Probe Mismatch in PicoScope 7
by Steve Smith

Ease of use has been one of the main driving factors behind PicoScope 7 and the new 4x25A Automotive scopes.

Probe Mismatch is a feature that supports this. When you want to recreate a test by loading an already saved waveform, the Probe Mismatch feature will help you make sure that your PicoScope is set up correctly to replicate that specific test. It will do this by notifying you if you do not have the “correct” probes connected to your scope. Please note that the saved psdata file used for this test, will have to have been saved with a 4x25A scope and PicoBNC+ probes in use.

In the screenshot below, we have used all four channels on a PicoScope 4425A to capture the secondary ignition event on one cylinder. We have used a mix of PicoBNC+ and conventional BNC ignition probes. The file was then saved to the local computer and uploaded to the Waveform Library.

Why? Because we can, and also, it is a great way to demonstrate the Probe Mismatch feature.

Channel A: PicoBNC+ Secondary ignition pick up

Channel B: PicoBNC+ COP Probe

Channel C: BNC Secondary ignition pick up

Channel D: BNC COP Probe

If I now load this file with any automotive scope connected, the waveform will be displayed as normal (see image below).

Before running the scope, to replicate the test, I will need to manually configure the probes (for each channel) to match those used in the original capture. If I am using a 4423 or 4425, for example, I will have to use the BNC equivalent of the PicoBNC+ probes connected to channels A and B in the original capture. This procedure has always been necessary, as you will know if you have ever reloaded a psdata file or downloaded a waveform from the Waveform Library. I.e. you need to manually match your probes to the original waveform if you wish to replicate the capture.

With Probe Mismatch, the same procedure still applies but with a prompt at hand to help you select the correct probe.

Let’s assume I have a 4425A scope connected and I load the waveform we saved above (see Image 1). Remember that this waveform contains both BNC and PicoBNC+ probes. Once again, the waveform will be displayed as normal. However, depending on the probes currently connected to my scope, when I press the Start/Stop button to run the scope, the Probe Mismatch dialog box may appear to inform me of the expected and found probes.

The following image will help clarify:

The dialog box for Probe Mismatch has appeared before the scope starting to inform me of the current device/probe configuration.

The headings within the Probe Mismatch dialog box indicate the following:

Channel: Displays the channel letter to which the expected and found probes refer to.

Probe Expected: Displays the type of PicoBNC+ probe used during the original capture or, “No Probe” if either a conventional BNC probe was used or there was no probe connected (vacant).

Probe Found: Displays the type of PicoBNC+ probe that is currently connected to the scope or “No Probe” if either a conventional BNC probe is used or there is no probe connected (vacant).

Probe State: Indicates whether the expected PicoBNC+ probe matches the found PicoBNC+ probe

 

Let’s start with Channel A:

The expected probe was a PicoBNC+ Secondary ignition pick up.

The probe found currently connected to the scope was a PicoBNC+ Secondary ignition pick up.

The probe state is therefore correct and indicated with a tick mark.

 

Channel B, however, is a different story:

The expected probe was a PicoBNC+ COP Probe.

The probe found currently connected to the scope was PicoBNC+ 60 A Current Clamp.

The probe state is, therefore, incorrect and indicated with a cross.

 

Channel C differs for yet another reason:

The expected probe is indicated as “No Probe”.

The probe found is also indicated as “No Probe” as no PicoBNC + probe was connected to Channel C at that time.

The probe state is therefore correct and indicated with a tick mark.

Because a conventional BNC Secondary ignition pick up was used on Channel C for the original capture, no information can be stored about this style of probe, meaning it cannot be displayed to the user within the Probe Mismatch dialog box.

Please do not confuse Probe Mismatch with the Probe settings within Channel Options as these remain intact and separate. (Channel C Options loads the conventional BNC Secondary ignition pick up that was used during the original capture).

 

And finally, Channel D:

The expected probe is indicated as “No Probe”.

The probe found currently connected to the scope was a PicoBNC+ COP Probe.

The probe state is therefore incorrect and indicated with a cross.

As the original capture utilized a conventional BNC COP Probe on channel D, Probe Mismatch cannot recognize non-BNC+ probes, so it displays No Probe under Probe Expected.

The Probe Mismatch dialog box will update live, so in the above scenario, the probe found on Channel D (the PicoBNC+ COP Probe) can be removed and connected to Channel B to match the expected probe (replacing the incorrectly connected PicoBNC+ 60 A Current Clamp).

As soon as the PicoBNC+ COP Probe is connected to the correct channel (in this case, Channel B) the Probe Mismatch dialog box will clear and the scope will run automatically. The PicoBNC+ Probe configuration is now correct.

To Conclude:

The Probe Mismatch dialog box will appear when you are using a 4x25A scope, loading a psdata file (which has been saved using PicoBNC+ probes), and there is a mismatch with the PicoBNC+ probes found connected to the scope. (Channels B and D above are examples of mismatches. They are marked with a cross in the Probe Mismatch dialog box.)

The Probe Mismatch dialog box will not appear when you are using a 4x25A scope, loading a psdata file (which has been saved using PicoBNC+ probes), and the PicoBNC+ probes connected to the scope already match the expected probes. You are good to go and the scope will run as normal.

The Probe Mismatch feature is a handy tool to have, just to make sure that you are using the right accessories for the job. However, when all is said and done, the user has the final say and can choose to ignore the mismatch warning and Run with found probes, (meaning run the scope with the currently connected probes) or click Cancel to close the Probe Mismatch dialog box.

We hope this makes the purpose and function of this feature clearer and welcome any feedback you may have.

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