Re: [volt-nuts] Temperature sensor
On 3/16/2016 4:47 PM, John Phillips wrote: > You should use oil so that you do not get evaporative cooling. Better still, but more potential to be messy. Another advantage is that there's no need to waterproof the sensor. I was thinking along the lines of sticking the wire through a small hole in a bottle cap, so there's next to no evaporation or spill potential. Even using an open glass of water, evaporation isn't likely to make enough of a difference given the accuracy/resolution of a DS18S20. ___ 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.
Re: [volt-nuts] Temperature sensor
On 3/16/2016 3:19 PM, Joseph Gray wrote: > I would like to shield > the sensors from direct air currents due to AC and heating system. Because that's not really making it colder or warmer? :-) Sounds like you want a moving average, so you don't see the sudden changes, even when they exist. Add some thermal mass to the sensor. Easy way: waterproof it (epoxy, Plasti-Dip, etc.) and stick it in a bottle of water. ___ 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.
Re: [volt-nuts] HP-3458A Zero Reading
On 7/27/2015 10:26 PM, Mike S wrote: > On 7/27/2015 7:54 PM, Bill Gold wrote: >> You will observe that the HP/Agilent/Keysight manual for the 3458A >> does not give any "zero" stability specs, at least that I can find. > > On DC 100 mV range, the standard model is spec'd for 14+3 ppm of range @ > 2 years from calibration, not considering temperature. That's 1.7 uV, > from my reckoning. The OP's reading of 0.7 uV is well within that - it > even beats the 90 day spec. Doh. That 14+3 actually equates to ~=3 ppm ~= 0.3 uV (since reading is essentially zero), but there's also temperature, which contributes > 0.115 / C. ___ 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.
Re: [volt-nuts] HP-3458A Zero Reading
On 7/27/2015 7:54 PM, Bill Gold wrote: > You will observe that the HP/Agilent/Keysight manual for the 3458A > does not give any "zero" stability specs, at least that I can find. On DC 100 mV range, the standard model is spec'd for 14+3 ppm of range @ 2 years from calibration, not considering temperature. That's 1.7 uV, from my reckoning. The OP's reading of 0.7 uV is well within that - it even beats the 90 day spec. ___ 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.
Re: [volt-nuts] plastic caps on 3458A reference board
On 1/28/2015 9:00 AM, J. L. Trantham wrote: In the days of 3D printers and CAD/CAM, it might be possible to have a 'run' of these 'made to order', so to speak. I'd think a couple of pieces of pink (non-conductive) closed cell antistatic foam, one hollowed out a bit with a penknife, would work well. It would both shield from airflow and provide insulation. ___ 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.
Re: [volt-nuts] Old HP3458A - SN: 2823A 03939
On 10/8/2014 4:23 AM, acb...@gmx.de wrote: the EPROMs are in sockets, no soldering needed. but again, buying a precision instrument but reprogramming cal data that is years old does not make any sense. unless of course if you are just a collector and do not use its accuracy. It makes perfect sense, for the same reason that HP doesn't touch the cal if it's in spec - for tracking/characterization. By keeping the same cal constants, if and when he does send it in for calibration he'll be able to know how much it drifted since it was last cal'd (25 years ago?). -- Mike ___ 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.
Re: [volt-nuts] LM399 Long term drift specification
On 9/10/2014 7:00 PM, Tony wrote: I've just noticed that TI and Linear's specs for 'Long Term Stability' (typical) are different. TI state 20ppm/1000Hr while Linear state 8ppm/SQRT(kHr). That's a big difference - is this likely to be a real difference or just specmanship? I note that Linear (in Note 4) also state that "Devices with maximum guaranteed long-term stability of 20ppm/SQRT(kH) are available." Presumably they would be a special order as there doesn't appear to be a unique part no. Would they be likely to be much more expensive? Isn't 8ppm/SQRT(kHr) better than 20ppm/SQRT(kH)? Why would the latter be more expensive? Or is it the difference between "typical" and "guaranteed?" -- Mike ___ 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.
