Overview

This guide outlines the comprehensive steps for installing an accelerograph and its accompanying GPS antenna within a building structure. It covers mounting procedures, necessary clearances, and accessibility considerations to ensure optimal performance and ease of maintenance.

Tools and Materials Required

• Drill and drill bits
• Mounting brackets and hardware (screws, anchors, etc.)
• Screwdriver
• Level
• Measuring tape
• Cable conduits (if necessary)
• Sealant (for outdoor installations)

Pre-Installation Planning

1. Location Selection: Choose a location that minimizes vibrations from non-seismic sources (e.g., heavy machinery, and HVAC systems). Ideally, the accelerograph should be positioned close to the building’s structural core. It is better to install it on the floor inside an NEMA enclosure.

• GPS Antenna Placement: The GPS antenna requires a clear view of the sky to maintain satellite communication. It should be placed on or near a window sill or mounted externally with a clear path to the sky, avoiding obstructions such as tall buildings or heavy foliage. The GPS provides absolute timing to the instrument for time-stamping of the waveforms recorded.

• Accessibility: Ensure the installation site is easily accessible for maintenance and data retrieval. An access panel or removable ceiling tiles are recommended for indoor installations.

• Clearances: Maintain at least 1 foot (~0.3 meters) of clearance around the accelerograph for ventilation and to ensure unobstructed access.

Installation Steps

1. Mounting the Accelerograph:

• Use the measuring tape and level to mark the drill point for the mounting anchor ensuring the accelerograph will be level.
  • Drill a hole at the marked point and insert the anchor.
  • Secure the mounting anchor with a screw.
  • Attach the accelerograph to the mounting anchor following the manufacturer’s guidelines.

Example of floor mounting

In the following picture, you can see a floor-mounting installation of a unit with an internal sensor with the use of a bolt in the concrete.

Drawing is courtesy of SARA

The leveling pads do not necessarily need the counter-lock paddle (not drawn in the figure), even if it is always good to have. They would work in a counteraction, so the paddles shall be adjusted forcing the sensor to go up, while the bolt keeps it fixed down.

Photo is courtesy of SARA

The same principle will work for wall and ceiling installations as follows.

Example of wall mounting or ceiling

If the unit needs to be mounted in buildings, it often requires a vertical or ceiling-flipped installation. In these cases, is essential to use the central key-hole hooking slot.

Drawing is courtesy of SARA

In both cases, especially for mounting equipment over 1 meter of elevation we absolutely recommend the use of a safety chain or steel cord.
It can be anchored to any suitable threaded hole. If necessary and appropriate you may decide to use 2 or more threaded holes to anchor the safety cord.
All safety retention devices must be checked every year. To be on the safer side a shaft or a large steel baseplate could be used instead of the use of a dowel.

Appropriate heavy-load dowel and proper bolt are necessary to anchor this way, also depending on type of material the wall is made of, concrete, bricks, etc.

The bolt head should be of 12 mm, maximum of 14 mm to allow a proper leveling degree of freedom. The diameter of bolt stem should be not less than 8 mm for wall or ceiling mounting.

NOTE – 1: It is very important to have a safety bonding for the wall and ceiling mount and check the tightness of it periodically else vibrations will be wrongly measured.

NOTE – 2: Do not overtight the feet else the case will be damaged.

• Installing the GPS Antenna (if applicable):

• If mounting externally, ensure the antenna is positioned securely with a clear view of the sky. Use a sealant to waterproof any drill holes.
  • For window placement, ensure the antenna is as close to the glass as possible, avoiding metal frames that might obstruct signal reception.
  • Route the antenna cable to the accelerograph, avoiding sharp bends. Use cable conduits if necessary to protect the cable from damage.

• Cabling and Power Connection:

• Connect the GPS antenna to the designated port on the accelerograph.
  • Ensure all cables are neatly routed and secured.
  • Connect the accelerograph to a power source, using a surge protector. Make sure that the power outlet is grounded.

• Initial Setup:

• Follow the manufacturer’s instructions to power on and configure the accelerograph.
  • Verify the GPS connection and perform any required calibrations.

