Rtd calibration labview labjack

Question

Hello my name is mike and i'm a student in London Ontario, I'm taking an instrumentations class and was recently given an assignment to complete:
Objectives:
The instrumentation project consists of taking a sensor and implementing a computer interface. It should incorporates the following:
· Sensor signal conditioning
· A microcontroller (HC11/PIC) or data acquisition unit
· LabVIEW (and/or Visual Basic, Visual C, Visual C#)
· System calibration and data reduction
· Documentation
Description
The students will typically work in groups of 2 (unless discussed in advance with the lab instructor). The project consists of the sensor signal conditioning, microcontroller software and hardware development. The microcontroller (or data acquisition unit) performs the A/D conversion and transmits the raw data to PC (running LabVIEW, Visual Basic, or Visual C). The data is processed on PC and displayed in real time as a graph/chart.
Calibration is an essential part of this instrumentation project. The students have to use proper calibration procedure, similar to the procedures followed in industry.
The user is offered the following choices (through visual interface)
a) Time interval between successive measurements (units of 0.01 second)
b) Total number of measurements to be taken.
A calibration should be carried out over a suitable range that is both functional and easily attainable in laboratory, e.g. a temperature range of 0 – 100 (»90) °C is quit acceptable for temperature sensors.
Submission
· Demonstrate the program during any scheduled laboratory time.
· Submit the following both as hardcopy as well as on a floppy disk
· Project description and operation
· All design calculations related to circuit design.
· A brief - user guide (1 or 2 pages)
· Commented source files
· Schematic diagrams of signal conditioning circuit
· Clearly identify the names of individuals in the group, on the diskette and all associated documentation
Evaluation Criterion:
(30%) Documentation
(20%) Calibration Procedure
(50%) Overall project
Submission: April 8/2005.
Last date for submission (without penalty): April 20, 2005
I have choosen to do RTD using lab jack with lab view... If anyone can help me even with where to start it owuld be greatly appreicated.
thank you
Mike

Answer 1

That's a pretty open ended question but I'll suggest some directions
It sounds like your requirement is to demonstrate in the lab, so you
can probably get away with assuming 1) fixed wire length and 2) fixed
environmental temperature. If so, the easiest measurement will be a
two-wire approach. 3 and 4 wire measurements provide better accuracy
but may not be necessary.
Some background on RTD measurements:
http://www.omega.com/temperature/Z/pdf/z054-056.pdf
Typical use of an RTD is to supply a reference current and measure the
voltage across the RTD. Keep the current small to avoid self-heating
in the element. A pulsed current source can reduce effective heating
while allowing a larger peak current. Use the voltage and currents
measured to calculate the resistance of the RTD which will be
approximately linear with temperature over a given range.
Once you know the resistance, calculate the temperature. Find a table
for your RTD and pick two values, one each near the upper and lower
ends of your desired range. Do a linear interpolation between the
known values to determine your unknown temperature from the resistance.
Calibration can be accomplished by adjusting the known points chosen
for the interpolation or by a distinct calibration process, depending
on how accurate you are trying to get and over what range.
Hope this is useful.
Matt