Functional Safety for CompactRIO


The recent addition of C Series Functional Safety Modules to the CompactRIO platform provides more capabilities to an already full-featured and rugged measurement and control product line. The functional safety modules add IEC 61508 safety integrity level (SIL) 3 capabilities to CompactRIO to offer integrated safety, measurement, and control in a single system. You can use these modules to control critical safety functions in manufacturing assembly and test cells, large physical systems tests, condition monitoring applications, and process monitoring and control.


CompactRIO with Functional Safety

Figure 1. CompactRIO with Functional Safety 

Introduction to C Series Functional Safety Modules

C Series Functional Safety Modules feature a self-contained logic solver that you can use to independently control safety functions. While the modules provide the status of the inputs to the CompactRIO controller, the safety logic running in the onboard FPGA continues to perform the safety function regardless of the state and condition of the controller. The required external power source for the functional safety modules is connected via the front connector.

You program the safety logic on each module with the Functional Safety Editor, a powerful and easy-to-use stand-alone tool that incorporates a graphical programming technique. With state diagrams featuring up to eight individual state machines on the NI-9350 and four on the NI-9351, you can complete your programming. You can use AND, OR, and NOT logic along with programmable timers to determine when to transfer between the various states. In addition, you can assign up to 24 Boolean variables. After you download the safety logic onto the module, you can monitor AI, DI, DO, variables, and diagnostics in the LabVIEW Real-Time Module.

The Functional Safety Editor allows you to easily develop safety logic

Figure 2. The Functional Safety Editor allows you to easily develop safety logic.

The C Series Functional Safety Modules are certified by exida to be SIL 3 capable under IEC 61508, IEC 62061, and IEC 61511. With a hardware fault tolerance (HFT) of zero for the module, you need only a single input and output channel to meet SIL 3 levels. The logic solver is contained within the module using an FPGA-based solution. This approach provides a unique and diverse logic solver architecture that you can use alongside traditional safety PLCs in applications that require unique and diverse electronics to minimize common cause failures. Using an FPGA also yields some of the fastest safety response times.

With the built-in diagnostics of the C Series Functional Safety Modules, you can test the system periodically to detect and prevent possible unsafe failures. User-configurable diagnostics allow you to monitor and detect various faults related to your sensors, cabling, and final elements. Automatic self-diagnostics continuously check for module hardware and power supply faults.

The NI-9350 is a digital I/O C Series Functional Safety Module. Its 24 V industrial logic levels allow you to directly connect to a variety of sensor types such as light curtains and emergency e-stop buttons as well as final elements such as relays, contactors, and motor drives.  The NI-9351 is a multifunction analog input and digital I/O C Series Functional Safety Module. It allows you to directly connect to a variety of sensor types such as pressure transducers, temperature sensors, light curtains, and emergency e-stop buttons as well as final elements such as relays, contactors, and motor drives.

Table 1 shows some specifications for  the NI-9350 and NI-9351.



NI-9350 DIO

NI-9351 AI/DIO 


8 DI, 8 DO

4 AI, 4 DI, 4 DO

Type of DI/DO

Sinking DI, Sourcing DO

Type of AI


0–20 mA, 16-bit

Rated DIO voltage

24 V DC

Input voltage range,“1”;

input current,“1”

11–30 V

1.1 mA @ 24 V

Input voltage range,“0”;

input current,“0”

0–6 V

Output current

250 mA max

Safety response time

250 μs max

2.1 ms max

SIL levels

Certified up to SIL 3 capable

Functional safety certifications

IEC 61508, IEC 62061


Spring terminal


Inputs: ±30 V;

Outputs: short circuit protection from COM to Vsup

Digital Inputs: ±30 V;

Analog Inputs:  20 V single channel up to 55°C

Outputs: short circuit protection from COM to Vsup


60 V DC (bank)

Operating Temperature

-40 to 70 °C


Table 2. Specifications for NI-9350 and NI-9351


CompactRIO Platform Advantages

Adding functional safety to the CompactRIO platform presents many advantages. The CompactRIO platform itself offers unparalleled performance for measurement and control tasks. From controlling complex machines to monitoring critical assets, CompactRIO gives you unsurpassed benefits in any application. Connect to sensors, displays, cameras, motors, databases, and the enterprise directly from CompactRIO controllers to create a powerful and reliable system that you can customize and reconfigure through software even after you deploy it in rugged environments.

