may have to rely on straight O2 monitoring.....I'd reach out to public health and ask their assistance on this one