I have served as advisor to some HR managers and growing startups on these issues, and we have found that the first principle is guaranteed anonymity for any software-initiated polls. While open ended answers give more data, they also open the employee up to identification and pollutes our information.

Best approach is a mix of in person approach and online polling, the personal touch allows for people to share attitudes they didn't even know they had. That of course requires a specifically trained staff, so online methods are preferred by industry.

This polling would be better aligned with events and important dates rather than periodic weekly intervals to prevent a "punch a button" feeling.

I'd be happy to elaborate more on best practices for polling in a call and show how even the in person methods can be introduced to complement them!