Experimental Physics and
Industrial Control System

Carl Dickey <[email protected]> · Mon, 28 Nov 1994 16:20:35 -0500

   We have implemented both Allen-Bradley and CAMAC systems here at Duke. 
I agree with everything that Bob, Steve and Chip have said about the systems.
However there are a few additional comments that I would like to make:

1. The AB system is capable of extremely high distance connectivity using
standard balanced transmission line. Fiber optic interfaces can be installed
for even greater distances. The Hytec VME based serial drivers connect using
low capacitance twisted pairs. I think that with U-Port adapters that we might
expect quality transmissions up to perhaps five hundred feet. (Our longest 
connection is probably around three hundred feet. Perhaps Chip's group has 
a more exact figure.) Also, Hytec makes an optical fiber adapter for this 
serial CAMAC system. (Perhaps CEBAF is using this.) But I think that you 
need to understand your distribution requirements in addition to your data
rate, or scan rate requirements.

2. We had a lot of standard CAMAC equipment on hand of SLAC origin. This 
equipment was basically limited DAC, ADC and digital I/O functions. In order
to utilize the existing equipment, we implemented a number of conditioning 
and fuctional I/O standards. For instance, when reading back the T-type 
thermocouples on the Stanford accelerating sections, we utilized the 
Analog Devices style I/O module system. This system also proved to be handy
for interfacing some RTD signals. In the case of the Analog Devices I/O rack,
we scanned the racks with CAMAC BIRA SAM modules. When controlling our 
screen diagnostics and vacuum valves we interfaced standard BIRA digital     
output modules (IDOMs) into solid state relays that energize solenoids. 
(We specifically avoided stepper motors, but they can be handled in a 
similar manner, I believe.) My point is that it is possible to limit the 
number of CAMAC function modules and to utilize the old CAMAC equipment
by employing low cost, conditioning standards. Limiting the number
of CAMAC function modules that are required will potentially reduce your
software development overhead also.

3. Finally, I think that cost should be considered in the selection process. 
While CAMAC is not the latest, and it is somewhat painful to work with     
particularly in physical I/O layer, the medium is entirely functional and 
sufficient for many if not most of the problems that we encounter in 
acclerators, I believe. The question is, does CAMAC meet your requirements? 

To recap, I would like to say that my experience with both the AB and CAMAC 
extensions to EPICS is that they will both work and get the job done, in a 
similar manner. There are positive and negative aspects to both systems, I
think. First, will both systems actually meet your requirements for data 
rates, connection distance, and functionality? Second, if both system meet
the requirements, will existing equipment significantly reduce your costs. 

Best wishes to all,

Carl Dickey, DFELL

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System