EMERSONDeltaV SISTM Logic Solver

Control Network: The DeltaV Control Network provides 

communication between the nodes in the DeltaV network. 

Refer to the Installing Your DeltaV Digital Automation 

System manual for complete information on the Control 

Network.

Local Bus: The Local Bus provides communication 

between DeltaV controllers and Logic Solvers and 

between DeltaV controllers and SISnet Repeaters.

Local Peer Bus (SISnet): Logic Solvers communicate 

with other Logic Solvers and with local SISnet Repeaters 

through the carriers over a 2 channel local peer bus. The 

same message is broadcast over both channels. The local 

peer bus must be terminated at both ends. The local peer 

bus is terminated at the left end through the 2-wide 

power/controller carrier and at the right end through a 

terminated 1-wide carrier.

The SISnet Repeaters can be located anywhere on a local 

peer bus – between the DeltaV Controller(s) and the 

terminated 1-wide carrier.

Remote Peer Ring: SISnet Repeaters hosted by one 

DeltaV controller communicate with SISnet Repeaters 

hosted by a different DeltaV controller over a fiber-optic 

remote peer ring. A local SISnet Repeater collects locally 

generated messages that have been designated as global

variables into a single message and sends it to the next 

SISnet Repeater in the ring. Upon receipt of a message, 

the receiving SISnet Repeater broadcasts it on its local 

peer bus (SISnet) and forwards the message to the next 

SISnet Repeater in the ring. A global message is 

forwarded around the ring once. The primary SISnet 

Repeaters form one fiber-optic ring and the secondary 

form a separate, independent ring.

Carrier extender cables and local peer bus extender 

cables connecting a DeltaV controller and 8-wide carrier 

with standard DeltaV I/O and DeltaV SIS Logic Solvers to 

a second 8-wide carrier (hosted by the same controller) 

are installed with Logic Solvers, SISnet Repeaters, and a 

terminated 1-wide carrier. Logic Solver messages are 

communicated to a remote DeltaV SIS (hosted by a 

separate controller) through fiber-optic cables.

DeltaV SIS Product Data Sheet

May 2013 – Page 5 DeltaV SIS Logic Solver

Unique Redundancy Methodology

Introduction to Redundancy

Unlike other SIS Logic Solvers, the SLS 1508 is rated 

suitable for use in SIL 3 applications in simplex mode. 

Redundant SLS 1508 Logic Solvers run in parallel at all 

times. Both read the inputs from the I/O terminals, both 

execute the logic and both drive the outputs at the I/O 

terminals. There is no concept of primary and backup or 

master and slave, which is unlike any other SIS. The only 

difference between the two is that one communicates with 

both the engineering and operator workstations and the 

dedicated safety network (SISnet); this is the one with the 

Active light on the bezel. The other (Standby) is 

communicating only on the SISnet.

In the event that a failure is detected in one of the SLS 

1508 Logic Solvers, it automatically goes to a failed state. 

In this condition all its output channels are de-energized; 

this has no impact on the other Logic Solver or the 

physical outputs because the other Logic Solver continues 

to read inputs, execute logic and drive outputs. The 

transition from redundant to simplex mode is therefore 

completely bumpless.

Redundancy

The redundant SLS 1508 Logic Solver modules are 

connected to the field at the redundant terminal block. No 

control strategy configuration is required to take 

advantage of SLS 1508 Logic Solver redundancy, as the 

system’s auto-sense capability automatically recognizes 

the redundant pair of Logic Solvers.

An integrity error alarm in a redundant Logic Solver pair 

will notify the operator of a failure. Both Logic Solvers in a 

redundant pair are monitored for integrity alarms at all 

times.

Events that can cause integrity alarms include:

 Hardware failure within a Logic Solver

 Communications failure between a Logic Solver and 

the SISnet

 Communications failure between a redundant pair of 

Logic Solvers

 Communications failure between a Logic Solver and 

an DeltaV Controller

 Removal of a Logic Solver from the carrier

The health and status of both Logic Solvers and their 

channels are available in the diagnostics explorer.

When one of a redundant pair of SLS 1508 Logic Solvers 

is removed online there is no disturbance to the process. 

When the missing Logic Solver is replaced with another 

Logic Solver, the new Logic Solver completes its power-up 

self-tests before the active Logic Solver cross-loads the 

current database. In safe areas, failed Logic Solvers can 

be replaced under power. In hazardous areas, appropriate 

installation procedures must be followed.

Automatic proof testing can be selected on a redundant 

pair of Logic Solvers. The desired proof-test interval is set 

in the configuration and the Logic Solvers perform the