Although I can pretty well judge when aluminium is ready to pour an accurate way of measuring the temperature is desirable.
I had a go at making a pyrometer a couple of years ago using a K type thermocouple with a stainless steel probe, but was not happy with the result. I think the problem was that as the thermocouple was in free air inside a tube it took a long time to reach a stable reading.
This was thermocouple used https://goo.gl/aQNXDH from Banggood.com
It has glass fibre insulation so the heat does not effect it.
I had previously bought this PID controller from an Ebay trader. It gives a nice clear display in all lights and can display in Celsius or Fahrenheit. It can also be used with other types,of thermocouple e.g, type T, R, J, etc.
Some multimeters have a thermocouple connection and this could be used instead. You can also get cheap thermocouple LCD displays.
The graphite probe was sold as a laboratory stirring rod, mine came from Amazon, also available from Ebay. It was 300m long and 8mm dia.
I found a PC board with a push button switch fitted in my scrap box and this was fitted to the PID with double stick tape. The tape was also used to hold this assembly to the box that houses the 12v battery to power the unit.
A thermocouple socket was fitted to the board so the thermocouple could be simply connected.
A little care is needed so the graphite does not get damaged when stored and handled so I made the stand that you can see in the video.
The pyrometer can be set in 2 different positions on the stand. In the lower position the probe is over the exhaust gas of the furnace so it can be preheated. The other position gives a safe place to store it whilst waiting for the metal to melt and the height was made so the probe can go into the metal whist still on the stand, I don't have to hold it in my hand.
The advantage of the graphite probe is the metal does not stick to it.
I have since added a spring to the graphite rod so it does not snap off if knocked.
The video below shows the construction of my pyrometer.
