EPICS

This article is about the software environment. For the astronomical instrument, see European Extremely Large Telescope. For other uses, see EPIC (disambiguation).
EPICS
Developer(s) Free software community
Initial release January 19, 1994 (1994-01-19)
Stable release
3.14.12.5 / March 24, 2015
Repository code.launchpad.net/epics-base
Operating system Cross-platform
Type Open Source
License EPICS Open License
Website www.aps.anl.gov/epics/

The Experimental Physics and Industrial Control System (EPICS) is a software environment used to develop and implement distributed control systems to operate devices such as particle accelerators, telescopes and other large experiments. EPICS also provides SCADA capabilities. The tool is designed to help develop systems which often feature large numbers of networked computers providing control and feedback.

EPICS uses client/server and publish/subscribe techniques to communicate between the various computers. One set of computers (the servers or input/output controllers), collect experiment and control data in real-time using the measurement instruments attached to it. This information is given to another set of computers (the clients) using the Channel Access (CA) network protocol. CA is a high bandwidth networking protocol, which is well suited to soft real-time applications such as scientific experiments.

Look and feel

EPICS interfaces to the real world with IOCs (Input Output Controllers) . These are either stock-standard PCs, VME, or MicroTCA standard embedded system processors that manage a variety of "plug and play" modules (GPIB, RS-232, IP Carrier etc.) which interface to control system instruments (oscilloscopes, network analyzers) and devices (motors, thermocouples, switches, etc.). Some instruments also can come with EPICS already embedded within them, like certain Oscilloscopes . The IOC holds and runs a database of 'records' which represent either devices or aspects of the devices to be controlled. IOC software used for hard-real-time normally use RTEMS or VxWorks, though work has been ongoing in porting to other systems. Soft real-time IOC software sometimes runs on Linux or Microsoft Windows based machines.

Other computers on the network can interact with the IOC via the concept of channels. For example, take a particle accelerator with shutters between sectors. There would typically be several channels corresponding to a shutter: an output channel to activate shutter motion; an input channel to see the status of the shutter (e.g. shut, open, moving, etc.); and, probably some additional analog input channels representing temperatures and pressures on each side of the shutter. Channel names are typically in the form EQUIPMENT:SIGNALNAME (e.g. ACCELERATOR_RING:TEMP_PROBE_4, although they can be much less verbose to save time).

Most operations are driven directly from a standalone GUI package such as EDM (extensible display manager) or MEDM (Motif/EDM). These allow creation of GUI screens with dials, gauges, text boxes, simple animations, etc. Newer control systems and GUI interfaces such as CSS/BOY are being investigated.

However it is not just GUI software which can interact with EPICS: any software which can speak the CA protocol can get and put values of records. For example, on the EPICS website there are several extension packages which allow CA support in things like MATLAB, LabVIEW, Perl, Python, Tcl, ActiveX, etc. Hence it is easy to do things like write scripts that can activate EPICS controlled equipment.

Record types

There are different types of records available in EPICS. Here are some common types. Note that in addition to the other records not mentioned here, it is possible to create your own record type to interact with a device.

Each record has various fields in it, which are used for various tasks. AI and AO Analog Input and Output records can obviously store an analog value, and are typically used for things like set-points, temperatures, pressure, flow rates, etc. A limited amount of conversion to and from raw device data is available natively in the record (typically scaling and offsetting, but not advanced conversion like two's complement or logarithmic). BI and BO Binary Input and Output records are generally used for commands and statuses to and from equipment. Calc and Calcout These two records can access other records and perform a calculation based on their values. (E.g. calculate the efficiency of a motor by a function of the current and voltage input and output, and converting to a percentage for the operator to read). Stepper Motor Control of a stepper motor. Allows settings of things like accelerations and velocities, as well as position.

Record processing

The processing of a record is configured in a number of fields that allow scheduling to be periodic, triggered by a hardware event from the I/O, triggered from another record in a processing chain, or triggered by a read reference from another record or a Channel Access write. With this variety of scan mechanism, control and data acquisition strategies can be configured to minimize latency or assure coherence in a configured processing chain such as a PID (Proportional, Integral, Derivative) feedback loop or interlock.

Facilities using EPICS

A partial list of facilities using EPICS:

References

  1. ↑ http://www.lnl.infn.it/~epics/
  2. ↑ http://www.ganil-spiral2.eu
  3. ↑ http://www2.keck.hawaii.edu/realpublic/epics/

External links

General sites

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