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The invention relates to systems and methods for calibrating and using resistance temperature detectors. In one embodiment, the system includes a calibration circuit comprising a resistance temperature detector in a bridge circuit with at least one potentiometer, and a programmable gain amplifier co

The invention relates to systems and methods for calibrating and using resistance temperature detectors. In one embodiment, the system includes a calibration circuit comprising a resistance temperature detector in a bridge circuit with at least one potentiometer, and a programmable gain amplifier coupled to the bridge circuit. Embodiments of the invention further comprise methods for calibrating the bridge circuit and the programmable gain amplifier for use with the resistance temperature detector and methods for determining the self heating voltage of the bridge circuit.

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1. A microfluidic system comprising: a microfluidic chip having a first microchannel in thermal communication with a first resistance temperature detector incorporated into the microfluidic chip to heat and cool a fluid in the first microchannel; anda tunable temperature measurement circuit comprisi

1. A microfluidic system comprising: a microfluidic chip having a first microchannel in thermal communication with a first resistance temperature detector incorporated into the microfluidic chip to heat and cool a fluid in the first microchannel; anda tunable temperature measurement circuit comprising: a source node maintained at a predetermined source voltage;a ground node maintained at a predetermined ground voltage; anda bridge circuit comprising: the first resistance temperature detector connected between the source node and a first measurement node, a first reference resistor connected between the first measurement node and the ground node, a potentiometer connected between the source node and a reference node, and a scaling resistor connected between the reference node and the ground node, wherein a resistance of the first reference resistor is adjusted based upon the resistance of the first resistance temperature detector to optimize a sensitivity of the first resistance temperature detector; anda first programmable gain instrumentation amplifier wherein a first input to the first programmable gain instrumentation amplifier is connected to the reference node, a second input to the first programmable gain instrumentation amplifier is connected to the first measurement node and the output of the first programmable gain instrumentation amplifier is representative of the temperature sensed by the first resistance temperature detector. 2. The microfluidic system of claim 1, wherein the potentiometer is a programmable digital potentiometer. 3. The microfluidic system of claim 1, further comprising a capacitor connected in parallel with the scaling resistor. 4. The microfluidic system of claim 1, further comprising a low-pass filter coupled to the output of the first programmable gain instrumentation amplifier. 5. The microfluidic system of claim 1, further comprising a bypass circuit connected between the first measurement node and the ground node, wherein the bypass circuit comprises a bypass switch in series with a bypass resistor. 6. The microfluidic system of claim 5, wherein the bypass switch comprises a digital switch. 7. The microfluidic system of claim 5, wherein the bypass circuit is configured to pulse width modulate a current passing through the first resistance temperature detector. 8. The microfluidic system of claim 1, further comprising a power control circuit connected to the first measurement node, wherein the power control circuit comprises: a bottom power switch connected between the measurement node and a bottom power node maintained at the predetermined source voltage; and a grounding switch connected in series with a bypass resistor between the measurement n and the ground node. 9. The microfluidic system of claim 8, further comprising a shunt circuit connected between the reference resistor and the ground node, wherein the shunt circuit comprises a shunt switch in parallel with a shunt resistor. 10. The microfluidic system of claim 1, further comprising: a selector switch disposed in between the first detector and one or more second resistance temperature detectors on one side and the first measurement node; andthe one or more second resistance temperature detectors connected to the source node in parallel with the first resistance temperature detector;wherein the selector switch is configured to connect alternatively one of the first resistance temperature detector and the one or more second resistance temperature detectors to the measurement node. 11. The system of claim 10, wherein a second resistance temperature detector is in thermal communication with the second microchannel of the microfluidic chip. 12. The system of claim 10, wherein the second resistance temperature detector and the second reference resistor are incorporated into the microfluidic chip and the second programmable gain instrumentation amplifier is incorporated into a temperature control system. 13. The system of claim 10, wherein the first and second resistance temperature detectors have resistances with different temperature characteristics, the temperature characteristics selected based upon different ranges of temperatures controlling different biological reactions in the first and second microchannels of the microfluidic chip. 14. The system of claim 10, wherein each of the first and second resistance temperature detectors is in thermal communication with first and second microchannels of the microfluidic chip, respectively, wherein the first and second resistance temperature detectors provide heating and temperature sensing functions for the first and second microchannels, respectively. 15. The microfluidic system of claim 1, further comprising: a second resistance temperature detector connected between the source node and a second measurement node, a second reference resistor connected between the second measurement node and the ground, wherein the second resistance temperature detector and the second reference resistor are connected in parallel to the first resistance temperature detector and the first reference resistor; anda second programmable gain instrumentation amplifier wherein a first input to the second programmable gain instrumentation amplifier is connected to the reference node, a second input to the second programmable gain instrumentation amplifier is connected to the second measurement node, and the output of the second programmable gain instrumentation amplifier is representative of the temperature sensed by the second resistance temperature detector, wherein a voltage of the reference node is shared among the first and second programmable gain instrumentation amplifiers. 16. The microfluidic system of claim 15, further comprising a unity gain buffer, wherein the reference node is connected to the programmable gain instrumentation amplifiers via the unity gain buffer. 17. The microfluidic system of claim 1, wherein one or more of the first reference resistor and the scaling resistor are also potentiometers. 