Available from Hampshire Controls Corp.
The Model LD-200 uses a single probe/sensor for monitoring liquid nitrogen level, while automatically providing audible and visual alarm indication should the liquid nitrogen level drop below the end of its special probe.
In operation, a special, 1/4-inch diameter probe (up to 2 feet long) is inserted into a cryogenic tank (used for a laboratory freezer or other application), to an optimum level within the liquid. Once in place, a thermistor at the end of the probe is able to detect any slight rise in temperature should the liquid drop below the end of the probe - below which where a given process or use for the cryogenic liquid is endangered. The special probe is extremely sensitive and highly repeatable.
The standard package is a wall-mounted box (approximately 2.5" wide x 4.75" high x 1.75" deep) and has a small plug-in power supply to operate the system.