Sine Test Control Parameters
August 18, 2022
In a closed-loop vibration testing system, the controller sends an output through an amplifier to the shaker. A transducer then sends the response of the device under test (DUT) back to the controller. The system uses feedback to monitor and adjust the output based on the parameters set by the technician.
A control loop refers to the physical system and control functions that make adjustments to achieve the desired output. Adjusting these parameters determines how the control algorithm responds to the DUT’s response.
In the VibrationVIEW Sine test mode, the technician can define the control loop parameters under the Parameters tab in the Sine Test Settings dialog box.
The startup time defines the approximate time it will take for the controller to reach the drive limit output. A startup time of 10 to 20 seconds is recommended as a safety precaution because the operator will have time to abort the test if necessary.
Response time and Min response time
The Response time and Min (minimum) response time are the primary loop-tuning parameters in the VibrationVIEW Sine test mode. They help to shape the frequency response of the closed-loop system. The parameters of the closed-loop frequency response determine the speed and stability of the time domain’s control response.
The Response time parameter defines the high-frequency loop response, and the Min response time parameter defines the low-frequency loop response. A lower response time results in faster control response, but a higher response time increases loop stability.
If the Min response time value (number of cycles at a given frequency) is greater than the Response time value, then the Min response time value determines the loop response.
Increasing and Decreasing rate
The Increasing rate and Decreasing rate are slew rate parameters. They set the output’s minimum and the maximum rate of change.
What is the Slew Rate?
The slew rate is a logarithmic value that determines the test level’s rate of change per second (dB/sec). In Sine, the slew rate is used as a tuning parameter. A faster slew rate allows the voltage to adjust through sharp resonances, and a slower slew rate improves stability.
The slew rate can be entered for the increasing and decreasing output signals. A slower increasing slew rate can be used to sweep through resonances while preventing overshoot as the signal rapidly decreases past the resonance. For example, a slew rate of 20dB/sec allows the signal to increase by 10x in 1 second.
Input Filter Parameters
The Input Filter Parameters determine the bandwidth of the tracking filters.
The Sine test mode also offers the option to apply adaptive feedback.
What is Adaptive Feedback?
Adaptive feedback permits the system to automatically adjust the control loop parameters. This option allows for tighter control outside a resonance while ensuring stability at sharp resonances.
In the Sine test mode, the Low setting intervenes minimally, while the High setting provides significant intervention at resonance. The Manual settings option offers control of the adaptive algorithm beyond the automatic preset values.
Sine Vibration Testing Software
The VibrationVIEW Sine test mode detects resonances using a swept and/or fixed-frequency sine wave test with control of acceleration, velocity, and displacement. When paired with a VR9500 or VR10500 vibration controller, the user can define the feedback parameters of the system in order to control the actual output or select adaptive feedback for automatic control.
Download the free demo of VibrationVIEW today to set up and design tests before running them on a shaker, view and playback data files, and more. Interested in learning more? Visit the software page.
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- Landau, I.D., R. Lozano, and M. M’Saad. “Introduction to Adaptive Control.” In Adaptive Control. Communications and Control Engineering. London: Springer, 1998.
- N.A. “Chapter 11 Loop Shaping.” Caltech Department of Computing and Mathematical Sciences, 2006.