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Implementing linearization in the hardware or software component of a measurement system
How can 'Linearization' be implemented in either the hardware or software component of a measurement system?
By Rushi Shroff on 30 August, 2018 - 9:42 am

Signal conditioning is a basic component of all measurement devices. It converts incoming measurements into a form acceptable to digitization hardware.

Linearization - Often sensors do not have a linear relationship between their signal value and the physical quantity they are measuring. A thermocouple's nonlinear temperature-to-voltage relationship is a prime example. Linearization maps the relationship between a sensor's signal value and the physical quantity it is measuring so that an incremental change in the physical quantity corresponds to a similar incremental change in the signal. It can be implemented in either the hardware or software component of a system.

How can Linearization be implemented in either the hardware or software component of a measurement system?

I've seen Linearization of Analogue signals achieved by hardware and software - as you have confirmed. So it's unclear why you are raising the point.

Hi Rushi,

I am assuming that the non linear correlation between input and output is following this basic equation:
y = vx

This correlation found on the gas flow measurement and calculation using orifice pressure where the volume flow rate is proportional to squared of differential pressure between the orifice plate.

To do a linearization, in my opinion you can use one of these below method:

Hardware Method:

1. Using op amp multiplier circuit to squaring the input signal, basically the circuit will be like this.
http://nopr.niscair.res.in/bitstream/123456789/6896/1/IJPAP%2048(1)%2067-70.pdf

2. Using this math function transmitter and use square function to the input signal.
https://api-usa.com/pdf/api/apd44xx.pdf

Software Method:

1. using this formula and implement on your PLC calculation instruction.
OutputLinear = (InputSqRt)^2

For example, if you are using Allen-Bradley Controllogix PLC and RSLogix 5000 software, there is function block called CPT that can be used to implement math formula

2. Using look up table. One of the example, If you are using Allen-Bradley Controllogix PLC and RSLogix 5000 software, there is function block called FGEN that you can arrange Look Up table to linearized the square root type input signal. Another controller should have similar instruction.

Hope this will help

it can be implemented both ways.

With firmware versions, the linearization is specific for one application only.

With digital/software versions the one device may be re-applied for many uses with appropriate transducer and software.

Price and reduced maintenance for the digital versions tends to dominate the choice.

At least one vendor of piezo-resistive technology smart pressure transmitters 'characterizes' each sensor element over the range of spec'd operating temperature while applying various reference pressures and recording the resulting pressures, which is the unique characterization data set for that pressure sensing element. A PROM burned with the characterization data is used to provide correction of the sensed pressure at meter body's sensed temperature.

Another vendor characterizes each magnetic flowmeter flow tube and ships the magtube with a SensorProm with characterization data that is used by the converter/transmitter to report 'corrected' flow rate/total.