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equipment:oscilloscopeprobes [2016/05/02 08:04]
tggzzz
equipment:oscilloscopeprobes [2020/05/30 11:13] (current)
tggzzz
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-==== Oscilloscope Probes ====+===== Oscilloscope Probes ====
 +Probes must be used with oscilloscopes, so it is necessary to understand //and apply// the information on the [[equipment:oscilloscopes|oscilloscopes]] page. If in doubt (particularly about safety), please ask before damaging equipment or people.
  
-//Safety: do not use any scope probe for measuring mains equipment and voltages. Carefully read and understand the safety references in the "Praxis" section of [[https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/|Scope Probe Reference Material]] and [[http://www.tek.com/document/primer/abcs-probes|Tektronix' ABCs of Probes Primer]] pp55-56 - they might save someone's life//+==== Safety ==== 
 +**Do not use any of HackSpace'scope probes for measuring mains equipment and voltages**, and that includes inside SMPSs
  
-Scope probes are much //much// more than "bits of wire". There are many different types for different purposes. They are surprisingly sophisticated pieces of technology containing very thin wires and precision components: +Carefully read and understand the safety references in the "Praxis" section of [[https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/|Scope Probe Reference Material]] and [[http://www.tek.com/document/primer/abcs-probes|Tektronix' ABCs of Probes Primer]] pp55-56 - //they might save someone's life// 
-  * **expensive**: when buying a second-hand scope the rule-of-thumb is to //spend more on the probes than on the scope//. The Agilent probes cost £130+VAT //each//, and they are relatively low-cost for a decent probe. Many probes cost >£700, Farnell sells a probe costing £5,500, and some probes cost much more than that. The latest Tektronix probe //tips// cost £250/5, and each one can be used 5 times; yes, each time they //touch// your circuit costs £5.+ 
 +==== Types of Probe ==== 
 +There are many types of scope probe, including *1, *10 "high" impedance, *10 "low" impedance Z0 resistive divider, current, EHV, envelope, active, differential, isolated. Each has advantages and disadvantages, and **some are essential in some situations**. See [[https://download.tek.com/document/60W_14232_9_MR_Letter.pdf|Tektronix' Probes and Accessories, Your Guide to Selecting the Right Probe]] 
 + 
 +Hackspace only has the common-or-garden *1 and *10 "high" impedance probes, but it may be possible to borrow others from members. 
 + 
 +Clearly scope probes are much //much// more than "bits of wire". They are surprisingly sophisticated pieces of technology containing very thin wires and precision components: 
 +  * **expensive**: when buying a second-hand scope the rule-of-thumb is to //spend more on the probes than on the scope//. The Agilent probes cost £130+VAT //each//, and they are relatively low-cost for a decent probe. Many probes cost >£700, Farnell sells a probe costing £5,500, and some probes cost much more than that. The latest Tektronix probe //tips// cost £250/5, and each one can be used 5 times; yes, each time they //touch// your circuit costs £10.
   * **fragile and easily damaged**: a damaged probe is as useful as a chocolate teapot - and can easily waste a day of your (remaining) life   * **fragile and easily damaged**: a damaged probe is as useful as a chocolate teapot - and can easily waste a day of your (remaining) life
     * **do not kink, twist, stretch, or coil the leads**, or, as you often see in EBay listings, put a rubber band around them!     * **do not kink, twist, stretch, or coil the leads**, or, as you often see in EBay listings, put a rubber band around them!
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     * **do read the probe's manual**, especially to check the max-voltage-vs-frequency graph and also the compensation range; the former often catches out those experienced with probing digital logic voltages     * **do read the probe's manual**, especially to check the max-voltage-vs-frequency graph and also the compensation range; the former often catches out those experienced with probing digital logic voltages
     * **shield/ground lead is connected to //mains earth//**, so only attach the shield/ground to circuits that can tolerate it. Get that wrong and your circuit might blow up or large currents could damage the probe, scope and circuit     * **shield/ground lead is connected to //mains earth//**, so only attach the shield/ground to circuits that can tolerate it. Get that wrong and your circuit might blow up or large currents could damage the probe, scope and circuit
-    * **don't lose the accessories** such as grabbers and ground springs - they are vital to the correct operation of the probe+    * **don't lose the accessories** such as "witches' hat" grabbersground springs, insulating tips - they are vital to the correct and safe operation of the probe. //Place accessories in the marked bag underneath the scope probe rack//
   * **vital**: your measurements will only be as good as your scope probes //and// the accessories   * **vital**: your measurements will only be as good as your scope probes //and// the accessories
  
