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test-and-measurement:guides:probe-compensation [2024/02/26 19:51] – [Inventory] James Colvintest-and-measurement:guides:probe-compensation [2024/02/28 22:38] (current) – [Compensating BNC Oscilloscope Probes] James Colvin
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 ====== Compensating BNC Oscilloscope Probes ====== ====== Compensating BNC Oscilloscope Probes ======
-<WRAP todo> + 
-== Under Construction == +{{  test-and-measurement:guides:ProbeSplashScreen.png?800&nolink  }}
-</WRAP>+
  
 ===== Overview ===== ===== Overview =====
  
-FIXME write an overview, add a picture of some BNC probes +BNC oscilloscope probes are commonly used for analog inputs on many oscilloscopes, offering both the ability to read higher voltages than an oscilloscope natively supports as well as higher bandwidth, providing users better insight into the high-speed signals they are observing with much more accuracy than what is offered by MTE cables. However, as the 10x mode of the BNC probe adds extra resistance to correspondingly attenuate the input signal down by a factor of 10, the capacitance of the BNC probe is not likely to match the capacitance of the analog input channel you are using, resulting in the measured signal to be over- or under-compensated rather than accurately showing the signal you are viewing. Luckily, this can be mitigated by adjusting the capacitance of the BNC probe. 
- +
-BNC connectors are a commonly used interface for analog inputs on many oscilloscopes, offering both the ability to read higher voltages than oscilloscope natively supports as well as higher bandwidth to provide users better insight into the high speed signals they are observing with much more accuracy than is offered by MTE or coax cables. However, as the 10x mode of the BNC probe adds extra resistance to correspondingly attenuate the input signal down by a factor of 10, the capacitance of the BNC probe is not likely to match the capacitance of the analog input channel you are using, resulting in the measured signal to be over- or under-compensated rather than accurately showing the signal you are viewing. Luckily, this can be mitigated by adjusting the capacitance of the BNC probe. +
  
 This guide walks through how to make this adjustment for Digilent's Test and Measurement devices.  This guide walks through how to make this adjustment for Digilent's Test and Measurement devices. 
- 
  
 ---- ----
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   * A BNC probe to be compensated   * A BNC probe to be compensated
-    * This guide will be using the BNC probes come with corresponding bundles of Digilent's various T&M devices.+    * This guide will use the BNC probes kitted and included with Digilent's various T&M devices.
   * An oscilloscope with a BNC connectors:   * An oscilloscope with a BNC connectors:
-    * Analog Discovery Pro (ADP5250) +    * [[test-and-measurement:analog-discovery-pro-5250:start|Analog Discovery Pro (ADP5250)]] 
-    * Analog Discovery Pro (ADP3450/3250) +    * [[test-and-measurement:analog-discovery-pro-3x50:start|Analog Discovery Pro (ADP3450/ADP3250)]] 
-    * Analog Discovery Pro (ADP2230) +    * [[test-and-measurement:analog-discovery-pro-2230:start|Analog Discovery Pro (ADP2230)]] 
-    * Analog Discovery 3 or Analog Discovery 2 with the BNC Adapter+    * [[test-and-measurement:analog-discovery-3:start|Analog Discovery 3]] or [[test-and-measurement:analog-discovery-2:start|Analog Discovery 2]] with the [[test-and-measurement/bnc-adapter-board/start|BNC Adapter]]
   * A square wave source:   * A square wave source:
     * Analog Discovery Pro (ADP5250) features dedicated Probe Compensation tabs     * Analog Discovery Pro (ADP5250) features dedicated Probe Compensation tabs
     * For other devices, the built-in Arbitrary Waveform Generator can be used to produce 5 kHz square waves     * For other devices, the built-in Arbitrary Waveform Generator can be used to produce 5 kHz square waves
 +      * An example WaveForms workspace to compensate a BNC probe on Scope Channel 1 is available for download [[https://files.digilent.com/resources/test-and-measurement/guides/ProbeCompensation.dwf3work|here]]. 
 +  * A flathead screwdriver to adjust the compensation trimmer on the BNC probe
 +    * A small plastic screwdriver is typically included with BNC probe packs.
  
