Re: [volt-nuts] Calibration of voltage standards --- DIY switch/scannors
Hi M K, Sorry about that, I have posted a new thread on EEVBLOG with added photos. http://www.eevblog.com/forum/projects/diy-low-thermal-emf-switchscanner-for-comparisons-of-voltage-and-resistor-stand/ lymex/bg2vo -邮件原件- 发件人: volt-nuts [mailto:volt-nuts-boun...@febo.com] 代表 M K 发送时间: 2015年2月13日 14:45 收件人: volt-nuts@febo.com 主题: Re: [volt-nuts] Calibration of voltage standards On 13/02/2015 01:40, 张利民 wrote: Dear Ken Peek, I designed a powerless automatic 2*4 low thermal EMF switch for 3458A, 34401A and 34420A(works also on my R6581T and 1281). It performs great and I use it as my main comparison tool for 10V and 10k standards. http://bbs.38hot.net/thread-1186-1-1.html lymex/bg2vo -邮件原件- 发件人: volt-nuts [mailto:volt-nuts-boun...@febo.com] 代表 Ken Peek 发送时间: 2015年2月12日 1:35 收件人: volt-nuts@febo.com 主题: Re: [volt-nuts] Calibration of voltage standards I forgot to mention that I also own a PPM Inc. Model AVM-100 null meter. Works great on AC but I need to replace the NiCd batteries for it to work on batteries. It has a 1uV scale, and it is a bit noisy on that scale. I intend to modify it to get batter 1/f noise specs on the 1uV scale. Does anyone know where I can get [or how to make] a low-thermal-EMF switch [or relay]? This would need to be a DPDT type to be able to reverse the connection to the meter. Ideas? Hi Lymex, Great idea. I will have to spend some time looking over the google translate version of your text, as unfortunately it seems that here in the United Kingdom we cannot see any in line images from 38hot. I guess I would have to sign up to see them? And even the video of your box would not stream for 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. ___ 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] Calibration of voltage standards --- DIY switch/scannors
On 16/02/2015 06:45, 张利民 wrote: Hi M K, Sorry about that, I have posted a new thread on EEVBLOG with added photos. http://www.eevblog.com/forum/projects/diy-low-thermal-emf-switchscanner-for-comparisons-of-voltage-and-resistor-stand/ lymex/bg2vo -邮件原件- 发件人: volt-nuts [mailto:volt-nuts-boun...@febo.com] 代表 M K 发送时间: 2015年2月13日 14:45 收件人: volt-nuts@febo.com 主题: Re: [volt-nuts] Calibration of voltage standards On 13/02/2015 01:40, 张利民 wrote: Dear Ken Peek, I designed a powerless automatic 2*4 low thermal EMF switch for 3458A, 34401A and 34420A(works also on my R6581T and 1281). It performs great and I use it as my main comparison tool for 10V and 10k standards. http://bbs.38hot.net/thread-1186-1-1.html lymex/bg2vo -邮件原件- 发件人: volt-nuts [mailto:volt-nuts-boun...@febo.com] 代表 Ken Peek 发送时间: 2015年2月12日 1:35 收件人: volt-nuts@febo.com 主题: Re: [volt-nuts] Calibration of voltage standards I forgot to mention that I also own a PPM Inc. Model AVM-100 null meter. Works great on AC but I need to replace the NiCd batteries for it to work on batteries. It has a 1uV scale, and it is a bit noisy on that scale. I intend to modify it to get batter 1/f noise specs on the 1uV scale. Does anyone know where I can get [or how to make] a low-thermal-EMF switch [or relay]? This would need to be a DPDT type to be able to reverse the connection to the meter. Ideas? Hi Lymex, Great idea. I will have to spend some time looking over the google translate version of your text, as unfortunately it seems that here in the United Kingdom we cannot see any in line images from 38hot. I guess I would have to sign up to see them? And even the video of your box would not stream for me. Hi Lymex, Amazing lab you have there. Thanks. M K ___ 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] Calibration of voltage standards
Dear Ken Peek, I designed a powerless automatic 2*4 low thermal EMF switch for 3458A, 34401A and 34420A(works also on my R6581T and 1281). It performs great and I use it as my main comparison tool for 10V and 10k standards. http://bbs.38hot.net/thread-1186-1-1.html lymex/bg2vo -邮件原件- 发件人: volt-nuts [mailto:volt-nuts-boun...@febo.com] 代表 Ken Peek 发送时间: 2015年2月12日 1:35 收件人: volt-nuts@febo.com 主题: Re: [volt-nuts] Calibration of voltage standards I forgot to mention that I also own a PPM Inc. Model AVM-100 null meter. Works great on AC but I need to replace the NiCd batteries for it to work on batteries. It has a 1uV scale, and it is a bit noisy on that scale. I intend to modify it to get batter 1/f noise specs on the 1uV scale. Does anyone know where I can get [or how to make] a low-thermal-EMF switch [or relay]? This would need to be a DPDT type to be able to reverse the connection to the meter. Ideas? ___ 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 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] Calibration of voltage standards