-Use the right probe for your job:+==== Usage ==== 
 + 
 +Basic hints and tips:
   * **safety** don't use //any// of the HackSpace probes for measuring mains equipment unless you //really// understand what you are doing; get it wrong and you will kill the scope, the probe, and //yourself//. The [[https://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect|Dunning-Kruger effect]] is unforgiving, and nobody wants the extra paperwork.    * **safety** don't use //any// of the HackSpace probes for measuring mains equipment unless you //really// understand what you are doing; get it wrong and you will kill the scope, the probe, and //yourself//. The [[https://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect|Dunning-Kruger effect]] is unforgiving, and nobody wants the extra paperwork. 
   * read [[http://www.tek.com/document/primer/abcs-probes|Tektronix' ABCs of Probes Primer]] to understand the different types of probes, when they should //and should not// be used (don't bother to fill in the marketing information :) ) **Safety**: read pages 55 and 56   * read [[http://www.tek.com/document/primer/abcs-probes|Tektronix' ABCs of Probes Primer]] to understand the different types of probes, when they should //and should not// be used (don't bother to fill in the marketing information :) ) **Safety**: read pages 55 and 56
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     * the effect of inductance in wires can resonate with capacitances and cause circuits to become unstable. E.g. a 6" ground lead has 150nH of inductance      * the effect of inductance in wires can resonate with capacitances and cause circuits to become unstable. E.g. a 6" ground lead has 150nH of inductance 
   * use a *1 probe for low-voltages, and a *10 probe for high frequencies   * use a *1 probe for low-voltages, and a *10 probe for high frequencies
-  * if using a *1/*10 probe, you will eventually find you have it on the wrong setting+  * if using a *1/*10 probe, you //will// eventually find you have it on the wrong setting. Consider whether that will damage anything.
   * when using a *10 probe, make sure it is compensated for the scope you are using; if not the waveforms will be distorted. //Some scope/probe combinations cannot be properly compensated//.   * when using a *10 probe, make sure it is compensated for the scope you are using; if not the waveforms will be distorted. //Some scope/probe combinations cannot be properly compensated//.
   * digital logic is surprisingly fast, with a correspondingly high bandwidth (N.B. the clock or bit rate is irrelevant, only the rise/falltime matters). 1980s Schottky TTL (which had a fearsome reputation back then!) has a 14ns risetime. Modern jellybean LVC components have a 0.6ns risetime. Some FPGAs are even faster, as is some ECL. If someone can let me use a RPi, then I might be able to verify rumours that the GPIO risetime is ~2ns.   * digital logic is surprisingly fast, with a correspondingly high bandwidth (N.B. the clock or bit rate is irrelevant, only the rise/falltime matters). 1980s Schottky TTL (which had a fearsome reputation back then!) has a 14ns risetime. Modern jellybean LVC components have a 0.6ns risetime. Some FPGAs are even faster, as is some ECL. If someone can let me use a RPi, then I might be able to verify rumours that the GPIO risetime is ~2ns.
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 For more pointers about safety, choosing and using probes, plus when and how to make your own probes, see [[https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/|Scope Probe Reference Material]]. For more pointers about safety, choosing and using probes, plus when and how to make your own probes, see [[https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/|Scope Probe Reference Material]].
  
-The following table shows the frequency domain and time domain performance of [[oscilloscopes|scope]]/probe combinations, with examples of HackSpace equipment.+There are some unused probes in plastic bags on or near the scopes. //Those should **not be used** routinely.// Why? See the warnings below about probes' fragility and ease of damage - and how expensive they are to replace. Instead **use the probes hanging on the equipment rack**. If it is necessary to use one of the probes in the plastic bags, please //put a message on the mailing list// noting why it was necessary. That will enable people to ensure we have the right equipment when members need it. 
 + 
 +Note: a scope without a working probe is as useful a bandsaw without a band: i.e. it is junk! 
 + 
 +{{ :equipment:oscilloscope_probes.jpg?nolink |}} 
 + 
 + 
 +==== Probes with Scopes ==== 
 + 
 +The following table shows the // approximate// frequency domain and time domain performance of [[oscilloscopes|scope]]/probe combinations, with examples of HackSpace equipment.
  
-| ^  Scope Bandwidth  ||||||| ^ Examples  ^+| ^  Scope Bandwidth  ||||||| ^ Example Probe  ^
 ^ Probe Bandwidth  ^ 20MHz  ^ 40MHz  ^ 60MHz  ^ 100MHz  ^ 250MHz  ^ 500MHz  ^ 1000MHz  | ::: | ::: ^ ^ Probe Bandwidth  ^ 20MHz  ^ 40MHz  ^ 60MHz  ^ 100MHz  ^ 250MHz  ^ 500MHz  ^ 1000MHz  | ::: | ::: ^
 ^ 20MHz | 14MHz 24.7ns  | 18MHz 19.6ns  | 19MHz 18.4ns  | 20MHz 17.8ns  | 20MHz 17.6ns  | 20MHz 17.5ns  | 20MHz 17.5ns  ^ | T5020 | ^ 20MHz | 14MHz 24.7ns  | 18MHz 19.6ns  | 19MHz 18.4ns  | 20MHz 17.8ns  | 20MHz 17.6ns  | 20MHz 17.5ns  | 20MHz 17.5ns  ^ | T5020 |
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 ^ 1500MHz  | 20MHz 17.5ns  | 40MHz 8.8ns  | 60MHz 5.8ns  | 100MHz 3.5ns  | 247MHz 1.4ns  | 474MHz 0.7ns  | 832MHz 0.4ns  ^ | HP10020A | ^ 1500MHz  | 20MHz 17.5ns  | 40MHz 8.8ns  | 60MHz 5.8ns  | 100MHz 3.5ns  | 247MHz 1.4ns  | 474MHz 0.7ns  | 832MHz 0.4ns  ^ | HP10020A |
 | ^ ^ ^ ^ ^ ^ ^ ^ | |  | ^ ^ ^ ^ ^ ^ ^ ^ | | 
-Examples   Kenwood cs4125  |  Topward 7042  |  Agilent 54621  |  Schlumberger 5602  |  |    |    | |  | +Example Scope   Kenwood cs4125  |  Topward 7042  |  Agilent 54621  |  Schlumberger 5602  |  |    |    | |  |
 ^ ::: | Hameg hm203  | ::: |  Tek 2213  |  Tek tds340  | ::: | ::: | ::: | ::: | ::: | ^ ::: | Hameg hm203  | ::: |  Tek 2213  |  Tek tds340  | ::: | ::: | ::: | ::: | ::: |
 ^ ::: | Metrotest ox2030| ::: | ::: | ::: | ::: | ::: | ::: | ::: | ::: | ^ ::: | Metrotest ox2030| ::: | ::: | ::: | ::: | ::: | ::: | ::: | ::: |
  • equipment/oscilloscopeprobes.1462172668
  • Last modified: 5 years ago
  • by tggzzz