Re: [volt-nuts] AC calibration
Dave, the title is: Thermal Voltage Converters and Comparator for Very Accurate AC Voltage Measurements by E.S.Williams. Adrian Gesendet: Montag, 25. August 2014 um 19:32 Uhr Von: Dave M dgmin...@mediacombb.net An: Discussion of precise voltage measurement volt-nuts@febo.com Betreff: Re: [volt-nuts] AC calibration Adrian, Do you have a link or title for the NIST paper that you mentioned? Dave M acb...@gmx.de wrote: fred, generally you raise a good point, I had the same issue of calibrating an ac voltage to a high level of accuracy. you need this e.g. to validate the self.cal of a 3458a or other precison stuff like the 8506a0. what i would recommend to do if you want to keep costs down is: in a nutshell, get a thermal converter in the lowest range you need and a second one on range above. build a set of resistor range extenders (rf type with appropriate connectors and housings) to expand the range to where you need to be max. get one of the thermal converter calibrated (the higher one usually, and you need to havr good cal lab, should be 10ppm accuracy) and use it to calibrate the rest. generally, up to 20khz, the accuracy is some 20 ppm anyway for thermal converters! at higher frequencies, due to reflections and stray capacitance/inductance influences, the accuracy decreases. the resistor range extenders though, if build up correctly, only have a few ppm impact (there is a paper from nist on that, but this is only typical). you can calibrate all converters to the one you got externally calibrated. do some research in the web, when you do the calibration, you need to determine the so-called constant N. then do an ac, dc+, ac, dc-, ac measurement between the the two and establish the deviation, also establish the error propagation. the end result will be a set of highly precise (low inaccuracies9 thermal converters good enough to calibrate a 3458a an better devices. if you want to spend the money, you could also buy a set of converters/range resistors (with/without a 540), that typically is a few k altogether, while a single device sometimes is available for below 100 bucks. you need to have a stable 7.5 digit nanovoltmeter though for the measurements of the tvcs (34420a or 2182 typically ) and precision (stable) dc and ac sources. but in the end, all you need is a single calibrated thermal converter. adrian Gesendet: Montag, 25. August 2014 um 18:38 Uhr Von: Dave M dgmin...@mediacombb.net An: Discussion of precise voltage measurement volt-nuts@febo.com Betreff: Re: [volt-nuts] AC calibration Well, you sort of answered your own question. The equipment is called a Thermal Transfer Standard, but instead of thermistors, it uses a thermocouple. Look at the manual for the Fluke 540B (http://bama.edebris.com/manuals/fluke/540b/) and you'll see how it's done. Basically, the AC source is input into the transfer standard, and the standard's internal reference voltage is adjusted for a null on the galvanometer. Leaving the reference voltage setting alone, a DC voltage is input into the unit, and the DC source is adjusted for a null on the galvanometer. At that point, the AC voltage source is equal to that of the DC voltage source. Ther are thermocouple-type thermal converters used for RF voltage measurements with the transfer standard. They aren't cheap, and you have to have a converter for each range of voltages that you need to measure. The thermal converters used with this type of transfer standard isn't great (50 MHz or so typical), but their accuracy far surpasses that of the thermistor type sensors. There are other brands and models of thermal transfer standards, but I have a Fluke model 540 and a few thermal converters. That's why I referred you to the manual for it. Cheers, Dave M pa4...@gmail.com wrote: Is there a way to link an AC voltage to a DC source for compare. I can check my calibrators (like a Fluke 332, 760 , 731 and a Philips) against standardcells. But for AC I can not do that. I have two AC+DC TRMS 7,5 digit meters but the last calibration was 2 years ago. My idea is in theory simple. It is based on the thermal converters used in RF powermeters. Two resistors, two high resolution temperature meters. AC on the first en DC on the second. If both are the same temperature the AC voltage is the same as the DC voltage. But I'm sure some people here have done this in the past. I would like to use it for 50 to 100 kHz (or less) and something like for 1V, 10V and 100V (and use several resistors/heaters.) Or mabey there is an other way to convert AC (for RF it can be done with lightbubs but I never tryed that) I do not mind if it is slow etc, I like this sort of experiments. You can learn a lot from it. Fred, pa4tim
Re: [volt-nuts] AC calibration
In message trinity-9076c25b-a0a9-4b28-b29a-20f9e06039a3-1409072175101@3capp-gm x-bs56, acb...@gmx.de writes: Tellurium/copper is used because it machines much better than pure copper, (20% - 90%) without ruining the conductivity too much. Most other metals which can improve its machinability has big negative impacts on the conductivity of copper. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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
