Data Acquisition. NHMFL Summer School 2016 William Coniglio. with many slides from Scott Hannahs

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1 Data Acquisition NHMFL Summer School 2016 William Coniglio with many slides from Scott Hannahs

2 Generic Data Acquisition Experiment Analysis Publication Physical Measurement Digital Representation Raw Data Files Analysis Processed Data & Graphs Presentation

3 Probe wiring (your best defense against interference)

4 Wiring electromagnetics Everything at different voltages has capacitance Everything that conducts current has inductance Nearby inductors have mutual inductance.

5 E field of charged wires also B field of current-carrying wires

11 Near-field around wires gets much smaller when you get them close together!

12 What is ground?

13 Shield vs. Return Ground is ambiguous. Circuit must be complete. How does current return? Does it return along a nasty interference shield? Separate them. Actual current path is important, not just possible current paths.

14 Cable selection flow chart Is one side of signal grounded? YES f > 1 MHz? YES COAX. Ground shield everywhere. NO NO TWISTED PAIR WITH DIFFERENTIAL INPUTS. Do not ground pair wires. Optional grounded shield. Ungrounded shield helpful if f > 1 MHz TRIAX. Ground guard at one end only.

15 Triax tricks Problem: too much capacitance to ground in coax/ triax causes slow response. Solution: drive the shield at the same voltage as the signal, but through a 1:1 buffer amplifier. Result: No voltage difference means no capacitance and a more responsive, yet still shielded signal. Beware your return current.

16 Front-end instrumentation depends on frequency and impedance MΩ-GΩ Ω-kΩ mω SLOW (< 1 khz) FAST (< 1 MHz) RADIO (MHz+) Electrometer, JFET inputs Guarded cables, JFET inputs, good luck Capacitive coupling? High-Q crystal resonators? Very hard. Typical lab instrumentation: amplifiers, lock-ins, oscilloscopes Consider Ω inputs, minimize and balance capacitance 50Ω RF instrumentation Inductive coupling, transformer inputs up to 50Ω

17 Analog to digital

18 ΔΣ modulation Digital out Analog in bit ADC Digital filter and decimation 1-bit DAC

19 Speed vs. Accuracy But remember 1/f noise!!!

20 More Bits = Better

21 Sampling Speed Nyquist Frequency

22 Digital delivery

23 Transferring Data (or catching the right bus) Protocol MBytes/sec Mbits/sec Width (bits) Length (m) # Nodes Thunderbolt / Light Peak 2,500 20, USB 3.1 Superspeed+ 1,000 10, USB 3.0 only 500 5, Firewire 1394b 400 3, USB 2.0 only Firewire 1394a Base-T Enet USB Base-T GPIB/ (961) Serial 230kbaud RS

24 Interconnect latency

25 Serial (RS232 / RS422 / Slow Cheap RS == Recommended Standard Connectors Vary Wiring Varies No handshaking No data integrity No addressing (except 485) Can be Isolated

26 GPIB (General Purpose Instrument Bus) IEEE-488 Standard Connectors - Daisy Chain! Handshaking Moderate Speed Instrument Language (488.2 / SCPI) 15 Devices Bulky Connectors and Cable Expensive Hard to Electrically Isolate

27 USB (1.0 & 2.0) Moderately Fast to Fast Cheap - Need Hubs Can be Isolated Need Driver for Each Device Not Addressable Instrument Bus No Handshaking / Data Integrity Cheap Small Cables

28 Ethernet Native Isolation High Speed / Cheap Small Cables Need Hubs Well Developed Protocols / Handshaking / Data Integrity Network Bandwidth Problems Can Have High Latency (indeterminate) Non-local (Where is my voltmeter?) Web Server in Every Voltmeter?

29 You get to tell the data where to go and what to do.

30 Programming in LabVIEW

32 Plug-in Architecture

33 All Writes and Reads use this (easy debug) In parallel for efficiency Resource locking for traffic control

34 Producer/Consumer

35 Organize your data for effective analysis Record everything, take lots of pictures Filename strategy filer.vi Be consistent with naming Write down everything you do with file names Ongoing question: integrate paper and digital logs?

Example log file Files Clark_CuPzClO4.### # Type B-supply T[K] Iph[mA] Rate Comments 001 T 0 1.4->base 0 Cooldown 002 t 0 step steps Current step 003 T 0 0.085->7 0.

37 4.5.05T/min to 0.1,.1T/min to 0.5,.2 T/min to 1, then 0.4T/min 009 B 18->-0.1 6.37 4.5 same 010 t -0.1 5.5 3.85 011 B -0.1->18 5.5 3.85.05T/min to 0.1,.1T/min to 0.5,.2 T/min to 1, then 0.4T/min 012 B 18->-0.

36 Example log file Files Clark_CuPzClO4.### # Type B-supply T[K] Iph[mA] Rate Comments 001 T >base 0 Cooldown 002 t 0 step steps Current step 003 T > >5 12 hr sweep (linear sweep) min 004 bad 005 T > >5 12 hr sweep (log! sweep) 006 B -0.1->18-> field sweep 007 t > Temp stabilize 008 B -0.1-> T/min to 0.1,.1T/min to 0.5,.2 T/min to 1, then 0.4T/min 009 B 18-> same 010 t B -0.1-> T/min to 0.1,.1T/min to 0.5,.2 T/min to 1, then 0.4T/min 012 B 18-> same 021 T > >1 1 hr sweep 022 B 0.03(0) Sweep to nominal "0" field 023 T 0.03(0) > >1 1 hr sweep 024 t 0.03(0) Temp Stabilize 025 bad 026 T > >1 2 hr log sweep of Iph 027 t 0.03(0) Temp Stabilize 035 t Temp Stabilize 036 T > >1 2 hr log sweep of Iph 037 t Temp Stablize

37 Analysis strategy LabVIEW? Igor? Origin? Makefiles and Python scripts? Basically anything higher level than Excel. In the end, you re going to want to automate this for consistency. Keep original, intermediate, final Can you plot the derivative of that for me? I need that graph in blue. Here s last year s experiment. See how they compare.

38 Interpolation and change of basis 1.0 Linear, cubic, 0.5 Data points Linear interpolation Cubic interpolation True behavior Smooth cubic splines: C. Reinsch, Numerische Mathematik 10, (1967) Local polynomial fit? x Cubic spline error

39 Keithley Low Level Measurements Handbook knowledgecenter_pdf/lowlevmshandbk.pdf Stanford Research About Lock-In Amplifiers ApplicationNotes/AboutLIAs.pdf National Instrument interconnect white paper

40 Add Noise - Better Measurements!!

Data Acquisition. NHMFL Summer School 2015 Scott Hannahs

Data Acquisition. NHMFL Summer School 2015 Scott Hannahs Data Acquisition NHMFL Summer School 2015 Scott Hannahs Keithley Low Level Measurements Handbook http://www.keithley.com/knowledgecenter/knowledgecenter_pdf/ LowLevMsHandbk.pdf Stanford Research About