melted brass temperature measurement

Optical pyrometer, surface thermocouple, etc. Call your local sensor rep and give the problem to him.

I would use an infrared thermometer / pyrometer as TVP suggested.

That's what they were designed for.

John.

OK but there are two main problems:

1) scoria in the surface of melted metal - the temperature is different from the temperature of melted brass

2) vapours of zinc - that condenzates in all surfaces, it means during the measurement the optics will be gradually covered by whitepowder...

How to solve them?

More information please:

1. What type of furnace are you using?
2. Is it a simple lift out crucible, a tilting or a lip tilt furnace ?

When casting brass, bronze, aluminium and magnesium alloys from tilting or lip tilt furnaces, we have used crucibles with a pocket in the crucible wall into which we insert a thermocouple (type dependant on temperature range). This takes the operator out of the temperature control system.

Having used infrared transduces in many applications I would not offer to try it on a molten metal surface unless the surface was protected by an inert atmosphere. Surface oxidation will really change your measured temperature despite the metal temperature remaining constant. As previously mentioned protecting the lens from zinc fume would be tricky but not impossible. A compressed air jacket as supplied by the IR cell manufacturer should do the trick for that problem, but it would not improve the affect of oxidation on surface emmissivity.

If there is a site port, your best choice would be infrared technology.