[time-nuts] Low noise power supply recommendations

[Will Matney]

Paul,

Remember the HP 412? It used incandescent bulbs, a spinning disc, and a
syncronous motor. I actually still use two of these, and the bulbs are the
only fault.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 6/14/2011 at 10:21 PM paul swed wrote:

>Though its a bit off topic
>Ran into this chopper issue also on a HP410. I replaced the thing with a
>modern chopper amp. I think an LTC. This was quite a few years ago (10
plus
>easily) and it works very well. Still does actually. It did take a bit of
>rework to get things back in balance correctly.
>
>On Tue, Jun 14, 2011 at 10:14 PM, J. Forster <jfor at quik.com> wrote:
>
>> The reason I asked is that most microvolt bridges use choppers and have
BP
>> filters at the chopper frequency, so noise is largely uncorrelated.
>>
>> On the neon photochoppers, it has been discussed at length several times
>> on the HP-Agilent Yahyoo Group. A similar thing is used in the 410C.
There
>> are apparently issues with the CdS cells.
>>
>> Best,
>>
>> -John
>>
>> ===============
>>
>>
>> > John,
>> >
>> > No, it's DC. I'm trying to meet the original specs of the batteries in
>> not
>> > only voltage/current, but cleanliness of the current.
>> >
>> > Now inside the Fluke 844, it has a chopper, and it uses an AC power
>> supply
>> > internally to feed its circuitry. The Vishays bridge uses the
batteries
>> > voltage, and one small AC power supply to run the digital portion of
the
>> > bridge for the PPM readout. The bridge itself is half analog and half
>> > digital. The analog for the measurement, and the digital for the PPM
>> > difference.
>> >
>> > By the way, has anyone ever converted a neon NE-3 driven chopper to
using
>> > LED's? The bulbs have a sqaure wave coming into them of around 100-200
Hz
>> > if I recall.
>> >
>> > Thanks,
>> >
>> > Will
>> >
>> > *********** REPLY SEPARATOR  ***********
>> >
>> > On 6/14/2011 at 6:50 PM J. Forster wrote:
>> >
>> >>Is the bridge excitation AC or DC. If it's AC, you may not even need
>> >>low-noise power supplies.
>> >>
>> >>-John
>> >>
>> >>==============
>> >>
>> >>
>> >>
>> >>> Hi Will,
>> >>>
>> >>> You could consider building your own power supply system for the
>> >>> replacement of
>> >>> the batteries.  Use a separate power transformer which, I suspect,
>> >>> would
>> >>> be small
>> >>> as the current requirements would be low for driving a bridge
circuit.
>> >>>
>> >>> The main company to look toward for high quality, low noise
regulators
>> > is
>> >>> Linear
>> >>> Technology.  Here is a candidate part to look at :
>> >>> http://www.linear.com/product/LT3082
>> >>>
>> >>> This is the lowest noise (33uv/10Hz to 100KHz) low dropout regulator
>> > that
>> >>> can
>> >>> handle regulating 24 volts and is adjustable, meaning use can use
this
>> >>> part for
>> >>> all three voltages (i.e., three regulators).  You will have to
decide
>> >>> if
>> >>> it noise
>> >>> specs are suitable for your needs.  Keep in mind that battery noise
is
>> >>> typically
>> >>> random whereas the noise out of a regulated system tends to be
>> >>> constant.
>> >>>
>> >>> If you really think you need lower noise then you could consider an
>> > LT1000
>> >>> shunt
>> >>> reference.  Typically the circuit designs for LT1000 type devices
are
>> >>> as
>> >>> references and lack current capability above about 10 milliamps.
>> >>> Adding
>> >>> additional current circuitry would add more noise.  See:
>> >>>
>> >>> http://www.linear.com/product/LTZ1000
>> >>>
>> >>>
>> >>> Bill....WB6BNQ
>> >>>
>> >>>
>> >>> Will Matney wrote:
>> >>>
>> >>>> Hello,
>> >>>>
>> >>>> I am in need of a very clean 24 Vdc power source, to replace some
old
>> >>>> mercury cell batteries with. What would a good low noise, clean,
power
>> >>>> supply be in your recommendations? I thought of using two 12 Vdc
>> >>>> lead-acid
>> >>>> batteries in series, and making a charging circuit with regulators,
>> >>>> but
>> >>>> I
>> >>>> am hoping to purchase a good used supply off ebay, etc. The old
>> >>>> circuit
>> >>>> used two 12 Vdc snap terminal mercury batteries in series, for 24
Vdc,
>> >>>> along with a 7 Vdc mercury cell, and two plain AA carbon 1.5 Vdc
>> >>>> batteries
>> >>>> in series for 3 volts. Any help and or ideas would be appreciated.
>> >>>>
>> >>>> Thanks
>> >>>>
>> >>>> Will
>> >>>>
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>> >>
>> >>
>> >>
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