Author Topic: Dual impedance multimeter recommendations?  (Read 3296 times)

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Offline 2N3055

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Re: Dual impedance multimeter recommendations?
« Reply #25 on: August 07, 2019, 07:03:52 am »
Circuit uses same PTC as for protection, one or few of them , with surge rated resistor in series, to limit initial current and to have current limit in case something goes wrong with PTC .
It starts at 3 kOhm (I presume Fluke one will have 1.1k PTC and 2.2k surge rated resistor in series) when cold (25°C) and then resistance of PTC goes up in megaohm range when heated. So much lower current later.

P.S. Found the mentioned video, Fluke probably uses two 1.1 K PTC  (like the YS4020) and one 1k surge resistant resistor in series.
« Last Edit: August 07, 2019, 07:25:01 am by 2N3055 »
 

Online HKJ

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Re: Dual impedance multimeter recommendations?
« Reply #26 on: August 07, 2019, 07:10:59 am »
...then resistance of PTC goes up in megaohm range when heated. So much lower current later.

Not really, as you can see on my curve above. Typically a bit above 1 Watt is needed to keep the PTC heated, this means at around 1000V it might just reach 1Mohm.
 

Offline 2N3055

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Re: Dual impedance multimeter recommendations?
« Reply #27 on: August 07, 2019, 07:37:59 am »
...then resistance of PTC goes up in megaohm range when heated. So much lower current later.

Not really, as you can see on my curve above. Typically a bit above 1 Watt is needed to keep the PTC heated, this means at around 1000V it might just reach 1Mohm.

That is what I said.  ^-^  It reaches order of magnitude of megaohms when heated.  I wasn't talking about voltage coefficient..
In Fluke adaptor they use two in series, so heating will be divided between the two of them.

How did you measure that curve? Did you sweep the voltage in one go, or did you measure current at voltage points one by one, letting it cool down for few minutes. If you did a sweep, did you wait at discrete points for it to reach thermal equilibrium? It would be interesting to know the method.
Also what would be interesting is to record current with a scope on connect to see how it draws larger current in the beginning, and how that curve is different at different voltages......
 

Online HKJ

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Re: Dual impedance multimeter recommendations?
« Reply #28 on: August 07, 2019, 08:42:15 am »

That is what I said.  ^-^  It reaches order of magnitude of megaohms when heated.  I wasn't talking about voltage coefficient..
In Fluke adaptor they use two in series, so heating will be divided between the two of them.

100kOhm at 250V is hardly in the megaohms magnitude.


How did you measure that curve? Did you sweep the voltage in one go, or did you measure current at voltage points one by one, letting it cool down for few minutes. If you did a sweep, did you wait at discrete points for it to reach thermal equilibrium? It would be interesting to know the method.

I sweep the voltage measuring in 1V steps from 10 to 250V, each point takes 1 second, i.e. a total of 4 minutes for the test.

 

Offline Electro Detective

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Re: Dual impedance multimeter recommendations?
« Reply #29 on: August 07, 2019, 10:15:36 am »
youtube.com/watch?v=IOoJmMBE5D8

The not impressed Youtuber paid 80 bucks (US?) for a boutique 3K resistor and PTC (50 cent total?) in a plastic box,
that appears to have been spit soldered with lashings of planned obsolescence and assembled at ThreeHungLow Industries
with perhaps a QC (Questionable Crap) sticker
slapped on by ailing wheelchair bound honorable great great grandad gathering peanuts for the grandkids to go to school and or eat  :clap:

Just how much percentage are the shareholders demanding, or the brokers that stitched up their life savings promising nowadays?  :-//

I don't even want to think how much this toy costs today in Kangaroo Land,
I bought an unloved unused 114 and NEW Klein meter (both with Low-Z) for the same price a while back,
as one of these overpriced Low-Z interfaces, stashed inside a repurposed USB charger housing.

You could chain solder the 3 components, put the lot in a clear zip lunch bag with flying leads,
save a bundle,
inspection and servicing would be a breeze    :-+

;D



« Last Edit: August 07, 2019, 10:32:00 am by Electro Detective »
 
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Offline 2N3055

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Re: Dual impedance multimeter recommendations?
« Reply #30 on: August 07, 2019, 10:38:38 am »

That is what I said.  ^-^  It reaches order of magnitude of megaohms when heated.  I wasn't talking about voltage coefficient..
In Fluke adaptor they use two in series, so heating will be divided between the two of them.

100kOhm at 250V is hardly in the megaohms magnitude.


