How to calibrate TEK 465B 'scope?

Greetings All, A couple years ago I installed the meter kit in my TEK 465B oscilloscope. I have all the manuals for the 'scope but not anything against which to test it. It seems to be OK but calibration would be great so can anybody point me to a good place to buy the proper signal generator? I'm just a rank amateur but the thing has beenh helpful. A good example is how I tuned up my neighbor's generator after some hack had messed up all the adjustments. I looked at the output from a 9 volt AC wall wart that I first plugged into the mains. I noted the wave form (not a perfect sine wave, but bent over) and the frequency. The frequency was correct for the scale I used so at least I know that's working correctly. I then plugged the wall wart into his generator and used both an optical tach and the 'scope to measure frequency. Along with a DVM I adjusted the carb and governor so that the generator put out 60 cycles and 120 volts with at least a 300 watt load. Unloaded the frequency went up to about 66 cycles and the voltage went up to about 130 volts. With a full load the frequency is pretty steady and the voltage drops to 115 volts. He now loads it up with a little space heater before he plugs in his fridge and some lights. There was no way to keep the voltage above 105 volts and the frequency above 52 Hz when the thing was loaded if the unloaded frequency was 60 and the voltage 120. ERS

Reply to
Eric R Snow
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You can download my Daqarta software and use its free sound card signal generator. (You don't have to buy the software: When the

30-day/30-session trial period expires, only the signal *input* stops working. The signal generator keeps working, along with all the spectrum and waveform analysis displays.)

Since sound cards have crystal-controlled sample rate clocks, the signal generator accuracy and stability will be excellent. However, note that the output is limited to frequencies (typically

20 kHz or less). That's fine for calibrating the slower sweep ranges, but not much use for the fast end. With (say) a 10 kHz square wave output, you'd have 100 usec per cycle, or 50 usec per phase. With the scope on 5 usec/div, this will just fill a 10-div trace. Still, it's a good start, and it's free.

Note that sound cards don't come with any sort of level calibration. Daqarta can be calibrated for your card, and has some features to help automate this. But somewhere along the line you will need to provide a reference level to tie into the calibration. This gets into a chicken-and-egg problem unless you can borrow a known-good generator to get you going.

Another sound card issue is that they don't pass DC, so you can't (for example) just measure a battery with your DVM and then adjust Daqarta to read the same. And most inexpensive DVMs lack a sensitive AC Volts range, or you could just read the sound card output and adjust the calibration to match the meter. One workaround I have come up with is to measure a battery with the DVM (since they always have sensitive DC ranges), then use the sound card to read the peak voltage that the AC coupling passes. You have to keep shorting the input and repeating until you get a good bounce-free spike capture, then assume the peak is the same as the battery voltage.

If you are more adventuresome, you can use the DVM to measure a high AC voltage, say from an isolation transformer on the 120V mains, and divide it down to a volt or so for the sound card to read. It's easy to get a known divider ratio, so you should be able to get a fairly accurate reference.

Best regards,

Bob Masta D A Q A R T A Data AcQuisition And Real-Time Analysis

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Scope, Spectrum, Spectrogram, Signal Generator Science with your sound card!

Reply to
Bob Masta

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