SIL & SIS Compliant Process Control Instrumentation

In hazardous industrial environments, maintaining safe operating conditions is critical. Safety Instrumented Systems (SIS) are designed to monitor processes and automatically take action when predefined limits are exceeded.

At the heart of these systems is SIL (Safety Integrity Level) rated instrumentation, which ensures that measurements and control actions meet defined safety performance requirements.

Allison Engineering supplies SIL 1 and SIL 2 compliant flow measurement and flow switch solutions used within safety systems across oil & gas, chemical, biogas and process industries, helping operators achieve reliable and compliant functional safety.

 

The Problem

Standard process instrumentation is not designed to perform reliably in safety-critical scenarios where failure could result in hazardous conditions.

Common challenges include:

• Lack of reliable protection against abnormal process conditions
• Instrument failure leading to unsafe operation
• Inability to meet safety compliance standards (IEC 61508 / IEC 61511)
• Poor visibility of critical process parameters
• Increased risk of equipment damage, environmental impact or safety incidents
• Difficulty demonstrating compliance during audits and inspections

Without SIL-rated instrumentation, operators cannot guarantee that safety systems will perform when required.

 

The Solution

SIL and SIS compliant systems are designed to monitor, detect and respond to abnormal process conditions automatically.

A typical Safety Instrumented System (SIS) consists of:

• Sensors (Input) – measure key process variables such as flow, pressure or temperature
• Logic Solver (Control) – evaluates conditions and determines if action is required
• Final Element (Output) – executes the safety function (e.g. shutdown valve, alarm or trip)

Allison Engineering provides SIL-rated instrumentation for the sensor layer of SIS, including flow switches and flow meters that are proven in demanding industrial applications.

These solutions are widely used alongside applications such as Pump Protection Using Flow Monitoring and Flow Switches, Combustion Air Flow Measurement for Industrial Processes and SIL Rated Oxygen Analysis for Biogas, where reliable measurement is critical to maintaining safe operation.

 

Technical Insight

 

What is SIL (Safety Integrity Level)?

SIL is a measure of the reliability required for a safety function. It defines the probability that a system will perform correctly when needed.

• SIL 1 – basic risk reduction
• SIL 2 – higher reliability for more critical processes

Allison Engineering supplies instrumentation designed for SIL 1 and SIL 2 applications.

 

What is an SIS (Safety Instrumented System)?

An SIS is a complete system designed to bring a process to a safe state when hazardous conditions are detected.

 

Key standards

• IEC 61508 – Functional safety standard for systems
• IEC 61511 – Process industry application standard

These define how safety systems should be designed, implemented and maintained.

 

Key performance considerations

• PFDavg (Probability of Failure on Demand)
• Hardware Fault Tolerance (HFT)
• Proven-in-use data

From experience, selecting instrumentation with strong real-world reliability is just as important as meeting theoretical standards.

 

Where SIL-rated instrumentation is used

• Pump protection systems
• Combustion and burner management
• Gas detection and safety systems
• Oxygen control in biogas upgrading
• Chemical injection and process control

 

Recommended Products

Flow Switches

SIL-rated thermal flow switches used for detecting flow, low flow and no-flow conditions in safety-critical systems.

Thermal Mass Flow Meters

Reliable gas flow measurement used within control and safety systems across industrial applications.

Biogas Analysers

Used in SIL-rated oxygen control systems for biogas upgrading and process safety.

 

Key Benefits

• Reliable protection against unsafe process conditions
• SIL 1 and SIL 2 compliant instrumentation for critical applications
• Improved safety for personnel, equipment and environment
• Supports compliance with IEC 61508 and IEC 61511 standards
• Proven performance in demanding industrial environments
• Enables automated safety response and process shutdown