Used but very clean and in good cosmetic condition. Powers up (requires a screw-terminal 6VDC battery or equivalent - not included), and I was quickly able to set the CURRENT ADJUST to 120.0. Using an inert gas (not hydrogen) for testing, I could produce the TCD (Thermal Conductivity Detector) katharometer effect with approximate, consistent, repeatable results. If I sound a bit cautious here, it's because I can't find any instructions on how to operate this cool piece of tech - so, "I'm kind of making it as we go," as they say.
Here's what the Ametek brochure says:
"The 120HD analyzer functions as a katharometer. It operates by having two parallel tubes, both of which contain gas and heating coils. The gases are examined by comparing the rate of loss of heat from the heating coils into the gas. The coils are arranged in a bridge circuit so the resistance changes due to unequal cooling can be measured.
One channel contains moisture-saturated air and the mixture to be tested is passed through the other channel. Hydrogen has a much higher thermal conductivity than air and so the 120HD is very sensitive to it, but it will also respond to any gas whose thermal conductivity is different from that of air."