I got three of these off ebay for $120, unknown condition, etc. Was hoping I could put pieces together and make one working one... turns out they all work!
I was quite happy with that deal... they work by measuring time of flight of an ultrasonic pulse between each of the three transducers. It outputs in several different formats, I'm using the RS232 option. I'm in the process of building a little PIC controller to put the data on a 16x2 LCD or something.
Anyway, they have an intel 80C51 processor inside that seems to do all the calculations and signal processing. Code is stored in a 27C256 PROM. Only one of the three had reasonably new firmware so I read the code out of all the PROMs and then programmed some new ones so all three sensors have the newest firmware. I figured I would post the bin files here just for fun in case someone else gets one with older firmware like I did. I'll put my display design up too once it's finished. Version 6.01 is the latest and seems to be what is described by the documentation on Vaisala's site. I ran a quick disassembly on it just for grins too - that's where the .asm file came from.