Re: [volt-nuts] Fluke 5200A extender board.
On 8/29/2014 2:16 PM, Tom Miller wrote: Did you remove the two holes? :) You mean the two pin 1 markers on the silkscreen? ___ 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.
Re: [volt-nuts] 732A and Prologix received
After some more research, I think I've answered some of my own questions - Tellurium copper is used for binding posts, not because it has any special thermal or EMF mojo, but because it machines much better than pure copper. And, I suppose, because it sounds like it's extra special. The Seebeck coefficients (uV/C, relative to Cu) of some relevant materials: Cu 0.0 Ag .2 Au .5 Yellow brass 1.5 Phosphor bronze 2.0 63/37 solder 3.0 Sn 3.1 Stainless steel 3.1 Beryllium copper 5.0 Fe -12.3 Ni 22.3 Te -49.25 Based on the extreme Seebeck coefficient of pure tellurium vs. copper, I'd expect that there might be some coefficient between Cu and CuTe (0.5% Te), but I could find no reference. The relatively large number for CuBe is interesting, since that's a common material for banana plug springs, where one might expect the greatest temperature differential to occur in such a connection (between the thermal masses of the binding post/jack and the bulk of the banana plug). Heat has to flow a considerable distance through the springs, very much more than when it flows through a surface plating. The Pomona (Fluke) EM5295-48-0# uses CuBe (gold plated) for the spring contacts. It seems there might be an improvement to be had by using the older style pin plugs, where a solid pin was partially sliced into 4 sections which were then spread apart a bit to create tension. That could eliminate relatively large thermocouples at a thermal gradient, and might also be expected to have less thermal resistance, allowing the connection to settle quicker. But maybe not - I'm still not clear on how plated conductors behave in this situation. For a high impedance voltage measurement where almost no current flows, the gold plating may carry the signal, so there is no real thermocouple (or more correctly, it's entirely contained within the connector). But if that's the case, why fool around with special copper connectors when common brass ones would be easier/cheaper? For current or resistance, the signal would also flow through the base metal, so does this have an effect (especially for tinned copper test leads, where there may be a larger temperature difference between the ends??? Nickle is avoided as a contact material largely because it is subject to fretting corrosion. Tests done by AMP (http://www.te.com/documentation/whitepapers/pdf/p154-74.pdf) show that a Ni to Ni contact can increase from 8 mOhm to 5 Ohms (sic!) in a short time due to this, while Ag and Au plated contacts exhibit negligible changes. Cu (with Be for better machining) seems to be used as the base material for jacks/plugs to get thermal EMF cancellation to the wiring on both sides (i.e. use copper everywhere except where there is a minimal thermal gradient, like platings). -- ___ 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.
Re: [volt-nuts] 732A and Prologix received
On 8/25/2014 9:54 PM, Don@True-Cal wrote:
Why?
Let me count the ways.You can never count on any Seebeck voltage to
be immediately offset, there are far too many variables.
...
> A set of
5440A-7002 (banana plug) cables comes with this calibrator
(5440A-7003 spade lugs for 5720A)
For those leads, Fluke says they have the advantage of "minimizing the
emf caused by temperature difference between the ends of the leads." I
don't have much argument with that - if there's a temperature difference
between the ends, you won't have an equal thermocouple offset, so
minimizing such effects makes sense.
But, since those leads use pure copper wiring ("Belden 8262 or 8719 or
equivalent"), how does having only the contact itself made of tellurium
copper (TC) make a difference? Shouldn't they be TC end-to-end, with gas
tight crimped connections? Does the tinning on that copper cable have an
effect? What's the Seebeck coefficient for a copper to tellurium copper
connection?
