> John, > > I will check it out, and may do some experiments myself on these. Also, I > will take a look at the photo-FET's, as I had forgotten about those. > > What has me wondering is how neon bulbs act in the circuit, their low > brightness, and their drop out times, as I think the on voltage is around > 90 volts or so,
More like 70. They need a higher voltage to turn on (strike). > but the square wave going to them is around 100-115 volts > if I recall. I thought about using a simple 10:1 resistive divider, then > using a series resistor from that junction going to the LED, the same as > for a 10-15 volt supply. Neons run at very low currents. > The neon bulbs light goes through two Lucite tubes > to the CDS cells, and it couldn't be too bright by the time it reached > them. Tubes or rods (as a light guide)? > I also thought about using a new form of chopper, as Paul mentions, but > making it fit and work could get complicated. ESI quit using the HP 419 in > the last models of their 801 DC supply and detector-null meter, and > started > using a Keithly 155. I either figured it was over this very thing, or HP > dropped the 419 from its line. An engineer at Vishay told me that they > quit > using the Fluke over this neon problem, and went to the Keithly in the > last > versions of this bridge. OK. > I'm going to be using the bridge not only as it was intended, but to do > other null measurements, as I added a circuit to use the meter circuit > seperatly from the bridge. > > Thanks, > > Will Good luck. BTW, the HP thread referred to degradation of the CdS cells. You should read it. It is possible to makle a very high Z chopper with CdS. I'm not so sure about other ways. -John ================ _______________________________________________ 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.