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Electronics => Beginners => Topic started by: Cyclone1 on June 05, 2020, 10:05:05 am

Title: DMM max allowable common mode voltage ?
Post by: Cyclone1 on June 05, 2020, 10:05:05 am

Does DMM or DAQ have max common mode voltage rating before it blows up? Let's take the attached image for an example, is there a cap of how high V2 can be before it causes problem to the DMM?
Just wondering what would happen if it is exceeded, would v2 get shorted out ? What component in the DMM/DAQ dictate this limit? Is it clamping device, transformer or etc?

Title: Re: DMM max allowable common mode voltage ?
Post by: Kleinstein on June 05, 2020, 10:46:22 am

There is a limit to the common mode voltage. Normally this limit should be listed somewhere in the specs, though one may not find it with battery operated ones.

The limiting parts can be the case (with battery operated ones), the transformer or some DC/DC converter or opto-coupler.  In most cases there would be no defined clamping but just a chance to see arc over or isolation failure from some point on. Once an arc starts the voltage can drop relatively far.