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" <randyevans2...@gmail.com>
To: "Discussion of precise voltage measurement" <volt-nuts@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 <wpgold3...@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" <randyevans2...@gmail.com>
To: "Discussion of precise voltage measurement" <volt-nuts@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 <tmical...@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 <
randyevans2...@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
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