EEVblog #417 - Fluke CNX3000 Wireless Multimeter Teardown

[EEVblog]

Inside Fluke's new CNX3000 Wireless Multimeter.
Also, the CNX t3000 K-Type Thermocouple, CNX i300o iFlex probe, CNX v3000 wireless ac voltage meter, and CNX a3000 wireless ac clamp meter.

http://youtu.be/0Pplmg9Seao

Dave.

[petemate]

So, did you try pressing the internal CAL button?

[EEVblog]

So, did you try pressing the internal CAL button?

That would not be wise unless you intend to calibrate it...

Dave.

[madires]

AFAIK thermocouples just measure the temperature difference between the object they "touch" and the ambient. To get a absolute temperature you need to measure the ambient temperature too. That's the internal temperature sensor thermally coupled with the jacks.

[EEVblog]

AFAIK thermocouples just measure the temperature difference between the object they "touch" and the ambient. To get a absolute temperature you need to measure the ambient temperature too. That's the internal temperature sensor thermally coupled with the jacks.

Yes.
That's why multimeters that have temp probe ability can also (usually) display the ambient temp as well, because of the required built in temp sensor.
But in the case of every multimeter I've ever seen, they don't do cold junction compensation like you see in the CNX as such, they just use the general internal ambient temp of the meter. It's pretty crusty.

Dave.

[justanothercanuck]

The wires on that clip-on ammeter look rather thin for 400 amps...  Is that normal?

[EEVblog]

The wires on that clip-on ammeter look rather thin for 400 amps...  Is that normal?

Yes, it's a current transformer. There would be a huge turns ratio, giving only a small fraction of the 400A full scale on the secondary winding.

Dave.

[Lightages]

Sorry Dave, but that was one of the least interesting videos you have done for a long time. Not because of you, but the subject matter was rather repetitive and there was nothing to learn or see really.

I guess you never know until you open things up but....

[EEVblog]

Sorry Dave, but that was one of the least interesting videos you have done for a long time. Not because of you, but the subject matter was rather repetitive and there was nothing to learn or see really.

Well, yeah, it's a multimeter...

Dave.

[BravoV]

Just wonder why there is no wireless DC current measurement module using hall sensor (current clamp) for huge DC Amps range.   

[retiredcaps]

Not because of you, but the subject matter was rather repetitive and there was nothing to learn or see really.

It may not be educational not for many advanced eevblog members, but I found the video blog interesting and will be watching it multiple times over the next several weeks to catch all the little nuances.

Thanks Dave. 

[dougg]

Just wonder why there is no wireless DC current measurement module using hall sensor (current clamp) for huge DC Amps range.   

I'll second that. Actually I would like a small DC amp range (resolution around 1 mA) using a hall sensor.

And Dave, please say after me: "intr-est-ing, intr-est-ing". The word might look like it has 4 syllables, but not when it is pronounced in English, Canadian and Australian. Please consult your Macquarie dictionary :-)

[BravoV]

Just wonder why there is no wireless DC current measurement module using hall sensor (current clamp) for huge DC Amps range.   

I'll second that. Actually I would like a small DC amp range (resolution around 1 mA) using a hall sensor.

Don't think low amp range like mA is easy or at least cheap when using current clamp style, at least not for this technician/field grade market multimeter. I was expecting like a high current DC like hundreds Amp range up to 1000 Amps, and probably with 100mA resolution, that sounds more suitable for the targeted market.

High resolution and low current clamp meter in mA domain is quite a niche market and more suitable for lab grade/desktop measurement rather than field work, cmiiw.

[madires]

That's why multimeters that have temp probe ability can also (usually) display the ambient temp as well, because of the required built in temp sensor.
But in the case of every multimeter I've ever seen, they don't do cold junction compensation like you see in the CNX as such, they just use the general internal ambient temp of the meter. It's pretty crusty.

Had any of those multimeters a dedicated terminal for thermocouples or just used the COM and V banana jacks or some cheap jack for the thermocouple plug? The CNX is designed well, the thermally coupled internal temperature sensor and the large thermal mass acting as a low pass filter. A typical handheld multimeter has no space for that.

