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.

### Closed-Loop Parameters

In a closed-loop system, the vibration controller sends an input through an amplifier to the shaker. A transducer then sends the output of the device under test (DUT) back to the controller. The system uses feedback to monitor and adjust the actual output based on the desired parameters.

A control loop refers to the physical system and control functions that make the adjustments to achieve the desired output. In the Sine test mode, the user can define the control loop parameters under the Parameters tab in the Sine Test Settings dialog box. Adjusting these parameters determines how the control algorithm responds to the output.

### Startup Parameters

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.

### Running Parameters

#### Response time and Min response time

The Response time and Min (minimum) response time are the primary loop tuning parameters in Sine. They are used 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/seconds). 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/second allows the signal to increase by 10x in 1 second.

#### Input Filter Parameters

The Input Filter Parameters determine the **bandwidth of the tracking filters**.

**What Are Tracking Filters?**

During a sine test, the amplitude of the output frequency is of interest to the engineer. They want to test the device with the specified amplitude and at the specified frequency. However, vibration controllers pick up the noise and harmonics of the shaker system in addition to the pure sine tone. The background noise alters the reading of the amplitude.

Tracking filters are applied to isolate the drive output’s pure sine tone. As the test changes frequencies, the software filters out noise at frequencies of non-interest and maintains a narrow bandwidth, thereby isolating the pure sine tone at each frequency. Bandwidth is the range within each frequency band.

To learn more about tracking filters, read the blog titled Sine Tracking Filters to Remove Harmonics and Noise.

The Fractional bandwidth parameter defines the bandwidth of the tracking filters at low frequencies and is specified as a percentage of frequency. The Maximum bandwidth parameter defines the bandwidth of the tracking filters at high frequencies. The Fractional bandwidth cannot exceed the Maximum bandwidth.

Tracking filters with a smaller value provide increased filtering that results in greater stability. This stability can improve performance when sweeping through sharp resonances. However, increased filtering comes at the cost of increased response times. Reduced filtering (larger bandwidths) improves performance at extremely low frequencies.

### Adaptive Feedback

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 Sine, the Low setting intervenes minimally, while the High setting provides significant intervention at resonances. The Manual settings option offers control of the adaptive algorithm beyond the automatic preset values.

### Optional: Dual Loop Sine Control

Both the VR9500 and VR10500 vibration controllers can perform dual-loop control in the Sine, Random, and Shock test modes. The drive and COLA outputs from one controller are used to drive two different shakers with the same test profile. In Sine, the user can adjust the phase angle between the two outputs +/- 360 degrees.

### Sine Vibration Testing Software

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.