How did you measure that curve? Did you sweep the voltage in one go, or did you measure current at voltage points one by one, letting it cool down for few minutes. If you did a sweep, did you wait at discrete points for it to reach thermal equilibrium? It would be interesting to know the method.

I sweep the voltage measuring in 1V steps from 10 to 250V, each point takes 1 second, i.e. a total of 4 minutes for the test.
Thank you for details.
FYI looking at the datasheet for a Vishay PTC and it is 1 Meg at 135C and 10 Meg at 150C. It is 100k at cca 130C. Slope is very steep at that point, ambient temp will have large influence together with thermal design.
Regards..
 

Offline 001

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Re: Dual impedance multimeter recommendations?
« Reply #31 on: August 07, 2019, 12:10:48 pm »
youtube.com/watch?v=IOoJmMBE5D8

Thanx  a lot

Color code at 2:17 says resistor is only 17 Ohm?   (I can be confused with my monitor color and eyes) What real values of two PTCs and resistor are?
« Last Edit: August 07, 2019, 12:13:32 pm by 001 »
 

Offline Shock

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Re: Dual impedance multimeter recommendations?
« Reply #32 on: August 07, 2019, 01:28:03 pm »
Been already discussed in this other thread, I read the value as 1K which makes sense, it looks like brown black red gold red in the video. https://www.eevblog.com/forum/testgear/brymen-bm867-bm869/

Looking inside the Fluke 117 confirms the resistor and PTCs are there.




« Last Edit: August 07, 2019, 02:36:17 pm by Shock »
Soldering/Rework: Pace ADS200, Pace MBT350
Multimeters: Fluke 87V, 117, 27/FM       >>> WANTED STUFF <<<
Oszilloskopen: Lecroy 9314, Phillips PM3065, Tektronix 2215a, 314
 
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Offline Per Hansson

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Re: Dual impedance multimeter recommendations?
« Reply #33 on: August 07, 2019, 07:52:03 pm »
youtube.com/watch?v=IOoJmMBE5D8

The not impressed Youtuber paid 80 bucks (US?) for a boutique 3K resistor and PTC (50 cent total?) in a plastic box,
that appears to have been spit soldered with lashings of planned obsolescence and assembled at ThreeHungLow Industries
with perhaps a QC (Questionable Crap) sticker
slapped on by ailing wheelchair bound honorable great great grandad gathering peanuts for the grandkids to go to school and or eat  :clap:

Just how much percentage are the shareholders demanding, or the brokers that stitched up their life savings promising nowadays?  :-//

I don't even want to think how much this toy costs today in Kangaroo Land,
I bought an unloved unused 114 and NEW Klein meter (both with Low-Z) for the same price a while back,
as one of these overpriced Low-Z interfaces, stashed inside a repurposed USB charger housing.

You could chain solder the 3 components, put the lot in a clear zip lunch bag with flying leads,
save a bundle,
inspection and servicing would be a breeze    :-+

;D
I agree with your post, the price is just silly, for me I use it for work.
But I also just want to highly underline that there is another side to this, safety:
The Adapter is specified for CAT III 1000V/CAT IV 600V per EN61010.

I use my SV225 for a secondary purpose: to discharge capacitors in servos, as can be seen in the curve above it's not the best, but so far it has been useful to me.
Now imagine what would happen with an adapter actually assembled at ThreeHungLow Industries as you say.
Here I will give an idea: https://youtu.be/OEoazQ1zuUM?t=345
Just something to keep in mind when measuring high energy circuits which is the whole idea if you need this adapter in the first place.
I agree that buying a meter with LoZ mode is better, be careful though: I thought my Fluke 28-II had such a mode but it's a low pass filter, not low impedance!
 
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Offline 001

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Re: Dual impedance multimeter recommendations?
« Reply #34 on: August 07, 2019, 07:59:02 pm »
Been already discussed in this other thread, I read the value as 1K which makes sense, it looks like brown black red gold red in the video

Thank You!

I google for PTCs but most of them have limited work cycles about 100 only

What PTCs are used by FLUKE?
 

Offline Electro Detective

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Re: Dual impedance multimeter recommendations?
« Reply #35 on: August 07, 2019, 10:05:55 pm »

I agree with your post, the price is just silly, for me I use it for work.
But I also just want to highly underline that there is another side to this, safety:
The Adapter is specified for CAT III 1000V/CAT IV 600V per EN61010.

