Performance of Several Low-Cost Accelerometers

Several groups are implementing low-cost host-operated systems of strong-motion accelerographs to support the somewhat divergent needs of seismologists and earthquake engineers. The Advanced National Seismic System Technical Implementation Committee (ANSS TIC, 2002), managed by theU.S. Geological Survey (USGS) in cooperation with other network operators, is exploring the efficacy of such systems if used in ANSS networks. To this end, ANSS convened a working group to explore available Class C strong-motion accelerometers (defined later), and to consider operational and quality control issues, and the means of annotating, storing, and using such data in ANSS networks. The working group members are largely coincident with our author list, and this report informs instrument-performance matters in the working group’s report to ANSS. Present examples of operational networks of such devices are the Community Seismic Network (CSN; csn.caltech.edu), operated by the California Institute of Technology, and Quake-Catcher Network (QCN; Cochran et al., 2009; qcn.stanford.edu; November 2013), jointly operated by Stanford University and the USGS. Several similar efforts are in development at other institutions. The overarching goals of such efforts are to add spatial density to existing Class-A and Class-B (see next paragraph) networks at low cost, and to include many additional people so they become invested in the issues of earthquakes, their measurement, and the damage they cause. Classes A, B, and C are defined in terms of performance by ANSS (2008). Class A refers to the highest performance, stateof-the-art instrumentation, presently for accelerometers with useful resolution of about 22–24 bits peak-to-peak over 2 to 4g ranges (sensor roughly US$2000–4000). Class B is illustrated well by the NetQuakes instrument (GeoSIG model GMS-18) that is an effectively 16-bit (vertical) and 18-bit (horizontal) instrument over 3g ranges (notwithstanding that longer sample words are recorded; Luetgert et al., 2009, 2010; sensor roughly US$500–1000). Class C is the lowest performance level potentially usable by ANSS and has useful resolution from about 12 to 16 bits, typically over 2g ranges (sensor roughly US$100–200). E We describe the design of typical Class-C accelerometers and provide links on the subject in the electronic supplement to this paper. In order to facilitate the use of Class-C sensors in regional networks it is critical that we are able to understand the capabilities and limitations of these instruments. This report describes performance-test results for the following five types of triaxial Class-C sensors together with their recording systems, public or private: 1. Droid smart phones, one example of a Google Nexus One (we call this, Serial Number 2[SN2]; https://sites.google .com/a/pressatgoogle.com/nexusone/; November 2013), and two examples of HTC Magic phones (we call these SN3 and SN4; there is no SN1; http://www.htc.com/us/; November 2013); note that iPhones, laptop computers, and probably others have similar capability, so we will refer to tested devices generically as smart phones; 2. Gulf Coast Data Concepts (GCDC; gcdataconcepts.com) model X6-2 shipping monitors used to detect drops and bumps of valuable packages during shipment and handling (SNs 4086, 4097, and 4128); 3. JoyWarrior model 24F14 accelerometers (“JWF14”; Code Mercenaries Hardund Software GmbH, codemercs.com), a type often used to control video games (SNs 1–6; SNs 1, 2, and 5 are 1g devices, the other three are 2g devices); 4. two models of similar video-game controllers from O-Navi LLC (o‐navi.com), models 23567-A (“O-Navi A”) and 23567-B (“O-Navi B”); and 5. two models of Phidgets (phidgets.com), five of model 1056 (SNs 145444–252220), and one prototype model 1043 (SN 999990); these devices are aimed at general prototyping (often for navigation) and amateur users. Unless otherwise stated, these are 2g devices. The tests performed were 1. “box flip” tests for 0 Hz sensitivity, offset, and axis orientations; 2. transfer function tests (response functions) in this case for amplitude, but not phase;