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Transcript of Chennai 6.2.10 j Jepal Yokogawa
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2010 Fieldbus Foundation
2010 FFIC-Chennai Conference
Jigish JepalExecutive Manager
Yokogawa India LimitedE-mail ID : [email protected]
Fieldbus Foundation India Committee
Fieldbus FoundationFFIC + ISA Fieldbus Foundation Conference-2010
Date : 6th February, 2010 ( Saturday)
Time : from 09:00 am to 05:30 pm.
Venue : IIT Convention Centre
Gajendra Circle, IIT Campus,
Adayar, Chennai.
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2010 Fieldbus Foundation
2010 FFIC-Chennai Conference
Importance of Device Capabilities for Achieving Desired
Macro Cycle and Control Performance
Typical Fieldbus Device
Specifications
Availability of function blocks ITK Compliance
EDDL/FDT/DTM support /
compliance
Maximum current drawn
Function block execution
time (some times)
Entity/FISCO/FNICO
approval
06-Feb-2010 2
Un-specified specifications Availability of VCR
Device operation parameters
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2010 Fieldbus Foundation
2010 FFIC-Chennai Conference
Fieldbus Project Engineering Considerations
Fieldbus Segment design considerations
Segment design concepts (Entity, FISCO, FNICO, HPT)
Power supply requirements
Macro Cycle time
Communication (Schedule and unscheduled communication times)
Control philosophy (Control in Host system, Control in the field, Mix of control in Host
system and in the field)
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Device Capabilities which influence Fieldbus segment are
Availability of different function blocks in field devices
Function Block Execution time
VCR
Device Operation parameters
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2010 Fieldbus Foundation
2010 FFIC-Chennai Conference
Segment Design
Maximum number of devices per segment (20 mA per device
and no losses)
FISCO FNICO HPT
No. of devices 6 in IIC 9 in IIC *
13 in IIB 16 in IIB
* RIL and BORL projects Maximum 12 devices per segment
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2010 Fieldbus Foundation
2010 FFIC-Chennai Conference
Typical Macro Cycle- 1 sec(AI and AO execution time of 100 msec, PID execution in the Host System, 16 devices per segment, 3 final control
element in the segment)
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2010 Fieldbus Foundation
2010 FFIC-Chennai Conference
Typical Macro Cycle-1 sec(AI and AO execution time of 50 msec, PID execution in the Host System 16 devices per segment, 3 final control
element in the segment)
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2010 Fieldbus Foundation
2010 FFIC-Chennai Conference
Typical Macro Cycle-500 msec(AI and AO execution time of 50 msec, PID execution in the Host System 7 devices per segment, 3 final control
element in the segment)
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2010 Fieldbus Foundation
2010 FFIC-Chennai Conference
Typical Macro Cycle-1 sec(AI and AO execution time of 100 msec, PID execution in positioner, 16 devices per segment, 3 final control element in
the segment)
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2010 Fieldbus Foundation
2010 FFIC-Chennai Conference
Typical Macro Cycle-1 sec(AI and AO execution time of 50 msec, PID execution in positioner, 16 devices per segment, 3 final control element in
the segment)
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2010 Fieldbus Foundation
2010 FFIC-Chennai Conference
Observation
Maximum number of devices per segment does not have
effect on macro cycle with respect to Function blockexecution time
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2010 Fieldbus Foundation
All function blocks control logic are implemented in the field devices
Control in the field concept
This control concept would be ideal as
- it minimizes communication traffic
- control is not affected even in case of H1 card failure
- Host control system execution time and I/O scan rate does not affect
control performance. This gives flexibility of adding more devices per H1
card and enable future expansion without needing additional controllers,
unless the expansion is big
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2010 Fieldbus Foundation
Limitations in Fieldbus segment design :
1. Power Supply Requirement
2. Macro Cycle Consideration3. Communication Limitations
First two limitations are normally taken care while designing the segments
Control in the field concept- concerns and remedy
However, third limitation is not noticed and hence, may pose great limitations
while implementing the control strategy or modification at later date or while
adding new devices in the segment.
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2010 Fieldbus Foundation
Communication Through VCR
VCR stands for Virtual Communication Relationship that
provide for the transfer of data between FF devices
Analogous to various fields of contact book of a mobile phone.Each mobile phone has defined address book limit.
