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 <j...@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 > >>>> > >>>> _______________________________________________ > >>>> time-nuts mailing list -- time-nuts@febo.com > >>>> To unsubscribe, go to > >>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > >>>> and follow the instructions there. > >>> > >>> > >>> _______________________________________________ > >>> time-nuts mailing list -- time-nuts@febo.com > >>> To unsubscribe, go to > >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > >>> and follow the instructions there. > >>> > >>> > >> > >> > >> > >>_______________________________________________ > >>time-nuts mailing list -- time-nuts@febo.com > >>To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > >>and follow the instructions there. > >> > >>__________ Information from ESET Smart Security, version of virus > > signature database 5851 (20110206) __________ > >> > >>The message was checked by ESET Smart Security. > >> > >>http://www.eset.com > > > > > > > > > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > > > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.