1. The heating current is 5mA, the emission sits on top of that.
It is current limited--so the bad batch of filaments that went out a
while ago looked like they might have been too thick and carried too
much current--so the over all current limit was hit before you got
good emission. If the leads are (close to) touching in the source,
then the current bleeds thru that way. Probably not a problem for
you Also I remember hearing about a bad batch of source
heaters--they would leave a deposit on the insulators--so a small
leak to ground at voltage.
2. Our set up has the HV showing in Volts--and it goes from 0 to
3000 mV. So it should go all the way to 0 mV. You can even check
for problem with voltages at say 1000 mV? Everything should float
on the hV, which, at least according to the readbacks, bounces
around a little. It may also float a little away from your
ground--depending on what you're using for ground--but that
shouldn't be much.
On 1/12/2016 10:38 AM, Andrew Schauer
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1) Does anyone know what the current range THROUGH the
filament is supposed to be? I am not referring to the emission
(~ 1.0 mA). We are having a complete loss of signal and right
now it looks like the current through the filament is not
varying as a function of the potentiometer (physical
potentiometer on the face of the instrument). When I vary the
potentiometer I see no variation for most of the travel and
the a sudden drop to zero volts (across a resistor that
escapes me at this moment).
2) For the Isodat software 2.x on windows xp, if I vary the
HV [steps], from 0 to 3000, what should I expect in terms of
real high voltage variation? For example, if I measure voltage
between (yes using appropriate high voltage probes and
caution) ground and "col".
To call out two of you that may be listening (Peter and
Christie), we talked at the clumped conference about this loss
of signal issue. The source connections are all sound (I
vented it and checked each connection which were all very
solid). I also measured no connection between any feedthrough
and another (apart from the 0.2 ohms for the filament). I also
observe expected magnet strength when I hold a metal object
near the magnet during hysteresis.