• Testing:

• Conduct initial tests to ensure the accelerograph is recording data accurately.
  • Verify that the data can be retrieved and is consistent with expectations.

Post-Installation

• Documentation: Keep a record of the installation details, including the location, date of installation, and any specific configurations.

• Maintenance Schedule: Establish a regular maintenance schedule to inspect the accelerograph, its connections, and the surrounding area to ensure continued accuracy and performance.

Notes

• Always refer to the manufacturer’s installation guidelines for specific instructions related to your accelerograph model.

• Consider local building codes and regulations when installing external components.

• For installations in areas with extreme weather conditions, additional protective measures may be required for the outdoor components.

By following these comprehensive instructions, you can ensure the successful installation of an accelerograph and its GPS antenna within a building, facilitating accurate seismic data collection and analysis.

Questions?

Email us at support@quakelogic.net or call us at +1-916-899-0391.

Processing infrasound signals is a critical step in analyzing data from phenomena that generate low-frequency acoustic waves. These waves can originate from various sources, including natural events (volcanic eruptions, tornadoes, etc.), man-made explosions, and large machinery. The goal of post-processing infrasound data is to enhance signal quality, making it easier to detect and analyze these phenomena. Here’s a detailed explanation of the post-processing steps, including baseline correction and bandpass filtering:

1. Pre-Processing:

Before diving into specific post-processing techniques, it’s essential to ensure that the raw infrasound data is correctly pre-processed. This might include steps like digitization (if working with analog signals), ensuring correct time synchronization, and initial data cleaning to remove any obvious errors or outliers.

2. Baseline Correction:

Infrasound signals can be affected by drift and shifts in the baseline, which can obscure the true signal or make analysis more difficult. Baseline correction aims to adjust the signal so that its baseline is stable over time, which is crucial for accurate measurement and analysis.

• Identify the Baseline: Using statistical methods or by visually inspecting the signal, determine the baseline level. This could be a constant value that the signal should nominally return to in the absence of any events.

• Correction Methods: Apply a method to correct the baseline drift. This might involve subtracting the identified baseline value from the entire signal or using more sophisticated methods like polynomial fitting or moving average subtraction to adjust dynamically for baseline changes over time.

3. Bandpass Filtering:

Bandpass filtering is used to remove noise and irrelevant frequencies that do not contribute to the signal of interest. By focusing on a specific frequency band, it enhances the signal’s detectability and clarity.

• Determine Frequency Band: Based on the source and nature of the infrasound signal, identify the relevant frequency range. Infrasound signals typically fall below 20 Hz, but the exact band of interest can vary depending on the source and environment.

• Apply Filter: Use a bandpass filter to retain only the frequencies within the desired range. Common types of bandpass filters include Butterworth, Chebyshev, and Bessel filters, each with its characteristics in terms of phase shift and roll-off rate. The choice of filter depends on the analysis requirements and the characteristics of the signal.

• Filter Design: The filter can be designed digitally in software, specifying the passband (the range of frequencies to keep), the stopband (frequencies to be attenuated), and the filter order (which affects the steepness of the roll-off). Higher-order filters provide sharper cutoffs but can introduce phase distortion.

4. Convert to Pascal Values:

After filtering, the signal is often converted into physical units (e.g., Pascals) for analysis. This step involves calibrating the signal based on the sensitivity of the infrasound sensors used to record the data and any known reference levels. Calibration ensures that the signal amplitude reflects the true pressure variations caused by the infrasound source.

For detailed information on this step, visit this link:

Converting Infrasound Sensor Data to Pascal: A Step-by-Step Guide

5. Additional Processing Steps:

Depending on the application, further processing steps might be necessary, such as:

• Detrending: Removing linear trends from the data to focus on the signal fluctuations.

• Windowing: Applying a window function to manage the signal’s start and end points, useful for Fourier analysis.

• Noise Reduction: Implementing additional noise reduction techniques, such as spectral subtraction or signal enhancement algorithms, to improve signal quality.

6. Analysis:

After post-processing, the signal is ready for analysis, which could involve identifying specific events, measuring their characteristics (amplitude, frequency content, phase, duration), and interpreting their source and impact.

