Technical Specifications for Narrow range Infrasound Monitor.pdf

Technical Specifications for Acoustic Monitoring Sensor

The USGS Volcano Hazards Program (VHP) requests an infrasound acoustic monitor. This request is on behalf of three departments in the USGS Volcano Hazards Program. The VHP is charged with monitoring US volcanoes in the protection of lives and property. The Volcano Disaster Assistance Program (VDAP) is within the VHP and is charged with assisting a world-wide community of official government programs to monitor high threat volcanoes.

The quantities desired by the Volcano Hazards Program may be difficult to supply within the typical 90-day award period. Requester will accept a partial delivery schedule if necessary or will accept an extended award period.

Individual sensor calibration must be within +-5% of nominal values reported by manufacturer. Higher levels of uncertainty will reduce confidence in the device performance. Software and techniques used to interpret the information from the sensor are of a precise nature and require a precisely calibrated sensor. Nominal calibration value must be traceable to nationally accredited external laboratory calibration chamber to meet industry specifications. Selected unit must be in current production and have established, proven and acceptable performance history. This request is directed at an existing product, not at product design and development.

We request a device with the following characteristics:

Signal Characteristics:

Sensitivity and full-scale range are inversely proportional. A less sensitive sensor can have a higher full-scale range. A lower full-scale range sensor can have a higher level of sensitivity. We request a sensor with a balance of these two specifications to be sensitive to the volcano generated infrasound signals of interest.

Nominal Sensitivity: 25mV/Pa@1Hz or greater. 1Hz is a commonly accepted base line frequency of measurement. At 1Hz, a less sensitive than 25mV instrument will not react to the signals of interest and the signal will not be recorded. The signals of volcanic activity can be subtle in nature. This level of sensitivity is required to see low level signals generated by small air disturbances in the vicinity of the volcano.

Full Scale Range: 720Pa peak to peak full-scale input range or greater. The full-scale range establishes the maximum signal generated by volcanic activity before the sensor information becomes unusable due to signal being too strong for the sensor to stay within calibration values. 720Pa is determined to be the maximum signal level required for the monitoring methods and existing software techniques that will be used with this sensor.

Sensor output specifications:

Output type: Differential. Single ended not acceptable. Differential output using signal plus and signal minus is less sensitive to electrical disturbances generated by lighting, nearby power lines, or power generation equipment.

Maximum output: 20V or 40V. +-5V tolerance is acceptable output range. The output range of the sensor must be matched to a digitizer that samples the signal voltage. Output voltage outside of this range or tolerance will be a poor match to the digitizers used by the VHP and will either underutilize the digitizer gain or overshoot the scale of the digitizer during larger events.

Operational frequency band and self-noise

Frequency response: Flat to within = +-3dB from .05Hz to 200Hz or wider band. +-3dB is a scientifically determined level of tolerance of the sensor to accurately represent the frequency content of the infrasound signal. Beyond this tolerance, the signal is considered to be over or under represented by the calibration of the sensor and the data will not be useful. Infrasound signals generated by volcanoes come from a wide variety of sources that vary in their frequency component. The wide frequency band requested allows a single sensor to be sensitive to the entire band rather than using multiple sensor that are sensitive to the frequencies generated, leading to savings in power ind infrastructure required to monitor the signals.

Band limited Self Noise: 2mPa RMS from.05 to 200Hz or less noise. This is the measured level of self-noise generated by the sensor electrical component construction. This specification is relevant in the frequency response band mentioned above. Higher self-noise will interfere with low level signals of interest. Self-noise outside of the requested frequency response is irrelevant.

Dynamic Range: 115dB or greater.

Power requirements:

Short Circuit Protection: Protected against momentary shorts from signal+ to signal- and signal to ground. This is required in the case of accidental momentary short circuit in the power supply during installation on removal.

DC supply range: 11.5V to 20V or wider. Remote monitoring station supply voltages do not use voltage regulators. These sensors will be used at remote monitoring stations and may have a range of voltage supply values due to the available solar input and battery capacity systems.

DC current consumption: 175mW or less. Due to the nature of limited power availability at remote stations, this must be a low power device. Higher current consumption will require higher cost burdens of station power infrastructure including more batteries and solar panels.

Physical Characteristics:

4” diameter or smaller. A larger instrument will require re-design of existing enclosures and cases. A larger sensor will not be a drop-in replacement for existing networks of these devices.

3.5” tall or shorter. A larger instrument will require re-design of existing enclosures and cases. A larger sensor will not be a drop-in replacement for existing networks of these devices.

Must include 3 or more acoustic entry points for signal averaging over multiple azimuths. Fewer entry points will introduce a directional component to the infrasound signal. The directional component will reduce sensitivity from off-azimuth signals.

Operating temperature: -40C to +60C. A wide operating temperature is required. These sensors will be used in extremely cold arctic and extremely hot tropical environments.

Humidity: 90% or greater immunity to humidity. Lower tolerance to humid environments will mean the sensor will not function in wet, tropical, or coastal environments.

Housing must be of corrosion resistant material(s) that are isolated from ground. These sensors may be directly in contact with the earth. In these cases, the sensor must be isolated from electrical disturbances from lighting that is common in volcanic environments.