vtvm question??

[Gary L. Sanders]

Why would the grid Voltage be affected by capacitance in the DC mode? In an AC
mode, there is a low-pass filter produced by the 1Meg resistor and the cable
capacitance, which I don't see reducing the problem of cable capacitance
affecting readings.
--
Regards,
Gary L. Sanders, Staff Analog Eng., gsanders at csidaq.com
Celerity Systems, Inc. --- http://www.csidaq.com
Cupertino, CA USA (408) 873-1001 fx (408) 873-1397
Ultra Fast Acquisition & Data Generation Systems

Alan Dean Martin wrote:

> Additionally the 1 meg resistor helps isolate the effect of cable
> capacitance from the circuit under test. This permits testing grid d.c.
> voltages, for example, which might otherwise become erroneous reading if the
> cable capacitance were connected without the 1 megohm isolation.
>
> Alan Martin
> Linear Technology Corporation
>
> Gary L. Sanders wrote:
>
> > The 1Meg resistor in the probe prevents dangerous high Voltage shorts if
> > the probe is carelessly disconnected while on a high Voltage. This
> > divider results in the meter having to be calibrated to compensate for
> > the .90909 loss. When a Hi Voltage probe is used, a 909Meg resistor is
> > used in the probe resulting in a 100:1 divider that is only off 1%. If
> > there is some leakage around the big resistor, such as sweat, oil, or
> > grime, then the accuracy is off in the right direction to get better.
> > --
> > Regards,
> > Gary L. Sanders, Staff Analog Eng., gsanders at csidaq.com
> > Celerity Systems, Inc. --- http://www.csidaq.com
> > Cupertino, CA USA (408) 873-1001 fx (408) 873-1397
> > Ultra Fast Acquisition & Data Generation Systems
> >
> > Steve Lords wrote:
> >
> > > greetings
> > >  does anybody know why heathkit on the
> > > im-13 vtvm put the extra 1 meg resistor in the
> > > probe and not in the unit,without the probe
> > > the vtvm is only 10 meg
> > >
> > > when reading articles about rf probes
> > > they mention the probe will work with
> > > 11 megohm vtvms however without the probe that
> > > comes with the im-13,the input is only 10 megohm
> > > which will affect the reading,
> > > maybe the 1 meg should be put into the rf probe
> > > when using the im-13...
> > > thanks
> > > steve
> > > wa7isl :)
> > >
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