Custom Curve Linearization Software
Easy programming for custom nonlinear curve fits. Applicable to the Extended version of Laureate™ meters, counters and transmitters.
Custom curve linearization software curve.exe can be installed in the Extended version of all Laureate digital panel meters, counters, and transmitters, except in Laureate thermocouple and RTD meters and transmitters, which already have built-in linearization curves.
Applications. Custom curve linearization solves application problems where there is a non-linear relationship between the input and the desired reading. A common application is the volume of irregularly shaped tanks based on liquid level or pressure at the base of the tank. Custom curve linearization can be used to display temperature from the changing resistance of a thermistor. It can provide exceptional accuracy from lower cost transducers if these are repeatable.
Implementation. Linearizing is implemented in the form of 20 curvilinear quadratic segments, which provide much better accuracy than a larger number of straight line segments. The typical error will be from 0.1% to 0.01% of full scale, depending on the number of data points used for setup, the error in the data points, and the severity of non-linearities or discontinuities.
Setup of a Laureate linearizing meter or trasnmitter requires an external PC which is connected to the instrument via an RS232 or USB cable. Laurel's linearizing software can be downloaded as an executable .exe file at no charge from our Software Download Page. An RS232 or USB serial communications board is required in a meter or counter, but can be removed after programming. Simply click on the downloaded file and follow the prompts. Use Device Manager under the Windows Control Panel to set to set the COM port, which has to be COM1, 2 or 3.
Three programming methods are offered:
- Spreadsheet Method: Data points consisting of the input signal and the desired reading are entered into an Excel spreadsheet, which then outputs an MS DOS .txt text file which uses a space delimiter. There can be up to 180 data points. A minum of 6 data points are required for best results. Laurel's software calculates 20 spline-fit segments and downloads their coefficients into the instrument.
- Polynomial Method: The mathematical formula relating the input to the output is entered into the computer, which then calculates the spline-fit segments. A good way to obtain a polynomial formula for actual data points is to enter these into Excel 2010 or above, have Excel display the data as an XY (Scatter) plot, have Excel add a Trendline to the plot, and select Polynomial. The best-fit polynomial curve will be shown for the data points along with the formula used. This a good method to visualize random errors in measurements.
- Actual Input Method: The instrument is hooked up to the actual signal source, and the user enters the desired readings for different signal levels. There can be up to 180 input / reading combinations. Laurel's software then calculates 20 spline-fit segments and downloads their coefficients into the meter. This method automatically compensates for any errors in the transducer.
- Extended version of a Laureate digital panel meter, counter or transmitter.
- A Windows PC with available port COM1 to COM3.
- Altimeters, since the relationship between pressure and altitude is very non-linear.
- Rate of ascent based on successive altimeter readings.
- Volume of irregularly-shaped tanks, such as tanks with cylindrical and conical sections, based on measured liquid level or pressure at the base of the tank.
- Non-linear transducers, such as thermistors or CdS cells.
- Fine-calibration of linear transducers, since even nominally linear transducers will have nonlinear components.
- Extending the working range of transducers, since many transducers become nonlinear at their low and high ends.
- Compensating for inaccuracy of low-cost transducers