BNMR: EPICS: Difference between revisions
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Revision as of 16:30, 2 November 2018
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Purpose
This page gives bnmr or bnqr DAQ users information about the ISAC EPICS Control Pages and the Access required for running bnmr or bnqr experiments.
Introduction
The EPICS system is used at TRIUMF for the control system for beamlines etc. Experimenters will need to display the Epics Control Pages in order to run the bnmr or bnqr experiments. They must also ensure that BNMR has been granted write access to the required Epics parameters as described below, or they will not be able to change the relevant beamline controls.
Display ISAC Epics Control Pages
Switch onto a different desktop on linux box isdaq01 (or isdaq06) so the Epics Control page does not clutter the desktop used for running the experiment. Access the epics control pages on isacepics1 with ssh from an xterm window, as follows (if you don't know the password, ask a group member).
ssh bnmr@isacepics1 ( Type in the password )
You should see the main ISAC EPICS control page come up after a few seconds (Figure 1).
- Note
- There is no bnqr user account on isacepics1. The bnmr account is used for both experiments and the same EPICS access permission (i.e. BNMR) applies to both.
Write access to Epics Polarizer Parameters
Most Epics parameters can be read by anyone, but write access has to be granted by the Controls Group. Several experiments have been granted write access to the same polarizer IOCs, and to avoid conflict, only one of these experiments is granted overall Access. During the beam period, and for testing the helicity switching etc, access must be granted to expbnmr.
To check whether expbnmr has access, display the main EPICS control pages.
On the main EPICS Control Page (cf Figure 1) click the button labelled "Access". A page similar to Figure 2 will be displayed.
Clicking on the View access button (Figure 2) will show the current access. This should be set to expbnmr as in Figure 3.
If the Access is not set to expbnmr, ask the operators to switch the access by pressing the button Polarizer Access for bNMR/bNQR (Figure 2).
Even when "Access" is granted to BNMR, only those EPICS IOCs to which BNMR has been granted write access can be changed by the experimenters from the EPICS Control pages, e.g. Helicity, NaCell Voltage, and all BNMR/BNQR parameters for single/dual channel mode control.
Some of these parameters are also writable by the bnmr and bnqr BNMR and BNQR VMICs (lxbnmr,lxbnqr). They have been granted write access by the Controls Group to allow the frontend programs to flip helicity and turn the beam on/off via PPG signals. The frontends use EPICS Channel Access software to scan the NaCell voltage, for example.
The names of the IOCs accessed for read or write by the frontend are listed in the file bnmr_epics.c.
WARNING
There is NO protection against bnmr and bnqr experimenters changing Epics parameters via the Epics Control pages or the frontend programs while an experimental run is in progress on either bnmr or bnqr. When running in Single Channel Mode, there is also no protection against each experiment interfering with each other by both flipping the helicity for example. Users must ensure that they know what they are doing!
EPICS Troubleshooting
See Troubleshooting.
EPICS Checking
EPICS checks are done by various clients. They are enabled in the ODB under /Equipment/FIFO_Acq/Frontend/Hardware/ and should be enabled when taking data. The key /Enable all hel checks enables checking that the helicity set value and readback agree. This check was previously done by reading back the EPICS value. This only worked for Single Channel Mode and was not particularly reliable. For Dual Channel Mode, the readback has to be of the latched value of the helicity at the time when beam is sent to that channel. This is done using a specially programmed VME IO Register. The key Enable epics switch checks checks that the EPICS switches for selecting Dual or Single Channel Mode match the value of the key Enable dual channel mode. The actual check is done by the client rf_config so the run may be prevented from starting if the EPICS switches are set in the wrong position.
This will be moved to Frontend ----
EPICS Alive
A frontend equipment (see ODB path /Equipment/EpicsAlive) runs periodically to keep the Epics Channel Access channels open for the frontend. This prevents them timing out during a run. The Epics channels that must be kept open are usually the Helicity and the Epics scan variable(s), e.g. NaCell voltage and readback.