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Old 16th February 2008, 05:32 AM   #1
mabie is offline mabie  United States
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Default Oscilliscope reading 1/2 voltage

Hi,

Let me start by saying I am totally new to oscilloscopes. I just got my first scope (free!) a Kikusui COS5020. I have all the knobs off or zero'd I think...

When take try to take the voltage of a nine volt battery with the voltage units set to 1v the line jumps 4.5 lines or 4.5 volts.

When I attach the probe to the calibration lead which is .5 (Vp-p) I get a square wave that reads .25 v peak to peak.

Everything seems to be reading 1/2 voltage...am I missing something?

Thanks!

Mike
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Old 16th February 2008, 06:07 AM   #2
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Have you turned the Cal D pot all clockwise ?
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Old 16th February 2008, 06:10 PM   #3
mabie is offline mabie  United States
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Hi,

Yes the CAL'd pot is turned clock wise and clicked off. The VAR pots on the volt/div selector are pushed in and both positions are clicked off.

The line voltage selector on the back for the power supply is set to 110-120 volts. I assume this is a regional thing.

Both sets of probes and both channels behave the same. One question is - the input for the probes reads 25pf and the probes read 14pf...could this be my problem?

Here are some photos:

Click the image to open in full size. Click the image to open in full size.

Thanks,

Mike
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Old 16th February 2008, 07:22 PM   #4
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Quote:
Originally posted by mabie
Hi,

Yes the CAL'd pot is turned clock wise and clicked off. The VAR pots on the volt/div selector are pushed in and both positions are clicked off.

The line voltage selector on the back for the power supply is set to 110-120 volts. I assume this is a regional thing.

Both sets of probes and both channels behave the same. One question is - the input for the probes reads 25pf and the probes read 14pf...could this be my problem?

Here are some photos:

Click the image to open in full size. Click the image to open in full size.

Thanks,

Mike

It looks like the square wave in the bottom pic IS 0.5V pk-pk. Isn't that what it was supposed to be?

Jan Didden
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Old 16th February 2008, 08:45 PM   #5
mabie is offline mabie  United States
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I assumed peak to peak is the distance from the lowest point of the square wave to the highest point.

In this case the the volt/div is set to .1v and the square wave is 2.5 lines peak to peak.

Am i reading this correctly?

Thanks,

Mike
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Old 17th February 2008, 03:56 AM   #6
mabie is offline mabie  United States
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Hi,

My issue has been fixed. I was reading the measurements incorrectly.

Thanks!

Mike
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Old 17th February 2008, 04:35 AM   #7
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Default and the answer is...

For sake of my peace of mind and for the benefit of other novice users of oscilloscopes, let's state the solution. As I understand it, the voltage measurement are based on the major divisions, so with the 0.1 volt per division setting, the square wave show a 0.05 volt p-p amplitude. Since it should be 0.5 volts; I suspect that the probe was switched to the 10x position. Therefore, the measurement on screen should be multiplied by 10 giving us the correct 0.5 volts.

Does this summarize the solution? Just my
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Old 17th February 2008, 05:30 PM   #8
mabie is offline mabie  United States
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You are absolutely correct!

When I was given the scope I was told that Volts/DIV referred to MINOR Divisions, and was told nothing about 10X probes. So basically because there are 5 minor div per major div...I was inadvertently multiplying my readings by 5 (instead of 10) giving me half readings.

Thanks,

Mike
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