Field Bus and Controller Specifications

Introduction

There are innumerable possible choices for sensors, actuators, etc. for use in Hall D, independent of the slow controls framework chosen (EPICS, PVSS, DOOCS/TINE, etc, see Slow Controls Framework Choice for a discussion of the software running on top of the field busses). These devices communicate using one of large number of control network systems (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 an application needs a special sensor or controller that is not compatible with the set below, please contact me.

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, and early EPICS systems could not communicate with PLC's). 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 for our solenoid (Allen-Bradley, model TBD). 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 control loops can be strictly 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
• gas and cooling systems

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

I believe Allen-Bradley PLC's talk to their connected devices via DEVICENET, which is a layer on top of CAN-bus. I'm not sure this is the only possibility...

Hall D Subsystem Slow Controls Specifications

Below are tentative choices based on my best guess as to which hardware we will purchase.

Notes:

• OPC servers often connect to their device via Ethernet, but sometimes use a separate field bus.
• SNMP run over Ethernet.
• CAN and I2C each have their own connectors and physical layer.

Subsystem	Control System
solenoid	Allen-Bradley PLC
cryo-target	Allen-Bradley PLC
gas systems	Allen-Bradley PLC
FDC cooling system	Allen-Bradley PLC
high voltage	OPC
low voltage	OPC
VXS crates	OPC or SNMP
Cockroft-Walton bases	CAN
goniomenter	OPC or Allen-Bradley PLC
network devices	SNMP
misc temp, etc.	CAN and I2C