You said that "Tellurium Copper is usually not used for a device's
terminal posts but used as the lead wire..." But, Fluke does exactly the
opposite - those Fluke leads use TC connectors and are characterized
"while engaged in a five-way binding post of Tellurium Copper Alloy 145,
half hard." Since they use pure copper cabling, I'd think they'd work
even better with a pure copper binding post, since the offsetting
thermocouples would be in close proximity, and not at different ends of
the cable.
You earlier said "Any type of Silver or Gold plating on the terminal or
wire will introduce the undesirable dissimilar metal properties, both
at the plating junction and at the plating metal to DUT terminal." Now
you emphasize that by saying "If someone used a set of gold-plated
interconnects for this procedure, they would be laughed out of the lab
and the calibrator would be useless until recalibrated properly..."
But, the specs for the Fluke 5440A-7003 which you say are appropriate
for the 5720A state: "Connector materials: Copper space lug with gold
plating over silver plating." (Both platings!!) Is someone to be laughed
out of the lab for using the cables they're supposed to use? The
5440A-7002 specs aren't clear, but if they're not plated, are you
required to clean them of copper oxide for every use? It seems that
would be necessary, since a gold-copper thermocouple is ~0.5 uV/C, while
a copper-copper oxide one is ~1000 uV/C.
You seem to be stating one thing, but then giving evidence which
contradicts your claim. It seems that Fluke uses TC where there's
thermal mass, and pure copper where there's little, and uses plating in
addition.
Please clarify, this isn't making sense to me.
___
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.
Re: [volt-nuts] 732A and Prologix received
On 8/25/2014 11:02 AM, Don@True-Cal wrote: Silver or Gold plating on the terminal or wire will introduce the undesirable dissimilar metal properties, both at the plating junction and at the plating metal to DUT terminal. Why? Any Seebeck effect is immediately offset in the opposite direction, since both junctions are (under normal conditions) at essentially the same temperature (e.g. there's a copper-gold thermocouple, the minimal thermal resistance of a micron of gold on the contact(s), then a gold-copper thermocouple). It seems to me that the improved consistency of the contact outweighs any loss from the thermocouples. A more typical contact would be copper-nickel plate-gold plate, but the concept is the same. Unless there is heat flowing through the entire assembly so one thermocouple is warmer than the offsetting one (e.g. shortly after plugging in a banana plug warmed by body heat), they simply cancel. Even if connecting gold plated to nickel plated contacts, it works out the same - a copper-nickel-gold-nickel-copper connection is completely offset. It's when the offsetting thermocouples occur across a temperature gradient that you have problems. -- Mike ___ 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.
Re: [volt-nuts] Question for Fluke 732A owners
On 2/26/2014 6:53 PM, J. L. Trantham wrote: Oh!! THAT's what they mean by 'male' and 'female'. I get it! :^)) You jest, but it's not always clear. Take the common Cannon "D-sub" connectors. A connector with male contacts will have have a female shield, making gender ambiguous. That's why they come in P (pin) or S (socket) forms, and not male/female. Or the old Token Ring connectors (or even older GR-874), which were hermaphroditic. ___ 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.
Re: [volt-nuts] HP 3457A
On 8/12/2013 2:23 PM, John Phillips wrote: A calibration indicates that the unit under test is withing manufactures specification. The equipment and procedure used has to be "good enough" (bad words in a cal lab) to have a high probability (nothing is 100%) of insuring the calibration documentation is valid. Things can can be a little looser if you are calibrating a 1% meter with a 10 ppm meter but it does not work the other way around. You can calibrate either way. You can't however, calibrate the 10 ppm meter so it's in spec using a 1% meter. That's different. Calibration merely means that it's documented how close it is to a reference, such as NIST, not that it's within the manufacturer's spec. The 10 ppm meter would end up with a 1%+ calibration - precise but not accurate. Not particularly useful, but valid. A good cal lab would do a calibration to specification, where the uncertainties place the 10 ppm meter within spec. As I cited and someone else already quoted, calibration is the "property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty." Nothing to do with making a device meet its specifications. That's why an eBay seller can claim they'll do a "calibration traceable to NIST," because they're not claiming any particular accuracy. It's really not worth anything, unless they give specific uncertainties or claim calibration to manufacturer's specification. ___ 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.
