Last Updated: 03/16/2010
The PSN-ACCEL triaxial accelerometer sensor board is based on piezoresistive silicon accelerometer chip made by Measurement Specialties, Inc. The specifications on the sensor chip can be viewed here. Each axis has two outputs. The low gain channel is used to record very large local earthquakes without saturating the system. This channel has a +- ~2g full scale (10 volts) output. The high gain channel is used to record smaller events. This channel has a +- ~ 70 mg full scale output. With this channel cultural noise, large trucks going by etc, can be seen with a 16-bit A/D converter system. Each channel has a 20 Hz 7-pole lowpass anti-aliasing filter and low impedance output driver that can directly drive an A/D board channel or chart recorder.
The board can be powered with either a DC or AC power supply. A three axis board draws ~160 mA at the minimum input voltage of 15.5 VDC or ~ 2.5 watts of power. At 30 VDC, the maximum input voltage, the board draws ~115 mA or ~3.5 watts. The board size is 7.750 x 5.750 inches or 19.655 x 14.605 centimeters.
Each sensor chip has a serial number and is calibrated by the manufacturer. A calibration datasheet will be supplied for each axis. This datasheet contains information on the sensitivity of the sensor chip expressed in millivolts / g, with a typical chip producing about 7 to 8 mV / g. The calibration datasheet looks like this. Since the amplifier and filter sections on the sensor board have fixed gains, the overall sensitivity for each channel (high and low gain) can be calculated using the following information or the calculator below:
Low Gain: The gain through this channel is 723.16. To calculate the sensitivity multiply the output of the sensor chip by 723.16. Example: If the sensor chip has a sensitivity of 7.42 mV / g then the output of the low gain channel is 5.366 volts per g. Since the maximum output voltage is 10.0 volts peak the maximum g that can be recorded using this channel is 1.86 g (10.0 volts / 5.366 v/g).
High Gain: The gain through this channel is 19,163.74. To calculate the sensitivity multiply the output of the sensor chip by 19163.74. Example: If the sensor chip has a sensitivity of 7.42 mV / g then the output of the high gain channel is 142.195 volts per g. Since the maximum output voltage is 10.0 volts peak the maximum g that can be recorded using this channel is .0703 g (10.0 volts / 142.195 v/g).
If the sensor is going to be used with PSN software and hardware (WinQuake / SDR / WinSDR) the sensitivity of the sensor should be included with the other channel information like latitude, longitude and sensor orientation. SDR and WinSDR have a sensitivity field expressed in centimeters / sec**2 (acceleration) per A/D count used by WinQuake to display the actual amount of acceleration. To convert from g to cm / sec**2 multiply g by 980.665 and to convert to cm / sec**2 / A/D count divide the maximum cm / sec**2 by the number of maximum A/D counts / 2.
Example: Using the example above, the maximum output of the high gain channel, with a sensor chip that has a sensitivity of 7.42 mV per g, is .0703 g. To convert to cm / sec**2 multiply this number by 980.665 or 68.94 cm / sec**2 maximum (10.0 volts). The number of A/D counts for a 16-bit A/D chip is 65536 making the sensitivity of this channel 0.002104 (68.94 / (65536 / 2)) cm / sec**2 / A/D count. This number should be placed in the Sensitivity field in SDR or WinSDR. The Magnitude Correction field should be left blank.
Below are several seismograms of local events that were recorded using this sensor.
More seismograms from this sensor can be found on the PSN event file archival system here or here. The event file extensions to look for are *.LCANH.PSN, *.LCAEH.PSN and *.LCAZH.PSN. Currently only the high gain channels of this sensor are being recorded.
One Channel: $275.00 + S&H
Two Channel: $475.00 + S&H
Three Channel: $675.00 + S&H
The board comes with a wall mounted 110 VAC 60 Hz 500 ma power supply. Please contact us if you need a power supply that works on 220 VAC / 50 Hz.
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