[volt-nuts] AC calibration
pa4tim at gmail.com
pa4tim at gmail.com
Mon Aug 25 09:43:25 EDT 2014
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
Verzonden met Windows Mail
Van: Bill Gold
Verzonden: maandag 25 augustus 2014 15:40
Aan: volt-nuts
Randy:
Sorry my fault. You have to use the "RMATH" command to get the various
values stored in the registers. See the "RMATH" command in the User's Guide
for a list of what registers you can read.
I sure haven't found any other guides other than the 4 manuals. User's
Guide, Quick Reference Guide, Calibration Manual, and Assembly Level Repair.
It is just a matter of reading the guides and trying to remember what
commands are available. It took me a lot of time to figure out what
commands I use now. I am sure I am missing other commands that might be
useful.
Bill
----- Original Message -----
From: "Randy Evans" <randyevans2688 at gmail.com>
To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
Sent: Sunday, August 24, 2014 6:04 PM
Subject: Re: [volt-nuts] 732A and Prologix received
> 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 <wpgold3637 at 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 the
> > readings. So that is the base noise of the 3458A without the 732A,
> > somewhere below .2uVolts. When hooked up to the 732A 1.0 volt output I
got
> > a variation of 0.159 uVolts using the same 40 reading method above. I
> > would
> > use this to determine where your problem might exist. Just having the
> > meter
> > input shorted will point you in the right direction. Meter, cables or
> > 732A.
> >
> > Sorry for the long dissertation. Friends get mad at me for being so
> > detailed sometimes.
> >
> > Bill
> >
> > ----- Original Message -----
> > From: "Randy Evans" <randyevans2688 at gmail.com>
> > To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
> > Sent: Sunday, August 24, 2014 7:22 AM
> > Subject: Re: [volt-nuts] 732A and Prologix received
> >
> >
> > > Bill,
> > >
> > > I have convinced myself that the problem I an seeing is due to
thermals.
> > > If I move the cables (with gold-plated banana plugs) using a small
towel
> > > rather than letting my hand touch the plugs, it is much more stable.
If
> > I
> > > then hold the banana plug with my hand after the reading has
stabilized,
> > > the reading drifts rapidly upward. I am trying to check the stability
of
> > > the reading but I haven't figured out the MATH function yet. I assume
> > this
> > > is a programmed function using GPIB only?
> > >
> > > The stability I am seeing by manually recording readings (using NLPC
of
> > 100
> > > and 1000) is much greater than what you are measuring on your system.
> > Not
> > > sure how to ascertain if it's the 3458A or the 732. The value of the
> > > readings are very different between the two - the 3458 reads about 50
uV
> > > high on the 10 V output and about 12 uV low on the 1V output. Rather
> > large
> > > differences (this is after an ACAL). I need to find some better
cables
> > to
> > > make sure the errors are not due to thermals again.
> > >
> > > Randy
> > >
> > >
> > > On Sat, Aug 23, 2014 at 10:21 AM, Bill Gold <wpgold3637 at att.net>
wrote:
> > >
> > > > Randy:
> > > >
> > > > I get 6 volt 4 amp/hr (or 4.5 amp/hr) batteries and they will
fit
> > > > perfect. Power Sonic PS-640, Genesis NP4-6, Panasonic LC-R064R5C
and
> > > > others
> > > > that are in this size and package. Order from one of the usual
> > electronics
> > > > distributors like Allied, Mouser, Digikey. This is a very common
> > battery
> > > > as
> > > > it is used in a lot of "EXIT" signs so they are lighted when the
power
> > goes
> > > > out. I don't see how the 12V 7AH will fit as they are too large. I
> > guess
> > > > you could use a 12V 5AH (PS1250) as it is the same size as 2 x 6
volt 4
> > AH
> > > > but the terminals are in the wrong place so you will have to
"nibble"
> > out
> > > > the aluminum plate that holds them in the 732A battery pack. You
have
> > to
> > > > be
> > > > careful if you use the 12v 5AH as you will have 4 extra battery
> > connection
> > > > leads to deal with and connect correctly. I would stick with the 6V
> > 4AH.
> > > > New batteries will last around 12 to 14 hours before the "CAL" light
> > goes
> > > > out when AC power is not applied. So shipping to Cal Lab can be a
> > problem
> > > > if it is a distance away, or you have to use a shipper like UPS or
> > FEDEX
> > > > and
> > > > you ship the night before and then use their "Morning delivery" and
the
> > Cal
> > > > Lab is expecting your 732A. Same on the way back to you. Of course
> > you
> > > > could always strap another battery on the 732A and hook it up to the
> > "ext
> > > > power" plug to last longer. I have seen it done. The issue is to
get
> > the
> > > > Cal Lab to charge the extra battery before they ship the 732A back
to
> > you.
> > > >
> > > > When you remove and work on the battery pack always have the AC
> > power
> > > > plugged in. The "CAL" led will stay on because the 18.6 v regulated
> > supply
> > > > is working.
> > > >
> > > > The "CAL" light is to indicate that power has not been lost to
the
> > > > Reference Amp or other associated circuits. When the raw supply
> > (battery)
> > > > voltage drops below about 21 volts the "CAL" light will go out.
Below
> > that
> > > > voltage the heater circuits will not work correctly and the 18.6
volt
> > > > regulated supply will not regulate. The requirement is that the
> > Reference
> > > > Amp be kept "alive" at all times to maintain the output voltage that
> > was
> > > > measured at the time of the most recent Calibration or
Certification.