In summary, the post-processing of infrasound raw signals, including baseline correction and bandpass filtering, is essential for accurately interpreting the data. These steps help in enhancing the signal quality by eliminating noise and irrelevant information, thereby facilitating a more precise analysis of the infrasound phenomena captured by the sensors.

Questions?

Email us at support@quakelogic.net or call us at +1-916-899-0391.

In the world of environmental and geophysical monitoring, infrasound sensors play a pivotal role in detecting low-frequency sound waves emanating from natural or man-made sources. These sensors capture invaluable data that can be used for monitoring volcanoes, detecting avalanches, or even tracking artificial explosions.

However, the raw data from these sensors, often stored in digital counts by dataloggers, require conversion into physical units (Pascals) to be meaningful for analysis and interpretation. This article provides a comprehensive guide on how to perform this crucial conversion.

Understanding the Signal Path

The journey of an infrasound signal from physical pressure changes to digital data involves several stages, including the sensor itself, potential preamplification, and finally, analog-to-digital conversion (ADC) by a datalogger. Each stage influences how the final digital count corresponds to the actual pressure change it represents.

Key Components

1. Sensor Sensitivity: Defined typically in V/Pa or mV/Pa, this parameter indicates how much voltage change the sensor produces for a given pressure change. It’s a fundamental characteristic that varies between sensor models.

2. Datalogger ADC Resolution: The ADC’s role is to convert the analog voltage signal from the sensor into digital counts. The resolution of the ADC (e.g., 16-bit, 24-bit, 32-bit) determines the granularity of this conversion, affecting the precision of the digital data.

Conversion Steps

The process of converting digital counts to Pascals involves two main steps

• From Counts to Voltage: First, the raw count values are converted to voltage using the formula:

Here, the ADC Offset is the count value for 0 V input, ADC Max Count are based on the ADC’s bit resolution, and Voltage Range is the full-scale voltage range the ADC can measure.

• From Voltage to Pressure: Next, the voltage is converted to pressure using the sensor’s sensitivity:

This step requires careful attention to unit consistency, especially when converting mV to V.

Practical Example

Let’s go through a clear example of converting digital count values from a datalogger connected to an infrasound sensor into physical pressure units (Pascals). This example will illustrate the step-by-step process using hypothetical yet realistic values for an infrasound monitoring setup.

Example Setup:

• Infrasound Sensor Sensitivity: 50 mV/Pa (millivolts per Pascal)

• ADC Resolution: 24-bit

• Voltage Range of the ADC: ±2.5V (total range 5V)

• Raw Count Value from Datalogger: 10,000,000 counts

• ADC Max Counts: The maximum count value for a 24-bit ADC is 2^24=16,777,216 counts.

• ADC Offset: For a bipolar signal range (±2.5V), the offset (the count corresponding to 0V) is half of the ADC’s maximum count, which is 16,777,216/2=8,388,608 counts.

Step 1: Convert Counts to Voltage

First, we convert the raw count value to voltage using the formula:

Step 2: Convert Voltage to Pressure

Now, we convert the voltage to pressure using the sensor’s sensitivity:

In this example, a raw count value of 10,000,000 from the datalogger corresponds to a pressure change detected by the infrasound sensor of approximately 9.58 Pascals. This process demonstrates how to translate the digital data captured by a datalogger into meaningful physical measurements, allowing researchers and technicians to analyze and interpret infrasound signals accurately.

Important Note: Calibration factors not discussed here (e.g., corrections for frequency response, temperature effects) might also be necessary depending on the precision required for your application. Always refer to the sensor and datalogger manuals for the exact parameters and formulas relevant to your specific setup.

Conclusion

Converting digital counts from an infrasound sensor datalogger to Pascals is a critical step in processing and analyzing infrasound data. Understanding the sensor’s sensitivity and the ADC’s characteristics is essential for accurate conversion. This guide provides a foundational approach for researchers and technicians working in fields where precise environmental monitoring is crucial. By following these steps, one can transform raw digital counts into meaningful physical measurements, unlocking the potential to analyze and interpret infrasound signals for various applications.

Click HERE for our infrasound web pages for your infrasound sensor and software needs.

Questions? Contact us at support@quaklogic.net