Rigol DS1054Z Bandwagon Tips?

[mtdoc]

I suppose my head is just spinning from the handheld debacle I'm dealing with. It won't hold its calibration for more than a minute.

To be fair eKretz, the issue you're experiencing with your Micsig really has nothing much to do with holding calibration.  You seem to have had bad luck getting a Micsig handheld with an issue that needs to be resolved but it is not really a calibration issue per se.

[ebastler]

Since I don't use the scope too often, I think I am going to deploy an automated weekly or monthly self-cal.

The scope have Ethernet connectivity so self cal can be initialized and queried by my always-on server. Just power the scope with an Ethernet-enabled power strip (so I can bypass the clunking power button, leaving it always on, and switch the power to it in software)

I need to cook up software for this task, and set up a cron job on my server to run it periodically.

Hey, glad you are still following this thread! Apologies for having spent so much time on the self-calibration, which is certainly not the most important topic to familiarize yourself with in your new scope.

I don't think it is worthwhile to invest so much effort in an automated, periodic self-calibration setup. The consensus here seems to be that doing it once per year is enough, especially if your scope remains on the bench under stable ambient conditions.

[tggzzz]

That kind of info is useful to new or potential users - I sure would like to know that before purchasing - it would be an unhappy surprise to me. It doesn't kill the scope in my eyes by any means, but geez that's almost an hour before you can trust measurements.

Hmm... How often do you guys typically run self-calibration?

Me? Almost never. Maybe after a firmware update or when winter/summer arrives.

I never imagined my scope as a multimeter, I know the voltage readings are only about 5% accurate even when perfectly calibrated (it says so in the manual!)

If you know that simple fact you can relax and use it for what it's meant to be used for, ie. look at the wiggly lines and see if they're the right shape or not.

5% accuracy is enough to see if there's a problem in the circuit. Everything else is just volt-head obsessing.

I'd change the last sentence to "Everything else is using the wrong tool for the job".

[Fungus]

Since I don't use the scope too often, I think I am going to deploy an automated weekly or monthly self-cal.

The scope have Ethernet connectivity so self cal can be initialized and queried by my always-on server. Just power the scope with an Ethernet-enabled power strip (so I can bypass the clunking power button, leaving it always on, and switch the power to it in software)

I need to cook up software for this task, and set up a cron job on my server to run it periodically.

You could do that, but it won't make anything better. Devices don't decalibrate themselves on time spans measured in weeks/months, it takes many years if it's in a stable environment.

A much better action plan is to grok the idea that the voltage readings on screen are only approximate. Good enough to see if there's a problem but that's all.

Use a multimeter for important measurements (aka "the right tool for the job").

Here's some numbers for your perusal, taken from the DS1054Z manual:


(I just saw a typo in the manual - "Analog channe"  )

[Fungus]

You need to do some more study why equipment have Self Cal capability and why there is a need to use it occasionally.

Measurements are affected by primarily temperature and the combination of runtime and ambient might not equate to the temp when equipment was calibrated and if this is the case that Cal will not be valid.

Any calibration needs to be verified. What if the internal voltage reference is broken? What if you didn't warm it up properly?

For corporate use, don't mess around. No boss wants legal liability because some intern pressed 'calibrate' every day right after he switched on all the test gear.

For hobby use I say go ahead and calibrate it yourself. Maybe verify it against a multimeter. Just don't imagine that frequent calibration will make the slightest bit of difference in real terms.

Maybe you work in a place that's freezing cold in the mornings and baking hot in the afternoons after The Machine has been on for several hours. You could calibrate twice a day, or... just relax and accept that the numbers on screen won't be exact even if you do that. You want exact numbers? Get a bench multimeter with temperature compensation, ie. the right tool for the job.

[tggzzz]

Since I don't use the scope too often, I think I am going to deploy an automated weekly or monthly self-cal.

The scope have Ethernet connectivity so self cal can be initialized and queried by my always-on server. Just power the scope with an Ethernet-enabled power strip (so I can bypass the clunking power button, leaving it always on, and switch the power to it in software)

I need to cook up software for this task, and set up a cron job on my server to run it periodically.