A Data Proof scanner seems to be the standard of some primary labs. They don't show up often on the auction site. This company makes one that fits the front of a 732B. I have never seen it in use. http://www.hpd-online.com/reversing_switch.php There also appears to be a Guildline 9600 up for auction. It is misspelled Guideline. I don't know the specs of that item, I have just noticed it has been listed for a while. Some of the Keithley instruments take low thermal cards, but they are not reversible as far as I can tell. You might be able to do so with two separate inputs. It is a Keithley 7168 nanovolt scanner card. If you can get one, I am pretty sure you can plug it into a 7001/7002 scanner. A home made switch might be cheaper if you can source some good low thermal latching relays. Todd On Wed, Feb 11, 2015 at 12:35 PM, Ken Peek ken.p...@diligentminds.com wrote: I forgot to mention that I also own a PPM Inc. Model AVM-100 null meter. Works great on AC but I need to replace the NiCd batteries for it to work on batteries. It has a 1uV scale, and it is a bit noisy on that scale. I intend to modify it to get batter 1/f noise specs on the 1uV scale. Does anyone know where I can get [or how to make] a low-thermal-EMF switch [or relay]? This would need to be a DPDT type to be able to reverse the connection to the meter. Ideas? ___ 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 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] Calibration of voltage standards
The most noiseless and stable nullmeter is any of the EM Electronics nanovoltmeter. Even the oldest EM N1a I have, gives about 1 nV p-p noise and 1 pA input current. Regards, Mickle KP ___ KP volt-nuts mailing list -- volt-nuts@febo.com KP To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts KP and follow the instructions there. ___ 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] Calibration of voltage standards
I have both the Keithley 155 and several Fluke 845AB's. I too prefer the Keithley 155 over the Fluke and I'm not a big fan of Keithley equipment. Jeff - KDØORH - Original Message - From: R.Phillips phill...@btinternet.com To: volt-nuts@febo.com Sent: Wednesday, February 11, 2015 6:00:42 AM Subject: Re: [volt-nuts] Calibration of voltage standards I think I was the Keithley 155 owner that ask the question. Since then I have added an HP3245A to my equipment which I have set to 1.00 V DC, read by my in calibration HP3458A, and then compared by the Keithley 155 against my Fluke 732A's 1.000 v output - this is showing a steady -1 uV on the 155's , 1 or 3uV range. I have replaced the batteries in the 155 with 9 volt (6LF22/MB1604) batteries, works fine. I also have a Fluke 845AB which I would suggest is less stable. Best regards Roy Phillips. -Original Message- From: acb...@gmx.de Sent: Wednesday, February 11, 2015 10:00 AM To: volt-nuts@febo.com Subject: Re: [volt-nuts] Calibration of voltage standards for those interested, and for simplicity, wanted to add this from David which was in voltnuts in 2012. From: Charles P. Steinmetz charles_steinmetz at lavabit.com To: Discussion of precise voltage measurement volt-nuts at febo.com Sent: Saturday, 15 December 2012, 10:28 Subject: Re: [volt-nuts] Fluke 335A versus HP 740B David wrote: I have a Keithley 155 Null Detector how does that rate? The three usual suspects are the Fluke 845AB, the HP 419A, and Keithley 155. I have one of each, and they are all good meters. The received wisdom is that the Fluke is the one to have. However, in my view, the Keithley is the best of the bunch. It is a bonus if you find one with the rare 1554 AC power module (the 1554 mounts to the rear panel and allows AC operation -- otherwise, it is battery-only). The main problem today with the HP is that it uses impossible-to-find batteries. Not only are the original batteries unobtainable, I have yet to find a satisfactory replacement strategy. It also does not have a +/- 1 uV range, although I do not count that as a major fault since thermocouple noise in the measurement setup frequently prevents taking full advantage of the 1 uV range. The Fluke's batteries (sub-C NiCd cells) are readily replaced (though not inexpensively, if you get the best cells). Keithley used four, # 246 9 V carbon cells, which can easily be replaced with common 9 V alkalines or 9 V primary lithium cells that simply plug into the existing connectors. The HP and Fluke both use photocell choppers. Fluke published pre-release information indicating that they had designed a FET chopper for later production, but I have never seen an 845 with a FET chopper or a schematic of the FET chopper. (Does anyone here have either?) The Keithley was designed with a MOSFET chopper from the start. Not only is the Keithley the most modern design and the most likely to remain reliable, it also performs the best in my lab. I have had fewer ground loop and shielding problems with it than with the Fluke, and it has less noise and less drift. It is not enough better that most people should sell their Fluke to get a Keithley just for the performance difference (reliability may be another story), but -- IME -- it does perform better. They are all good meters, but IMO the Keithley is the best of the three. If I had only one, that is the one I'd want. Best regards, Charles ___ 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] Calibration of voltage standards
