Slg 700 Ff Level Transmitter Operation; Operational Considerations; Las Capability; Special Non-Volatile Parameters And Nvm Wear-Out - Honeywell SLG 700 Option Manual

4. SLG 700 FF Level Transmitter operation

4.1 Operational considerations

There are a number of considerations that must be noted when configuring a transmitter to operate in a
fieldbus network.

LAS Capability

The transmitter is capable of operating as the Link Active Scheduler (LAS). The LAS is a fieldbus
feature which controls traffic on the network, such as controlling token-rotation and coordinating data
publishing. This fieldbus function is active in only one device at any given time on a network. Devices
which can be designated as the LAS may be an operator station or a field device. The transmitter can
be designated as LAS, in the event of a failure of the primary LAS, control in the field could continue.
ATTENTION
Note that the transmitter can be used only as "backup" LAS.

Special Non-volatile parameters and NVM Wear-out

All function block parameters designated as Non-Volatile (N) in the FF specifications are updated to
non-volatile memory (NVM) on a periodic basis. NV_CYCLE_T parameter in the resource block
specifies this update interval.
To provide predictable restart behavior in the transmitter, the following Non-Volatile parameters are
updated to NVM each time they are written over the fieldbus.

MODE.TARGET for all blocks

SP.VALUE for the PID block
Since these are user-written parameters, these additional updates to NVM contribute negligibly to
NVM wear out. However, users are cautioned to not construct control configurations where the above
parameters are written continuously (via a computer application for example) or at rates greater than
the NV_CYCLE_T interval. This consideration helps to minimize the possibility of NVM wear-out.
In the case of MODE this must not be a problem. When users wish to provide set-points to the PID
block via a computer application, users should use RCAS mode with its corresponding setpoint value
RCAS_IN. RCAS_IN is updated only at the NV_CYCLE_T update rate and this mode supports full
shedding functionality and PID initialization necessary for a robust application.

Mode Restricted Writes to Parameters

Some block parameters have restrictions on having write access to them. These are specified in the FF
specifications. Writing to certain function block parameters are restricted based on the block's Target
and/ or Actual mode.
Page 114 FOUNDATION Fieldbus Option User's Manual Rev.5