CompactRIO features a range of embedded controllers with two processing targets: (1) a real-time processor for communication and signal processing and (2) a user-programmable FPGA to implement high-speed control and custom timing and triggering directly in hardware. By leveraging the latest commercial technology, NI can continually deliver high-performance and high-quality products to its customers at a competitive price. The latest processors from Intel and ARM deliver industry-standard parts, the latest FPGAs from Xilinx help push signal processing algorithms to the edge to accelerate measurements, and the latest data converters from TI and ADI continually increase the measurement range and performance of NI instrumentation.

By combining these benefits with the more than 150 NI and third-party C Series modules for measurement, control, and communication, you can connect C Series I/O to any sensor, signal, or bus. You can insert C Series I/O modules in any CompactRIO chassis or controller to create a mix of channel counts and measurement types within one system. In addition to built-in signal conditioning, these hot-swappable modules feature numerous options for sensor connectivity and operate in the harshest of environments. They offer extended operating temperature ranges of -40 to 70 °C (-40 to 158 °F), a 50 g shock rating, and a variety of international safety, electromagnetic compatibility (EMC), and environmental certifications and ratings. The compact size of the system allows you to easily integrate it in systems of all sizes.

Combined Safety, Measurement, and Control Platform Advantages

With C Series Functional Safety Modules, you can also integrate functionally safe I/O in a CompactRIO system. When you use the same platform for safety, measurement, and control, you reap the benefits of a single integrated development environment. More traditional PLC systems that offer a combined approach can’t always provide the precise control and timing capabilities of CompactRIO, and they have limited analog measurement capabilities such as strain and vibration measurements.

Some users have chosen CompactRIO for its control and measurement capabilities and added a safety PLC to manage the safety functions of the system. Unfortunately, this leads to inefficient development, integration, and maintenance. With the new functional safety modules, these inefficiencies are eliminated. A single developer can now create both the safety program and the measurement and control program.

You can easily integrate the status of the safety module signals and diagnostics in the control program via LabVIEW and present it to the user. Additionally, you can use the NI-9351 to read back the actual 16-bit analog input data into LabVIEW and to control the system. This eliminates redundant wiring and sensor costs. The flexibility to integrate both safety critical and non-safety critical portions of the design does not affect the safety levels because the safety module has its own dedicated built-in safety logic solver. With up to eight separate state machines on the NI-9350 and four on the NI-9351, you have the option of adding simple non-safety critical control to the functional safety module logic. This works well when a system has higher reliability needs and extra I/O left over on the functional safety module. You can place the outputs of the functional safety module in a passthrough mode so they can be controlled via LabVIEW. The passthrough mode, which you should use only in non-safety critical operation modes, can be incredibly beneficial if you need automated proof testing.

To guarantee seamless integration, NI fully tests the integration of the C Series Functional Safety Modules with the CompactRIO platform. Purchasing a platform from a single-sourced supplier reduces support and maintenance costs. A single technician trained on the CompactRIO platform can be sent into the field to troubleshoot problems instead of sending multiple platform-specific personnel.

The addition of SIL 3 capable functional safety modules to the CompactRIO platform presents many advantages and efficiencies for system development and deployment. Combining measurement class I/O and advanced control with safety I/O in a small rugged platform provides you with unparalleled performance and integration ease when working with all kinds of machinery and equipment in manufacturing assembly and test cells, large physical systems tests, condition monitoring applications, and process monitoring and control.  For more information refer to the following: 


CompactRIO Overview Page

Functional Safety Overview Page

Functional Safety Product Page