Bill, I measured the time between SMPL symbols with NPLC set to 1000 and it is approximately 33 seconds. It takes an hour to complete 100 readings. Randy On Mon, Aug 25, 2014 at 10:01 PM, Bill Gold wpgold3...@att.net wrote: Not that I know of. Just wait and when you don't see a SMPL on the display it is done. But then with 1000 PLC that is around 16.66 seconds per reading times 100 readings is somewhere around 28 minutes and there is probably some overhead time so around 30 minutes. Not from the front panel at any rate. Bill - Original Message - From: Randy Evans randyevans2...@gmail.com To: Discussion of precise voltage measurement volt-nuts@febo.com Sent: Monday, August 25, 2014 9:23 PM Subject: Re: [volt-nuts] 732A and Prologix received Is there any way to tell when the function key routine is complete? In the case of taking multiple readings using the DEFKEY and MATH function, I don't see any indication when the routine is complete. In one particular case, I am taking a 100 readings with NLPC set for 1000 so its a long while before it's complete, but i have to guess when it's done. Thanks, Randy On Sun, Aug 24, 2014 at 6:04 PM, Randy Evans randyevans2...@gmail.com wrote: Bill, I am trying to figure out the MATH function without much success. I input the sequence you said (I looked up the instructions to understand what you did - seems logical), BLUE DEFKEY BLUE F1 MATH 14;NRDGS 40;TRIG 4;TRIG; and it shows up on the display when I input BLUE F1. I hit ENTER and it takes the 40 measurements and the MATH symbol shows on the display during the measurements. After the SMPL symbol no longer blinks I hit MATH 2 and I get a MATH ERR symbol on the display. I tried it a couple of times and the same result so I am doing something wrong. Is there a better source for explaining how to do front panel masurements than the User Guide, which seems oriented at programming automatic rather than manual measurements. Randy On Sun, Aug 24, 2014 at 4:46 PM, Bill Gold wpgold3...@att.net wrote: Randy: The MATH function is accessible from the keypad. I don't have an IEEE interface right now that works. You can also program the numeric keypad keys to have preprogrammed functions. DEFKEY I have made my own low thermal measurement leads from Pomona #4892 banana plugs and Belden #9272 wire. Why 9272, because it was handy at the time. It is tin plated copper, shielded twisted pair 20 ga. I have plans to do custom cables with 16 ga. bare copper wire that I will twist and then put a braided shield over it. I simply cannot find what I want so I will build my own cable. I have done something like this before and it worked fine. When I get a round toit. I have 6 ea. Pomona 1756-48 spade lug low thermal leads that I have used in the past to verify my homemade low thermal leads as described above. Frankly I cannot see any difference between using the 1756 cables and my homemade cables once I give them a few minutes for the thermals to go away. As far as I can tell and measure the differences, if any, are below 0.1 ppm at 10 volts. Since the 10 volt, 1.0 volt and 1.018 volt outputs on the 732A are all adjustable you may be seeing a misadjusted 1 volt from the 732A. As far as the instability of the readings it is hard to determine which is causing the problem. I have programed (DEFKEY) a numeric keypad key #1 with the following code. MATH 14;NRDGS 40;TRIG 4;TRIG ; So what this does is set the MATH to Statistics (store high reading/low reading/ and mean of the readings) in the registers, the number of readings to 40, the trigger to hold (which keeps the meter from triggering until I press ENTER and then trigger the sequence of 40 readings when I push the ENTER button. You can do all of this manually from the keypads but since I use this sequence a lot I have preprogrammed it. This is after I set digits to 8 and PLC to 100. Once those 40 readings are finished then you can access the various MATH statistic registers, using the menu, by entering MATH and then a 2 for low, a 4 for mean, and 13 for high. Of course you could do all of this through the IEEE also. The 3458A has a very rich set of measurement commands. I am still learning all of them. It depends upon what I am trying to accomplish. Since the 1.018 and 1.0 volt outputs are passive and derived from resistive dividers from the 10 volt, I don't see how they could contribute to the varying readings you are measuring. I think I would put a short on the input of the 3458A and manually set the range to 1 volt and then observe the variations that way without the 732A involved. When I do this I see a variation from low
Re: [volt-nuts] AC calibration