 ---- ----
 ===== Guide ===== ===== Guide =====
  
-This guide is broken up into sections for each type of device that might require probe compensation. Open the dropdown corresponding to your device to view the required steps:+This guide is broken up into sections for each type of device that might require probe compensation. Open the dropdown corresponding to your device to view the required steps. 
 + 
 +==== Hardware Setup ====
  
 --> Analog Discovery Pro 2000 Series (ADP2230) # --> Analog Discovery Pro 2000 Series (ADP2230) #
 <WRAP group> <WRAP group>
  
-FIXME+<columns 100% 50% 50%> 
 +Connect the probe that is to be compensated to the desired BNC input channel of the oscilloscope and set the probe to its 10x attenuation setting.  
 + 
 +Note that the BNC probe is connected in such a way to provide easy access to the compensation trimmer. 
 +<newcolumn> 
 +<figure center|ADP2230ConnectProbe> 
 +{{test-and-measurement:guides:ADP2230_connectProbe.png|The PCB ruler is there to hold up the ADP2230 for photo purposes.}} 
 +<caption>//Connect the BNC probe to the preferred oscilloscope channel and slide the switch to the 10x attenuation setting.//</caption> 
 +</figure> 
 +</columns> 
 + 
 +<columns 100% 50% 50%> 
 +If using one of the Analog Discovery Pro 3000 series with no other source of a square wave, attach a BNC minigrabber (or similar) to a Wavegen output and connect the positive end to the probe tip and the ground end to the probe ground clip. 
 + 
 +<WRAP center round tip 100%> 
 +It is recommended to use BNC to minigrabber cables instead of BNC Probes on the analog output BNC port to avoid any bandwidth limitations on 1x mode or corresponding signal attenuation on 10x mode. 
 +</WRAP> 
 + 
 +<newcolumn> 
 +<figure center|ADP2230ConnectProbe> 
 +{{test-and-measurement:guides:ADP2230_connectSquare.png|The PCB ruler is there to hold up the ADP2230 for photo purposes.}} 
 +<caption>//Connect the BNC probe ground clip to AWG ground clip and the BNC probe tip to the AWG output.//</caption> 
 +</figure> 
 +</columns> 
 ---- ----
  
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 <columns 100% 50% 50%> <columns 100% 50% 50%>
-Connect the probe to the BNC input of the oscilloscope and set the probe to its 1x attenuation setting. +Connect the probe that is to be compensated to the desired BNC input channel of the oscilloscope and set the probe to its 10x attenuation setting. 
  
-Connect the probe tip directly to the source of the square wave and connect the grounding tip to an associated ground point.  +Note that the BNC probe is connected in such a way to provide easy access to the compensation trimmer.
- +
-INFO: The reason you want to connect directly to the source, as opposed to through another probe, is that we want to calibrate the probes with an accurate signal source. Probes themselves, both passive and active, have additional internal circuitry which can distort the square wave, causing the probes to be incorrectly calibrated. +
 <newcolumn> <newcolumn>
-<ADP3450_connectProbe.jpg>+<figure center|ADP3000ConnectProbe> 
 +{{test-and-measurement:guides:ADP3000_connectProbe.png|Scope channel 2 is used in this photo, but connect the probe to whatever channel you plan on using.}} 
 +<caption>//Connect the BNC probe to the preferred oscilloscope channel and slide the switch to the 10x attenuation setting.//</caption> 
 +</figure>
 </columns> </columns>
  
 <columns 100% 50% 50%> <columns 100% 50% 50%>
-If using one of the Analog Discovery Pro 3000 series with no other source of a square wave, attach a BNC minigrabber (or similar) to a Wavegen output and connect the positive end to the probe tip and the ground end to the probe ground clip.  +If using one of the Analog Discovery Pro 3000 series with no other source of a square wave, attach a BNC minigrabber (or similar) to a Wavegen output and connect the positive end to the probe tip and the ground end to the probe ground clip.
-<newcolumn> +
-<ADP3450_connectSquare.jpg> +
-</columns>+
  
