EEVblog #417 - Fluke CNX3000 Wireless Multimeter Teardown

[Everett_Tom]

Thanks for the tear down.. Any idea when you'll have a chance to put them though their paces rather then just rip their guts out?

[EEVblog]

Thanks for the tear down.. Any idea when you'll have a chance to put them though their paces rather then just rip their guts out?

No idea. I have a ton of backlog.

Dave.

[Wytnucls]

You did learn that Fluke has no overvoltage protection, on the AC volt CATIII 1000V CATIV 600V module. 

I bet it does.
It's stamped as being independently CSA tested, so I'm sure it's been thoroughly tested and meets the CAT III and CAT IV standards as claimed. Fluke take this stuff seriously.
In this case they determined that the MOVs were not required like in regular multimeters. Probably due the direct input through suitable protections resistors designed for pulse transients.

Dave.

I don't doubt the Fluke module passed the CAT rating tests with high voltage transients, without any damage to the meter.
Against conventional wisdom, like I argued before, I just wanted to highlight the fact that PTCs and MOVs are not required on the Volt range of multimeters with high input impedance, as long as there is no chance of arcing on the volt traces and jacks. The currents involved stay within uA and mA magnitudes, even with high transients.
To be sure, a one dollar high voltage MOV can't be a bad idea, to be on the safe side.

[MartinX]

I don't doubt the Fluke module passed the CAT rating tests with high voltage transients, without any damage to the meter.
Against conventional wisdom, like I argued before, I just wanted to highlight the fact that PTCs and MOVs are not required on the Volt range of multimeters with high input impedance, as long as there is no chance of arcing on the volt traces and jacks. The currents involved stay within uA and mA magnitudes, even with high transients.
To be sure, a one dollar high voltage MOV can't be a bad idea, to be on the safe side.

I don't see the benefit of the MOV, as you say the current can be µA or mA and the meter will survive the transients without drama, why add the MOV and introduce the problems of kA currents and lots of peak power dissipation?

[fcb]

Why would a competent electronic design engineer add a MOV or any other component to a design "to be on the safe side"?

As Arthur Wellington said: "An engineer can do for a dollar what any fool can do for two"....

[NiHaoMike]

I think DC voltage and current measurement would be very useful, especially for alternative energy systems and automotive uses. DC voltage would be trivial to implement so I'm surprised that wasn't done. DC current would take a little more but something like a 400A range with a 1A or so resolution would be very useful for checking the starter motor in a car. Just put the clamp on the battery wire (and connect the voltage module if you need to), take the handheld unit inside, turn the key and now you know the condition of the starter circuit and battery.

Can the voltage and current modules sync up to measure AC power?

[BravoV]

I think DC voltage and current measurement would be very useful, especially for alternative energy systems and automotive uses. DC voltage would be trivial to implement so I'm surprised that wasn't done. DC current would take a little more but something like a 400A range with a 1A or so resolution would be very useful for checking the starter motor in a car. Just put the clamp on the battery wire (and connect the voltage module if you need to), take the handheld unit inside, turn the key and now you know the condition of the starter circuit and battery.

This is exactly what I thought, since the wireless feature, imagine hook up the DC current clamp wireless module at the battery wire while sitting inside the car facing the dashboard with the meter to read & trouble shoot the current consumption while switching on/off appliances in the car, definitely very handy & useful. Agree, DC 1 Amp resolution is good enough in automotive.

[Wytnucls]

I don't doubt the Fluke module passed the CAT rating tests with high voltage transients, without any damage to the meter.
Against conventional wisdom, like I argued before, I just wanted to highlight the fact that PTCs and MOVs are not required on the Volt range of multimeters with high input impedance, as long as there is no chance of arcing on the volt traces and jacks. The currents involved stay within uA and mA magnitudes, even with high transients.
To be sure, a one dollar high voltage MOV can't be a bad idea, to be on the safe side.

I don't see the benefit of the MOV, as you say the current can be µA or mA and the meter will survive the transients without drama, why add the MOV and introduce the problems of kA currents and lots of peak power dissipation?

The MOV would act as a crowbar across the input jacks in an overvoltage situation, immediately tripping the circuit breaker on the high voltage circuit under test, or at least reducing the internal voltage to a reasonable level .
Without it, the high voltage would remain on the traces and jacks, not necessarily compromising the module, but increasing the chances of an accident for anybody handling the module, with the only warning of a very high voltage present being an 'OL' message on the LCD screen.

[MartinX]

Yes MOV would trip the circuit breaker, if there is one that will trip before the meter melts down, if you wanted to destroy the meter now you would have to connect it to a voltage source of significantly more than the 1000v it is rated for, and that is gross misuse, you can't hold Fluke responsible for that. I think there is a good chance this meter goes though the EN/IEC 61010 testing without a hitch, working perfectly afterwords, no blown fuses or MOV's, simply withstanding the test voltage is an pretty elegant solution I think.

[Pat Pending]

None of this "Don't turn it on - take it apart" rubbish  Only kidding!

Head on over to the FCC ID search database and tap in T68 for the grantee code.
Here you'll find user manuals, internal photos and emc test reports.
Of course, the knack is in first locating the FCC code.

http://transition.fcc.gov/oet/ea/fccid/

[billclay]

Thanks for the tear down.. Any idea when you'll have a chance to put them though their paces rather then just rip their guts out?

No idea. I have a ton of backlog.

Dave.

Please check the "standby" current consumption.  Fluke blundered on their first wireless meter (the 233) in that aspect.

[billclay]

Did anyone notice this URL on the back of the main meter?  Doesn't seems to do anything useful though.

http://www.patentlabel.com/oem/fluke