Jeff wrote: I have both the Keithley 155 and several Fluke 845AB's. I too prefer the Keithley 155 over the Fluke and I'm not a big fan of Keithley equipment. There's a 155 with a halfway reasonable BIN on ebay right now. It has the rare and (IMO) desirable 1554 AC power supply. I doubt it will be there long. (I have no connection to or knowledge of the seller.) There are manuals on ko4bb.com. Best regards, Charles ___ 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] Calibration of voltage standards
the 3458A is very well suited as a nullmeter (there e.g. also is an appnote from Fluke on this). I have checked this against other meters such as the e.g. the keithley 155 and 34420A, and for my setup (Fluke 732A, Datron 4910 and others) I have the least problems with noise, common mode issues and so. The nullmeter method should only be used when the DUT is adjusted. ie., low voltages differnces of a few mV should not be measured, the accuracy is, at least formally, not specified there sufficiently precise. The second method frequently used and that I am using most of the time (since I do not adjust references, especially the 732A is known to potentially increase its drift thereafter, the 4910 uses digital adjustment, so there it would be ok) is to measure the absolute voltage of both standards with a 3458A and reference the DUT to the standard. This can be done because of the excellent linearity of the 3458A. If I remember correctly the accuracy related to the standard is in the 0,1ppm range at 10V. Gesendet: Mittwoch, 11. Februar 2015 um 08:36 Uhr Von: Chuck Harris cfhar...@erols.com An: Discussion of precise voltage measurement volt-nuts@febo.com Betreff: Re: [volt-nuts] Calibration of voltage standards To do a comparison of the sort you are asking about, the sensitivity of the null meter is much more important than its ultimate accuracy. So, neither of your meters is really the right meter to use for this task. What you want is called a null meter, and is generally sensitive to the microvolt region. -Chuck Harris Ken Peek wrote: Hi Group, I have heard of a few different ways to measure one 10V voltage standard against another 10V voltage standard. Assume we have two 10V voltage standards. One is calibrated, the other not only needs to be calibrated, but probably adjusted. For the sake of simplicity, let's say the two standards are Fluke 732B's. I *think* the best way is to connect the two units' (-) terminals together, then connect a calibrated meter in between the (+) terminals, and measure the difference. I have also heard that to remove thermal EMFs, you should use a low-thermal-EMF DPDT switch or a low-thermal-EMF relay to reverse the connections on the DMM, so you can take the reading forward and reversed, then split the difference. There is the possibility to introduce thermal-EMF errors from the switch/relay as well, so I'm wondering if this is a good idea. This sort of makes sense to me, but I'm not a metrologist, so I would like to hear what others in this group think about this. So, just what is the proper way to accomplish this task? BTW-- I have an Agilent 34420A and an HP 3458A, which would be the better instrument for this task? Best Regards, Ken Peek = ___ 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 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 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] Calibration of voltage standards
Hello Ken, generally, the difference (bridge) method is always the most sensitive and precise one. Thermal voltages and amplifier noise pose a lower limit to the achievable precisison. About 10nV may be achieved at best, even in metrological environment.. That's the reason, why the 1e-18 stability / uncertainty between two JJ arrays against each other, (superconducting environment), can be transferred to the analogue world to 1e-9 uncertainty only (10nV / 10V). To compare two 10V standards, an uncertainty of only 1µV is required, as this will yield 0.1ppm uncertainty of the 10V transfer - totally sufficient in practical terms. Btw.: the unit 'Volt' currently is 0.2ppm uncertain only in the SI system. (Will probably change in 2018!) Good low thermo voltage cables are required, maybe also a low thermal switch. Therefore, both of your instruments can of course successfully and easily compare and null these two 10V references, and would also be able to give a precise difference reading, so to assign the DUT a calibrated standrad value, differing from a clean 10.00V. The 34420 is better suited, as it has better noise and higher resolution (100pV). This instrument can even be used to make a transfer from a JJ array primary standard to a 732B secondary standard. Rem.: There's a good application note from FLUKE, where they promote their 8508A reference multimeter as good replacement for differential meters like their famous 845A... The 3458A on the other hand is capable of making ultra precise absolute value transfers (better than the 720A), i.e. you may measure the absolute value of your 732B reference standard, and then measure the DUT 732B also on the 3458A, to compare their values in absolute terms. This transfer can also be made uncertain to 0.1ppm, good thermal connections and maybe thermo voltage cancellation provided. This again is equivalent to 1µV level uncertainty, which is not so difficult to achieve. Frank --- Alle Postfächer an einem Ort. Jetzt wechseln und E-Mail-Adresse mitnehmen! Rundum glücklich mit freenetMail ___ 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] Calibration of voltage standards