I use my SV225 for a secondary purpose: to discharge capacitors in servos, as can be seen in the curve above it's not the best, but so far it has been useful to me.
Now imagine what would happen with an adapter actually assembled at ThreeHungLow Industries as you say.
Here I will give an idea: https://youtu.be/OEoazQ1zuUM?t=345
Just something to keep in mind when measuring high energy circuits which is the whole idea if you need this adapter in the first place.
I agree that buying a meter with LoZ mode is better, be careful though: I thought my Fluke 28-II had such a mode but it's a low pass filter, not low impedance!

TBH I would rather have the resistor and PTC inside a CAT rated meter housing, that I can physically check on,
rather than a glued up re-purposed USB box with a CAT rating,
that may have been soldered together and gooped up by a friday afternoon pub crawling assembler  ::)

and yes, I use the Low-Z mode for poor mans discharging duties as well, and may wait a while...  :=\

Still a better bet than dealing with surprise zaps  :o


EDIT:
Zap City  > youtube.com/watch?v=oahQRSRx_38

Every New Yorker should be issued with a Low-Z accessory and app for their phones   :popcorn:

« Last Edit: August 07, 2019, 10:31:49 pm by Electro Detective »
 

Offline rauldm

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Re: Dual impedance multimeter recommendations?
« Reply #36 on: September 08, 2019, 04:30:35 am »
If you consider buying used, there is also the Metrahit12/14 from GMC (look for a thread named 'show your multimeter', there you can see mine.)
Also, some of the newer GMC multimeters have such a feature.

Really I didn't know nothing Metrawatt meters, I impressed with the price, normally all brands it has a high-end models to same price, Metrawatt is really expensive even with same specs, also I impressed with high-end are very especialized, for example the CAT rating is to low but 6.5 digits in a portable device is amazing. I think this meters play on other scale of market. I have Fluke 289, 28II, 87V and 117, also  keysight U1282A and Amprobe 37XR-A.
 

Offline BB3553AM

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Re: Dual impedance multimeter recommendations?
« Reply #37 on: April 14, 2020, 05:47:16 pm »
Dear HKJ,

my sincere thanks and congratulations on your website : https://lygte-info.dk/review/DMMBrymen%20BM869s%20UK.html
I just bought a BM869s and a AN870 based on your reviews.

( I have a question about the AN870, but let's not pollute this thread)

regarding the PTC that were observed, are we able to identify the part number ?

I plan to do my own low impedance "network" for lowZ measurement , we can see indeed to 2 PTC on either side and a power resistor in the middle of those in this video about the sv225.

Thanks for help.
 

Offline BB3553AM

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Re: Dual impedance multimeter recommendations?
« Reply #38 on: April 14, 2020, 09:05:20 pm »
Maybe this (family of) device could do the job ?

https://www.vishay.com/docs/29072/ptccl.pdf

 

Offline Per Hansson

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Re: Dual impedance multimeter recommendations?
« Reply #39 on: April 15, 2020, 04:15:39 pm »
Not sure about the part number for the PTC.
But it would make sense that they reuse the same PTC as in their meters?
Check out some schematics for Fluke DMM's, some do exist for their slightly older models...
 

Offline BB3553AM

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Re: Dual impedance multimeter recommendations?
« Reply #40 on: April 15, 2020, 08:20:23 pm »
Thanks for your contribution.

I think the C885 from epcos (now tdk) should be a good match : https://www.mouser.com/datasheet/2/136/OC_B59884_B59885_B59886-62199.pdf

By using 2 of them plus a 4w resistor of 1KOhm, we could achieve something very close to the sv225.

 

Offline Shock

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Re: Dual impedance multimeter recommendations?
« Reply #41 on: April 15, 2020, 11:16:01 pm »
I checked a couple of Fluke service manuals with parts listings and got 1.1k 20% tolerance for the PTCs. Part numbers were YS3961 and 911P67E112MW07.

What about B59774C0115A070 it's 1.1k.
I get the feeling Fluke has special order part dimensions for their MOVs and PTCs so if they are ever going into a multimeter check that first. I suspect they are probably manually sorted as well as 3.6K is a bit out there.
Soldering/Rework: Pace ADS200, Pace MBT350
Multimeters: Fluke 87V, 117, 27/FM       >>> WANTED STUFF <<<
Oszilloskopen: Lecroy 9314, Phillips PM3065, Tektronix 2215a, 314
 

Offline BB3553AM

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Re: Dual impedance multimeter recommendations?
« Reply #42 on: April 16, 2020, 10:45:42 am »
Thank you Shock for the information. Much appreciated.

Indeed, the B59774C0115A070 is also a very good option.
« Last Edit: April 16, 2020, 12:24:49 pm by BB3553AM »
 


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