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 and their controllers). These devices communicate with their controller in one of many ways (CAN, I2C, DEVICENET, ControlNet, Ethernet/IP, ProfiBus, WorldFIP, TCP/IP, etc). For practical reasons we need to minimize the number of network and controller types we deploy in the hall.

Thus in the following I propose a minimal set of busses and controllers 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). Typical uptimes for PLC's are measured in decades (during the past 4 years or so the Hall C magnet PLC has NEVER crashed!).

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
• any system that requires a control loop

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.

Note that with careful choice of sensors and actuators, test setups can be controlled using a simple PC instead of a (very expensive) PLC. Test setup control algorithms would then be implemented in the PLC when the systems arrive in the hall.

Finally, I propose that we do NOT use the Allen-Bradly HMI (Human Machine Interface) facility to create operator control screens. Rather, to maintain a consistent look and feel, the PLC itself should be controlled via the slow controls framework. Expert screens, on the other hand, may be developed using HMI if desired.

Hall D Subsystem Controller and Field Bus and Controller

Online systems communicate with device controllers, which then controls the sensor or actuator via a field bus. There are many choices for both. Below are tentative choices based on my best guess as to which hardware we will purchase.

Subsystem	Controller	Field Bus
solenoid	Allen-Bradley PLC	analog, others
cryo-target	Allen-Bradley PLC	analog, others
gas systems	Allen-Bradley PLC	analog, others
FDC cooling system	Allen-Bradley PLC	analog, others
Crate/rack cooling	Allen-Bradley PLC	analog, others
high voltage	OPC	Ethernet
low voltage	OPC	Ethernet
VXS crates	OPC or SNMP	Ethernet
Cockroft-Walton bases	tbd	CAN
goniomenter	manufacturer-supplied	Ethernet
network devices	SNMP	Ethernet
misc temp, etc.	tbd	CAN and I2C