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Understand how to use them safely before using them.

This page summarises our scopes in terms of their target application domains, who might use them, and where they can be stored. The “details” section lists unique benefits. From this we can choose which scopes to cull, and to see what would be interesting in the future.

One way of categorising scopes is by how often we expect to use them, which translates into where they should be stored:

  • electronics test bench: small, robust, easy-to-use scopes for casual use and everyday tasks
  • accessible shelf over the electronics test bench: unique features necessary for specific tasks, but may be large or awkward
  • high shelf elsewhere in G11: unique but flawed, or duplicated capabilities, or used if several scopes are required simultaneously for workshops
  • dispose, because poor quality or too many duplicates or slightly faulty

Another is by target application domain likely to be found in typical HackSpace projects. There is significant overlap between categories, and there are many other application domains.

Oscilloscopes are useless on their own - they also need probes to connect to the circuit. Probes are surprisingly fragile and significantly affect your measurements - see the Oscilloscope Probe page for more information. Note than none of the HackSpace probes are suitable for measuring mains voltages directly.

Oscilloscopes can be used dangerously, especially when connecting to anything connected to the mains voltages. Getting it wrong can result in loud noises followed by deathly slience. Obviously electrocution is a potential danger, but incorrect connections can also melt scope probes, cause fires, as well as destroying the scope or unit being tested. You may be surprised how mains earths can and do cause those problems. Internally scopes contain >8kV, and they can retain the charge long after the scope is switched off.

Read and understand the references in the 'Formal' and 'Praxis' sections of this page, and Tektronix' ABCs of Probes Primer pp55-56 - and apply the knowledge before you make a connection.

Summary:

  • probe class: choose a suitable class (EHT, HV differential, etc) probe for your measurement
  • voltage limits, don't forget:
    • oscilloscope (including input coupling)
    • probe (including derating at high frequencies)
  • high voltages: don't probe anything >50V without an EHT probe or an HV differential probe
  • earthed shields: if you connect a probe shield to anything other than earth, high currents will flow since the case is earthed. If you forget that, then see EEVblog #279 How NOT To Blow Up Your Oscilloscope!
  • floating measurements: to measure voltages not earth referenced, use an HV differential probe. See Fundamentals of Floating Measurements and Isolated Input Oscilloscopes
  • never ever ever “float a scope” by disconnecting its ground lead, unless you also fully implement the mods shown in this page's footnote. Then don't do it; use the right probe
  • accidental shorts: due to slipped ground leads and exposed probe tip ground, or the tip shorting adjacent tracks/pins
  • overvoltage: a *1/*10 probe switched to *1
  • voltage not divided: a cheap *100/*1000 probe plus scope AC coupled puts the whole mean input voltage across the scope's input capacitor, not 1/100 or 1/1000
  • 50ohm resistor melting: a scope with a 50ohm input impedance has a very limited input voltage spec
  • CRT brightness: don't have it too bright or too dim:
    • a bright unchanging display can cause irreversible phosphor burn
    • leaving the spot in a single place (XY mode) can irreversibly warp an expansion mesh (and therefore warp the display) or overheat and crack the CRT
    • conversely, if the brightness is left turned right down, then the tube can be destroyed by cathode poisioning

Do not, under any circumstances whatsoever, disconnect an earth; the results can kill you or - worse - can kill someone else. Use the proper type of probe! (If you really think you need to “float a scope” see the picture in the footnote to understand the necessary minimum. Then don't do it :) )

Test Bench Accessible Shelf High Shelf Dispose Typical spec and examples
Audio Kenwood CS4125 Tektronix DM63 Metrotest OX8020 <100kHz, mV - audio signals, sensors
Mechatronics Kenwood CS4125 Topward 7042 Metrotest OX8020 Wavetek 9020 <10MHz, 50mV-50V, - motors, actuators, machines
Agilent 54621 Tektronix DM63 Hameg HM203 Gould OS300
Digital Agilent 54621 Schlumberger 5602.C Tektronix TDS340 <=60MHz, 500mV-5V, - well-behaved logic e.g. Arduino
Topward 7042
Tektronix DM63
Signal Integrity Schlumberger 5602.C Tektronix TDS340 >=100MHz, 500mV-5V, medium-speed logic and checking valid logic levels, e.g. generic TTL, CMOS
High-speed - - - - >=250MHz, note not MS/s!

