Agilent E3632A calibration

[yo0]

hello to all!, the 0.01 ohms 0.01% resistor value called in the service manual for current calibration is critical? can be subs with let say 0.06, 0.12, 0.22 etc? same about tolerance, seems dificult find 0.01% resistors in those ohms values.

any help will be really appreciated.


best regards.


Pio

[Muxr]

There is usually a good reason why they specified that tolerance.

With that said if you're really in a bind. You could substitute 0.01 ohms resistor with 6x 0.06 resistors in parallel. This will bring the resistance down to 0.01 Ohm. Your current reading may be a bit off, but since it's a PSU it's not that critical.

[Ordinaryman1971]

There are 0.01 resistors with 1% tolerance available for about a $1 a piece, I would just buy few... well, lets say 10 and measure them with some fancy miliohm meter and just pick your winner. If you are lucky, you got yourself a nice as-close-as-possible resistor for your current calibration for about $10.

[yo0]

thank you both for your valuable advices, just a question wich size is enough for that use? 1, 2, 3, 5 watts?



best regards.


Pio

[HighVoltage]

The E3632A Power Supply has a maximum current of 7A in the 15V range.
With a resistor of 0.01 Ohm you have only 1/2 Watt in power dissipation.

But ...
To be sure the resistor would not heat up much during the calibration, take at least a 5W or better a 10W resistor.
I have a E36xx and calibrated them with my really nice Burster resistor. But they are kind of expensive.
 

[yo0]

Thank you, i think i will buy 5 watts axial ones from Mouser.

Best regards.

Pio

[e61_phil]

Thank you, i think i will buy 5 watts axial ones from Mouser.

Best regards.

Pio

How do you measure these resistors within 100ppm uncertainty?

[yo0]

Thank you, i think i will buy 5 watts axial ones from Mouser.

Best regards.

Pio

How do you measure these resistors within 100ppm uncertainty?

i am kind of newbie in this hobby, can you  explain me what do you mean please?, i was following the idea from Ordinaryman1971

as for the measure device luckly have friends in a local Technology institute as well as some friends in some Technology industries with access to the required micro-milli ohmeters for the resistor selection from the batch. 

There are 0.01 resistors with 1% tolerance available for about a $1 a piece, I would just buy few... well, lets say 10 and measure them with some fancy miliohm meter and just pick your winner. If you are lucky, you got yourself a nice as-close-as-possible resistor for your current calibration for about $10.

best regards

p.s.

sorry about my poor english.



Pio

[e61_phil]

How do you measure these resistors within 100ppm uncertainty?

i am kind of newbie in this hobby, can you  explain me what do you mean please?, i was following the idea from Ordinaryman1971

as for the measure device luckly have friends in a local Technology institute as well as some friends in some Technology industries with access to the required micro-milli ohmeters for the resistor selection from the batch. 

If you have access to the required instruments it should be ok. Otherwise it isn't easy to measure 100mR within 100ppm uncertainty. Even a 3458A has an uncertainty of 515ppm at 100mR (direct ohms measurement. With a stable current source it might be better).

[Ordinaryman1971]

Phil is right, you have to make sure that the resistor you do your calibration with will be as close to the required resistance as possible.
I think you have to judge yourself how often would you use this resistor to do calibration. Is it going to be only once in a year or two event.
Or you would use it repetitively and calibrate several power supplies.
I would go the el cheapo way... but it's just me.
Buy cheaper ones with lets say 1% accuracy and measure them with equipment that would give you the resistance with the best accuracy and pick the one as close as possible to the one stated in the calibration procedure.
I have Instek GOM-802 with temperature compensation, this one measures of course with four wire Kelvin probes.

30000 Counts Display
High Accuracy 0.05%
Hi/Lo Comparator and Limit Percent Setting
Measurement of REL, Actual and % Value
Continuous or Triggered Measurement Mode
Temperature Compensation and Measurement
Four-Terminal Measurement Technique
Auto-Recall Last Setting After Power OFF and ON Again
Alarm Setting for PASS/FAIL
Scan, Handler Interface(Standard)
Manual or Autoranging
RS-232C+GPIB (Option)

I've had actually delivered 8 of 0.01ohm 3W resistors with 1% accuracy and here are the measurements for each of them:
Really quick measurements, I did wait for about a minute for the readings to stabilize, didn't have more time. I've left the last one to soak up so I will post the results bit later with all the resistors being "up" for an hour or so.
Here are the measurements for 8 resistors:
0.009428
0.009432
0.009482
0.009556
0.009453
0.009490
0.009421
0.009341
Well, that's what you get for $6 delivered.

[Ordinaryman1971]

Some more info about the GOM-802
Range/Test Current   30m?/1A, 300m?/100mA, 3?/100mA, 30?/10mA, 300?/1mA, 3k?/100uA, 30k?/100uA, 300k?/10uA and 3M?/1uA 9 ranges
Accuracy   30m?: ±1% reading + 6 digits
300m?: ±0.05% reading + 6 digits
3?: ±0.05% reading + 3digits
30?~3M?: ±0.05% reading + 2 digits
Resolution   1u?, 10u?, 100u?, 1m?, 10m?, 100m?, 1?, 10?, 100?

[0.01C]

hello to all!, the 0.01 ohms 0.01% resistor value called in the service manual for current calibration is critical? can be subs with let say 0.06, 0.12, 0.22 etc? same about tolerance, seems dificult find 0.01% resistors in those ohms values.

any help will be really appreciated.


best regards.


Pio

you can also use 0.001R or 0.1R to calibrate your psu , Isabellenhutte PBV is also a good choice ,it is a 4 wires resistor. I bought a used 0.01R 0.5% at $1.x 

[texaspyro]

With these low ohm resistors, what I have done is find one close to, but slightly lower in resistance to the correct value.  Then solder a regular resistor lead (or other wire to it).   Then use a precision ohm meter (HP-3458A) to find where on the added lead the resistance is 0.01 ohms.   Well, actually I had some 0.005 ohm leaded resistors and just found where on the leads the resistance of two in series was actually 0.01 ohms... for mine around 0.9" of lead was the magic spot.

Or if the resistor is over 0.01 ohms, calculate the value of a parallel resistor that will bring it to 0.01 ohms.

I also made a precision 300 meg resistor out of a bunch of nominal 10 meg ones plus a couple of other values to tweak it in.
 

[alm]

Reading through the service guide (calibration starts on page 45), the value of that current monitoring resistor does not seem at all critical. You could probably use a 0.1 Ohm resistor with a sufficient power rating (would need at least 50W) without any issues. The burden voltage does not seem critical either.

The only things that seem important is that the value is stable (hence the high power rating or low resistance) and that its value is accurately known. I see no compelling reason to aim for exactly 0.01000 Ohm. Just measure the value before calibration (a shunt resistor should ideally be measured under load) and then calculate the current from Ohm's law. If you are unable to get an accurate resistor, it might be better to put your DMM in series to measure current so you use its internal shunt resistor. Although you will likely not achieve the accuracy required for a calibration to factory specs.