Real-Time Performance Benchmarks for the NI Compact FieldPoint Controllers

Compact FieldPoint is a programmable automation controller (PAC) designed for industrial control applications performing advanced embedded control, data logging, and network connectivity. Its rugged, reliable platform is designed for industrial environments with high shock, vibration, and temperature extremes from -40 to 70 °C. Most importantly, Compact FieldPoint is designed to be easy to use to help you build control applications within minutes. Compact FieldPoint controllers run NI LabVIEW Real-Time software, providing the functionality, connectivity, and flexibility of LabVIEW on a small, modular platform.

1. Introduction
2. cFP-2220 Benchmarks
3. Benchmark I - Execution Rate of a Single PID Loop/Digital Loop
4. Benchmark II - Multichannel PID Rate and Scalability
5. Benchmark III - Processing Speed for Mathematical Algorithms and Data Analysis
6. cFP-AI-118 Benchmarks
7. Conclusion

Introduction

National Instruments recently released a new family of Compact FieldPoint controllers to improve system performance and speed of control applications. The NI cFP-2220 is a LabVIEW Real-Time controller that delivers faster processing, more memory, and a 10X increase in Ethernet throughput. This white paper describes the improvements in the new cFP-2220 controller, compares its processing capabilities with the older NI cFP-21xx and cFP-20xx controllers, explores benchmarks for I/O and CPU performance improvements, and offers a glimpse into the technical advantages that make this controller faster and better suited for control applications. In addition, the last section offers additional benchmarks for the NI cFP-AI-118 module, an 8-channel analog input module with channel-to-channel isolation and 10 kHz sampling rate.

The cFP-2220 improves on the previous series of Compact FieldPoint controllers by offering:

• More processing power – The cFP-22xx controllers feature an industrial 400 MHz Freescale MPC5200 real-time processor for intelligent distributed applications requiring industrial-grade reliability. For extreme reliability and determinism, they run the LabVIEW Real-Time Module on the Wind River VxWorks real-time operating system (RTOS).  The combination of the new processor and operating system technology yields a processing performance equivalent to 3X to 5.5X the processing power of the NI cFP-2020 controller.
• More memory – The cFP-2220 controller includes 256 MB of SDRAM and 256 MB of nonvolatile onboard memory, 2X the memory of previous Compact FieldPoint controllers.  For additional storage and embedded data-logging applications, the controller features a removable CompactFlash slot and a new USB port for USB mass-storage devices.
• More Ethernet throughput – The new dual Ethernet ports on the cFP-2220 provide additional connectivity to both enterprise and dedicated I/O networks. Combined with the three RS232 ports and one RS485 port, it can communicate via TCP/IP, UDP, Modbus, and serial protocols, as well as take advantage of the built-in Web (HTTP) and file (FTP) servers.

Figure 1. Ethernet Throughput for Compact FieldPoint Controllers

cFP-2220 Benchmarks

National Instruments performed a number of benchmark tests to compare the speed of the cFP-2220 controller to that of its predecessors, the NI cFP-2120 and cFP-2020. These benchmarks analyzed I/O speed improvements, PID loop rates, and raw processing power due to the faster CPU and memory.

Setup
The test setup for the benchmarks consisted of the three different NI cFP-2x20 controllers and/or the NI cFP-AIO-610, cFP-AI-118, and cFP-DIO-550 modules. NI engineers wrote the control VIs in LabVIEW and ran the VIs embedded on the Compact FieldPoint controllers.

The benchmark tests simulated PID loops where engineers used a module to write and read data and then complete a PID calculation. Figure 2 illustrates an example of such a control VI. The FP Write/Read VI was implemented in the benchmarks because it provides better performance than separate FP Write and FP Read VIs.

Figure 2. Simple PID Control System

The control VIs were executed in two modes: normal priority and time-critical priority. In normal priority, the control VI must wait for higher-priority tasks to finish executing. By setting the VI to run in time-critical priority, the control VI always executes deterministically above other processes and/or VIs.

Benchmark I - Execution Rate of a Single PID Loop/Digital Loop

To compare the processing speed of the three controllers, the cFP-AIO-610 module was used for benchmarking the execution rate of a single PID loop. This data only represents software overhead because there was no verification of the data in these loops. As shown in Figure 3, the cFP-2220 controller processing speed was about 4X to 5.5X faster than that of the cFP-2020 controller, while the NI cFP-2120 is about 2X to 2.5X faster than the cFP-2020.

