When I worked in a USDA plant (we made soup, quiche and meat pies) - we had a temperature data logger with external probes. The data logger was set to record temperatures every 2 minutes (This can be changed: we had some products that would be very close to completing the cooling within the time limit so we chose the interval based on what we were willing to lose if the cooling went beyond the limit - pretty much nothing hence the 2 minute interval.)
The data logger was set up outside the cooler and the probe wires were about 6 ft long, I think. Pop the probes into a (sacrificed) product and head home. Next morning - first thing! - remove the probes and data logger (from the wall; it attached by hooks) and take it to the computer to download the data. Then, print the data - this is now a record, an official record of cooling. And, CHECK the data - check the cooling ensure the CCP was met within the specified time frame. (You know what to do if it doesn't.) I always marked the start and end of the cooling, what the product was, and indicated total time of cooling (3 hours and 24 mins), then signed and dated the print out. And, as always, clean and sanitize the probes right away so they don't get forgotten.
As for calibration: we checked the probes regularly and once a year it needed to be sent out for calibration by the company we purchased it from. I believe there are several types of temperature data loggers out there; just do some homework for which will work best for your purpose and don't hesitate to contact the manufacturere and ask their opinion. I think there are options for different types of probes to go with the data loggers as well.
