[time-nuts] Low noise power supply recommendations

Wed Jun 15 03:13:57 UTC 2011

Hi Will,

I don't know. Check the HP Group archives. I only vaguely followed the
thread. I'm not so sure a phototransistor will work without circuit mods.
A photoFET might.

Best,

-John

===============

> John,
>
> I wondered about that, as using a LED is generally in conjunction with a
> photo-transistor, and not a CDS cell. The reason I thought it might work
> is
> that a company years back used them together to form a safety light
> curtain.
>
> The Fluke, and the HP, had a bad rep for those neon bulbs going out and
> having to be replaced. I am going to replace the ones in the 844 before I
> button it up, but was wondering if something else could be done. I looked
> up the life cycle for the NE-3 and it's kind of low, especially compared
> to
> a LED. I imagine the problem has to do with the brightness of the LED, as
> compared to a neon bulb, when using a CDS cell.
>
> As far as the power supply is concerned, I think I am going to go with
> Ni-Cad batteries, and regulate the voltages. I think what they had was
> nothing more than four step voltages from the battery supply, going from
> 3,
> 6 (7), 12, and 24 Vdc, or X2 of the other. From what I saw in the article
> earlier, an easy zener with emotter follower regulator should do the trick
> by the comparison with batteries. They used some resistance in series with
> the zener to reduce noise, but it did decrease the stability somewhat. I
> have seen this used in some old bias regulation circuits for tubes years
> ago.
>
> As far as the noise, I also wondered about this, as ESI used a current
> limited DC power source to do the same thing, and it was ran off the AC
> line.
>
> Thanks,
>
> Will
>
> *********** REPLY SEPARATOR  ***********
>
> On 6/14/2011 at 7:14 PM J. Forster 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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