[time-nuts] Low noise power supply recommendations

paul swed paulswedb at gmail.com
Wed Jun 15 02:21:20 UTC 2011


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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