Author Topic: DMM6500 or 34465A  (Read 2496 times)

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Offline TrickyNekro

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Re: DMM6500 or 34465A
« Reply #25 on: June 20, 2021, 06:43:35 pm »
Since I frequently need to access the 10A terminal, I find its front-panel location in the 34465A quite convenient in this regard.

To tell the truth, this also went on my nerves with the DMM6500 and a lot of people are commenting about it. It is not an absolute deal breaker,
I would guess that the 1A / 3A shunt is low voltage burden enough.

Last experience I had, was with a BLE IoT I was developing was ~7μA sleep current, 20 - 40mA (depending on the mode) working current, which I guess
you can get away with a higher burden voltage. But I guess, if you have some kind of small motor, valve or anything on there that draws a bit more,
then it could potentially become a problem.

But in the end of the day is it not a deal breaker, I could always wire the back panel to the front externally. Though yeah, at 1.2k€ you don´t really call it optimal.
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Online Kleinstein

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Re: DMM6500 or 34465A
« Reply #26 on: June 20, 2021, 07:54:13 pm »
For the higher current ranges, close to the limit of the fuses used, a large part of the buden voltage is often due to the fuse, not the actual shunt. The numbers in the spec sheet tend to be upper limites in this aspect. So the actual value may be a little lower.
Especially for the higher currents, the drop at the actual shunt is usually in the 100-200 mV or below range to avoid excessive heating. The rest is from the fuses and switches.

Measuring the supply current of a IoT thing is usually about the large dynamic range, but not much about absolute accuracy: nobody really cares if the average current is 100 µA or 110 µA, but the point is averaging current that may range from µA to 100 mA. If the burden is critical one may still want to use an external shunt resistor (and maybe an extra amplifier similar to the µCurrent), even though the absolute accurcy is relatively poor.In this case less protection can make the difference and a larger value for the shunt may be feasable than for high accuracy at the peak currents. For the short current peaks the circuit should have buffer caps.
 

Offline TrickyNekro

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Re: DMM6500 or 34465A
« Reply #27 on: June 20, 2021, 08:33:39 pm »
Measuring the supply current of a IoT thing is usually about the large dynamic range, but not much about absolute accuracy: nobody really cares if the average current is 100 µA or 110 µA, but the point is averaging current that may range from µA to 100 mA. If the burden is critical one may still want to use an external shunt resistor (and maybe an extra amplifier similar to the µCurrent), even though the absolute accuracy is relatively poor.In this case less protection can make the difference and a larger value for the shunt may be feasible than for high accuracy at the peak currents. For the short current peaks the circuit should have buffer caps.

To tell the truth a 10% difference when building something that should last a couple years on primary cells is not exactly inconsequential, but I get your point.
Usually sleep currents are around 1uΑ - 10uA, so you need to be accurate there.

The thing is that that´s your sleep current. If you got a auto-power on feature, say you activate some sensors, do some readings etc. to see if your device that has an analog input
is somehow excited and you need to wake-up the rest of the device, some of these sensors when converting can actually consume in the lower 10s of mA (say 20 - 40mA) add to that
a couple LEDs when waking up, plus a BLE radio, you can go well in the 40 - 50mA where the shunt burden voltage is then really a problem.

I really can´t decide between the two to tell the truth right now. The funny thing is that how the instruments function, it makes me want to buy a 34465A now, as a "daily" bench drive
and a DMM7510 later, when and if I need the extra resolution. Now, of course this is a hunch, but the Keysight instrument gives me the feeling that it was designed for engineers but
the Keithley was designed for scientists.

And since I guess I am a bit of both, I will probably stick long term to the plan above. But I will have to address the "typicality" of the low current measurement of the 34465A first.

