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I have a measurement that needs 4 scope channels simultaneously, but I only have two identical 2 channel oscilloscopes. Is there a way that I can still do my measurement accurately?

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    \$\begingroup\$ " two identical 2 channel oscilloscope" Which model? \$\endgroup\$
    – devnull
    May 16 at 22:36
  • \$\begingroup\$ Are you measuring mains frequency voltages? Many scopes can trigger on the mains. \$\endgroup\$ May 17 at 9:17
  • \$\begingroup\$ @devnull high Z, Tektronix TD320 \$\endgroup\$
    – ShS
    May 24 at 22:17

3 Answers 3

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You should be able to trigger both scopes from the same signal using external trigger on one or both scopes.

To verify the trigger timing, temporarily view the same signal on both scopes while triggered from the desired trigger signal.

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  • \$\begingroup\$ You may need to fiddle with the termination settings of your trigger signal of course. For example if you'd normally terminate with 50R, do that on the scope at the end of the line, with high impedance and a T connector on the other scope, which should be near the one with the termination. If you'd normally use high impedance on a single scope, use it on both \$\endgroup\$
    – Chris H
    May 17 at 15:24
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    \$\begingroup\$ Or if one's lucky, the scope has a trigger output in the back that can be used to daisy-chain, this could be useful or necessary for complicated triggers. \$\endgroup\$
    – pipe
    May 17 at 21:58
  • \$\begingroup\$ If it is a recurring trigger you might get one from one and one from the other, \$\endgroup\$
    – lalala
    May 18 at 9:26
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There are never enough scope channels, learn to be creative. If you have 4 repetative signals ABCD, take 3 measurements, keeping one channel the same for a reference. AB, AC, AD.

You can also use the external trigger input of the second scope. But, there will be a slight delay that may or may not be significant to you.

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It really depends on the definition of "accurately". If your measurements need to be precise (within the specification of your oscilloscopes) for an arbitrary trigger voltage level, signal shape, ambient temperature, etc. you'd better use a 4-channel scope, or accept that you cannot make an accurate measurement.

If you do your measurements with two scopes, you will only be able to calibrate the trigger delay for a couple of trigger levels. Make sure you do this after the scopes had the time to warm up. Nevertheless, as you proceed with your measurements, the delay in each scope will drift as the trigger signal shape changes, or you tune the trigger voltage level, and the precision will inevitably get worse.

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