Measuring UPS switchover time with Zoyi ZT-703S?

[artv]

Hi

I've bought this scope for one task - to measure the switchover / transfer time of portable power stations I'm testing.

I can see the switch - please see attached pic. But it's not showing the wave for the switch - just an instantaneous change?

I'm on the 1.3.8 firmware FWIW. For some reason the very latest firmware 1.3.9 doesn't work at all measuring AC voltage. Auto range just hangs and have to reboot!

There's not loads of settings on the Zoyi. I've tried triggering on rising and leading edge, enabling high speed operation mode, DC and AC coupling (not sure which one to use?)

Any help much appreciated!

Thanks.

[rstofer]

What if we assume the image is correct?  That would seem to imply that the 2d source isn't perfectly in phase with the first source.  It's too early by some number of degrees.

[Phil1977]

Are you sure the scope is triggered together with the switching?

What kind of switch does the power station use?

I suppose we see anything here on the scope pic but not the switching. A mechanical relay never is so clean, a solid state relay never switches without any dead time.

I recommend you to set the trigger voltage over the peak voltage of sine wave. With some luck some line inductance gives you more than 300V when a mechanical relay is switching.

Just as a friendly disclaimer: I would practise this kind of measurement with safe voltages. Power stations with their inconclusive PE-connections can be malicious even for professionals.

[MLXXXp]

If you have a variac or a step down transformer that could lower the line voltage to something lower than the voltage that you get when it switches to off-grid but still high enough not to be considered a brown out, you might be able to set the trigger level to something slightly above that line voltage, for the rising edge, and set the trigger to mode to "single".

[artv]

Thanks.

It does sound like a relay but not sure what switch PS uses. I tried setting the trigger a little higher but got same result. Can you expand on safety concerns? Not sure what you mean by inconclusive PE connections?

Don't have a variac unfortunately.

I've seen many tests like this online that show the delay - so don't know whether it's an issue with this scope or something I'm doing?

I'm running Auto trigger and then just moving trace backwards. I don't know how to get it to trigger on switchover since the sine wave looks pretty much the same?

Thanks for all your help.

[Phil1977]

It does sound like a relay but not sure what switch PS uses. I tried setting the trigger a little higher but got same result. Can you expand on safety concerns? Not sure what you mean by inconclusive PE connections?

Most powerstations allow operation of class-I appliances, that need a PE-connection to be safely operated. Powerstations are sometimes grounded by a mains connection or ground wire, but sometimes they are not.

More over that, the power from the mains grid has one neutral and one live wire. The neutral is also near earth-potential. In case of a powerstation you don't have this connection, you should assume that both wires are live, but they may be galvanically isolated.

The Zoyi-scope probably uses probes with a ground clip. Usually a scope only is safe if you safely can touch the ground level of the probe.

In the setup of a battery-powered scope like the Zoyi with a battery powered power station you have combined everything that makes a safety concern.

I don't say don't do you experiments - but please do it together with someone who has experience.  Take great care to not touch anything conductive - but to be honest if "take great care to not touch anything conductive" is the whole safety consideration, then it´s too dangerous.

[MLXXXp]

Don't have a variac unfortunately.

The ZT-703S has two channels, so you could use the second channel as an external trigger. With this, you could create a setup that could trigger on a signal resulting from mains power being cut. A simple way would be to use a single pole double throw (two way) AC switch to switch the mains to the UPS on and off. When switched off, mains power that was feeding the UPS would be switched to the other pole of the switch. You could attach the scope's second channel probe to that pole and trigger on the detection of a high voltage on that channel. With the scope in single shot mode, you should be able to capture the switchover on the first channel, attached to the UPS output.

As has already been mentioned, be cautious that you're dealing with high AC voltages here.