Figure 3. Execution Rate of a Single Analog PID Loop

A similar test was conducted with the cFP-DIO-550 to calculate the execution rate of a digital control loop. The cFP-DIO-550 16-channel digital I/O module has a faster update rate than the cFP-AIO-610 module. Therefore, the loop rates in Figure 4 are slightly faster for the DIO module when compared to analog modules. The cFP-2220 controller performed 5X to 5.5X faster than the cFP-2020 controller.

Figure 4. Execution Rate of a Single Digital PID Loop

Benchmark II - Multichannel PID Rate and Scalability

This benchmark is used to compare the three controllers’ speed in processing multiple PID loops in conjunction with the cFP-AIO-610 module. The test simulated the execution of several concurrent PID loops on a single controller. To optimize for speed, the test used multichannel FieldPoint items for write/read and parallel PIDs in a single while loop. The data only represents software overhead because there was no verification of the data in these loops. Figure 5 shows the comparison of the execution rates of the multiple PID loops. In each of the four cases, the cFP-2220 had the fastest execution rate over the other controllers, ranging from 3X to 5X improvement over the cFP-2020.

Figure 5. Analog Multichannel PID Loop Rates

Benchmark III - Processing Speed for Mathematical Algorithms and Data Analysis

To compare the computation speeds of the three controllers, the tests were run to calculate the time it took each controller to process a complex mathematical algorithm – in this case, a fast Fourier transform (FFT) on a simulated sine wave. FFT is not a typical analysis done on Compact FieldPoint, but this analysis is computationally intensive and helps demonstrate the power of the new processor. As shown in Figure 6, cFP-2220 is about 12X faster at normal priority and 18X faster at time-critical priority.

Figure 6. Execution Rate of FFT Loop

cFP-AI-118 Benchmarks

With the release of the cFP-AI-118 analog voltage input module with channel-to-channel isolation, engineers now can perform better acquisition with Compact FieldPoint systems. The cFP-AI-118 module is built on a newer architecture that supports dual memory access. With this architecture, the controller has access to the module memory immediately and can retrieve the acquired data faster, which significantly reduces the jitter.

For this benchmark, a sine wave was supplied to the module, and the module read the signal at 100 Hz. The white curve (smooth) represented the input sine wave and the red curve (jagged) represented the acquired data. A significant difference was seen when the acquired signal was compared on the cFP-AI-118 (Figure 7a) and the cFP-AIO-610 (Figure 7b) with the cFP-2120 controller. With the cFP-2120/cFP-AI-118 combination, a much closer representation of the sine wave was obtained than with the cFP-2120/cFP-AIO-610 combination. This was made possible by the faster sample rate on the cFP-AI-118 module and the immediate controller access to module memory.

Figure 7a. cFP-2120 and cFP-AI-118 Combination


Figure 7b. cFP-2120 and cFP-AIO-610 Combination

Related Links:
NI cFP-AI-118 Product Page

Conclusion

These benchmarks illustrate the improvements in the processing speed and power of the Compact FieldPoint controllers. The cFP-2220 controller software execution speed is up to 5.5X faster for simple PID loops than the cFP-2020 controller software execution speed. The new controller also performs other computations such as FFT by about 18X faster than the cFP-2020. With the latest Compact FieldPoint controller and analog input module, engineers can achieve better command of their control applications, process more information in a given time frame, and acquire reliable data at a faster rate. For more benchmarks on Compact FieldPoint, see the articles below.

Related Links:
NI cFP-2220 Product Page
Benchmarking LabVIEW Real-Time FieldPoint Systems
Benchmarking Single-Point Performance on National Instruments Real-Time Hardware
National Instruments Data-Logger Hardware

19 Ratings | 4.53 out of 5

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Reader Comments | Submit a comment »

10kHz sampling? How?
Why doesn't the cFP allow analog sampling similar to sampling on the DAQ boards? i.e., why can I only take one sample per read per loop instead of multiple samples at a given frequency? This severely limits the types of signals that can be monitored adequately with the cFP and 10kHz is unattainable in reality (cfp-ai-118 specs)
- allan.robinson@cleancurrent.ca - Mar 07, 2007

Great!
Does it have a CAN module?
- Skip Frosty,Ford Motor Company. sfrosty@ford.com - Jul 22, 2005