> > When
> > > > the semiconductor junctions are unbiased and cool off when power is
> > lost,
> > > > and then power is restored the result will be a different 10 volts
than
> > > > before the power failure. My experience is that after all of the
years
> > > > that
> > > > these units have been powered up, this won't happen and when power
is
> > lost
> > > > and then restored, even months later, the 732A will come back to
almost
> > > > exactly the same 10 volts as when they lost power, usually with in
0.2
> > PPM
> > > > after 24 hours of "warm up".
> > > >
> > > > What type of hookup leads are you using when measuring the 1
volt
> > > > output? What is the PLC set to? I always use 100 PLC to measure
this.
> > If
> > > > you don't have "low thermal" connection leads you can experience uV
> > changes
> > > > for a minute or more after plugging in the leads due to the
"thermals"
> > > > generated because of the difference in temperature between the
banana
> > jacks
> > > > on the 732A and the banana plugs of the leads. I have found that
even
> > just
> > > > plugging in the lead will generate a thermal difference because of
> > > > difference of temps and some heating due to the physical act of just
> > > > inserting the plug because of friction between the jack and plug (my
> > theory
> > > > at any rate). You have to allow at least a minute or more before
being
> > > > able
> > > > to make a measurement after plugging in the leads. I just measured
the
> > > > variation of the 1 volt output of my 732A and using my 3458A and I
got
> > a
> > > > total difference of 0.159 uV over 40 measurements using 100 PLC on
the
> > 1
> > > > volt range of the 3458A. Using the MATH function and all of the
data
> > you
> > > > can collect. That was after waiting for several minutes after
plugging
> > in
> > > > the leads.
> > > >
> > > > I hope all of this helps.
> > > >
> > > > Bill
> > > >
> > > >
> > > >
> > > > ----- Original Message -----
> > > > From: "Randy Evans" <randyevans2688 at gmail.com>
> > > > To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
> > > > Sent: Friday, August 22, 2014 9:03 PM
> > > > Subject: Re: [volt-nuts] 732A and Prologix received
> > > >
> > > >
> > > > > Todd,
> > > > >
> > > > > Thanks for the info. I have several Panasonic 12V 7 AH batteries
> > that
> > I
> > > > > keep topped off and they have very low current draw (~2 to 3 mA at
> > 13.5
> > > > > VDC) when charged and at their float voltage, so I am pretty sure
> > they
> > > > are
> > > > > in good condition. I will look at getting those in the units
after I
> > > > > ascertain the condition of the 732.
> > > > >
> > > > > So now I have a what appears to be a functioning 3458A and a 732A
but
> > > > they
> > > > > slightly disagree. I am like the man with two watches that
disagree
> > on
> > > > the
> > > > > time - which is correct? For the moment, i am only concerned
with
> > > > > stability. The need for absolute accuracy will come later.
> > > > >
> > > > > Randy
> > > > >
> > > > >
> > > > > On Fri, Aug 22, 2014 at 8:06 PM, Todd Micallef
<tmicallef at gmail.com>
> > > > wrote:
> > > > >
> > > > > > Randy,
> > > > > >
> > > > > > You have two possible choices. It can be configured with 4 x 6v
4Ah
> > > > > > batteries or 2 x 12v 7Ah batteries. Hopefully the previous owner
> > has
> > > > > > modified the battery pack already. A couple of mine needed a
> > nibbler
> > > > tool
> > > > > > to remove enough of the aluminum cover that fits over the tops
of
> > the
> > > > > > batteries. The original cover will short out to the battery tabs
> > > > regardless
> > > > > > of the battery configuration if this is not done.
> > > > > >
> > > > > > You can find larger capacity batteries that will give you
slightly
> > more
> > > > > > battery life. I lost a couple sets of mail-order batteries after
a
> > few
> > > > > > extended outages. I would recommend going with locally bought
> > batteries
> > > > > > instead of the cheaper mail order. My local Batteries Plus will
> > > > typically
> > > > > > have some warranty if I remember correctly. Moving forward I
will
> > only
> > > > use
> > > > > > 2 12v batteries and pre-charge them on a battery charger to
> > equalize
> > > > them
> > > > > > before putting them in the 732A. I think the cheap batteries did
> > not
> > > > > > discharge equally, and would not recover when power was applied.
> > > > > >
> > > > > > Inspect the back plane for damaged traces and look at the
> > capacitors. I
> > > > had
> > > > > > a few that looked questionable. So far, I have replaced all the
big
> > > > caps
> > > > on
> > > > > > the pre-regulator and regulator boards. My feeling is that once
> > these
> > > > go
> > > > > > online, they should run as long as possible between repairs.
> > > > > >
> > > > > > The battery charger circuit may need adjusting. I tweaked mine
and
> > it
> > > > > > seemed to work fine.
> > > > > >
> > > > > > Todd
> > > > > >
> > > > > >
> > > > > > On Fri, Aug 22, 2014 at 10:42 PM, Randy Evans <
> > > > randyevans2688 at gmail.com>
> > > > > > wrote:
> > > > > >
> > > > > > > I received my Fluke 732A today. Just powered it up but it
needs
> > new
> > > > > > > batteries. Any suggestions for sources (I haven't opened up
the
> > unit
> > > > > > yet -
> > > > > > > I want to make sure it works before doing that). Also
received
> > the
> > > > > > > ProLogix USB-GPIB adapter. I plan on using Mark Sims' CAL ran
> > data
> > > > > > dumper
> > > > > > > program to get the CAL data from my 3458A. Should be a busy
> > weekend.
> > > > > > >
> > > > > > > Randy
> > > > > > > _______________________________________________
> > > > > > > volt-nuts mailing list -- volt-nuts at febo.com
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> > > > > > >
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