Custom curve linearization is a feature available with the Extended option version of all Micro digital panel meters, counters and timers, excluding only temperature meters. The latter already include preset linearization for specific temperature sensors.
Custom curve linearization can provide exceptional accuracy from low cost transducers, provided that these are repeatable. It can extend the working range of transducers on the high and low ends. It can also solve special application problems where there is a non-linear relationship between the input and the desired readout.
Linearizing is implemented for Micros in the form of 20 nonlinear spline-fit 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 Micro Linearizing Process Meter requires an external PC, which is connected to the meter via an RS232 cable, and utilizes linearizing software furnished by Electro-Numerics. To download, go to our Downloads Page. A Micro serial communications board is required, but can be removed following setup. Three meter programming methods are offered:
Spreadsheet Method: Data points consisting of the input signal in Volts or Amps and the desired reading are entered into an Excel spreadsheet or into a text text file using a space, comma or tab as the delimiter. There can be from 2 to 240 data points. Our software then calculates 20 spline-fit segments and downloads their coefficients into the meter.
Actual Input Method: The meter is hooked up to the actual signal source, and the user enters the desired readings for different signal levels. There can be from 2 to 240 input / reading combinations. Our software then calculates 20 spline-fit segments and downloads their coefficients into the meter. This method automatically compensates for any errors in the transducer.
Polynomial Method: The mathematical formula relating the input to the output is entered into the computer, which then uses this data to calculate the spline-fit segments. This method is ideal if the mathematical relationship is knows, for example to calculate the contents of a tank based on the known geometry of the tank.
The ability to apply custom curve linearization opens many possibilities, including the following:
Altimeters, since the relationship between pressure and altitude is very non-linear.
Rate of ascent based on successive altimeter readings.
Square root extraction from differential pressure transducers, whose signal may have zero offset.
Volume of irregularly-shaped tanks, such as horizontal cylinders, based on measured liquid level or liquid 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 the low and high ends.
Compensating for inaccuracy of low-cost transducers.
Measuring tank volume
The Extended Micro process meter can display the volume of irregularly shaped tanks based on measured tank level or static pressure at the base of the tank. A common example is a cylindrical tank lying on its side. The tank can further be tilted to facilitate drainage, as illustrated. Spherical tanks or spheroidal water tanks are another example.
Rate from successive readings
The Extended process meter allows the display of rate based on successive readings, for instance flow rate based on changes in liquid level or static pressure in a tank. In the above illustration, the meter displays the rate in gallons at which a horizontal tank is being emptied. The input to the meter can be nonlinear, since only the linearized readings are compared for the determination of rate.