I want to display a message box to show some message in Java, and the box should have three buttons that the user can press such that the program can get value when user presses the button.


Question: Determining The Parameters Of A Wheatstone Bridge
Answer: With a 24 volt supply, the current thru the limb of the bridge containing the thermistor is: -


Nearly 11mA at 0C
Nearly 19mA at 50C


At 0C this produces a power in the thermistor of 132mW and 63mW at 50C. To me this is a problem. The self-heating of the thermistor will create a significant measurment error at 0C compared to 50C. I'd use an instrumentation amplifier and keep the excitation levels much lower to prevent significant self-heating errors: -



The picture above shows the AD620 powered from +5V and 0V but a better power regime (for the OP) is +/- 15V with 0V connected to pin 5 (the reference input). The excitation voltage can be much lower (say 2.5 volts) and this means the self-heating effects are 1.5mW at 0C and 0.7mW at 50C i.e. trivial.

However, there is another potential problem of a single thermistor in a wheatstone bridge and that is linearity. You may design a circuit that produces the correct voltages at the extremes of temperature you require but, between these two points, there is a non-linear mapping between voltage and temperature over and above the basic non-linearity of the thermistor's resistance change with temperature.

It might seem intuitive to place 2 thermistors at opposite sides of the bridge but, with voltage excitation, this won't improve linearity (but does double sensitivity). Here is a good document by ADI explaining all of this: -



However, if you adopted a current driven bridge configuration then you could use two thermistors and get perfect linearity: -



So, rounding up, try to avoid self-heating effects and, for greater linearity, use two elements in opposing faces of the bridge with the bridge excitation being a constant current like the one below: -



The important voltage to keep constant in the above diagram is that across R1 and, for high accuracy a precision shunt voltage reference would be used in place of R1.