Author Topic: Fluke 8845A experience/opinions ?  (Read 5148 times)

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Offline Soertier

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Fluke 8845A experience/opinions ?
« on: December 07, 2012, 07:27:51 am »
I have the chance to buy a Fluke 8845A at a good price. Now the question is what is the reliability of these instruments and how much they drift per year. I would actually buy a HP Agilent 34401A, however I really need to measure high currents at low voltages (3V-4V) and the 34401A is poor in that regard due to it's high burden voltage.

I read quite some criticism on this forum regrading the 8845A/8846A boot times and OS and the banana plugs being brittle.

Are there any persons from cal labs around here which have some facts on the 8845A? Does the instrument stay in spec well (voltage resistance) compared to 34401A?
Or are any users of the 8845A that frequently check how well stays in spec?
 

Offline nukie

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Re: Fluke 8845A experience/opinions ?
« Reply #1 on: December 07, 2012, 01:01:11 pm »
Three of my 34401A (year 1992, 1995, 1998) did not drift much. I bought all of them used, burn in for 4000 hours then sent it in for calibration. They were bought separately many ages ago. They stay in spec till today. I use three LTZ1000 powered as my references. They are also burned in for 4000 hours then voltage verified at a lab.

If you want absolute stability and very little long term drift, get the Keithley 2000. I have one used and it stayed true to the last digit for the pass 5 years.

The slow boot up of the 8845A would not be a problem if you run a lab most equipment would be on for long hours. 8845A is a newer device compared to the 34401A. I prefer Agilent products the vfd module is plenty for $100 if it dims after a few years.

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« Last Edit: December 07, 2012, 01:12:32 pm by nukie »
 

Offline Kibi

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Re: Fluke 8845A experience/opinions ?
« Reply #2 on: December 07, 2012, 01:17:20 pm »
Not a 8845A, but the same family I suppose, my 8840A which is very old is spot on accuracy wise.
I did a tear down and repair of it recently. Details on this thread.

https://www.eevblog.com/forum/reviews/fluke-8840a-teardown-and-repair/
 

Offline robrenz

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Re: Fluke 8845A experience/opinions ?
« Reply #3 on: December 07, 2012, 01:20:05 pm »
Rant mode on

As a very happy 8846A owner I don't get where the 15 second boot time has any relevance on a meter that has a specified 1 hour warm up time for stated accuracy :-//
Trend plot shows the meter is fully stable in 30 Min's.

Rant mode off

Offline Soertier

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Re: Fluke 8845A experience/opinions ?
« Reply #4 on: December 07, 2012, 01:47:51 pm »

If you want absolute stability and very little long term drift, get the Keithley 2000. I have one used and it stayed true to the last digit for the pass 5 years.


Keithely 2000 is in the same boat with 34401A when it comes to current measuremnts due to high burden voltage and low voltage circuits (3A-4V) at high currents ( 2A-4A) will be result in useless readings.
I have heard that the Keithley 2000's stay well in spec (what I am looking for), however I see most of them sold as defect of partially defect which is not enouraging at all for me.
 

Offline Soertier

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Re: Fluke 8845A experience/opinions ?
« Reply #5 on: December 07, 2012, 03:20:10 pm »
Not a 8845A, but the same family I suppose, my 8840A which is very old is spot on accuracy wise.
I did a tear down and repair of it recently. Details on this thread.

https://www.eevblog.com/forum/reviews/fluke-8840a-teardown-and-repair/

The 8845A/8846A are quite different, OS, display, specs, etc.
 

Offline grenert

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Re: Fluke 8845A experience/opinions ?
« Reply #6 on: December 09, 2012, 08:14:39 pm »
Is the burden voltage any different on the newer 34410A?
 

alm

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Re: Fluke 8845A experience/opinions ?
« Reply #7 on: December 09, 2012, 08:24:06 pm »
Better at the low current ranges (and it has additional low current shunts), but similar at high currents.
 

Offline kxenos

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Re: Fluke 8845A experience/opinions ?
« Reply #8 on: December 09, 2012, 08:26:53 pm »
I have 2 fluke 45 bought in 1999. They where calibrated some months ago for the first time (they are being used for repairs so calibration was not required) and I can report that the one that was used all the time was on spec. The other one was just a bit off and had to be reset to spec. I believe that this applies to 8845 as well. Go for it, you won't regret it!
 

Offline grenert

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Re: Fluke 8845A experience/opinions ?
« Reply #9 on: December 10, 2012, 02:04:25 am »
If burden voltage is your primary concern, why not just buy or build an external shunt?
http://www.precisionresistor.com/MS-40-Shunt/

That company will make you one with a sense resistor as small as 1 mOhm.
 

Offline Zad

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Re: Fluke 8845A experience/opinions ?
« Reply #10 on: December 10, 2012, 03:15:48 am »
Or better still, make yourself a transimpedance amplifier, its no harder than uCurrent style shunt and has zero burden.

Offline Soertier

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Re: Fluke 8845A experience/opinions ?
« Reply #11 on: December 10, 2012, 01:38:46 pm »
If burden voltage is your primary concern, why not just buy or build an external shunt?
http://www.precisionresistor.com/MS-40-Shunt/

That company will make you one with a sense resistor as small as 1 mOhm.

Measuring the voltage across a shunt would be nice. Say I have a precise current like 3.85A, then with a 0.001Ohm shunt, that would be 0.003850V.



Well the main use would not be to measure current, but I thought it would be a pity not to be able to measure it, because the 34401A or Keithley 2000 are not good at 3-4A on 3-4V circuits ( especially the 34401A with 2.5V burden voltage at 4A). If you think about that, then you can say there is no current measurement feature.
My main concern is how does the 8845A stay in spec (mainly DCV and Resistance), maybe it's a "drifter"?
So if the 8845A would stay in specs the same as 34401A then that would be great considering the extra capabilities, like current.


 


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