I'd like to measure different point temperature in my PA : bridge rectifier, MOS, Heatsink ... ect and that's why I'm looking for a cheap thermal measurement central (from 4 to 8 channel). I don't need much precision (2 to 4°C precision is enough)
I believe I know of just the device you're seeking, it's called a thermometer. Generally readily available made from an insulating material called glass and with (recently) non-toxic contents (red liquid). 4/8 of.
I'd like to measure several points at the same time. I have on which uses 8 optical fibers but the fiber are expensive (250E) and can break very easily. That's why I am looking for a less expensive one, using thermocouple for example.
What works really well is the IR thermometers used in the food industry. They look like a little gun with a laser pointer. You point at whatever it is you want to measure the temperature of, pull the trigger, and you get a nice digital reading. Non-contact, no thermal inertia, instant response.
The unit I use was bought at a cooking supply shop for about $75. I mostly use it in the kitchen, but have smuggled it into my workshop on occasion.