If someone can provide some examples, that would be great!
« Last Edit: June 20, 2021, 08:35:20 pm by TrickyNekro »
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Offline bson

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Re: DMM6500 or 34465A
« Reply #28 on: June 20, 2021, 09:38:15 pm »
I use the low μA range on my 34465A very frequently.  The burden voltage doesn't really matter since the meter goes between the power supply and onboard regulation.  Just need to make sure the supply is set high enough to accommodate the meter.  Either along the cable or using a 2-pin header.  In the latter case I'll also add a jumper to disconnect on-board regulation to measure the regulator quiescent current (and to null the meter).  Since its upstream of regulation and filtering/reservoir, it's pretty low frequency stuff and the digitizer can do pretty good 5-digit captures of current consumption for various operations, just to get a quantitative transient energy cost for various things.  (Also very useful when trying to tweak things to reduce power usage.)  It can even measure the current consumption of an MSP430 in various sleep modes and do some low-current SMU style transient captures.  (Though it just captures the data, plotting and analysis needs to be done on a computer in python or what have you.)  Of course, a load resistor can be used and the voltage measured, it's just handy to have an instrument that's calibrated and plug-and-go.
« Last Edit: June 20, 2021, 09:40:56 pm by bson »
 
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Offline TrickyNekro

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Re: DMM6500 or 34465A
« Reply #29 on: June 25, 2021, 12:50:16 am »
I use the low μA range on my 34465A very frequently.

I found out what the "typical" in their datasheets meant from the dealership. If I recall it correctly, that means that 80% of the devices meets the spec presented on the datasheet.
Now of course I do not expect that the other 20% will be out and about.

It´s probably the one conservative side of the 2σ being ruffly ~1.5σ, which of course it is not 100% but I can probably live with it.

Especially now that the dealership came through with a very sweet deal plus they are the official Keysight distributor and they also handle repair and calibration.
At this price point I have to consider after-sales.

So 34465A it is.
Still thanks everybody for their input. It helped me negotiate a bit, but also gave me a clear view on the trade-offs (which I guess they are not many).

Cheers!
Lefteris
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Offline Bravo

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Re: DMM6500 or 34465A
« Reply #30 on: July 01, 2021, 02:26:06 pm »
If you need speed without connecting it to PC, the DMM6500 is what you need. I use mine for monitoring uA  current draw in graph mode mostly, but also to see fast pulse current draw.  Check out the YouTube demos by Keithley, especially the one  testing the current draw by a Bluetooth device. Very easy to set up from the front panel.   
 

Offline Dr. Frank

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Re: DMM6500 or 34465A
« Reply #31 on: July 01, 2021, 03:04:26 pm »
I use the low μA range on my 34465A very frequently.

I found out what the "typical" in their datasheets meant from the dealership. If I recall it correctly, that means that 80% of the devices meets the spec presented on the datasheet.
Now of course I do not expect that the other 20% will be out and about.

It´s probably the one conservative side of the 2σ being ruffly ~1.5σ, which of course it is not 100% but I can probably live with it.

Especially now that the dealership came through with a very sweet deal plus they are the official Keysight distributor and they also handle repair and calibration.
At this price point I have to consider after-sales.

So 34465A it is.
Still thanks everybody for their input. It helped me negotiate a bit, but also gave me a clear view on the trade-offs (which I guess they are not many).

Cheers!
Lefteris

Hello Lefteris,
as you have decided to purchase the 34465A - congratulations - make sure that after receipt of the instrument you apply for the free 2MB memory upgrade. That's very useful, and also really needed to make full use of the DIG option, which is already built in the firmware from # 3.0 onwards. In conjunction with the very good 1, 10 and 100µA DCI ranges, you will be able to monitor low currents on IoT applications.

https://www.keysight.com/de/de/cmp/promotions/free-memory-upgrade-for-bench-solutions.html

Maybe you also get the  BenchVue Software for your DMM free, w/o timely limitations, as it's currently promoted here in Germany.

https://www.keysight.com/de/de/lib/resources/installation-guides/benchvue-licenses-included-with-instruments-3046463.html

Please ask your KS salesman for details in Greece.

As you are SW experienced, I assume that you're able to write something better on your own.

