Oscilloscope Calibration, Terms and Definitions

[blueicecube]

Hi,

I am new here. And I found the information posted here has been really helpful.

I am writing a procedure on how to calibrate oscilloscope. However, due to my limited experience with osci. I realized there are too may variations of osci. in the market and the terminologies used are quite different.

Please help with the following questions :

1. What is the difference between the term frequency response and
bandwidth in term of testing/calibration oscilloscopes?

Some UUT manuals refer to the term as frequency response, whereas some
call it bandwidth. Is it the same thing? While the standard reference
manual call it frequency response.

2. What does it mean by pulse, rise time, trigger sensitivity? Do they
necessarily means the same thing?

I highly appreciate any helps or reference on this matter.

Thank you,
Nadhra

[harry]

Welcome Nadhra,

Pending response from other Covers, have a look at this link for some Oscilloscope Terms and Definitions.

We have some threads on this subject. Just key in 'oscilloscope' to search for it - the search function is located at the right hand side of the 'blue' bar above your first post (top most). This is one good and informative post.

[Jerry Eldred]

Hi Nadhra,

First, I should mention that I visited Malaysia for a week a few years ago (Petaling Jaya and Penang). I stayed at the Sunway Lagoon which was a beautiful hotel. I am looking forward to some day having enough money to return. I visited Malacca and Batu Cave as well as touring KLM.

Enough off topic. See my answers below each question.

1. What is the difference between the term frequency response and
bandwidth in term of testing/calibration oscilloscopes?
-They are the same. Bandwidth is the highest frequency where the amplitude response of the oscilloscope degrades by <=-3 dB. It is very common in procedures to produce a 6 v deflection at a base frequency and check the upper bandwidth limit with a >=4.2 division deflection.

Some UUT manuals refer to the term as frequency response, whereas some
call it bandwidth. Is it the same thing? While the standard reference
manual call it frequency response.
- See answer above.

ALSO ---- FREQUENCY RESPONSE also includes a measure within the Bandwidth (when it is truly measured).

2. What does it mean by pulse, rise time, trigger sensitivity? Do they
necessarily means the same thing?
- Rise Time is ALMOST the same as bandwidth. Bandwidth refers to the highest frequency that the oscilloscope can accurately reproduce voltage transition. Risetime is a measurement of the 10% to 90% on the leading edge of a square or pulse wave. The formula to convert between risetime and bandwidth is BANDWIDTH = .35/RISETIME or RISETIME = .35 / BANDWIDTH.

Risetime is the method used by some to measure bandwidth. That is because a square wave is a fundamental frequency plus all of its odd order harmonics. The risetime of that square wave represents a measure of the highest odd order harmonic on that square wave (kind of a measure of the bandwidth of a square wave).

The main difference between risetime and bandwidth (frequency response) is risetime does not account for all the frequencies between the bottom and highest frequency. That is why when using risetime, overshoot and ringing are also measured (which account for the variation in response within a bandwidth).

If you want to write a generic procedure to measure bandwidth, be sure to include frequency response within the bandwidth.

This may be a little confusing, but I hope it helps.

[Hershal]

Excellent response Jerry

[blueicecube]

Thanks Harry,Jerry & Hershal,

This will take me awhile to go through on top of my current work

Looking at the references given, it shows that its more fortunate for me to be in the US to solve this problem rather than here. For instances, access to GIDEP would solve soo much problems, but I am not involved with supplying anything to the US government. We are merely a local company here in Malaysia.

As for NCSLI, I went to SIRIM (so-called malaysia standard industrial research), but they said anything related to American standard are unavailable for reference.

My background is in Mechanical Engineering. I went to school at the Gopher/Timberwolves/Twins-state (guess where). Hence, electronic is a bit fuzzy for me.

Alas, thank you for your help and I hope you won't be bored to read my postings for more questions.

[blueicecube]

Sorry about the post. Somehow my browser hang on an empty page while waiting for posting...

[blueicecube]

Another question : why does some manufacturer's calibrate the bandwidth/frequency response of an oscilloscope with an input of dB & freq, while some with input of voltage & frequency?

or are they solely dependent on which value is used by the manufacturer to judge whether the instrument is within specification and not?

would interchanging that have any effect on the result of the measurement?

[Jerry Eldred]

The difference between measuring bandwidth with dB versus Volts peak to peak is just units. If you substitute units, be sure to do calculations and test per correct tolerance.