3 Axis MEMs Accelerometer Box  Notes
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                                             Initial Rev.  30-Nov-2021
                                             Current Rev.   1-Dec-2021


This file is a set of notes about the 3 Axis MEMs Accelerometer
Box that uses an Analog Devices ADXL354 sensor.


 - This 3 Axis Accelerometer Box uses an Analog Devices
   ADXL354BEZ sensor.  As setup this sensor provides a full scale
   range of  +-2 g  on each of the 3 axes

 - The signal at the 3 BNC output connectors has a sensitivity
   of 2 Volts/g.  The accuracy of this sensitivity is +- 8%.

 - The frequency response is currently setup for DC up to about
   100 Hz.  I can change this if you want me to,  e.g. replace
   the DC response with a 1 Hz or something like that AC coupled
   output at the low frequency end  and/or  move the high
   frequency response up to 500 Hz or 1 kHz.  I started with the
   DC to 100 Hz setup because that typically matches their test
   data and demo board setup.

   With the DC coupling you can just watch one of the outputs
   with a hand held DC voltmeter as you rotate the box and
   verify which axis is which.

 - Driving a high impedance load (i.e. 10k Ohm or higher) the
   outputs of the 3 Axis Box can swing at least +-7 Volts  but
   anything past +-4 Volts is out of the guarantied linear range
   of the accelerometer sensor itself.

 - The orientation of the axes are labeled on the outside of
   the box.

 - Please don't drop the box as doing so would probably exceed
   the maximum g force that the accelerometer sensor can survive.
   But the sensor only costs about $35 and would not be hard to
   change.

 - If it is useful I could do a better job of aligning the
   orientation of the sensor's axes to match the flat bottom of
   the box.

 - The sensor and box electronics include a Self Test feature
   that injects an electrostatic force to the moving mass of the
   sensor.  To use this Self Test:

     Flip the toggle switch from "Measure" to "Self Test".

     Record the value of the X,Y,Z signals.

     Push the Self Test push button and record the new values
     of the X,Y,Z signals.

   The difference in the two readings of the X and Y signals
   should correspond to  0.3 g typically  (0.1 g min 0.6 g max).
   The difference in two readings of the Z signal should
   correspond to  1.5 g typically  (0.5 g min 3.0 g max).

 - With the 3 Axis Accelerometer Box sitting on my work bench
   (i.e. no special precautions to control mechanical vibrations)
   on the Z axis output I see a noise level of about 0.3 mV rms
   and about 5 mV pk-pk.  The bulk of this noise has a structure
   with a period of about 25 msec to 35 msec.  There is also
   an obvious high frequency component in the 100 kHz range.
   Dropping a small 6-32 screw from a height of 2 or 3 inches
   causes a Z axis response of about 60 mV pk-pk.  The X and
   Y axes outputs show a noise of about 0.2 mV rms and about
   3 mV pk-pk.  Recall that 1 g causes a 2 Volt output signal.

- The batteries that power the electronics in this box should
   have an operating life of about 60 hours.

 - The box is made of steel to provide some magnetic shielding.
   To increase the weight of the box,  to give it good mechanical
   contact to the surface where you set it,  I have included an
   additional 1/4" thick steel plate on the bottom of the box.

 - All electronics inside the box uses an isolated analog common
   that connects to the shell of the isolated BNC signal output
   connectors.  This leaves the question of how to "ground" the
   metal box itself so that it can provide shielding against
   pickup of electrical noise.  We don't want to make a ground
   loop with this connection to the box.  Two choices are
   provided for:

     Connect the metal box itself to the internal isolated analog
     common and put a sheet of insulating material on the bottom
     of the box so that it does not make an electrical connection
     (and thus a possible ground loop)  with the surface where you
     set the box.  This is how the 3 Axis Accelerometer Box is
     setup currently.

     Remove the link between the box and internal isolated analog
     common  and instead  proved an external "ground" connection
     to the box that is at the same noise free potential as the
     "ground" at the input to your DAQ system.  It's easy for me
     to open this box ground connection link if you want me to.

 - I've provided some thin very flexible 15 foot long BNC cables
   that you can use to connect the 3 Axis Accelerometer Box to
   the inputs of your DAQ system.  The intent is to limit the
   amount of mechanical vibration that is conducted to the box by
   its BNC output cables.  Because these BNC cables are thin and
   flexible they are relatively delicate.