The document discusses the use of F# for scientific instrument control, highlighting capabilities like real-time chart plotting, modular design, and robust error handling. It emphasizes the advantages of F#'s type system for clear modeling of hardware capabilities and experiment parameters, while also noting the challenges of a limited library and user base compared to other programming languages. The document also touches on async workflows and data acquisition methods for handling instrument communication and data processing.

1. SCIENTIFIC INSTRUMENT
CONTROL WITH F#
Anton Tcholakov, Colin Stephen, Gavin Morley
Department of Physics, University of Warwick
@ant_pt

2. CUSTOM SPECTROMETER

3. CUSTOM SPECTROMETER
• Apply microwaves to a
sample in a magnetic field
• Measure the reflected
power
• Vary the magnetic field
• Changes in the signal help
to characterise the sample

4. REQUIREMENTS

5. REQUIREMENTS
• Concurrent control of multiple
instruments
• Real-time chart plotting
• Ability to save data and
experimental parameters
• Modularity
• Robust error handling
14.125 14.130 14.135 14.140
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EPRsignal(arb.units)
Magnetic field (T)

6. DOMAIN MODELLING
• Records, unions and units of measure let us model hardware
capabilities and experiment parameters clearly and concisely
• We get structural equality and serialisation for free
type Frequency = FrequencyInHz of float<Hz>
type Amplitude = PowerInDbm of float<dBm>
type StepSpacing = LinearSpacing | LogarithmicSpacing
type Range<'T> = { Start : ’T ; Stop : 'T }
type FrequencySweep =
| FrequencySweep of range : Range<Frequency>
| FixedFrequency of frequency : Frequency
type AmplitudeSweep =
| AmplitudeSweep of range : Range<Amplitude>
| FixedAmplitude of amplitude : Amplitude
type StepSweep =
{ Frequency : FrequencySweep
Amplitude : AmplitudeSweep
NumberOfPoints : int
Spacing : StepSpacing }

7. INSTRUMENT CONTROL
• Communication to hardware is inherently async
• async workflows are great metaphor for
experiments
• Use asyncChoice (available in ExtCore) and
railway-oriented programming to handle errors

8. DATA ACQUISITION
type StreamingAcquisition =
{ Parameters : StreamingParameters
Buffers : AcquisitionBuffers
StopCapability : CancellationCapability<StreamStopOptions>
StatusChanged : Event<StreamStatus>
SampleBlockObserved : Event<SampleBlock> }
let run scope acquisition = asyncChoice {
use acquisitionHandle =
PicoScope.Acquisition.allocateHandle digitiser acquisition.Buffers
do! prepare scope acquisition
do! startStreaming scope acquisition
do! pollUntilStopped scope acquisition }
• Acquisition emits samples via Event<‘T>, so we can feed this straight
into FSharp.Charting
• Use Rx transformations to implement signal processing

9. WHAT DO OTHERS USE?
C / C++
• Low level, manual memory and thread management
Python
• Global Interpreter Lock can cause problems
• Pay the price for dynamic typing in large projects
C# (… in industry?)

10. LabVIEW
• Looks and feels like it belongs in the 90s
• … but has a vast library of instrument drivers

11. SUMMARY
• F#’s type system allows us to model our problem
domain clearly and concisely
• Many of the tools we need are already available
(async, Rx, FSharp.Charting)
• F# is very well suited to the task but lacks
instrument libraries and user base