current-amp recommendation
I've gotten involved with a project in which stabilization of the position of a monochromatic, soft X-ray beam is needed. The offending frequencies seem to be vibration frequencies like 57 and 116Hz. We have in mind to use a thin Au film with a gap in the middle, measuring the drain current from the films, much as people normally use the jaws of slits. Now, I'd like to find a couple of current amplifiers which are small enough so that they can be connected with very short cables to the BNC connectors on the air-side of this detector, and which would have decent frequency response and low noise with inputs of the order of 0.1-1nA. Although this topic is outside the realm of XAFS analysis with IFEFFIT, I figure that people on this group might have some good experience. mam
Hi Matthew, At NSLS-II, we use a solution developed here at BNL for quad BPMs and other current-measurement operations. (I am using it for ion chambers at my beam line.) It is a box developed in the Instrumentation Division with a current amplifier, an A2D converter, and a microprocessor all inside a box that's about the size of a box of Pop Tarts. It has 4 SMA input channels and a single gain for all four channels. SMA to BNC cables are readily available from all the standard vendors. The output is an ethernet cable. The microprocessor runs a small debian system and starts an EPICS IOC and a DHCP client on boot. the 4 current get exposed as 4 PVs and the IOC does a lot of useful statistics on the fly. Seems to work pretty well. You could contact Pete Siddons. (Search for Siddons at the BNL website. When I tried it, the second hit was his staff page.) B On 11/14/2017 03:16 PM, Matthew Marcus wrote:
I've gotten involved with a project in which stabilization of the position of a monochromatic, soft X-ray beam is needed. The offending frequencies seem to be vibration frequencies like 57 and 116Hz. We have in mind to use a thin Au film with a gap in the middle, measuring the drain current from the films, much as people normally use the jaws of slits. Now, I'd like to find a couple of current amplifiers which are small enough so that they can be connected with very short cables to the BNC connectors on the air-side of this detector, and which would have decent frequency response and low noise with inputs of the order of 0.1-1nA. Although this topic is outside the realm of XAFS analysis with IFEFFIT, I figure that people on this group might have some good experience.
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-- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Science Group at NSLS-II Building 743, Room 114 Upton NY, 11973 Homepage: http://bruceravel.github.io/home/ Beamline: https://www.bnl.gov/ps/beamlines/beamline.php?r=6-BM Software: https://github.com/bruceravel Demeter: http://bruceravel.github.io/demeter/
HI Matthew: One possibility is the Caen quad amplifier that they made for BPMs. http://www.caenels.com/products/tetramm/ Carlo On Tue, 14 Nov 2017, Matthew Marcus wrote:
I've gotten involved with a project in which stabilization of the position of a monochromatic, soft X-ray beam is needed. The offending frequencies seem to be vibration frequencies like 57 and 116Hz. We have in mind to use a thin Au film with a gap in the middle, measuring the drain current from the films, much as people normally use the jaws of slits. Now, I'd like to find a couple of current amplifiers which are small enough so that they can be connected with very short cables to the BNC connectors on the air-side of this detector, and which would have decent frequency response and low noise with inputs of the order of 0.1-1nA. Although this topic is outside the realm of XAFS analysis with IFEFFIT, I figure that people on this group might have some good experience.
mam _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit
-- Carlo U. Segre -- Duchossois Leadership Professor of Physics Interim Chair, Department of Chemistry Director, Center for Synchrotron Radiation Research and Instrumentation Illinois Institute of Technology Voice: 312.567.3498 Fax: 312.567.3494 segre@iit.edu http://phys.iit.edu/~segre segre@debian.org
Hi Matthew, Carlo,
On Tue, Nov 14, 2017 at 3:32 PM, Carlo Segre
HI Matthew:
One possibility is the Caen quad amplifier that they made for BPMs.
http://www.caenels.com/products/tetramm/
Carlo
Yes, I second this recommendation, at least in general. We've used caen amplifiers with thin-foil BPMs for awhile and they're good at going pretty fast (can definitely do 10 kHz) and giving a fairly low noise level. Nice features of the Tetramm include only two gain settings and the fact that it streams out floating point numbers in Amps. There is also decent Epics support. I played with using one of these for ion chambers and it works pretty well for large enough currents: the noise level on the lowest gain setting at 1kHz is around 0.7 pA, so it works well for measuring I0 of ~10 nA and above. So, I'm not sure how well it would work for doing feedback with currents of 0.1 to 1 nA. But, when I've talked to the Caen engineers they've been very knowledgable and helpful. --Matt
participants (4)
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Bruce Ravel -
Carlo Segre -
Matt Newville -
Matthew Marcus