Introduction to Objects - building Measurement Systems

Building Measurement Systems with Object Oriented Labview How can measurement systems be built from objects ? Scalable Architectures

Measurement systems can be naturally thought of as combinations of instruments.

A Real Some extra diagnostic DMMs Example A bunch of Lockin ampliﬁers A special multiplexor we built for this At least 4 project thermometers Some instruments are standalone - A couple of superconducting some are embedded magnets A (dual) magnet power supply in hardware.

Let’s start with a simpler example

Thermometry Example • this is a current source • this is a voltmeter • this is a resistor that varies its resistance with temperature - we can use it as a thermometer

Resistance First The actual circuit - we’ll make a 4-point resistance measurement. Let’s code to measure the resistance ﬁrst.

Resistance Example MyCurrSource A (dual) current source instrument Let’s identify the instruments that we might need to use. FirstVoltmeter A simple voltmeter

Thermometry Example Now something to describe MyCurrSource the measurement process... A (dual) current source instrument MyFirstResMeas Which current source ? Which voltmeter ? FirstVoltmeter A simple voltmeter

Thermometry Example MyFirstResMeas Measure the Resistance Process Which current source ? ‘Mycurrsource’ - set current to zero Which voltmeter ? - wait for 1s ‘FirstVoltmeter’ MyCurrSource - measure the dc voltage (V1) (take account of thermal offsets) A (dual) current source instrument FirstVoltmeter - set current to 100µA A simple voltmeter - wait for 1s - measure the new DC voltage (V2) - set current to zero - Calculate R as (V2-V1)/100µA An example of the process

Thermometry Example MyFirstResMeas Which current source ? ‘Mycurrsource’ Which voltmeter ? ‘FirstVoltmeter’ MyCurrSource FirstVoltmeter A (dual) current A simple voltmeter source instrument The structure of measurement systems naturally factors into measurement processes (green) and the instruments which they use (yellow).

Thermometry Example MyCurrSource Now add a second circuit A (dual) current source instrument SecondVoltmeter A simple voltmeter

Thermometry Example Myﬁrstresmeas MySecondResMeas Which current source ? Which current source ? ‘ MyCurrSource’ ‘MyCurrSource’ Which voltmeter ? Which voltmeter ? ‘FirstVoltmeter’ ‘SecondVoltmeter’ MyCurrSource FirstVoltmeter A (dual) current A simple voltmeter source instrument SecondVoltmeter A simple voltmeter Using object references allows different measurements to share the same instruments.

Being able to call objects by reference is a critical requirement for building a ﬂexible and reconﬁgurable system.

Making a thermometer • Actually we package the resistor and calibrate it to yield a thermometer calibration ﬁle X312 Calib.csv 20 15 + 10 5 SN X312 0 0 7.5 15.0 30.0

Now add the calibration Create a more specific measurement subclass MySecondResMeas Which current source ? ‘MyCurrSource’ MySecondThermMeas Which voltmeter ? ‘SecondVoltmeter’ Which current source ? ‘Mycurrsource’ X312 Which voltmeter ? 20 ‘SecondVoltmeter’ 10 Where’s the calibration ? ‘C:data\\X312.csv’ 0 0 7.5 22.5 Keep the basic resistance code but add a thermometer measurement subclass that has a path to a calibration file stored on the file system.

The Final Object Model MySecondThermMeas MyCurrSource X337 ‘C:data\\X337.csv’ SecondVoltmeter SN X337 SN X312 MyFirstThermMeas X312 FirstVoltmeter ‘C:data\\X312.csv’

What can we take from this example ?

Measurements and Instruments Measurements Almost all conceivable MySecondThermMeas MyFirstThermMeas measurements can be factored as a generic measurement process SecondVoltmeter linked to some FirstVoltmeter instruments that do work MyCurrSource in the real world. Instruments

Measurements, Instruments .... and Controls Measurements Controls MySecondThermMeas ProbeHeater MyFirstThermMeas SampleMagneticField SecondVoltmeter FirstVoltmeter Changes would be made MyCurrSource by accessing control New CurrSource objects not the Instruments instruments directly.

Control Loops TempControlledStage Measurements Controls get set MySecondThermMeas ProbeHeater MyFirstThermMeas SampleMagneticField SecondVoltmeter FirstVoltmeter MyCurrSource Control loops can be built New CurrSource by referencing both control Instruments and measurement objects.

Measurement systems can be naturally factored into Measurement, Instrument and Control objects that work together.

Measurement systems naturally factor into physical • Instrument and virtual Measurement and Control classes. •Accessing Objects by reference allows the system to be reconﬁgured very easily. This also allows instruments and measurements to • be shared for multiple purposes. Scalable Architectures specialises in developing measurement systems that scale continuously from prototype to ﬁnished product. St. Johns Innovation Centre Scalable Cowley Road Architectures Cambridge CB4 0WS, UK www.scalable-architectures.com

Introduction to Objects - building Measurement Systems

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