Important features indicated by emphasis.

Location: Electronics Test Bench

Kenwood CS4125 Agilent 54621
Location Test bench, since small and lightweight Test bench, since small and lightweight
Domain Audio, mechatronics Digital, mechatronics
Specification 20MHz, 1mV/div, analogue 60MHz, 10mV/div, digital
IEEE-488 interface
Waveform capture/measurements
Condition Excellent – everything just works Fully functional
Good standard controls Floppy inaccessible, repair unknown
Adequate UI
Comments First choice low-end scope First choice digital scope
Excellent for casual use UI makes it less suitable for casual use
Most sensitive scope Potential printout via IEEE-488 or floppy
See also Metrotest, Topward
USP Small, easy, sensitive Small, easy, fast

Location: Accessible Shelf Above Test Bench

Schlumberger 5602.C Topward 7042 Tektronix DM63
Location Floor under test bench, on end Test bench shelf Test bench shelf
Domain Medium speed digital, signal integrity Digital, mechatronics, when Kenwood CS4215 insufficient Sensitive audio, mechatronics, isolated events
Specification 100MHz, 10mV/div, digital 40MHz, 5mV/div, analogue 35MHz, 1mV/div
IEEE488 interface Dual timebase Three channel, dual beam
Waveform capture/measurements Standard controls Analogue storage
Condition Fully functional Excellent – everything just works as expected Fully functional
Appalling UI
Heavy, big, cannot keep on high/weak shelf
Comments The highest speed scopeExcellent scope Sensitive, three channels, good for transient events
Not for casual use Service and operation manual Only analogue storage scope, traditionally less convenient than digital storage
Potential printout via IEEE-488 Lightweight Extender cards and manuals for maintenance
See also Kenwood, Metrotest Dual beams very rare
USP 100MHz Small, medium speed, easy Sensitive, three channel, storage

Location: High Shelf

Tek TDS340 Hameg HM203 Metrotest OX8020
Location High shelf, for occasional use High shelf, for use during workshops High shelf, for when Kenwood CS4215 insufficient
Domain Digital, signal integrity Audio, mechatronics Audio, mechatronics
Specification 100MHz, 1V/div, digital 20MHz, 5mV/div, analogue 20MHz, 1mV/div, hybrid analogue/digital
Display saved on floppy Dual timebase
Limited DSO features
Manual voltage and time cursors
Prints HPGL/HP-PCL to centronics/serial
Condition Ch1 broken Mainly functional, works nicely Fully functional
Ch2 only 1V/div and above Poor or strange controls UI a little odd; dim lights indicate important settings
Adequate UI X-shift knob missing
Light
Comments One of the higher speed scopes OK, unremarkable On loan from Lee Wiltshire
Only scope with screen capture Similar to Kenwood CS4215, Topward 7042
Dispose after we get another 100MHz scope with screen capture. Would be best low-end scope, except for awkward UI
USP Screen capture Nothing ⇒ candidate for disposal Sensitive, printing

For Disposal

Wavetek 9020 Gould OS300
Location Dispose Dispose, for use
Domain General, audio, mechatronics General, audio, mechatronics
Specification 20MHz, 5mV/div, analogue 20MHz, 2mV/div, analogue
Dual timebase
Condition Some ringing on digital transition Some ringing on digital transition
Some channel crosstalk Some channel crosstalk
Trigger on -ve slope broken External trig broken
Delayed timebase noisy
Ch1, Ch2 uncal switch noisy
Vert mode controls quirky
Poor but could be functional Usable for simple purposes
Comments Adequate low-end scope Adequate low-end scope
Repair required Usable without external trig
Lightweight

This was on fleabay, and indicates the minimum necessary to “float a scope” by disconnecting the mains earth safety wire. In other words, don't do it!

tektronix-howtofloatascope.jpg

  • equipment/oscilloscopes.1492681025
  • Last modified: 5 years ago
  • by tggzzz