One further remark: These high resolution, low noise DMMs, as 3458A, 8508A, 34420A all are capable to replace the 845A null voltmeter! All have higher sensitivity, and at least same or better noise performance. (see also the FLUKE AN) Especially in this application, i.e. low impedance sources, the bias current plays no role. But also in the usual, higher impedance applications, like Wheatstone Bridges, where the 845A was intended for, the modern instruments can also be used without any problem. Their bias currents are all specified to be 20..50pA, and may be taken into account in the uncertainty budget. In practisey, my own 3458A shows 2pA only. In contrast to that, the 845A was never (!) specified for bias current. Fluke only claimed something like 10^12 Ohm when nulled to 10µV, or so. The 845A contains an optical chopper, but I'm not convinced that this design really is superior to modern FET choppers, which can be found in the instruments mentioned. Maybe, volt-nuts owners of an 845A can really determine its leakage / bias current. Maybe also, that this mystified instrument really is not as good in this aspect, as everybody assumed for the past decades. Frank --- Alle Postfächer an einem Ort. Jetzt wechseln und E-Mail-Adresse mitnehmen! Rundum glücklich mit freenetMail ___ 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] Calibration of voltage standards
To amplify Chuck's point, The only meter worth considering, if you are going to get one, is the FLUKE 845. Preferably, the battery operated version which has a higher isolation leakage resistance. However, the 110 volt rack mount model would do just as equally. BillWB6BNQ Chuck Harris wrote: To do a comparison of the sort you are asking about, the sensitivity of the null meter is much more important than its ultimate accuracy. So, neither of your meters is really the right meter to use for this task. What you want is called a null meter, and is generally sensitive to the microvolt region. -Chuck Harris Ken Peek wrote: Hi Group, I have heard of a few different ways to measure one 10V voltage standard against another 10V voltage standard. Assume we have two 10V voltage standards. One is calibrated, the other not only needs to be calibrated, but probably adjusted. For the sake of simplicity, let's say the two standards are Fluke 732B's. I *think* the best way is to connect the two units' (-) terminals together, then connect a calibrated meter in between the (+) terminals, and measure the difference. I have also heard that to remove thermal EMFs, you should use a low-thermal-EMF DPDT switch or a low-thermal-EMF relay to reverse the connections on the DMM, so you can take the reading forward and reversed, then split the difference. There is the possibility to introduce thermal-EMF errors from the switch/relay as well, so I'm wondering if this is a good idea. This sort of makes sense to me, but I'm not a metrologist, so I would like to hear what others in this group think about this. So, just what is the proper way to accomplish this task? BTW-- I have an Agilent 34420A and an HP 3458A, which would be the better instrument for this task? Best Regards, Ken Peek = ___ 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 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 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] Calibration of voltage standards
I think I was the Keithley 155 owner that ask the question. Since then I have added an HP3245A to my equipment which I have set to 1.00 V DC, read by my in calibration HP3458A, and then compared by the Keithley 155 against my Fluke 732A's 1.000 v output - this is showing a steady -1 uV on the 155's , 1 or 3uV range. I have replaced the batteries in the 155 with 9 volt (6LF22/MB1604) batteries, works fine. I also have a Fluke 845AB which I would suggest is less stable. Best regards Roy Phillips. -Original Message- From: acb...