Transferring Modes; Rcas Mode - GE Baker Hughes Masoneilan SVI FF Installation And Operation Manual

Digital positioner

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Transferring Modes

Once the PID and an Output block are scheduled, the PID can command the setpoint. Which

further is translated as a Final_Value to the Transducer block. All blocks must be in service

mode.

When the positioner is receiving it's position setpoint from a remote computer system, such as

a DCS, then the normal state for the positioner is RCas. In this example, the level control valve,

LV201, is receiving it's signal from a DCS. The Analog Output block (AO) is shown in RCas mode.

RCas mode cannot be manually switched to, it is automatically switched to after being

configured. For example:

Configure the set point of the positioner in DCS to receive remote data, when the

positioner turns to Normal mode, the mode of AO block shows RCas in the Block Actual

Mode field.

PID in RCas Mode

If an internal PID is used in a cascade where the PID receives a setpoint from a remote

computer system, then the normal state has the PID in RCas mode and the Analog Output

block (AO) is in Cas mode.

The Foundation Fieldbus Application Process specifies the mode handling for inter-operable

function blocks. It also specifies which mode a block must be in when each parameter is

written. SVI FF provides an intelligent, optimized, process for managing configuration and

calibration changes. It does not place blocks into Out Of Service mode unless the parameter

requires OOS. It analyzes the requested changes and then sets the correct mode for each

affected function block.

The Foundation Fieldbus specifies a mechanism for transferring between function block

modes. The user declares a target for the block mode but the actual mode is set by the block

in accordance with rules. The rules allow modes based on the state of input data. Function

blocks comply with the Fieldbus Foundation rules. SVI FF sets target modes for individual

function blocks as required by configuration, calibration, diagnostics and other services. It

sets target modes for a group of function blocks to achieve three operational states of the

positioner: Out of Service, Manual, and Normal.

CAUTION

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BHGE

The PID block remains in Out of Service mode or IMAN when

configuration changes are made. After returning to Normal

operating state, change the PID block mode. If the AO block is left

in Auto mode the valve cannot be moved. Refer to you DCS

manual.

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