Bill,
I have never been able to use banana plugs of any kind, with my 3458A,
due to their excessive thermal mass. I use 24 gauge wires to make a
twisted pair by hand with no connectors for precision voltage work. As
brought out in an earlier post by acbern, it doesn't matter about
plating or solder at least as long as your twisted pairs are made from
the same wire so the thermocouples balance out.
I am a big fan of M27500 shielded twisted pair wire for everyday use. It
is durable, heat resistant and capable of very low voltage use. The
insulator is Tefzel and the plating used to be silver but may be
something else now. It take a few minutes work for proper termination
but it can be done for free. I tend to use a lot of the 24 gauge M27500
STP wire since it is fast to come to temperature, flexible and durable
enough to last quite awhile.
eBay always has quite a few small lengths available and Sierra Nevada
Products has a bunch of it. Sierra Nevada Products says that it is
Teflon but I think it may be Tefzel. I can help with termination
instructions if wanted.
Charlie
On 8/24/2014 7:22 AM, Randy Evans wrote:
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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