Process Control Network Future –Part 1
March 27, 2021
The work of O-PAS (Open Process
Automation System) has focused on OPC UA that assumes an Ethernet base network
with these enhancements:
- PoE (Power on Ethernet)
- Network Time Protocol
- Parallel Redundancy Protocol
- Network Layer based on IPv6
- Transport Layer for time-critical applications based on UDP/IP
- Synchronized time-critical data transfers based on Publish/Subscribe (described in Part 14 of OPC UA)
Also in keeping with modern
security requirements, OPC UA specifies both of these features on the network:
- 128-bit AES Encryption of all
messages
- Certificate-based authentication for
all nodes joining the network
Additionally, the O-PAS Physical
Layer Working Group has proposed a field network as follows:
·
Field network connections to
field devices based on APL (Advanced Physical Layer, IEEE 802.3cg) Industrial
version
o 10
Mbps full duplex data rate
o Collision
avoidance protocol Network Layer
o Support
for Intrinsic Safety
o Use
of single STP (Shielded Twisted Pair) cable
o Up
to 1000 feet end-to-end
o PoDL
(Power on Data Line) for field devices requiring power
It remains to be seen if the O-PAS
work will be accepted by any of the vendors known for selling process control
systems. The following vendors have actively participated in the work of O-PAS,
and can be expected to support this standard when it is completed later in 2021
for products to appear in 2022:
- Schneider Electric (Formerly
Foxboro)
- ABB
- Siemens
- Yokogawa
- Azbil (Formerly Yamatake)
Notably attending early in the O-PAS
work, but not contributing to the final specifications:
- Emerson
- Honeywell
Can O-PAS succeed without Emerson
and Honeywell building conforming products? Will O-PAS conforming products be
interoperable/interchangeable? Will any O-PAS products be commercialized? Will
Emerson and/or Honeywell try to “leapfrog” O-PAS with more innovative products
for the next generation? Is O-PAS forward-thinking enough? …obsolete before its
release? Will OPC UA prove to be too big/slow/complicated for O-PAS to succeed?
Will the Application Layer of the FOUNDATION Fieldbus part of the FieldComm
Group ever be standardized?…incorporated into future products?..field
instruments?
FOUNDATION Fieldbus
FOUNDATION Fieldbus was based on the
ISA 50.02 standard, at least for its H1 segment. The H2 part of ISA 50.02
proved to be too slow and expensive and did not become part of the
international Fieldbus standard IEC 61158. Instead, the Fieldbus FOUNDATION formed
a committee and developed FOUNDATION Fieldbus HSE as the preferred form of the
H2 Fieldbus, and became a part of IEC 61158 in the year 2000. Interestingly HSE
is based on high speed Ethernet, and has ALL of the characteristics of the
network specified by OPC UA as described above, except the Security features. Unfortunately,
APL base technology was not available when the H1 network was designed in the
late 1980’s.
FOUNDATION Fieldbus was designed to
allow smart field instruments to perform more than 80% of the process control computations
formerly done in DCS Controllers. Embedded in the FOUNDATION Fieldbus function
blocks is all of the complex initialization, back-calculation, mode/state change
logic, and cascade data flow logic needed for a modern control system. It even
allowed location of function blocks to be in field instruments, or anywhere
else in the network, and to allow changes in that location to occur as the
dynamic needs of the process would change. [Note: none of this process control
data flow logic is to be found in current O-PAS specifications.]
The only reason that O-PAS network
support contains the enhancements mentioned above, is because FOUNDATION
Fieldbus HSE had these features and I wrote the requirements for them while I
was still participating in O-PAS work. I pulled these requirements directly
from the HSE specifications.
If the DCS companies had decided
to implement FOUNDATION Fieldbus HSE at the same time as they implemented FOUNDATION
Fieldbus H1 instruments, O-PAS would not be necessary. Instead, work would be
to add the desired security features to HSE and to convert H1 networks to APL.
