added appendix page about ion chambers

docs/index.rst

@@ -40,4 +40,5 @@ BMM is NIST's Beamline for Materials Measurement
 
    profile.rst
    plotting.rst
+   ionchambers.rst
    todo.rst

docs/ionchambers.rst

@@ -0,0 +1,119 @@
+
+.. _ionchambers:
+
+Managing ion chamber signal chains
+==================================
+
+In the 2023-3 and 2024-1 cycles, BMM went through a transition in how
+direct beam signals (I\ :sub:`0`, I\ :sub:`t`, I\ :sub:`r`) are
+measured.
+
+The old system
+==============
+
+BMM has been using the same ion chambers that were used at X23A2 at
+the old NSLS.  They are excellent ion chambers |nd| robust, linear,
+easy to use.  At BMM, we used a `QuadEM
+<https://epics-modules.github.io/quadEM/quadEMDoc.html>`__
+electrometer to read the current signal from each ion chamber.  The
+QuadEm is a four-channel device, so I\ :sub:`0`, I\ :sub:`t`, and I\
+:sub:`r` were fed into channels 1, 2, and 3.  The fourth channel was
+occasionally used for an electron yield detector.
+
+Voltage was supplied from the same Ortec high voltage supply used at
+X23A2.  The Ortec device sits outside the hutch.  The high voltage
+was fed via cabling through a roof labyrinth and patch panels.
+
+An IOC for reading the QuadEM lives on ``xf06bm-ioc2`` and
+communicates with the QuadEM device via a cat6 cable.
+
+.. subfigure::  AB
+   :layout-sm: AB
+   :gap: 8px
+   :subcaptions: above
+   :name: old_IC
+   :class-grid: outline
+
+   .. image:: _images/old_IC.jpg
+
+   .. image:: _images/quadem.jpg
+
+   (Left) The old I\ :sub:`r` detector.  (Right) The quadem
+   electrometer used to measure the three old-style ion chambers.
+
+
+The new system
+==============
+
+The new ion chambers are integrated devices.  The low half of the
+enclosure is a gas-filled volume with capacitor plates made from
+printed circuit board.  The plates are guarded at both ends and
+upright print circuit board pieces are used to guard the fringes of
+the fields.  These upright pieces are strips of copper bridged by
+surface-mounted resistors acting as a sequence of voltage dividers.
+This keeps the field lines art the periphery of the capacitor plates
+nicely parallel.
+
+The upper part of the enclosure has the full signal chain and a
+voltage supply.  This includes an amplifier, an analog-to-digital
+converter, and a microprocessor running an embedded Debian system and
+a two-channel version of the QuadEM IOC.  The voltage supply is fully
+adjustable up to 2000 V, but are run at 200 V.
+
+The electronics package and the voltage supply are powered a 6 V DC
+power supply.  A cat6 cable for each ion chamber allows the IOCs to
+communicate on the INST network.
+
+The ion chambers also have an optical fiber input port so that data
+can be time stamped with the global timing signal from the
+accelerator.  This will be used in the near future to implement
+continuous scanning on the monochromator.
+
+
+
+.. _fig-new_IC:
+.. figure::  _images/new_IC.jpg
+   :target: _images/new_IC.jpg
+   :width: 70%
+   :align: center
+
+   The new I\ :sub:`0` detector with integrated electronics and
+   voltage supply.
+
+Configuration in bsui profile
+=============================
+
+I am trying to make it easy to configure ``bsui`` to switch easily
+between ion chambers and electrometers.  This is a work in progress.
+Here I document the current, slightly awkward, state of affairs.
+
+In `BMM/user_ns/dwelltime
+<https://github.com/NSLS-II-BMM/profile_collection/blob/master/startup/BMM/user_ns/dwelltime.py#L26>`__
+three boolean parameters are set: ``with_ic0``, ``with_ic1``, and
+``with_ic2``.
+
+These are used to synchronize setting integration times across the
+various signal chains via the `LockedDwellTimes
+<https://github.com/NSLS-II-BMM/profile_collection/blob/master/startup/BMM/dwelltime.py#L40>`__
+object.
+
+Each new ion chamber in use needs to have its flag set to ``True``.
+
+The detectors themselves need to be configured correctly in `this file
+<https://github.com/NSLS-II-BMM/profile_collection/blob/master/startup/BMM/user_ns/detectors.py>`__
+using the flag values.
+
+The QuadEM and each individual ion chamber will be configured if
+available on the network.  If the network connection cannot be
+established, a ``noisy_det`` from ``ophyd.sim`` is created with the
+same name.
+
+Notes:
+
+#. If the ion chamber device can be made, it will be made even if its
+   flag is set to ``False``.  This allows interaction with an ion
+   chamber even if it is not expected to be used in a scan.
+#. Once all 3 new ion chambers are in place and in use, the QuadEM
+   device will still be made.  This will allow use of electron yield
+   and other detectors as well as measurement of any other current
+   signals. 

docs/plotting.rst

@@ -1,8 +1,3 @@
-..
-   This manual is copyright 2018 Bruce Ravel and released under
-   The Creative Commons Attribution-ShareAlike License
-   http://creativecommons.org/licenses/by-sa/3.0/
-
 
 .. _plotting: