PSN-ACCEL 4-Channel Strong Motion Accelerometer Sensor Board

Last Updated: 07/12/2013


PSN-ACCEL Board with Optional 4.5Hz Geophone Connected to the Auxiliary Channel

Block Diagram

Magnitude 5.3 event 180km (112 miles) from the PSN-ACCEL sensor.

Description:

The PSN-ACCEL 4-Channel 24-Bit Triaxial Accelerometer sensor board is based on a piezoresistive silicon accelerometer chip manufactured by Measurement Specialties, Inc. The specifications on the sensor chip can be viewed here. The board also includes an auxiliary 24-Bit channel that can be used with a weak motion sensor like a 4.5Hz or 1Hz geophone. Each channel is digitized using a 24-Bit Delta-Sigma Analog to Digital Converter (Note 1) manufactured by Cirrus Logic. The datasheet for the Cirrus Logic CS5532 ADC chip can be viewed here. Supported sample rate are: 15, 25, 30, 50, 60, 100, 120 and 200SPS.

The PSN-ACCEL board supports both USB and RS-232 Comm Port interfaces.  A GPS receiver can be connected to the board for accurate time stamping of the ADC data. 

Applications:

Features:

Specifications:

Cost:

Sensitivity:

The overall sensitivity to acceleration for each channel is controlled by Programmable Gain Instrument Amplifier (PGIA) on the ADC chip and the number of bits used from the ADC converter. As the sample rate increases the number of useful ADC bits decreases.  Below are some suggestions for the number of bits to use and PGIA gain value :

These settings should be added to WinSDR in the Channel Settings dialog box. Earthworm users will need to add these settings to the PsnAdSend.d file. See http://www.seismicnet.com/PsnAdSend76_ovr.html and http://www.seismicnet.com/PsnAdSend76_cmd.html for more information. 

Calibration:

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. Infield calibration is also possible by using the earth's 1 g force and rotating each axis 180 degrees.

Power Requirements:

The PSN-ACCEL sensor board can operate on a wide input voltage range. The minimum input voltage is ~7.5VDC and the maximum ~28VDC. A diode on the board is used to prevent damage to the board if the input power is reversed. The table below list the power requirements in milliamps with and without the Garmin GPS 18x receiver connected to the sensor board.

Input Voltage  No GPS W/GPS
7.50VDC  100ma 130ma
12.0VDC  60ma 80ma
15.0VDC  50ma 68ma
24.0VDC  36ma 46ma

Software:

WinSDR (Download) can be used to record data using the PSN-ACCEL sensor board.  This program is included with the purchase of the board.  WinSDR will run on Windows XP, VISTA and Win7. Both 32-Bit and 64-Bit version of the program are available. 

This Windows DLL Driver and Linux Library can be used by programmers who would like to write their own datalogger program or add the sensor board to an existing program.  The DLL Driver zip file or Linux Library includes an example, written in VC++ 8.0, showing how to use the PSNADBoard.DLL file.

Earthworm, a powerful seismic software package that can run under various operating systems, can receive data using the PSN-ACCEL board or WinSDR. See this link for more information.

Auxiliary Channel:

This channel has a differential input with a input voltage range of +-2.5V or 5V Peak-to-peak when the Programmable Gain Instrument Amplifier gain set to 1. With the gain set to 64, the maximum PGIA gain, the input voltage range is +- 39 millivolts. A differential voltage divider can be placed on the board to allow for larger input voltage swings. See schematic below. R2 can be used as a damping resistor for the sensor or used as one leg of the voltage divider.

The user should use shielded 2 conductor wire when connecting a senor like a Geophone to the input. The + output of the sensor should connect to J1 screw terminal 2 and the - output to terminal 1. The shielded part of the wire should be connected to terminal 3. At the other end of the wire the shield can be left open or connected to the metal case of the sensor. Before connecting the shield to the case of the sensor the should check with a Digital Volt Meter to make sure there is no resistance between the case and one of the output coil terminals. If the sensor is going to set right next to the PSN-ACCEL board the user can use a short run of twisted pair wire without the shield. Just leave the ground screw terminal 3 disconnected and only connect terminals 1 and 2 to the sensor's output coil. 

 If the user is going to drive the input with something other then a coil the put terminals must be biased at +2.5V and swing up to 5V and down to ground. Since the input is differential one terminal needs to be going +V while the other -V.

Auxiliary Channel Input Schematic


Input/Output Connector Information:

Auxiliary Input J1:

This connector is a three terminal screw block. See the above for more information. While looking at the top of the board with J1 to your left the connector pinout is as follows:

Power Supply Connector J2:

The power connector on the board is a standard 2.1mm X 5.5mm male jack. Positive voltage must be applied to the center pin. A diode on the board will prevent damage if the power is reversed. The DC input range is 7.5 volts to 28 volts. See power requirements above for more information.

GPS Comm Connector J3:

This connector is a 9 pin, DB-9 male connector used to communicate to a GPS receiver. A straight through serial cable should be used between the A/D board and the GPS's receiver interface board. See this page for a GPS timing system compatible with the PSN-ACCEL board. The connector has the following pinout:

Comm Connector J4:

This connector is a 9 pin DB-9 female connector used to communicate to the PC running WinSDR. A straight through serial cable should be used between the A/D board and the your computer. The connector has the following pinout:

The DTR line ( Pin 4 ) is used to reset the CPU on the A/D board. This line should be below 2 VDC for normal operation. If the LED on the board does not come on, it may be do to this line holding the CPU in the reset state. Position 1 of Switch SW1 can be used to disable this feature. If disabled, off position, the host computer can not reset the CPU on the A/D board.  

USB Interface J5:

This USB Type B connector is used to communicate with the PC. The USB interface chip used on the A/D board is a FTDI FT232RL. Windows or Linux drivers (32-Bit or 64-Bit) can be downloaded from here


Notes:

  1. Usable ADC bits dependent on sample rate and on-chip Programmable Gain Instrument Amplifier (PGIA) gain setting.
  2. We get the 4.5Hz geophone elements on the used market, so this item may not always be available. 

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