@gmx.de Sent: Wednesday, February 11, 2015 10:00 AM To: volt-nuts@febo.com Subject: Re: [volt-nuts] Calibration of voltage standards for those interested, and for simplicity, wanted to add this from David which was in voltnuts in 2012. From: Charles P. Steinmetz charles_steinmetz at lavabit.com To: Discussion of precise voltage measurement volt-nuts at febo.com Sent: Saturday, 15 December 2012, 10:28 Subject: Re: [volt-nuts] Fluke 335A versus HP 740B David wrote: I have a Keithley 155 Null Detector how does that rate? The three usual suspects are the Fluke 845AB, the HP 419A, and Keithley 155. I have one of each, and they are all good meters. The received wisdom is that the Fluke is the one to have. However, in my view, the Keithley is the best of the bunch. It is a bonus if you find one with the rare 1554 AC power module (the 1554 mounts to the rear panel and allows AC operation -- otherwise, it is battery-only). The main problem today with the HP is that it uses impossible-to-find batteries. Not only are the original batteries unobtainable, I have yet to find a satisfactory replacement strategy. It also does not have a +/- 1 uV range, although I do not count that as a major fault since thermocouple noise in the measurement setup frequently prevents taking full advantage of the 1 uV range. The Fluke's batteries (sub-C NiCd cells) are readily replaced (though not inexpensively, if you get the best cells). Keithley used four, # 246 9 V carbon cells, which can easily be replaced with common 9 V alkalines or 9 V primary lithium cells that simply plug into the existing connectors. The HP and Fluke both use photocell choppers. Fluke published pre-release information indicating that they had designed a FET chopper for later production, but I have never seen an 845 with a FET chopper or a schematic of the FET chopper. (Does anyone here have either?) The Keithley was designed with a MOSFET chopper from the start. Not only is the Keithley the most modern design and the most likely to remain reliable, it also performs the best in my lab. I have had fewer ground loop and shielding problems with it than with the Fluke, and it has less noise and less drift. It is not enough better that most people should sell their Fluke to get a Keithley just for the performance difference (reliability may be another story), but -- IME -- it does perform better. They are all good meters, but IMO the Keithley is the best of the three. If I had only one, that is the one I'd want. Best regards, Charles Gesendet: Mittwoch, 11. Februar 2015 um 08:55 Uhr Von: wb6bnq wb6...@cox.net An: Discussion of precise voltage measurement volt-nuts@febo.com Betreff: Re: [volt-nuts] Calibration of voltage standards To amplify Chuck's point, The only meter worth considering, if you are going to get one, is the FLUKE 845. Preferably, the battery operated version which has a higher isolation leakage resistance. However, the 110 volt rack mount model would do just as equally. BillWB6BNQ Chuck Harris wrote: To do a comparison of the sort you are asking about, the sensitivity of the null meter is much more important than its ultimate accuracy. So, neither of your meters is really the right meter to use for this task. What you want is called a null meter, and is generally sensitive to the microvolt region. -Chuck Harris Ken Peek wrote: Hi Group, I have heard of a few different ways to measure one 10V voltage standard against another 10V voltage standard. Assume we have two 10V voltage standards. One is calibrated, the other not only needs to be calibrated, but probably adjusted. For the sake of simplicity, let's say the two standards are Fluke 732B's. I *think* the best way is to connect the two units' (-) terminals together, then connect a calibrated meter in between the (+) terminals, and measure the difference. I have also heard that to remove thermal EMFs, you should use a low-thermal-EMF DPDT switch or a low-thermal-EMF relay to reverse the connections on the DMM, so you can take the reading forward and reversed, then split the difference. There is the possibility to introduce thermal-EMF errors from the switch/relay as well, so I'm wondering if this is a good idea. This sort of makes sense to me, but I'm not a metrologist, so I would like to hear what
[volt-nuts] Calibration of voltage standards
Hi Group, I have heard of a few different ways to measure one 10V voltage standard against another 10V voltage standard. Assume we have two 10V voltage standards. One is calibrated, the other not only needs to be calibrated, but probably adjusted. For the sake of simplicity, let's say the two standards are Fluke 732B's. I *think* the best way is to connect the two units' (-) terminals together, then connect a calibrated meter in between the (+) terminals, and measure the difference. I have also heard that to remove thermal EMFs, you should use a low-thermal-EMF DPDT switch or a low-thermal-EMF relay to reverse the connections on the DMM, so you can take the reading forward and reversed, then split the difference. There is the possibility to introduce thermal-EMF errors from the switch/relay as well, so I'm wondering if this is a good idea. This sort of makes sense to me, but I'm not a metrologist, so I would like to hear what others in this group think about this. So, just what is the proper way to accomplish this task? BTW-- I have an Agilent 34420A and an HP 3458A, which would be the better instrument for this task? Best Regards, Ken Peek = ___ 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.
