Good to see you last week.
What we`re really looking for with the filament supply is that the
supply can provide enough current for the filament to emit electrons.
As Gerry said, last year there were filaments whose characteristics
didn`t allow the emission to reach 1.5 mA before the filament hit the
maximum allowable current.
If you measure the filament current (contact me off line for detailed
instructions on how to do this as the filament is at 3000 volts and all
high voltage precautions need to be taken) what I would expect to see is
that from switch on the current goes towards 5 amps. Then the filament
starts to emit and once the emission current reaches 1.5 mA the filament
current will start to drop finally stabilising around 4`ìsh amps.
If you have 1.5mA of emission, the filament is emitting correctly.
The next question is where is the 1.5mA of emission going. If you 1.5mA
all going to the box then you will see no ions. However if you have at
least 0.5mA of trap current you should be generating ions.
For the high voltage; If you scan from 0 to 3000 and measure the actual
high voltage (again this is high voltage and dangerous, only trained
personnel should do this), you will see 0 to 3000 volts. The actual
value is not that important when looking for ions as normally we would
vary the magnetic field to find the ions. So at this stage we just need
to know if there is high voltage (around 3000) or not.
On 12/01/2016 9:38 AM, Andrew Schauer wrote:
> Greetings list,
> Two questions:
> 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.
> Thank you.
> Andrew Schauer
> [log in to unmask] <mailto:[log in to unmask]>
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