[time-nuts] Low noise power supply recommendations

[Will Matney]

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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