Thermistor Construction Journal
Along with the LabView program, another component of bending fibers will be to determine the temperature of the water and to make that information available to the program.
At first, I had thought that our best bet as far as reading/recording water temperature was to make a thermistor (as seen below).
A temperature measuring circuit that included a voltage divider, a resistor, and a thermistor.
This is the same circuit as to the left, except it is free of a breadboard and water resistant.
Although this thermistor is reasonably accurate, I feel that it would be possible to have (already purchased) thermocouples read the temperature instead. The signal from the thermocouple would need to be amplified in order to be read by the DAQ we are currently using because the thermocouple produces voltages in the micro range. Using an operational amplifier and the right resistors I am confident that I would be able to achieve a strong enough signal from the thermocouple(given enough time). The remaining hurdle in this endeavor would be to tweak the LabView program to use the temperature-voltage relationship equation of a type J thermocouple instead of a thermistor.
Some great resources for thermocouple theory and circuitry can be found here:
I feel that this is a place to start if I am to accurately read a thermocouple. Included in the circuit diagram is cold junction compensation and signal amplification; two things that are a requisite to accurate measurements.
After reading the material above, I have found two (cheap) ways to read a thermocouple accurately:
1. Create something in the software that compensates for the room temperature factor at the cold junction. If we end up using the thermistor to read the temperature at the cold junction then we will be introducing the error from one temperature measurement to another. Although the thermistor will read the water temperature within acceptable error, adding more error into the calculation seems unnecessary to me.
2. Follow the diagram above and create a hardware approach to cold junction compensation. After determining the voltage output of a type J thermocouple at zero degrees Celsius, I can introduce that voltage at the cold junction site. By following the circuit above, I would probably be able to construct a circuit that would have cold junction compensation and amplification for the signal. My concerns for this approach involve time constraints and the intricacies of this setup.
Although, after having found this, I think the problem may be solved.
Op amp designed for a type J thermocouple, with cold junction compensation