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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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

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Un-specified specifications Availability of VCR

Device operation parameters


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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)

06-Feb-2010 3

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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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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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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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


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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


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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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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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Observation

Maximum number of devices per segment does not have

effect on macro cycle with respect to Function blockexecution time

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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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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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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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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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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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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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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?



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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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06-Feb-2010 21

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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06-Feb-2010 22

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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Very Small Macro Cycle 250 msec

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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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Chennai 6.2.10 j Jepal Yokogawa

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