nA advice
Hello!
I would like to measure insulation resistance of some defective load cells.
The measurement should be done with no more than 50V and the full scale
reading should be >=5Gohm. Accuracy of +-10% is enough (in fact it could
suffice just to check if it's >=5Gohm or not).
I have not been able to find a ready made instrument that could do this within
a reasonable price (100 EUR); the normal insulation resistance testers go much
high with the probing voltage (on the purpose, but this also lighten much the
requirements on the sensitivity of the meter).
It could be as simple as a led indicator "pass/fail", but at this point, why
not to build a good frontend for a multimeter, so it could be much more useful?
There are many way to do this and also many ready circuits (like the
null detector in the mini metrology lab by Conrad Hoffmann) or in the AoE,
but instead of making it from scratch, someone knows if there is something
already made (or a kit)?
Best regards
Andrea Baldoni
Do you have a high Z input dmm on the 10V range? Perhaps you can characterize its impedance with another high value resistor of known value and then connect the UUT to the meter and measure its drop across the input with a test voltage.
Todd
Sent from my iPad
On Nov 13, 2015, at 11:15, Andrea Baldoni erm191ba3@ermione.com wrote:
Hello!
I would like to measure insulation resistance of some defective load cells.
The measurement should be done with no more than 50V and the full scale
reading should be >=5Gohm. Accuracy of +-10% is enough (in fact it could
suffice just to check if it's >=5Gohm or not).
I have not been able to find a ready made instrument that could do this within
a reasonable price (100 EUR); the normal insulation resistance testers go much
high with the probing voltage (on the purpose, but this also lighten much the
requirements on the sensitivity of the meter).
It could be as simple as a led indicator "pass/fail", but at this point, why
not to build a good frontend for a multimeter, so it could be much more useful?
There are many way to do this and also many ready circuits (like the
null detector in the mini metrology lab by Conrad Hoffmann) or in the AoE,
but instead of making it from scratch, someone knows if there is something
already made (or a kit)?
Best regards
Andrea Baldoni
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50V across 5GOhm is 10nA. Put a standard multimeter's 10MOhm input in
series and
you have 10mV per nA reading. Anything below 100mV is pass.
My 2 eurocents.
Rob Klein
Op 13-11-2015 om 17:15 schreef Andrea Baldoni:
Hello!
I would like to measure insulation resistance of some defective load cells.
The measurement should be done with no more than 50V and the full scale
reading should be >=5Gohm. Accuracy of +-10% is enough (in fact it could
suffice just to check if it's >=5Gohm or not).
I have not been able to find a ready made instrument that could do this within
a reasonable price (100 EUR); the normal insulation resistance testers go much
high with the probing voltage (on the purpose, but this also lighten much the
requirements on the sensitivity of the meter).
It could be as simple as a led indicator "pass/fail", but at this point, why
not to build a good frontend for a multimeter, so it could be much more useful?
There are many way to do this and also many ready circuits (like the
null detector in the mini metrology lab by Conrad Hoffmann) or in the AoE,
but instead of making it from scratch, someone knows if there is something
already made (or a kit)?
Best regards
Andrea Baldoni
volt-nuts mailing list -- volt-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.
Rob wrote:
50V across 5GOhm is 10nA. Put a standard multimeter's 10MOhm input
in series and
you have 10mV per nA reading. Anything below 100mV is pass.
Also, quite a few of the Fluke portable and handheld DMMs from the
last 35 years or so (including the faithful old 8050A and the
"80-series" DMMs) measure conductance (1/R) with a resolution down to
0.01nS (= 100G ohm). There are lots of them with this capability on
the used market for $10 and up, and several are still available new
(but not for less than Eu100, to my knowledge).
Best regards,
Charles
On Fri, Nov 13, 2015 at 12:27:28PM -0500, Todd Micallef wrote:
Do you have a high Z input dmm on the 10V range? Perhaps you can characterize
its impedance with another high value resistor of known value and then
connect the UUT to the meter and measure its drop across the input with a
test voltage.