-Open the Scope tool in the WaveForms software. Enable the appropriate channel corresponding to what your probe is attached to (probably channel 1) and set the time division to 200 us/div.+<WRAP center round tip 100%> 
 +It is recommended to use BNC to minigrabber cables instead of BNC Probes on the analog output BNC port to avoid any bandwidth limitations on 1x mode or corresponding signal attenuation on 10x mode. 
 +</WRAP>
  
-<columns 100% 50% 50%> 
-If connected to a square wave from a Waveform Generator on a Discovery device, set the time base to 200 us/div and leave the offset and range at their default values. 
-<newcolumn> 
-<AD2_ScopeSetup.png> 
-</columns> 
- 
-<columns 100% 50% 50%> 
-Then open the Wavegen tool and configure the output to be a 1 kHz Square wave with an amplitude of 1 V.  
 <newcolumn> <newcolumn>
-<AD2_WavegenSetup>+<figure center|ADP3000ConnectProbe> 
 +{{test-and-measurement:guides:ADP3000_connectSquare.png|Connect the BNC probe to the BNC minigrabber.}} 
 +<caption>//Connect the BNC probe ground clip to AWG ground clip and the BNC probe tip to the AWG output.//</caption> 
 +</figure>
 </columns> </columns>
  
-FIXME - use a screwdriver to adjust your probe's compensation capacitor until the square wave visible in the Scope plot looks appropriately square. 
  
 ---- ----
Line 86: Line 105:
  
 <columns 100% 50% 50%> <columns 100% 50% 50%>
-Connect the probe to the BNC input of the oscilloscope and set the probe to its 1x attenuation setting. +Connect the probe that is to be compensated to the desired BNC input channel of the oscilloscope and set the probe to its 10x attenuation setting. 
  
-Connect the probe tip directly to the source of the square wave and connect the grounding tip to an associated ground point.  +Note that the BNC probe is connected in such a way to provide easy access to the compensation trimmer.
- +
-INFO: The reason you want to connect directly to the source, as opposed to through another probe, is that we want to calibrate the probes with an accurate signal source. Probes themselves, both passive and active, have additional internal circuitry which can distort the square wave, causing the probes to be incorrectly calibrated. +
 <newcolumn> <newcolumn>
-<ADP5250_connectProbe.jpg>+<figure center|ADP5000ConnectProbe> 
 +{{test-and-measurement:guides:ADP5000_connectProbe.png|Connect the BNC Probe to the oscilloscope channel you wish to compensate for.}} 
 +<caption>//Connect the BNC probe to the preferred oscilloscope channel and slide the switch to the 10x attenuation setting.//</caption> 
 +</figure>
 </columns> </columns>
- 
-If connecting to the ADP5250's probe compensation tabs, connect the probe to the top tab with the square wave symbol, and the probe ground clip to the lower connector with the ground symbol. 
  
 <columns 100% 50% 50%> <columns 100% 50% 50%>
-<ADP5250_connectTabs.jpg> +Connect the probe tip to the top tab in the compensation box with the square wave symbol, and the probe ground clip to the lower connector with the ground symbol.
-<newcolumn> +
-<AD2ADP_connectTabs.jpg> +
-</columns> +
- +
-<columns 100% 50% 50%> +
-Open the Scope tool in the WaveForms software. Enable the appropriate channel corresponding to what your probe is attached to (probably channel 1) and set the time division to 200 us/div.+
  
-Adjust the offset to -1 V and the range to 1 V/div 
 <newcolumn> <newcolumn>
-<AD2APD_ScopeSetup.png>+<figure center|ADP5000ConnectProbe> 
 +{{test-and-measurement:guides:ADP5000_connectSquare.png|The compensation tabs directly on the device provide a constant square wave.}} 
 +<caption>//Connect the BNC probe to the compensation tabs that are provided on the device.//</caption> 
 +</figure>
 </columns> </columns>
  
-FIXME - use a screwdriver to adjust your probe's compensation capacitor until the square wave visible in the Scope plot looks appropriately square. 
  