You could do that, but it won't make anything better. Devices don't decalibrate themselves on time spans measured in weeks/months, it takes many years if it's in a stable environment.

A much better action plan is to grok the idea that the voltage readings on screen are only approximate. Good enough to see if there's a problem but that's all.

And I'd take that further, and try to get the people into the frame of mind that all readings from every instrument are approximate. The questions are how approximate, and what does the application require[1]

I have a suspicion that if someone measures voltages with a scope, they will also not understand probes, probing techniques, and the consequent lies you will see on a scope's screen.

[1]My favourite example is an expensive piece of test equipment with a resolution of 0.001dB but an accuracy of only 0.1dB. Guess which wasn't important in that application!

[tggzzz]

For corporate use, don't mess around. No boss wants legal liability because some intern pressed 'calibrate' every day right after he switched on all the test gear.

Just so.

That's why many instruments disable the "cal button" unless an internal jumper is in the right position. Good thing too.

[Fungus]

Also: You might have to use somebody else's oscilloscope one day.

Is that oscilloscope going to be calibrated?   

What will you do if you see 4.8 volts where it should say 5.0V? 

[technix]

Since I don't use the scope too often, I think I am going to deploy an automated weekly or monthly self-cal.

The scope have Ethernet connectivity so self cal can be initialized and queried by my always-on server. Just power the scope with an Ethernet-enabled power strip (so I can bypass the clunking power button, leaving it always on, and switch the power to it in software)

I need to cook up software for this task, and set up a cron job on my server to run it periodically.

Hey, glad you are still following this thread! Apologies for having spent so much time on the self-calibration, which is certainly not the most important topic to familiarize yourself with in your new scope.

I don't think it is worthwhile to invest so much effort in an automated, periodic self-calibration setup. The consensus here seems to be that doing it once per year is enough, especially if your scope remains on the bench under stable ambient conditions.

It sits on my desk where sunlight can reach. So probably not that stable ambient.

[Assafl]

Be careful of ground. Consider getting a differential probe for ungrounded and higher voltage work (such as power supplies).

BTW - One can utilize scopes, or a DMM, or any other device, for critical measurements (for example, you are measuring a single occurrence that will not happen again, or too costly to make happen again; or Need to refer to a physical property accurately like volt, ampere, ohm, Hz, SPL, lumens, etc. ; or Need great resolution for a very sensitive sensor).

Usually these types of measurements are run against external calibration. The simplest example (for a DMM) is if I work on mains I stuff the DMM in working mains. I don't trust a 0V shown until I am calibrated at 220v. It is even better to go back to the 220V and validate the DMM did not die between the two outlets... (It is critical because if the measurement is wrong I won't be around to do it again - becoming a 1 time measurement....)

Doing DC or ohms - compare against a fresh 9V battery (or better yet - a silver oxide battery) or a calibrator, measure a precision resistor salvaged from discarded T&M (in the same range as the DUT).

One can do the same with a scope. If one channel is down and both measure 4.8V instead of 5V - then the voltage isn't a clue. However, if one is 4.8v and the other reads 5v - it may be (per Fungus' post). The second (working) channel serves as a calibration reference against the first.

One can also work around limitations: If one is aware of the noise floor, one can raise the input signal for a good SNR using a calibrated amplifier. Use a mixer (properly) to work around bandwidth limitations, Etc. the options are endless...

Getting calibrated readings can get pretty complex pretty quickly - I did lots of these types of experiments in the Navy - it was all about calibrating the T&M chain. The hydrophone, the B&K charge amplifiers, the parametric and notch filters, the scopes, the recorders, the HP TRMS voltmeters, you had to plot and save a bathymetry (and work the predictions), plan the test with the operations team so that you know distances and depths fairly accurately, etc. In the ocean, everything needs to end up as dB re 1uPa @ 1yd in defensible accuracy.

Heck - eve a bad grounding scheme can destroy your test. So we'd calibrate the individual components and the setup as a whole for weeks prior to the live sea tests (and calibrate backup T&M in case something fell in the ocean - or decided to throw a tantrum) - Imagine the cost of redoing a test with a frigate or submarine because you could not figure out the SONAR equation...