Where can I obtain a free professional survey instrument to measure the culture of my company?
I need to establish a baseline and measure every 3 months to determine what the improvement in our workplace culture is.
I'm not sure what your criteria are for "professional" and it depends on who you're surveying. Younger demographics enjoy using TYPEFORM and I make excellent use of it on my website to collect clients and survey my newsletter subscribers for the kind of content they want to see.
Survey Monkey has several free sample surveys you could edit to suit your needs. https://www.surveymonkey.com/mp/employee-surveys/?ut_source=header