Tektronix TDS 220 question type thing

[holographicpencil]

Hello there,

Im just starting out in electronics and have brought myself a Tektronix TDS 220 second hand. The main question i have is when the probes are hooked up to the calibration circut which is marked as 5v 1khz, the scope calculates that there is closer to 6 volts though the frequency is still 1khz. Im wondering if this is a common issue with oscilloscopes or is mine wierd? is there a need to have it calibrated, does it really matter or is it just possesed and i should set it on fire and dance around it etc?

Thanks for your input in advance
Jack

[larry42]

Can you include a screenshot? You might need to adjust the probe compensation screw on the probe. The scope manual should tell you about this

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[holographicpencil]

thanks for the reply!

Unfortunatly the scope is at my weekend hangout so i cant take a picture until then. I have ajusted the probe so it shows a square wave with nice square corners etc. however i would of expected it to put out a voltage really close to the nominal 5v rather than the 5.9 or 6v the scope calculates it at?

Jack

[alm]

6 V sounds quite far off, but note that the probe calibration output is only intended to adjust the probe compensation. It's generally not an accurate reference for either frequency or amplitude. I wouldn't worry about it if amplitude measurements of other known signals are accurate (eg. DC voltage or 50/60 Hz sine from function gen or transformer that you check with your DMM). Note when comparing DMM values and scope readings that the meter indicates the RMS voltage, and the scope often peak-to-peak. I think the TDS-220 supports RMS as one of the automated measurements so you can directly compare the values.

[larry42]

If you don't have a function or signal gen, then you can measure a battery voltage (DC) with your scope probe and compare it with a multimeter.

NB Most multimeters should be better than 2% accurate, and few scopes are not much better than 3% accurate (though they often do quite well at DC, their 8bit ADCs are built for speed, not accuracy).