Great!!@! Many Thanks!! Dave M acb...@gmx.de wrote: Dave, the title is: Thermal Voltage Converters and Comparator for Very Accurate AC Voltage Measurements by E.S.Williams. Adrian Gesendet: Montag, 25. August 2014 um 19:32 Uhr Von: Dave M dgmin...@mediacombb.net An: Discussion of precise voltage measurement volt-nuts@febo.com Betreff: Re: [volt-nuts] AC calibration Adrian, Do you have a link or title for the NIST paper that you mentioned? ___ 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
hi randy, just for curiosity, why doing 100 measurements at nplc 1000. is this to sample a changing value? when i am doing 10 measurements from a stable signal at nplc 100 (only there many subsequent measuremnts with statistics make sense) I am already getting a stanard deviation below 0.1ppm. in a 30 minute test cycle, i would also be concerned about drifts (acal) unless the amb. temperature is really very stable (half a degree already adds about 0.25ppm at 10v) thanks Gesendet: Dienstag, 26. August 2014 um 04:23 Uhr Von: Randy Evans randyevans2...@gmail.com An: Discussion of precise voltage measurement volt-nuts@febo.com Betreff: Re: [volt-nuts] 732A and Prologix received Is there any way to tell when the function key routine is complete? In the case of taking multiple readings using the DEFKEY and MATH function, I don't see any indication when the routine is complete. In one particular case, I am taking a 100 readings with NLPC set for 1000 so its a long while before it's complete, but i have to guess when it's done. Thanks, Randy On Sun, Aug 24, 2014 at 6:04 PM, Randy Evans randyevans2...@gmail.com wrote: Bill, I am trying to figure out the MATH function without much success. I input the sequence you said (I looked up the instructions to understand what you did - seems logical), BLUE DEFKEY BLUE F1 MATH 14;NRDGS 40;TRIG 4;TRIG; and it shows up on the display when I input BLUE F1. I hit ENTER and it takes the 40 measurements and the MATH symbol shows on the display during the measurements. After the SMPL symbol no longer blinks I hit MATH 2 and I get a MATH ERR symbol on the display. I tried it a couple of times and the same result so I am doing something wrong. Is there a better source for explaining how to do front panel masurements than the User Guide, which seems oriented at programming automatic rather than manual measurements. Randy On Sun, Aug 24, 2014 at 4:46 PM, Bill Gold wpgold3...@att.net wrote: Randy: The MATH function is accessible from the keypad. I don't have an IEEE interface right now that works. You can also program the numeric keypad keys to have preprogrammed functions. DEFKEY I have made my own low thermal measurement leads from Pomona #4892 banana plugs and Belden #9272 wire. Why 9272, because it was handy at the time. It is tin plated copper, shielded twisted pair 20 ga. I have plans to do custom cables with 16 ga. bare copper wire that I will twist and then put a braided shield over it. I simply cannot find what I want so I will build my own cable. I have done something like this before and it worked fine. When I get a round toit. I have 6 ea. Pomona 1756-48 spade lug low thermal leads that I have used in the past to verify my homemade low thermal leads as described above. Frankly I cannot see any difference between using the 1756 cables and my homemade cables once I give them a few minutes for the thermals to go away. As far as I can tell and measure the differences, if any, are below 0.1 ppm at 10 volts. Since the 10 volt, 1.0 volt and 1.018 volt outputs on the 732A are all adjustable you may be seeing a misadjusted 1 volt from the 732A. As far as the instability of the readings it is hard to determine which is causing the problem. I have programed (DEFKEY) a numeric keypad key #1 with the following code. MATH 14;NRDGS 40;TRIG 4;TRIG ; So what this does is set the MATH to Statistics (store high reading/low reading/ and mean of the readings) in the registers, the number of readings to 40, the trigger to hold (which keeps the meter from triggering until I press ENTER and then trigger the sequence of 40 readings when I push the ENTER button. You can do all of this manually from the keypads but since I use this sequence a lot I have preprogrammed it. This is after I set digits to 8 and PLC to 100. Once those 40 readings are finished then you can access the various MATH statistic registers, using the menu, by entering MATH and then a 2 for low, a 4 for mean, and 13 for high. Of course you could do all of this through the IEEE also. The 3458A has a very rich set of measurement commands. I am still learning all of them. It depends upon what I am trying to accomplish. Since the 1.018 and 1.0 volt outputs are passive and derived from resistive dividers from the 10 volt, I don't see how they could contribute to the varying readings you are measuring. I think I would put a short on the input of the 3458A and manually set the range to 1 volt and then observe the variations that way without the 732A involved. When I do this I see a variation from low reading to high reading of 0.125 uVolts and then another 40 I get 0.155 uVolts. This is without the GUARD connected to the low side of the measurment terminals, GUARD connected doesn't seem to affect
