.On 7/21/22 13:19, Martin Brown wrote:
Protecting the instrument from coolant failure and the hard vacuum
from plasma flame out was a major part of the safety critical side of
things. It was worse in the early days when the vacuum pumps were
diffusion. Any sort of cock up and you had hot silicone oil all over
the place.
Why weren\'t you running Santovac 5 instead of silicone oil? Same base
pressure as dc705 and no worries about insulating films from ion
bombardment if a little didn\'t get cleaned up after a backstreaming
incident
On 22/07/2022 03:49, Carl wrote:
On 7/21/22 13:19, Martin Brown wrote:
Protecting the instrument from coolant failure and the hard vacuum
from plasma flame out was a major part of the safety critical side of
things. It was worse in the early days when the vacuum pumps were
diffusion. Any sort of cock up and you had hot silicone oil all over
the place.
Why weren\'t you running Santovac 5 instead of silicone oil? Same base
pressure as dc705 and no worries about insulating films from ion
bombardment if a little didn\'t get cleaned up after a backstreaming
incident
They might have been for all I know. I did the software and firmware for
the embedded control system. I wasn\'t involved with the actual filling
of the diffusion pumps with whatever gunk they used. All I knew about it
was that on flame out we had to close the gate valve very quickly or it
would be a painful strip down and clean operation for some unlucky
technician. Mostly it worked fast enough but not always.
Life improved considerably when they moved onto turbo-molecular pumps
and for a while performance was improved even more by maglev ones.
Then one day an earthquake in Tokyo suddenly moved the Earth sideways by
an inch instantaneously and every damn one of them was destroyed. I
remember it well since in the quiet of the evening I heard the
earthquake coming (I have no idea how but I was wondering about the
strange train like sound outside when the jolt suddenly arrived).
We were busy doing turbo pump swaps for weeks and after that
conventional bearings were specified for earthquake zones.
The maglevs had been out in the field for a couple of years before this
rather nasty vulnerability became apparent.
Why? It\'s super easy to protect against. There\'s no energy involved to
jlarkin@highlandsniptechnology.com wrote:
On Fri, 22 Jul 2022 12:30:37 +0300, Dimiter_Popoff <dp@tgi-sci.com
wrote:
On 7/22/2022 3:17, John Larkin wrote:
On Thu, 21 Jul 2022 23:53:53 -0000 (UTC), Mike Monett <spamme@not.com
wrote:
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
Mike Monett wrote:
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
[...]
Yup. Back in the long ago (1984ish), I built a power supply filter
that got rid of 10 Vpp of 120 Hz ripple on a 2 kV supply for some
piezo stacks. It worked by lifting the cold end, sensing the hot end
via a 100 nF, 3 kV film cap, and wiggling the cold end to keep it
still. (It had some TVS protection too, obviously.)
With an LF356 op amp, I got 100 dB of ripple rejection, which came in
pretty handy. I could probably have done considerably better with
that feedforward trick of Woodward\'s, where you use another op amp to
measure the error voltage of the main one, and add in its output.
Another approach like that is the Kanner Kap, which wasn\'t first
invented by Kanner, but he now owns it on account of the cute name.
That\'s the trick where you use an RC lowpass, and drive the cold end
of the cap with some super beefy amplifier to make the top stay still.
Cheers
Phil Hobbs
The CCFL inverter I got from Amazon runs at 40KHz.
A simple half-wave rectifier running at 40 KHz with a 1nF cap and 9e6
Ohm load will produce about 2V sawtooth ripple.
This is about 2/800 = 0.0025 * 100 = 0.25% ripple.
That should be good enough.
Totally. You can probably use one of the HV caps that came with it to
couple the anode pulses to the outside world.
Cheers
Phil Hobbs
That is a problem. The RH Electronics MCA expects positive pulses. These
won\'t come from the anode.
https://static.wixstatic.com/media/e43988_a63520f4ed07436a843ddc1be0fda46a~
mv2.jpg
https://video.wixstatic.com/video/e43988_8006efb319884c72b9d7f7418abdfa97/7
20p/mp4/file.mp4
I shall write them and ask where they get those positive pulses.
A transformer could invert pulses and take out the HV and the HV
ripple. You\'d need to take out ps ripple for pulse height analysis.
Never thought of doing it like this but sounds reasonable.
OTOH for PHA with a scintillator there is not much energy resolution
to speak of so just about any shaping method you come up with will do.
One could also hang an opamp on the anode to get some gain before AC
coupling down to ground. A clever circuit would subtract out the power
supply ripple up there, or couple into a grounded diffamp. There are
some cheap, low-capacitance dc/dc converters to power the opamp.
n
Well, the PMT has a gain of a million already.
On Fri, 22 Jul 2022 16:48:16 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:
jlarkin@highlandsniptechnology.com wrote:
On Fri, 22 Jul 2022 12:30:37 +0300, Dimiter_Popoff <dp@tgi-sci.com
wrote:
On 7/22/2022 3:17, John Larkin wrote:
On Thu, 21 Jul 2022 23:53:53 -0000 (UTC), Mike Monett <spamme@not.com
wrote:
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
Mike Monett wrote:
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
[...]
Yup. Back in the long ago (1984ish), I built a power supply filter
that got rid of 10 Vpp of 120 Hz ripple on a 2 kV supply for some
piezo stacks. It worked by lifting the cold end, sensing the hot end
via a 100 nF, 3 kV film cap, and wiggling the cold end to keep it
still. (It had some TVS protection too, obviously.)
With an LF356 op amp, I got 100 dB of ripple rejection, which came in
pretty handy. I could probably have done considerably better with
that feedforward trick of Woodward\'s, where you use another op amp to
measure the error voltage of the main one, and add in its output.
Another approach like that is the Kanner Kap, which wasn\'t first
invented by Kanner, but he now owns it on account of the cute name.
That\'s the trick where you use an RC lowpass, and drive the cold end
of the cap with some super beefy amplifier to make the top stay still.
Cheers
Phil Hobbs
The CCFL inverter I got from Amazon runs at 40KHz.
A simple half-wave rectifier running at 40 KHz with a 1nF cap and 9e6
Ohm load will produce about 2V sawtooth ripple.
This is about 2/800 = 0.0025 * 100 = 0.25% ripple.
That should be good enough.
Totally. You can probably use one of the HV caps that came with it to
couple the anode pulses to the outside world.
Cheers
Phil Hobbs
That is a problem. The RH Electronics MCA expects positive pulses. These
won\'t come from the anode.
https://static.wixstatic.com/media/e43988_a63520f4ed07436a843ddc1be0fda46a~
mv2.jpg
https://video.wixstatic.com/video/e43988_8006efb319884c72b9d7f7418abdfa97/7
20p/mp4/file.mp4
I shall write them and ask where they get those positive pulses.
A transformer could invert pulses and take out the HV and the HV
ripple. You\'d need to take out ps ripple for pulse height analysis.
Never thought of doing it like this but sounds reasonable.
OTOH for PHA with a scintillator there is not much energy resolution
to speak of so just about any shaping method you come up with will do.
One could also hang an opamp on the anode to get some gain before AC
coupling down to ground. A clever circuit would subtract out the power
supply ripple up there, or couple into a grounded diffamp. There are
some cheap, low-capacitance dc/dc converters to power the opamp.
n
Well, the PMT has a gain of a million already.
Don\'t the dynodes wear out after some numbers of coulombs?