Carbon film 10M should be stable as long as it is not subjected to voltages near its maximum ratings for extended periods of time. Long term drift could occur if for example a 1/4 watt carbon film (typ 300V rated) is soldered into a circuit whereby it sees 200 to 300V continuously for many, many hours. Heat buildup will compound the drift. Though, in no way would this drift approach that of a carbon comp.
But for a probe, I think you have no issue with stability. BTW, capacitance can be further reduced by putting resistors in series. It will already by low, but series resistors might help you with finding metal film of high enough value. It will also increase the voltage rating of your probe. The probe body is long so in-line series connections should fit. Dennis AE6C On 11/22/12, Paul Christensen <w...@arrl.net> wrote: >> Good solution, Paul! Mentally dividing by ten is easy enough and you >> retain all of the advantages of using the VTVM probe. >> >> Dennis AE6C > > Well....'sorta. The divide by ten works well and it's an easy mental > exercise. But in creating a 1 meg/100K divider, the load across the voltage > > sampling point is reduced from 10 meg to 1 meg. That undermines the purpose > > of the resistive probe except that the effects from cable capacitance and > lead inductance are swamped. But if the source Z providing grid voltage, > for example, is greater than 100K big errors will start setting in. > > So...next I'm going to change the 1 meg resistor in VTVM probe to 10 meg > (like the 100x probe), and then try a variable shunt at the DMM end to find > > the value where 10:1 is achieved. That 10 meg is a high value for low > voltage readings and I'm not sure how stable readings will be. I think 10 > meg is commonly available in carbon film, but tougher to find in metal > film. > > Paul, W9AC > > _______________________________________________ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
