This circuit with RTD sensor was found in the Radio Electronics magazine of April 1992. At the output we have 1 mV for each degree Celsius.
In the figure we have the way to implement a 5 to 45 V zener diode with 50 mA of maximum current...
This circuit is from a Radio Electronics magazine from December 1958. The indicator instrument is analog...
These integrated ones consist of class B amplifiers with gain fixed 24 internally for better...