Good idea. Yes, I can use a 34401A, whose input could be set for >10GR on
100mV, 1V and 10V ranges.
However I can let it be 10MR that need not to be characterized and just measure
the voltage from the divider DUT/10M. With 50V and 5GR will be just about
100mV.
I can think that the 100mV range is already in effect a 10nA range.
It's a high impedance ammeter, but taking in accunt that the source will be
50V the error fall under the precision of the 10MR input impedance, that's
only 1%.
Or, set the multimeter to >10GR and use a shunt resistor of, say, 1MR .1%
(still cheap). Taking in account the multimeter (6.5 digits) in this case will
measure only to 10% of the 100mV range, the fact that the >10GR input is not
better characterized, the overall accuracy should be anyway the one of my
resistor.
Thank you!
Best regards,
Andrea Baldoni
On Fri, Nov 13, 2015 at 01:56:19PM -0500, Charles Steinmetz wrote:
Rob wrote:
50V across 5GOhm is 10nA. Put a standard multimeter's 10MOhm input in
series and
you have 10mV per nA reading. Anything below 100mV is pass.
Yes, Rob. I late also thought about it that way while answering to Todd.
In effect I wasn't used to think to DMM the way it was for galvanometers :)
Also, quite a few of the Fluke portable and handheld DMMs from the last 35
years or so (including the faithful old 8050A and the "80-series" DMMs)
measure conductance (1/R) with a resolution down to 0.01nS (= 100G ohm).
There are lots of them with this capability on the used market for $10 and
up, and several are still available new (but not for less than Eu100, to my
knowledge).
Charles, I own two new generation fluke portables (one is a 177 and the
other is the cheap 15B) and no one has this characteristic anymore, who knows
why, but it's very interesting. According to
the new multimeters with conductance measure are 87V and 189. No one fits the
100 EUR range by far, but I can buy an used 80-series one, they are very
cheap and I can bring them on the field while I would like to let the 34401A
in the lab. I saw the 8060A resultion is only 0.1nS; I cannot find the specs of
the 8050A (neither the user's manual). Which one do you suggest?
Best regards,
Andrea Baldoni
the new multimeters with conductance measure are 87V and 189. No one fits the
100 EUR range by far, but I can buy an used 80-series one, they are very
cheap and I can bring them on the field while I would like to let the 34401A
in the lab. I saw the 8060A resultion is only 0.1nS; I cannot find
the specs of
the 8050A (neither the user's manual). Which one do you suggest?
I think any Fluke with an LSD of 0.01nS would be fine. Some (like
the 8050A) have full-range counts of 2000 (50M ohms), others have
full-range counts of 4000 or 6000 (25M ohms and 16.7M ohms,
respectively), which wouldn't make any difference for this
application (5G ohms is 20 counts with an LSD of 0.01nS). It may
matter for other uses you find for the meter.
I'd say decide first whether you want a battery-only handheld (I have
an 87 Series III) or a portable like the 8050A (line operated -- some
have a battery option, but if that is important to you you're
probably better off with a handheld). I bought 4, 8050As in 1981,
and they have all been perfectly trouble-free this whole time and are
still about 10x better than their specs on all functions (they are
checked annually but have never been adjusted). The same is true of
the 87-III, which I've had since 1997. The 8050As have had easy
lives as bench instruments, while the 87-III has been treated
respectfully but has been bumped around a fair amount -- up and down
dozens of towers and through hundreds of utility tunnels and
inspection hatches on a belt clip, sometimes in inclement weather or
noxious environments.
Fluke 8050A manual: http://assets.fluke.com/manuals/8050a___imeng0200.pdf
Fluke 80 Series III
manual: http://assets.fluke.com/manuals/8xiii___umeng0500.pdf
Best regards,
Charles