 ---- ----
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 <columns 100% 50% 50%> <columns 100% 50% 50%>
-Connect the probe to the BNC input of the oscilloscope and set the probe to its 1x attenuation setting. +Connect the probe that is to be compensated to the desired BNC input connector on the BNC Adapter that is associated with the oscilloscope channel you wish to compensate for and set the probe to its 10x attenuation setting. 
  
-Connect the probe tip directly to the source of the square wave and connect the grounding tip to an associated ground point. +Note that the BNC probe is connected in such a way to provide easy access to the compensation trimmer. 
 +<newcolumn> 
 +<figure center|AD3AD2ConnectProbe> 
 +{{test-and-measurement:guides:AD3AD2_connectProbe.png|The AD3 in the photo is a prototype, hence the different coloring on the plastic shell.}} 
 +<caption>//Connect the BNC probe to the preferred oscilloscope channel and slide the switch to the 10x attenuation setting.//</caption> 
 +</figure> 
 +</columns> 
 + 
 +<columns 100% 50% 50%> 
 +Connect the probe ground clip to the metal of one of the outside BNC connectors as that is tied to the system ground, and connect the probe tip to the right angle pin associated with Wavegen Channel 1 − this will be the "top" pin, 5th from the left, directly below the "W1" label. 
  
-INFO: The reason you want to connect directly to the source, as opposed to through another probe, is that we want to calibrate the probes with an accurate signal source. Probes themselves, both passive and active, have additional internal circuitry which can distort the square wave, causing the probes to be incorrectly calibrated.  
 <newcolumn> <newcolumn>
-<AD2BNC_connectProbe.jpg>+<figure center|AD3AD2ConnectProbe> 
 +{{test-and-measurement:guides:AD3AD2_connectSquare.png|Connect the BNC probe directly to the pin for the best signal clarity.}} 
 +<caption>//Connect the BNC probe directly to the Wavegen output and the ground clip to one of the BNC connector shells on the adapter.//</caption> 
 +</figure>
 </columns> </columns>
 +
 +
 +</WRAP>
 +<--
 +
 +----
 +
 +
 +
 +==== WaveForms Setup ====
 +A reference workspace with the recommended setup is available for download in the [[#inventory|Inventory]]. Instructions on how to recreate the workspace for yourself are provided below. 
  
 <columns 100% 50% 50%> <columns 100% 50% 50%>
-For the Analog Discovery 3 or Analog Discovery 2, connect to the Waveform generator pin directly. +Open the Wavegen tool within WaveForms and configure the output on Wavegen Channel 1 to be a 1 kHz Square wave with an amplitude of 5 V.  
 + 
 +Note: If using an ADP 5000 series device, this step is unneeded as you will be using the compensation tabs which automatically provide their own square wave of the appropriate settings. 
 <newcolumn> <newcolumn>
-<AD2BNC_connectSquare image>+<figure center|AD3WavegenSetup> 
 +{{test-and-measurement:guides:ad3_wavegensetup.png|A 5 V, 1 kHz square wave is created on Wavegen channel 1}} 
 +<caption>//A 5 V, 1 kHz square wave is created on Wavegen channel 1//</caption> 
 +</figure>
 </columns> </columns>
  
