Difference between revisions of "Field Bus and Controller Specifications"

Revision as of 17:45, 23 January 2008

Introduction

There are innumerable possibile choices for sensors, actuators, etc. for use in Hall D, independent of the slow controls framework chosen (EPICS, PVSS, DOOCS/TINE, etc). These devices communicate via one of number of control networks (CAN, I2C, DEVICENET, ProfiBus, WorldFIP, TCP/IP, etc). For practical reasons we need to minimize the number of network types we deploy in the hall.

Thus in the following I propose a minimal set of control networks for use in Hall D. If some particular application needs a special sensor or controller that is not compatible with the set below, contact me and we will find a way to accomodate it. The idea is that whenever possible detector and electronics designers should use devices compatible with the choices below.

Note on PLC usage in Hall D

PLC's (Programmable Logic Controllers) are highly reliable process controllers that are in widespread use in industry, and are routinely used in critical applications. They are not general purpose computers, and instead have a single purpose in life, to run a control loop at regular intervals. Although other labs use them routinely, JLab does not, and I'm not sure why (speculation: JLab is too EPICS-happy). PLC's are typically programmed by trained controls engineers, not by scientists, as special languages and techniques are used (similar to how FPGA programming is done by specially trained electrical engineers).

JLab typically uses PLC's in cryo-control systems, and we plan to use one (Allen-Bradley, model to be chosen) for our solenoid. We expect that the solenoid cryo-control system will use up less than one third of the PLC capacity, so we can use the PLC for other purposes. Note that PLC programming can be highly prioritized, so that e.g. solenoid control will not be compromised by a lower priority control loop.

The PLC is ideal to control the following systems:

• solenoid
• cryo-target
• all gas systems

An open question is what other systems might be controlled by the PLC. As reprogramming the PLC takes some time and requires a trained engineer, it may not be appropriate for many systems, particularly simple ones with benign failure modes. Further, we have to understand the cost of setting up a PLC-compatible system at a remote site (Tim and I are working on this).

Hall D Subsystem Slow Controls Specifications

Below I list choice of controls network for Hall D subsystems:

• solenoid: A-B PLC.
• cryo-target: A-B PLC.
• gas systems: A-B PLC.
• high-voltage:
• low-voltage:
• VXS crate control:
• Cockroft-Walton bases:
• goniometer:
• network devices: