Like Mark, my experience with the Koyo PLCs is that they are reliable and low-cost.
They were exceptional for an entry-level system as there was very good documentation
supplied before and after purchase and good support from the distributor.
Also, the high uptime of this simple systems is much appreciated by beam line staff.
(For example, their output bits don't have to toggle when an IOC is rebooted.)
Several of our APS beam lines use the Koyo PLCs, mostly for implementation of
equipment protection systems. Mark's EPICS support for Modbus/TCP communications
with the Koyo PLCs has been valuable.
The Koyo PLCs will fail the NSLS2 requirement for
> 4. Ability to produce and accept configurations and programs in a supported text format
This is of minor concern if you are not interested in running user code on the PLC.
But, for example, reading of ADC channels on the Koyo can be enhanced significantly
by running user code on the PLC.
The field experience with the Koyo PLCs (and this is likely common to other vendors)
is high reliability and easy field maintenance.
As APS has learned with our EPICS brick project, the Linux IOC may have
a cost advantage over the VME-based IOC if one can reduce or eliminate
any custom hardware that runs in the Linux IOC. Otherwise, the cost
savings is lost in field maintenance and the rapid obsolescence cycle of
the Linux platform hardware.
Mark Rivers wrote:
On a relatively small scale I've been pleased with the Modbus/TCP interface to Koyo PLCs from Automation Direct. These PLCs allow direct communication with the I/O points through Modbus. Some other manufacturers only allow Modbus access to memory registers, which the PLC program must read/write with the I/O point value. There is a scanner running, but the Koyo PLCs are very inexpensive so cost is really not much of an issue.
From: firstname.lastname@example.org on behalf of email@example.com
Sent: Wed 12/16/2009 6:44 AM
Subject: Remote I/O
At Diamond we are considering what to use for the next generation of
discrete I/O. Currently we have a lot of VME based hardware, but we are
considering a good architecture for a Linux world.
The model that we are considering is a soft IOC on a Linux system
communicating over Ethernet using an open, industry standard protocol to
distributed DIN-Rail mounted I/O points. These I/O points take in
Ethernet and are powered from a 24V bus that will run around the
This eliminates any dependence on a specialized bus architecture (apart
from Ethernet) on the Linux system, so they can be commodity PC's, and
hopefully allows us to use widely available, cheap, industrial modules
for I/O. It will not completely replace all of the requirements
currently serviced by VME, but would be able to satisfy most of them,
with the remaining few being serviced by the occasional VME system (or
FPGA, or some other bus, or something else entirely in the future...).
This email is to poll the EPICS community as to the experience people
have had, and recommendations for and against.
The sort of thing we have identified are:
1. Modbus/TCP based modules, such as the Acromag Busworks series
2. EtherCAT base modules, such as those from Beckhoff:
3. Standard PLC systems where (as distinct from the other two), you
take Ethernet to a PLC controller which then has a series of modules it
talks to in a variety of possible ways.
So, is anyone willing to share their experiences with these or similar
Principal Software Engineer Phone: +44 (0)1235-778430
Diamond Light Source Fax: +44 (0)1235-446713
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Pete R. Jemian, Ph.D. <firstname.lastname@example.org>
Beam line Controls and Data Acquisition, Group Leader
Advanced Photon Source, Argonne National Laboratory
Argonne, IL 60439 630 - 252 - 3189
Education is the one thing for which people
are willing to pay yet not receive.
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