QCN Sensor Performance

Sensor Noise

Sensor Comparison

Each sensor has a different sensitivity due to 1) accelerometer noise or electrical noise and 2) analog-to-digital resolution. Accelerometer noise is very hard to decrease with very small cantilever balances countered by very small electrical voltages. This is made even harder when coupled with standard devices such as USB, which may cause large power fluctuations. Digital resolution is limited by the number of bits and the quality of the analog-to-digital filter applied to the signal. In general, QCN’s sensors have higher noise and courser digital resolution than traditional research-grade seismometers, but then again, they cost less 1/100th to 1/1000th of the initial cost, and much even less for long-term maintenance.

Digital Resolution

All accelerations start as continuous properties, but must be digitized for computers to handle them. Digital resolution is given as sensor range (e.g., -2g to +2g, where 1g is Earth’s gravity or 9.8m/s/s) divided by the total number of digital units. For an 8 bit digitizer, there are 28=256 values.

Digital Resolution Table

Number of Bits Number of Digital Units Digital Resolution (in m/s/s)
8 256 0.15
10 1024 0.04
12 4096 0.01
14 16384 0.002
16 65536 0.0006

Sensor Noise


The noise level of each sensor is at minimum 1 digital unit, but can be as many as 30 digital units. The noise level (blue line) of each sensor type is plotted on the figure to the right. For comparison, the rough accelerations expected from an earthquake of various magnitudes (M1-8) are plotted as well. For sensors in houses and buildings, intermittent anthropogenic noise sources often mask low-amplitude signals. Higher amplitude intermittent noise is shown in light grey. Typical background noises are are illustrated by the dark grey area. Higher levels of noise (above 0.1 g) can often occur in homes and businesses. Doors slamming, air-conditioning units starting up and children running can often cause large vibrational noise above the light grey region. You should never expect to record a M2 earthquake. You will often miss M3 earthquakes because we try to filter out false positives that could be due to cultural noise.

Learn More About the Network

O-NAVI A

O-NAVI A:


The O-NAVI sensors are QCN’s latest addition to the QCN USB sensor group. The O-NAVI A is a 12-bit sensor that use the (KXRB5 MEMS accelerometer from Kionix. The O-NAVI A has only a few counts of digital noise, giving it a better noise floor than the JoyWarrior 24F14, even though the digital resolution isn’t as good.


The performance of the O-NAVI A is illustrated here. The blue line is the typical noise level. The green line indicates the analog-to-digital resolution. The black-to-red lines show the accelerations expected for various magnitude events (M1-8). The grey boxes show the range of typical noise.

O-NAVI B

O-NAVI B:


The O-NAVI sensors are QCN’s latest addition to the QCN USB sensor group. The O-NAVI B is a 16-bit sensor that use the (KXRB5 MEMS accelerometer from Kionix. The O-NAVI B has many more digital counts of digital noise, but generally provides a marginally improved noise floor relative to the O-NAVI A.


The performance of the O-NAVI B is illustrated here. The blue line is the typical noise level. The green line indicates the analog-to-digital resolution. The black-to-red lines show the accelerations expected for various magnitude events (M1-8). The grey boxes show the range of typical noise.

JoyWarrior 24F14

JoyWarrior 24F14:


The Code Mercenary sensors are perhaps QCN’s most stable, and user friendly sensors. The JW24F14 is a 14-bit sensor that has many more digital counts of noise than the JW24F8. However, the JW24F14 provides a marginally improved noise floor relative to the JW24F8.


The performance of the JoyWarrior 24F14 is illustrated here. The blue line is the typical noise level. The green line indicates the analog-to-digital resolution. The black-to-red lines show the accelerations expected for various magnitude events (M1-8). The grey boxes show the range of typical noise.

JoyWarrior 24F8

JoyWarrior 24F8:


The Code Mercenary sensors are perhaps QCN’s most stable, and user friendly sensors. The JW24F8 is a 10-bit sensor that has a few counts of noise, making it comparable to the MacBook, phone, and tablet sensors. However, by fixing it to the ground, there is usually less cultural noise on the JW24F8 than mobile devices.


The performance of the JoyWarrior 24F8 is illustrated here. The blue line is the typical noise level. The green line indicates the analog-to-digital resolution. The black-to-red lines show the accelerations expected for various magnitude events (M1-8). The grey boxes show the range of typical noise.

MacBook (Pro/Air)

MacBook (Pro/Air):


The MacBook series of laptops have internal sensors. The interface with this device is relatively programmer friendly, which made it easy to adopt. The MacBook series has 8-10 bit sensors that typically have a few counts of noise. The noise level of the MacBook is typical of mobile devices. QCN will soon start incorporating more mobile devices. Note that all mobile devices are less useful than mounted USB sensors because 1) they experience greater jostling, and 2) they are not strapped down, so they may rattle about when a big one hits.


The performance of the MacBook is illustrated here. The blue line is the typical noise level. The green line indicates the analog-to-digital resolution. The black-to-red lines show the accelerations expected for various magnitude events (M1-8). The grey boxes show the range of typical noise.

ThinkPad

ThinkPad:


ThinkPad was one if the first to addopt a MEMS sensor into their laptops. They made it available, and QCN uses this device to monitor earthquakes. The ThinkPad accelerometer is only an 8-bit sensor with one or two counts of noise. It has only 2 horizontal axes, rather than 3, so it is less desirable. Nevertheless, we have recorded earthquakes with the ThinkPad. ThinkPad represents the lowest end of sensor used by QCN.

The performance of the ThinkPad is illustrated here. The blue line is the typical noise level. The green line indicates the analog-to-digital resolution. The black-to-red lines show the accelerations expected for various magnitude events (M1-8). The grey boxes show the range of typical noise.