Hey, I just picked up an old teleqipment S51B Oscilloscope for free. I was just wondering how I can make sure it's calibrated accurately. It works and powers on. I've feed it a simple square wave and it seems to be working ok.

 

There is a variety of simple tests you can do.

Set it to DC and connect a say a 1.5 Volt battery to the input. The line on the screen should go up or down by 1.5V depending on which direction the battery is connected. Repeat with other batteries - ie. 3V, 4.5V, 6V, etc.

Connect say 6V AC from a transformer to the input.

6V is 16.97 V peak to peak (ie. 6 * 2 sqrt 2). Your AC is 60 Hz, so you can check the sweep rate calibration by measuring the period of the signal. 60 Hz has a period of 1000/60 = 16.67 millisec.

If you have an oscillator and frequiency meter, you can check the sweep calibration at other rates. eg. 1000 Hz has a period of 1 ms.

Hope this helps, Len

 

You will have to compensate your probe as well. The scope should have a little pin or something on it that you can connect the probe to, that pin outputs a square wave.

There should be a little slot to adjust the compensation on the probe with a screwdriver. Turn it until the square waves are just that: square. If its over-compensated, you will get very sharp peaks, undercompensated just hte opposite.

test the battery with a voltage meter, its unlikely that the battery is going to be exactly 1.5Volt.

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Correct, this also applies to the AC voltage. A 6 Volt transformer will not necessarily give 6 V, particularily with no load.

Len

 

The problem with calibration is finding something to calibrate it against!.

Also, unless you can get the workshop manual, I wouldn't bother touching any adjustments, from what I remember they are quite obscure in those Telequipment scopes? - with adjustments affecting each other.

For 99% of use there's no need for it to be accurately calibrated anyway!.

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Thanks for your tips.


I've found the Oscilloscope in the Dumpster! From what I see it works perfectly. I don't have the lab manual unforunately.

Can you elaborate on this a little more?

thanks

 

It's usually only required for specific institutions and large businesses, it's NOT about the scope being accurately calibrated, it's about having a certificate saying it is! - even on a brand new scope you have to pay for calibration if you require it!.

So your scope might be more than accurate enough for your needs anyway, considering the actual visible reading accuracy from the screen, if it's within 5% or 0.5% you wouldn't be able to tell the difference.

I've been using scopes professionally for 34 years, we've NEVER had a scope calibrated, nor had any desire or need to.

Everything in live has tolerences, and things you do should bear that in mind.

As already suggested, connect it to a battery and measure it's voltage, compare it to your multi-meter, and see if it's fairly similar, it should be, and that's accurate enough for a scope.

Bear in mind, how do you know your meter is accurate?, do you have it professionally calibrated and certified every year? (at great expense!). Digital meters have made people rather complacent, your meter might read 1.765V - but it's only going to be 1% or 2% accurate (even when new!), so you can throw the last digit away, and be very dubious about the next one as well!.

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That all depends on how much the meter cost in the first place, and el-cheapo will not be very accurate, something like a Fluke will have much better accuracy, but you pay for it!.

JimB

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A quick check in RS Components shows Flukes varying from +/-1.5% (3%) to slightly better than +/-0.1% for the really expensive ones.

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Nigel, The X-Axis line is Slightly Rotated at an angle, is there a setting to get it level and center

I tore the cover off, and on the bottom board theres six Variable resistors?

They are labeled RV89 - Link

RV92 - BLKG
RV88 - IPS
RV6 - SET Y GAIN
RV72 - TIME/CM
RV48 - Trig SENS

 

None of those sound to me like they will help your trace problem. Newer scopes often have an adjustment labelled "trace rotate", some even have it on the front panel. That's the one I would be looking for.
JB

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Don't see anything inside or out like that

 

Perhaps you could loosen the screws holding the CRT and rotate it by hand. Be sure to turn the power off and discharge the EHT first.

Len

 

yeah, there is a little hole drilled in the front of my scope and i can adjust trace rotation through it with a small screwdriver.

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I'm no electronics god, i just talk too much.

 

I've got an old D61b here at work, and it has two 'tabs' sticking out the back of the scope which can rotate the CRT.

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PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk