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Author Topic: Note: Keysight U1272A U1273A U1273AX ZLOW circuit is ON when range switch is OFF  (Read 4763 times)

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Online Kiriakos GR

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This is an information which I discovered all by my self at 2025.

By testing my new single phase bench-top AC power meter, this be especially designed for low power AC.
I did notice that ZLOW circuit is ON, even when DMM range switch is at OFF position.
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(It is no surprise to me, that this details never spotted before due wannabe product reviewers. :P
Because a in-depth organized product review, this requires a proper strategy, along personal skills, and allot of time at testing.)

I am currently perform an assessment at ZLOW circuit, because by the way that is implemented, its working as a permanent connected resistor in parallel to test leads.

This information matters, to the ones whom leave DMM test leads connected to a power source, and then they just switch OFF the DMM.   

I will get back with more information's, regarding caused loading at a range of voltages.
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Online Kiriakos GR

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It is amazing of how much of help it is the sum of my current tool-pack.   8)

DCUU PM9913 + data logging software (power meter)
FLK 8846A + TsDMMViewer data logging software 

And both instruments recording all the action simultaneously, of my U1272A with it range switch at OFF position. 

The test executed by active AC power supply, this stabilized at 225V, by the use of VARIAC transformer I do boost that at 230V ( both devices able to deliver 2KVA of power).   
-----------------------------------------------------------------------------
Test results along comments.

U1272A with it range switch at OFF and or at ZLOW position, due it internal Low impedance mode, this causes at fist connection to mains, a load of 41 Watt at 230V AC.
U1272A electronics circuit, will be called to handle high current condition for 3 seconds of time,and a peak of 178.8 mA.
U1272A electronics circuit, will self adjust within 5 seconds of time, and the loading this is now approximately 30mA
U1272A electronics circuit, will self adjust within 30 seconds of time, to a much lower current of 3.2 mA.

By the eyes of electric energy, U1272A causes 41 Watt peak value and 0.72 Watt of a constant load, for as long this stays connected to mains.
At the charts below they are plenty of information's.

At my eyes, it seems as very interesting even the Power Factor curve.
For a first time since ITTSB Europe foundation, I have such a complete set of recorded results.  8)
I can dive to more timing details by adjusting TsDMMViewer data logging software, and to set as first option of chart length, a window of 30 seconds, so to better record inrush current.  :)

About comments, I do not think that ZLOW as a Low impedance mode, this has any electronic design flaw.
Never read any customer feedback, that any of these U1272A, U1273A and U1273AX has been damaged at ZLOW circuit.
What I am exploring here this is the behavior of ZLOW.
For example at 1000V ACV or DCV, the instant loading, this might be four times higher = 164 Watt
And therefore I bet that Agilent / Keysight, it did their math at product design room, and any passive components that they did select, they are able to tolerate this inrush current with out damage.

My next data logging adventure  will be to record ZLOW behavior, with starting voltage of 15V, because I do perform long term 12V battery monitor, so to inspect top up charging events, at my APC UPS,  in this application I have two U1272A constantly connected at two battery cells.

After this new test, I will be able to decide of what is best?
Leaving then connected at DCV and use Auto power OFF timer, or to switch them OFF by the range switch? ;)
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Online Andrew-88

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It is amazing of how much of help it is the sum of my current tool-pack.   8)

DCUU PM9913 + data logging software (power meter)
FLK 8846A + TsDMMViewer data logging software 

And both instruments recording all the action simultaneously, of my U1272A with it range switch at OFF position. 


Excellent delivery of screenshots!
Your new DCUU PM9913, this appear as damn accurate to me  ;) 

Offline overvolt

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The HIOKI DT4282, this is another DMM with unusual impedance.
This has fixed impedance at 1 M Ohm.
According to Ohms Law......

1 M Ohm
230V
0.23 mA
52.9 milliwatt (0.0529) Watt  ;)


   

Online Kiriakos GR

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The HIOKI DT4282, this is another DMM with unusual impedance.
This has fixed impedance at 1 M Ohm.
According to Ohms Law......

1 M Ohm
230V
0.23 mA
52.9 milliwatt (0.0529) Watt  ;)


1) 0.23 mA confirmed by Fluke 8846A (A good proof that my unit this has spot on, calibration).  8)

2) 52.9 milliwatt ..  this value is at the threshold, in which DCUU PM9913, this begins to deliver power measurements.
Even so, the internal CT, this managed to sense and measure 0.36 mA as Average.
And regarding AC power,  61 milliwatt (0.061) Watt  8)

3) HIOKI DT4282 when entered at APS mode (Automatic power saving) a tiny change shown at it impedance.
Only the Fluke 8846A succeed to sense it and record it.  :)

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Online Kiriakos GR

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Not impedance measurement, but my 1M GST4020 0.25% from my calibration box.
These resistors can work up to 4000V.
Room temperature 18C.

My 8846A this recorded a more noise free 0.23 mA, at this 15 minutes test.
The screenshot below its truly impressive8)
 
The stability of my ACV power supply this is also impressive, 230.0 up to 230.1 ACV for more than two hours.   ;)
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Online Kiriakos GR

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My next data logging adventure  will be to record ZLOW behavior, with starting voltage of 15V, because I do perform long term 12V battery monitor, so to inspect top up charging events, at my APC UPS,  in this application I have two U1272A constantly connected at two battery cells.

After this new test, I will be able to decide of what is best?
Leaving then connected at DCV and use Auto power OFF timer, or to switch them OFF by the range switch? ;)

Did that testing at 2019   ;)
Testing of a battery with Z-low -- Keysight U1272A & U1273A multimeter
https://www.ittsb.eu/forum/index.php?topic=1554.0
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Online Kiriakos GR

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Here is a pack of Ohms measurements of my three U1272A.

Environmental temperature 13C (Winter time).
These are K Ohms at high resolution due my 8846A.
Sample 1:  1.80675   
Sample 2:  1.93138
Sample 3:  1.97465   

Agilent / Keysight at different documents it deliver different numbers.
They inform of 1.82 K Ohm,  but they give a nominal value of 2.0 K

Naturally at this ZLOW circuit, they are not used metrology class components.
And its difficult to asses the measurement results, what ever these might be.
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Offline overvolt

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An PTC 1.6K Ohm it might have tolerances 20%, I do not think that Agilent / Keysight did use any magical parts either.
Its a good though, that Kiriakos delivered actual measurements of U1272A ZLOW, within the past 15 years, no one did that before.
 
Kiriakos thank you for the HIOKI DT4282 confirmation measurements.     

 

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