Since the oscilloscope and probe become part of the circuit being tested, it is also necessary to understand and apply the information on the oscilloscope probes page. If in doubt (especially about safety), please ask before damaging scopes or people.

Safety

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 :) )

Do not use any of HackSpace's scope probes for measuring mains equipment and voltages, and that includes inside SMPSs.

General

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 “Specific Features” 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
  • we have disposed of some scopes, because they were poor quality or we had too many duplicates or they were slightly faulty. Details have been removed from this page, but can be found via the “Old revisions” link at the top of the page

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.

Using Our Oscilloscopes

Test Bench Accessible Shelf High Shelf Dispose Typical spec and examples
Audio Kenwood CS4125 Telequipment DM63 Metrotest OX8020 <100kHz, mV - audio signals, sensors
Mechatronics Kenwood CS4125 Telequipment DM63 Metrotest OX8020 <10MHz, 50mV-50V, - motors, actuators, machines
Agilent 54621 Topward 7042
Digital Agilent 54621 Telequipment DM63 Topward 7042 <=60MHz, 500mV-5V, - well-behaved logic e.g. Arduino
Tektronix 2245
IsoTech ISR-1014
Signal Integrity Tektronix 2245 >=100MHz, 500mV-5V, medium-speed logic and checking valid logic levels, e.g. generic TTL, CMOS
IsoTech ISR-1014
High-speed - - - - >=250MHz, note not MS/s!

Specific Features

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, OSD
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

IsoTech ISR-1014 Tektronix 2245 Telequipment DM63
Location Test bench shelfTest bench shelf, to reduce chance of accidental damage Test bench shelf
Domain Medium speed digital, signal integrity Medium speed digital, signal integrity Sensitive audio, mechatronics, isolated events
Specification 100MHz, analogue, 4 channel, OSD 100MHz, analogue, 4 channel, OSD 50MHz, 1mV/div
Autosetup Autosetup Three channel, dual beam
Manual time/freq/voltage measurementsManual time/freq/voltage measurements Analogue storage
Condition Fully functionalFully functional Functional, but triggering needs tewaking
Plan on replacing X/Y mains capacitors plus electrolytics Probably benefit from calibration and checking capacitors
May need to replace calibration battery Needs a PSU recap for 100Hz display intensity ripple
Comments First choice fast scope First choice fast scope Sensitive, three channels, good for transient events
Equivalent to the Tek 2245, but softbutton menus slightly less suitable for casual use Move “soft knobs” in both directions, including after autosetup Only analogue storage scope, traditionally less convenient than digital storage
Small size/weight Medium size/weight Extender cards and manuals for maintenance
OUT OF ACTION. Do NOT use. An unknown person “floated” this scope by disconnecting the protective mains earth. Apart from being lethally dangerous as noted above, it may have been damaged internally. It has been PAT tested, but must be disassembled and the PSU capacitors checked and/or replaced by a person skilled in that task. Dual beams very rare
USP Fast, 4 channels Fast, 4 channels, excellent triggering, standard controls Sensitive, three channel, storage

Location: High Shelf

Topward 7042 Metrotest OX8020
Location High shelf, for use during workshops High shelf, for when Kenwood CS4215 insufficient
Domain Digital, mechatronics, when Kenwood CS4215 insufficient Audio, mechatronics
Specification 40MHz, 5mV/div, analogue 20MHz, 1mV/div, hybrid analogue/digital
Dual timebase Dual timebase
Standard controls Limited DSO features
Manual voltage and time cursors
Prints HPGL/HP-PCL to centronics/serial
Condition Excellent – everything just works as expected Fully functional
UI a little odd; dim lights indicate important settings
Comments Excellent scope On loan from Lee Wiltshire
Service and operation manual Similar to Kenwood CS4215, Topward 7042
Lightweight Would be best low-end scope, except for awkward UI
See also Kenwood, Metrotest
USP Small, medium speed, easy Sensitive, printing

For Disposal

Since they were either faulty or a pain to use, and we had better scopes with these features, in February 2019 we disposed of these scopes: Wavetek 9020, Gould OS300, Tek TDS340, Schlumberger 5602.C, Hameg HM203.

If you want to see their features, look at an earlier revision of this page.


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
  • Last modified: 7 months ago
  • by tggzzz