Similarly each FF device has defined number of VCRs.
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MORE ON VCR
Similar to different types of contact labels such as land lineno., mobile no., e-mail address etc.; depending on applicationsrequirements, there are different types of VCRs.
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Control in the field concept- concerns and remedy
Each device requires
One Client/Server VCR for each MIB
One Client/Server VCR for the Primary Host
One Client/Server VCR for the Secondary host or maintenance tool
One Sink/Source VCR for Alerts
One Sink/Source VCR for Trends
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Control in the field concept- concerns and remedy
Example from AG-181
Total number of VCRs needed is:
1 (AI_1) + 2 (PID) + 5 (Basic Device) = 8
This example is not including one aspect..
The face plate update in host system shall be through client/server VCR.
Hence, one client/server VCR would be required for each function block
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2010 Fieldbus Foundation
Control in the field concept- concerns and remedy
Example from AG-181
Total number of VCRs calculated earlier:
1 (AI_1) + 2 (PID) + 5 (Basic Device) = 8
Un-noticed requirements :
1 C/S VCR for AI and PID blocks each
C/S for AI
C/S for PID
C/S for HHT
C/S for FBT
C/S for MIB
Some devices consume 2 C/S VCRs for System
management
Now total VCR requirement is : 13
Remember though there are two AI blocks shown in the
diagram, the calculation considers P/S VCR for only one AI
block
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2010 Fieldbus Foundation
IF ABOVE SOUNDS SENSIBLE,
THEN HOW MANY VCRs SHOULD BE SPECIFIED ?
SHOULD WE CONSIDER TODAYS REQUIREEMNT ONLY ?
The users who adopted FF technology for monitoring only in the beginning,
have subsequently moved control in the field.
Considering users confidence in FF technology, isnt it good to safe guard thepresent investment and select devices, which can be used in future also, when
the control from host is moved in the field?
Control in the field concept- concerns and remedy
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2010 Fieldbus Foundation
2010 FFIC-Chennai Conference
Device Operation Parameters
Slot time -V(ST): Time necessary for immediate reply of the
device. Unit of time is in octets (256 s).
Minimum-Inter-PDU Delay-V(MID) : Minimum value of
communication data intervals. Unit of time is in octets (256s).
Maximum-Reply- Delay-V(MRD): The worst case timeelapsed until a reply is recorded. The unit is Slot time.
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2010 FFIC-Chennai Conference
Device Operation Parameters
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V(ST) = 20
V(MID) = 14
V(MRD) = 6
CD DATA CD
30.72 msec 3.584 msec
V(ST) = 8
V(MID) = 12
V(MRD) = 6
CD DATA CD
12.288 msec 3.072 msec
V(ST) = 4V(MID) = 4
V(MRD) = 3
CD DATA CD
3.072
msec
1.024
msec
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2010 Fieldbus Foundation
2010 FFIC-Chennai Conference
Device Operation Parameters
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Fieldbus I/O
Host
Control bus
LAS Setting
V(ST) = 20
V(MID) = 14
V(MRD) = 6V(ST) = 4
V(MID) = 4
V(MRD) = 3
V(ST) = 8
V(MID) = 14
V(MRD) = 6
V(ST) = 20
V(MID) = 10
V(MRD) = 5
One odd device in the segment makes entire segment performance.
Then why not to specify these parameters?
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2010 Fieldbus Foundation
2010 FFIC-Chennai Conference
Very Small Macro Cycle 250 msec
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2010 Fieldbus Foundation
2010 FFIC-Chennai Conference
Device Capabilities
Are function block execution time, operation parameters and VCRs important
specifications?
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If yes, which one is more important ?
- In real life situation, device operation parameters have more impact on macrocycle time, schedule & unscheduled communication time, than function blockexecution time.
- From future expansion and modification point of view, availability of enoughVCR is very important.
- Function block execution time becomes important only in case of very shortmacro cycle time. However, the device operation parameters may not allow
shorter macro cycle unless no. of devices are reduced in the segment.
If above sounds sensible, standardize on these specifications..
- Minimum 13 + few spare VCRs
- Total communication time of a device should not be more than 15 msec
(CD + Maximum Response Delay + Data + Minimum Inter PDU delay)
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