principles of calibration of an oscilloscope

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raffay13
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what are the principles of calibration in terms of compliance with the test specification for a oscilloscope. please help.
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(Original post by raffay13)
what are the principles of calibration in terms of compliance with the test specification for a oscilloscope. please help.
Many oscilloscopes come out of the box already calibrated. When I received my scope from Textronix, there was a Certificate of Traceable Calibration included with my product. This certificate assured me that measurements would be accurate within the specification limits that I select in the instrument. However, after a year, this scope will need calibration.

What is Calibration?

Calibration is the comparison of a measurement device (an unknown) against an equal or better standard. A standard in a measurement is considered the reference; it is the one in the comparison taken to be the more correct of the two. Calibration finds out how far the unknown is from the standard. A “typical” commercial calibration uses the manufacturer’s calibration procedure and is performed with a reference standard at least four times more accurate than the instrument under test. Instrument calibration is one of the primary processes used to maintain instrument accuracy.

In short…calibration is the process of configuring an instrument to provide a result for a sample within an acceptable range.

Why Calibrate?

Calibrating your oscilloscope will maintain the integrity of your research. Oscilloscopes need to read data accurately. If the oscilloscope is out-of-tolerance (OOT), then the product that is being measured will result in false information. False information leads to more money being wasted on repair parts and expensive maintenance, as well as prolong your research. Calibration should be a proactive practice. Think of it as an oil change for your car. You would not dare drive your car without changing the oil would you? Most of us change the oil when scheduled to avoid costly repairs. Keeping your car maintained avoids unnecessary costs and expense. It is the same principle for your oscilloscope. You would not dare take readings without calibrating your scope?

What to calibrate?

Since calibration is an important standard for scopes, you need to know what to calibrate. Here is an ideal list of controls to calibrate on your device.

Vertical Channels
Channel switching

Deflection range and accuracy

Bandwidth, pulse response and risetime

Horizontal Channels
Timebase accuracy including delay, magnification and jitter

Trigger functions

X-Axis deflection accuracy and X-Y phasing

Internal calibration signals
Cursors and measurement readouts
Z-Axis bandwidth
Calibration Intervals

The instrument owner based on the manufacturer’s recommendations determines calibration intervals. The OEM’s intervals are typically based on parameters like mean drift rates for the various components within the instrument. However, when determining calibration intervals as an instrument “owner,” several other factors should be taken into consideration such as:

The required accuracy vs. the instrument’s accuracy,
The impact an OOT will have on processes and,
The performance history of the particular instrument in its application.
Consistency and accuracy is as necessary for your scope as a doctor is to your health, a dentist to your teeth, and an oil change to your car. If your scope is giving inaccurate results, it is time for your device to be calibrated.
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