18. A method of calibrating the potentiometer in the tunable temperature measurement circuit of claim 1, comprising the steps of: (a) setting the resistance value of the potentiometer to a first resistance value;(b) setting the gain of the first programmable gain instrumentation amplifier to a first gain value;(c) measuring the voltage output from the first programmable gain instrumentation amplifier;(d) in the case that the measured voltage is above a predetermined target value, adjusting the resistance value of the potentiometer in a first direction;(e) in the case that the measured voltage is below the predetermined target value, adjusting the resistance value of the potentiometer in a direction opposite to the first direction; and(f) repeating steps (c) through (e) until the measured voltage from the first programmable gain instrumentation amplifier is equal to the predetermined target value. 19. The method of claim 18, wherein the predetermined target value is selected to maximize the signal to noise ratio in the output of the first programmable gain instrumentation amplifier. 20. The method of claim 18, further comprising the steps of: (g) after performing step (f), storing the resistance value of the potentiometer in an electronic memory;(h) associating the stored resistance value with an identifier corresponding to the first resistance temperature detector,(i) repeating steps (a) through (h) for a plurality of resistance temperature detectors to create a plurality of associations between resistance temperature detectors and resistance values;(j) detecting the presence of one of the plurality of resistance temperature detectors; and(k) setting the resistance value of the potentiometer to the resistance value associated with the one of the plurality of resistance temperature detectors. 21. The method of claim 20, wherein the step of detecting the presence of one of the plurality of resistance temperature detectors comprises reading a machine readable bar code from a platform chip containing the one of the plurality of resistance temperature detectors. 22. The method of claim 20, wherein the step of detecting the presence of one of the plurality of resistance temperature detectors comprises reading an RFID tag from a platform chip containing the one of the plurality of resistance temperature detectors. 23. A method of calibrating the self-heating properties of the tunable temperature measurement system of claim 1 comprising the steps of: (a) setting the predetermined source voltage to a first source voltage value corresponding to a desired operational supply voltage;(b) setting the gain of the first programmable gain instrumentation amplifier to a first gain value corresponding to a desired operational gain value;(c) measuring the voltage output from the first programmable gain instrumentation amplifier;(d) determining a first ratio of the output from the first programmable gain instrumentation amplifier to the source node voltage multiplied by the gain of the first programmable gain instrumentation amplifier;(e) decreasing the predetermined source voltage to a new source voltage value;(f) measuring the voltage output from the first programmable gain instrumentation amplifier;(g) determining a new ratio of the output from the first programmable gain instrumentation amplifier to the measured source node voltage multiplied by the gain of the first programmable gain instrumentation amplifier;(h) determining an asymptote ratio by repeating steps (e) through (g) until the change of the new ratio determined at (g) between subsequent iterations is beneath a predetermined threshold; and(i) determining an operational self-heating voltage difference by multiplying the desired operational gain value by the source voltage and the difference between the first ratio and the asymptote ratio. 24. The method of claim 23, wherein: step (c) further comprises measuring the voltage at the source node;step (f) further comprises measuring the voltage at the source node; andsteps (d), (g), and (i) use the measured voltage at the source node as the source node voltage. 25. The method of claim 23, wherein step (e) further comprises increasing the gain of the first programmable gain instrumentation amplifier to a new gain value such that the product of the first source voltage value and the first gain value is equal to the product of the new source voltage value and the new gain value. 26. A method for performing thermal calibration of the tunable temperature measurement circuit of claim 1 comprising the steps of: (a) setting the predetermined source voltage to a desired operational supply voltage;(b) setting the gain of the first programmable gain instrumentation amplifier to a desired operational gain value;(c) bringing the resistance temperature detector to a known temperature;(d) measuring a voltage output from the first programmable gain instrumentation amplifier;(e) storing the measured output voltage in an electronic memory in association with the known temperature;(f) repeating steps (c) through (e) to store a plurality of associations between known temperatures and corresponding measured output voltages; and(g) utilizing the stored associations to calibrate the circuit for thermal variations. 27. The method of claim 26, wherein the step of bringing the resistance temperature detector to a known temperature comprises utilizing an externally controlled heating device that has been independently calibrated. 28. The method of claim 27, wherein the externally controlled heating device comprises a Peltier device. 29. The method of claim 27, wherein the externally controlled heating device comprises a resistive heater. 30. The method of claim 26, wherein the step of utilizing the stored correlations comprises utilizing a look up table for the plurality of known temperatures. 31. The method of claim 26, wherein the step of utilizing the stored correlations comprises calculating a suitable curve to interpolate output voltage between the known temperatures. 32. The system of claim 1, further comprising a bridge adjustment controller configured to: (a) set the resistance value of the potentiometer to a first resistance value;(b) set the gain of the first programmable gain instrumentation amplifier to a first gain value;(c) measure the voltage output from the first programmable gain instrumentation amplifier;(d) in the case that the measured voltage is above a predetermined target value, adjust the resistance value of the potentiometer in a first direction;(e) in the case that the measured voltage is below the predetermined target value, adjust the resistance value of the potentiometer in a direction opposite to the first direction; and(f) repeat steps (c) through (e) until the measured voltage from the first programmable gain instrumentation amplifier is equal to the predetermined target value. 33. The microfluidic system of claim 1, wherein a potentiometer resistance, Rj, and a scaling reference resistance, Rk, are selected according to following relationships: Rj=CRh(To) and Rk=CRi, wherein Rj is a reference resistance, C is a scaling factor, and Rh(To) is a known resistance of a resistance temperature detector.