Re: [volt-nuts] HP 3457A
On 8/12/2013 12:21 PM, Charles Steinmetz wrote: No, you could not perform ANY traceable calibration with the 3458A itself, much less with any instrument you had calibrated with the 3458A, because *you* are not accredited That's simply not true. Some organizations may require a lab to be accredited in order to accept their services, but it is not a requirement in order to legitimately claim traceability. The NIST Traceability Policy is found here: http://www.nist.gov/traceability/nist_traceability_policy_external.cfm ___ 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.
[volt-nuts] Looking for VREF - SZA263/LTFLU-1/MCA19xxN
These were used in the Fluke 332B (and others). Still used in the 732. They seem to be unobtainium. Lots of hits on questionable Chinese sites. It's easiest if I can find one for a reasonable price. Otherwise, I suppose I'll have to re-do the board with an LM399. -- Mike ___ 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.
Re: [volt-nuts] Some questions to zeners (thermoelectric effects)
On 1/28/2013 8:48 AM, Tony Holt wrote: > Could the sense wires be welded to > the ADC pins between the solder connection to the PCB and the package to > avoid the thermal EMFs of a solder joint? I don't think welding would make the difference, unless the wire is made of the same material as the pin. I'm also not clear to me how low-EMF solder helps in most cases. Solder joints tend to be small and local, and it's the temperature difference between the terminals which brings the thermoelectric effect into play. For example, two copper wires soldered together - you have a Cu-solder joint, followed by a solder-Cu joint, in very close proximity. As long as "close" is close, and/or there's good thermal mass/conductivity, don't the thermocouples simply offset each other? More realistically, take a device with common tinned brass terminals on a PC board. You have brass/tin, tin/solder then solder/copper thermocouples in very close proximity, essentially resulting in a brass/copper thermocouple. It seems that the temperature difference between that connection and the similar thermocouples at the far end device connection would overwhelm the local effects due to solder, which require a temperature gradient across some small fraction of a mm. Even with much larger, hand soldered terminals, something similar would seem to apply. Wouldn't thermally insulating the terminals (which by nature have pretty good thermal conductivity) to ensure a consistent temperature across them be as good or better than just low EMF solder? --- Mike ___ 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.
Re: [volt-nuts] Lm399 heater
On 9/14/2012 8:04 PM, Fred Schneider wrote: > Is the heater from a LM399 regulated, so it stayes at 85 degrees or > is it just drawing an vast amount of current like a lightbulb ? So if > it gets hotter around the LM the heater temp stays the same ? ... > I just building a refrence with it and If it is not regulated i want > to feed it through a current source The datasheet shows heater current to be inversely proportional to ambient temperature, so there's some level of regulation. I'd think that trying to force a constant current wouldn't be significantly different than not driving the heater at all (which is just the special case of constant current = 0). ___ 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.
Re: [volt-nuts] HP 3458A DC current accuracy
Apropos: http://www.sciencedaily.com/releases/2012/07/120711101042.htm With regard to the discussion, since in the SI, Amps are the base unit, Volts are derived from Amps, and Ohms from Volts - remarkable that Amps are the least realizable in practice? (I guess it's just the difference between NIST and everyone else) -- Mike ___ 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.
Re: [volt-nuts] HP 3458A DC current accuracy
On 7/11/2012 5:15 AM, Frank Stellmach wrote: This is the worst realized electrical unit, i.e. the 'mise en pratique' is difficult to an error level of about 1e-7 only. On 7/11/2012 6:50 PM, Bob Smither wrote: I may be off here, but I doubt that thermal (Johnson) noise would limit the precision of current readings. A one ohm resistor in a 1 Hz bandwidth would be 0.13 nV or 0.13 ppm of the 1 mV reading. It seems you just showed that it does (limit the precision). -- Mike ___ 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.
