I have a TEK 2467 4 channel scope, that is out of of calibration and needs to be calibrated.
The internal calibration signal must generate 0.4V p-p which it does, however the scope measures it at 0.2 V p-p

I dont have the service manual with me but I was hoping some one could tell me how to go about calibrating it? Has anyone had any experience with this scope?


Thanks,
Aditya

 

You are in a bad place. You can neither verify the P-P voltage of the calibrator, nor the absolute response of the vertical amplifiers. Unless you have an independently verifiable voltage/waveform source, it's hard to do.

Oscilloscopes hardly ever get used to measure voltage, though. If all four channels respond alike for a single waveform, then you can at least see if a voltage on one channel is different from another/the others.

The hardest part of calibration is in setting the time base. Timing measurement is where oscilloscopes are needed to be accurate. That requires something like a crystal, oven stabilized timing source. Outside of calibration facilities, those are hard to come by.

As a reasonable check, though, you can always obtain a CMOS oscillator with a good spec and see if the oscilloscope appears to show the proper time/division on the display. That should get you to within a percent (although knowing if it's plus or minus is always the hard part).

 

The frequency/time base measurement seems to be fairly accurate as measured by an independently calibrated signal generator.

We are using the supply to measure high voltages (using a x1000 HV probe ) which is why I am trying to see if I can get the voltage measurement right.

There is a "measure voltage" feature on the scope and it measure the peak to peak voltage of the captured waveform quite accurately. I was just trying to see if I can recalibrate it to make arbitrary waveform measurements too.

 

Personally, I do measure amplitude quite a bit with a scope, although it's usually to 1 or at most 2 significant figures. I agree with beenthere, though, that the scope's most useful feature is the ability to measure time and time differences.

One way to check the calibration of the scope is to measure a battery with a digital multimeter, then see that the scope measures the same value (make sure the vertical input channel is DC coupled and that you know the probe attenuation). You can use voltage dividers to construct other calibration voltages.

You can build a nice voltage reference with an LM285Z voltage reference IC. I made one with some AAA batteries, the IC, and a resistor or two. I measured its voltage output over a period of about 24 days; here are the data:

Date, time, voltage, room temperature in deg F
20 Nov 2007   3:00 pm 1.23505 70.1
21 Nov 2007  11:42 am 1.23504 66.9
21 Nov 2007   4:23 pm 1.23497 67.3
22 Nov 2007  12:05 pm 1.23501 66.6
22 Nov 2007  12:10 pm 1.23512 66.4
22 Nov 2007   4:21 pm 1.23487 70.7
22 Nov 2007  10:33 pm 1.23504 64.8
23 Nov 2007   2:28 pm 1.23485 69.0
24 Nov 2007  11:42 am 1.23492 66.4
24 Nov 2007   6:16 pm 1.23494 68.7
24 Nov 2007  11:27 pm 1.23505 62.8
25 Nov 2007  10:57 am 1.23507 61.4
25 Nov 2007   5:01 pm 1.23529 60.0
26 Nov 2007  11:31 am 1.23525 60.0
27 Nov 2007  11:00 am 1.23494 69.3
28 Nov 2007   1:13 pm 1.23509 65.1
 1 Dec 2007   5:36 am 1.23544 55.9
 1 Dec 2007   4:27 pm 1.23496 68.8
 2 Dec 2007   6:42 pm 1.23509 65.9
13 Dec 2007   5:07 pm 1.23502 67.9

The attached graph shows the variation with temperature; some or all of this variation could be due to my voltmeter (an HP 3456), so I don't know if the voltage reference performs better than this. However, the slope with respect to temperature from the graph is about -60 ppm/°C and the spec for this IC is usually about 80, so most of the variation is probably due to the IC, not the voltmeter.

The circuit can operate for years on the order of 10 μA, so I didn't even bother putting a switch in the circuit (well, the other reason was that I stuck it all in a plastic Maxim sample box and there wasn't room for a switch ).