 <columns 100% 50% 50%> <columns 100% 50% 50%>
-If connected to a square wave from a Waveform Generator on a Discovery device, set the time base to 200 us/div and leave the offset and range at their default values.+Open the Scope tool in the WaveForms software. Enable the appropriate channel corresponding to what your probe is attached to (likely channel 1) and adjust the following settings: 
 + 
 +  * Set the level of the rising edge trigger to be at 1 V. 
 +  * Set the Time //Base// to 500 μs/div 
 +  * Set the enabled channel voltage //Range// to 1.25 V/div. You can manually type in the box to set this value. 
 +  * If not visible, click the gear icon associated with the oscilloscope channel and change the //Probe attenuation// to 10x to have WaveForms automatically adjust the rendered scaling of the received signal.  
 +  * Uncheck any additional oscilloscope channels that you are not viewing for visual clarity. 
 + 
 +Click the Run All green arrow in the upper right hand corner to start both the Scope and Wavegen instruments.  
 + 
 +An example of an unattenuated signal that you might see is shown in {{ref>AD3ScopePrecompensation}}. Note that the provided square wave is in fact not "square" and instead has some overshoot. 
 <newcolumn> <newcolumn>
-<AD2_ScopeSetup.png>+<figure center|AD3ScopePrecompensation> 
 +{{test-and-measurement:guides:ad3_scope-precompensation.png|What you might see when initially compensating your BNC probe.}} 
 +<caption>//An example of what an unattenuated square wave might look like.//</caption> 
 +</figure>
 </columns> </columns>
 +
 +
 +
 +Use a small flathead screwdriver (a small plastic one is typically included with BNC probes) to adjust your probe's compensation capacitor until the square wave visible in the Scope plot looks appropriately square. The probe trimmer is often located on the BNC connector end of the probe as shown in {{ref>PhysicalAdjustProbeTrimmer}}.
 +
 +A small video showing an example of adjusting an overcompensated probe to instead be a flat square wave can be found in {{ref>AdjustProbeTrimmerUntilSquare}}.
  
 <columns 100% 50% 50%> <columns 100% 50% 50%>
-Then open the Wavegen tool and configure the output to be a 1 kHz Square wave with an amplitude of 1 V. +<figure center|PhysicalAdjustProbeTrimmer> 
 +{{test-and-measurement:guides:physicalprobetrimmeradjustment.png?500|I unironically love this screwdriver. The phillips and flat head ends are actually useful sizes.}} 
 +<caption>//Use a flat head screwdriver to adjust the BNC probe trimmer.//</caption> 
 +</figure> 
 <newcolumn> <newcolumn>
-<AD2_WavegenSetup>+<figure center|AdjustProbeTrimmerUntilSquare> 
 +{{test-and-measurement:guides:adjustprobetrimmeruntilsquare.mp4?550x412|A video showing an example of what you might see while compensating the probe}} 
 +<caption>//A video showing an example of what you might see while compensating the BNC probe.//</caption> 
 +</figure>
 </columns> </columns>
  
-FIXME - use a screwdriver to adjust your probe's compensation capacitor until the square wave visible in the Scope plot looks appropriately square. 
  
-</WRAP> +
-<--+
  
 ---- ----
 +
 ===== Next Steps ===== ===== Next Steps =====
  
-FIXME restate what was accomplished+You have now successfully compensated your BNC probe to a particular oscilloscope channel by adjusting its capacitance to match the capacitance of the oscilloscope channel.  
 + 
 +You can find more information about your Mixed-Signal Oscilloscope through its Resource Center, which can be found via the [[test-and-measurement/start]] page of this site. 
 + 
 +Other guides you might be interested in include our [[/test-and-measurement/guides/waveforms-calibration|Calibration]] guide, the [[test-and-measurement/guides/waveforms-external-triggers]] guide, and [[/test-and-measurement/guides/waveforms-sdk-getting-started]].  
 + 
 +All questions, comments, and observations about this and any of our other guides are welcome on the [[https://forum.digilent.com/forum/8-test-and-measurement/|Test and Measurement]] section of the Digilent Forum, where Digilent engineers will be able to respond to you directly. 
  
-You can find more information about your Mixed-Signal Oscilloscope through its resource center, which can be found via the [[test-and-measurement/start]] page of this site. 
  
-FIXME other call to actions?