Frank
« Last Edit: July 01, 2021, 03:15:18 pm by Dr. Frank »
 
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Offline bateau020

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Re: DMM6500 or 34465A
« Reply #32 on: July 02, 2021, 07:34:02 am »
Maybe you also get the  BenchVue Software for your DMM free, w/o timely limitations, as it's currently promoted here in Germany.

https://www.keysight.com/de/de/lib/resources/installation-guides/benchvue-licenses-included-with-instruments-3046463.html

Any idea why all the links that say "Basic instructions for how to redeem and activate this type of license" or "See instructions to check for eligibility and activation instructions." turn into "Page Not Found" (at least for a small list of EU countries I tried)? Is it over, or is that just a badly maintained website?
(Not that I personally would want to use it, as it is Windows only --requires me to launch a VM--, and I only have 1 Keysight instrument, so I don't see the use for me. TC or sigrok or python will do for me.)

About the low current measurements and digitizing, some feedback with my experiences and disillusions with this instrument. A "real" bench DMM brings a learning curve with it. Just hoping that the following might help others.

I bought the 34465A thinking it would be great for creating those fancy power-draw-over-time graphs, at high resolution. Yes, 50k samples/s is not much compared to the 1M samples/s of the DMM6500, but at least I would have "real" low current resolution.

Totally wrong. Totally naive. For 3 reasons:

1) autorange is disabled when digitizing, at least on a 34465A. You will need to pick a range, and accept the limitations of that range. Don't know about the DMM6500.

2) device bandwidth. DCI BW -3db = 10kHz (any range). Yes, the DMM6500 does significantly better on 100mA range: 340kHz, but drops to 25kHz on 1A. So when you measure a device that peaks to 200mA (easily the case when you do WiFi), the difference between the 2 instruments is not that big anymore. On both, more than 50k samples/sec is even useless. When you can stay below 100mA (or accept overloads), DMM6500 seems a lot better though.

3) resolution. The higher the sampling rate, the lower the effective resolution. When doing 10k samples/sec on the 1A range, the 34465A will give you 5 effective digits, so a 100uA resolution. Not great. The DMM6500 would give you 10uA. BUT, here is something that I cannot confirm, I only got it from the specs --"Typical Digitize Signal Characteristics"--, so I may misunderstand: the DMM6500 will not, and not even close, be able to deliver you that resolution. At that sample frequency, it will only give you 8 effective bits out of the 16. Your scope will likely do just as good or even better! You will gain 2 bits when going to the 100mA range though. Yay. Still not 5 digits though. The DMM6500 will even drop to 5 bits on the 10A range, over 10k samples/sec.

So it all depends on your needs, but you will need to read the fine print. A digitizing bench DMM is not a high resolution scope.
« Last Edit: July 02, 2021, 05:45:12 pm by bateau020 »
 
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Offline wizard69

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Re: DMM6500 or 34465A
« Reply #33 on: July 02, 2021, 11:29:33 pm »
In the end you need to fit the meter to your expected usage.    These days expanded diode test range may be valuable.   Low OHMs capability might be seen as a big positive in tracing PCB shorts.

As for inherent accuracy this is one of those things that I often lead with the question is it really that important?   Very often it isn't.   These are 5.5 digit and more meters and frankly I'm not sure many people look a the last digit in the display to determine if they have the right value.   If they do, most likely they already know what specs are needed, the required calibration schedule and have resolved a host of other factors impacting the reading.    So unless you have a specific requirement to squeeze every bit of accuracy out of a meter of this type I really wouldn't worry about the specs much.
 

Offline bson

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Re: DMM6500 or 34465A
« Reply #34 on: July 04, 2021, 07:11:07 pm »
You need greater precision than accuracy, and you need 5.5d accuracy to characterize a 16-bit ADC or DAC.  So in practice you want a 6.5d instrument for this.  You're not supposed to look at the last digit, it's just there for precision.  You care about the second least significant digit.

But of course, you may have a bit of output gain as well and a range that calls for a 7.5d instrument in many cases.
« Last Edit: July 04, 2021, 07:14:35 pm by bson »
 


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