[Wytnucls]

Sorry Dave, but that was one of the least interesting videos you have done for a long time. Not because of you, but the subject matter was rather repetitive and there was nothing to learn or see really.

I guess you never know until you open things up but....

You did learn that Fluke has no overvoltage protection, on the AC volt CATIII 1000V CATIV 600V module. 
Safety compliance: EN/IEC 61010-1:2010 to 1000 V Measurement Category (CAT) III
600  V Measurement Category (CAT) IV EN/IEC 61010-2-030:2010
EN/IEC 61010-031:2002+A1:2008

[Lightages]

Remember that the standards don't say that the meter has to survive and still work, just that any failure mode does not cause harm to the user. It is quite possible that the meter melts down inside but does not expose the user to anything during tests.

[Wytnucls]

I would expect such an argument from UNI-T, not so much from Fluke. 
But, they do have a lifetime warranty.

[Neilm]

The molded plastic around the fixing screws (12:20 ish) could also be providing a clearance to the screw from the PCB. If they were not there it looked as if it was close enough to jump in a transient situation. Tests are suppose to be done to "all exposed metal" after all.

Neil

[CarlG]

Just wonder why there is no wireless DC current measurement module using hall sensor (current clamp) for huge DC Amps range.   

How many amps do you need? More than 500 Arms? Otherwise this might do? But maybe you were thinking of something handheld?

EDIT: I put Tek A6304XL in as well as it has 700A peak, but under protest, since Tek needs you to sign in to get the datasheet

[CarlG]

Just wonder why there is no wireless DC current measurement module using hall sensor (current clamp) for huge DC Amps range.   

I'll second that. Actually I would like a small DC amp range (resolution around 1 mA) using a hall sensor.

Just as an example Agilent N2821A, but maybe you also where thinking of something handheld...or something cheaper I don't know the price but they're usually not cheap...(strange, the price of their stuff is normally displayed on Agilents site)

[MartinX]

You did learn that Fluke has no overvoltage protection, on the AC volt CATIII 1000V CATIV 600V module. 
Safety compliance: EN/IEC 61010-1:2010 to 1000 V Measurement Category (CAT) III
600  V Measurement Category (CAT) IV EN/IEC 61010-2-030:2010
EN/IEC 61010-031:2002+A1:2008

There may not be any need for over voltage protection components, if the input hybrid resistor can withstand the full test voltage then nothing will happen, there seems to be plenty of clearance to other parts in the design and the hybrid resistor looks like it could possibly take a 10kV pulse, and we have no input selector switch, ohms measurement or other stuff that may complicate things.

[Jovian]

AFAIK thermocouples just measure the temperature difference between the object they "touch" and the ambient. To get a absolute temperature you need to measure the ambient temperature too. That's the internal temperature sensor thermally coupled with the jacks.

Yes.
That's why multimeters that have temp probe ability can also (usually) display the ambient temp as well, because of the required built in temp sensor.
But in the case of every multimeter I've ever seen, they don't do cold junction compensation like you see in the CNX as such, they just use the general internal ambient temp of the meter. It's pretty crusty.

Dave.

In addition to this. One does not need to compensate for the input connectors as the junctions are in reverse polarity, so they compensate themselves.
Also thermocouples give a voltage indicating the difference between the probe tip and the connector case, so one needs to know the temperature of the connector to get the absolute temperature.

Regards,
Jovian.

[BravoV]

Just wonder why there is no wireless DC current measurement module using hall sensor (current clamp) for huge DC Amps range.   

How many amps do you need? More than 500 Arms? Otherwise this might do? But maybe you were thinking of something handheld?

EDIT: I put Tek A6304XL in as well as it has 700A peak, but under protest, since Tek needs you to sign in to get the datasheet

Do you realize the price of those "scope's" probe you quoted ? Those way over kill just for measuring plain slow current for handheld at field work.

Yes, I meant handheld meter (not a scope of course) DC current clamp, something comparable like this here -> U1213A that capable of "DC" up to 1000 Amps.

[EEVblog]

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.

[Paul Moir]

Being a Canuck, some of the things I see CSA stamp just makes me shake my head.

[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