Synchronization between motion control and data acquisition using RTSI bus - Database & Sql Blog Articles

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1. Introduction

In many test systems, real-time data acquisition is required while the system is in motion. If the testing process is not continuous or if the test position is at the front and the data acquisition is at the back, synchronization issues may arise, leading to measurement errors. To ensure accurate results, motion control and data acquisition must be synchronized. National Instruments (NI) offers PCI bus E-series data acquisition and motion control cards that are embedded with the RTSI (Real-Time System Integration) bus, allowing precise synchronization and real-time processing. This article explores how to use the RTSI bus for synchronizing motion control and data acquisition.

2. RTSI Bus

The RTSI bus is a high-speed digital interconnect designed for NI products, enabling fast communication between devices like data acquisition and motion control systems. It includes seven trigger lines that allow flexible synchronization between various instruments. These signals can be routed via software, making it possible to synchronize multiple devices using a single trigger signal. Applications include image acquisition, motion-based data collection, and capturing motion events based on external triggers.

For the E-series data acquisition card, there are 15 types of signals connected to the RTSI bus, such as time base signals, data acquisition clocks, D/A output clocks, and PFI signals. Figure 1 illustrates this connection.

3. Synchronization of Motion Control and Data Acquisition

There are two main methods for synchronization: one where the motion control card moves the motor to a specific position, and the data acquisition card collects data in real-time—this is known as an interrupt. The second method involves the data acquisition card triggering based on a condition when the motor reaches a certain point, referred to as capture. This article focuses on interrupt synchronization.

3.1 Interrupt Mode

Interrupts can be absolute, relative, or periodic. Absolute interrupts occur when the motor reaches a fixed position. Relative interrupts trigger when the motor’s position meets a set condition. Periodic interrupts happen at regular intervals. Choosing the right type depends on the test system's requirements.

3.2 Synchronization Principle

When the motion control card moves the motor to a specific position, the encoder sends a signal that generates an interrupt. This signal acts as a trigger for the data acquisition card, allowing real-time data collection. The RTSI bus connects the motion control card and the data acquisition card, enabling synchronization. The interrupt signal from the motion card is sent through the RTSI output pin and connected to the data acquisition card via an external cable. This allows the data acquisition card to scan and collect data each time an interrupt occurs.

4. Programming Implementation

The synchronization process is illustrated in Figure 2.

The author used LabWindows/CVI software along with NI-DAQ and NI-Motion libraries to implement the RTSI synchronization. The NI-Motion library allows motion and measurement hardware to run simultaneously using digital triggers. The RTSI bus connects these signals via software. The "Measurement & Automation Explorer" (MAX) tool assigns device numbers for identification during programming. Key functions include:

(1) Connecting interrupt signals to the RTSI bus.

(2) Setting motion parameters and interrupt modes.

(3) Configuring interrupt positions and enabling interrupts.

(4) Starting motor movement.

(5) Checking motion and communication status.

5. Conclusion

The RTSI bus provides high-speed hardware synchronization for various measurement and control systems. By implementing RTSI-based synchronization using LabWindows/CVI, real-time data collection during motion can be achieved with high accuracy. This approach is ideal for applications requiring precise coordination between motion control and data acquisition.