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• AccelerometerOne
  • Mounted on the ceiling in the receiver room.
  • Connected to gbtts1, port 2007.
  • The accelerometer positive X-axis corresponds to the GBT positive Xe axis (see attachment)
  • The accelerometer positive Y-axis corresponds to the GBT negative Ye axis.
  • The accelerometer positive Z-axis corresponds to the GBT negative Ze axis.
  • Todd's MATLAB fits to accel. 1 data vs. elev on 2007/12/04
  • plot of X,Y,Z outputs during tipping scan
  • See timeseries and FFT plots during elevation scan here
  • fit results for gravity curve of Y and Z axis
  • plot of python fits: cos(elev) fit to y-axis datasin(elev) fit to z-axis data
• AccelerometerTwo
  • Mounted on the left side EL bearing casting (opposite the elevator)
  • Connected to gbtts6, port 2006.
  • The accelerometer positive X-axis corresponds to the GBT negative Xa axis (see attachment)
  • The accelerometer positive Y-axis corresponds to the GBT negative Ya axis.
  • The accelerometer positive Z-axis corresponds to the GBT positive Za axis.
• AccelerometerThree?
  • Mounted on the right side EL bearing casting
  • Connected to gbtts6, port 2007.
  • The accelerometer positive X-axis corresponds to the GBT negative Xa axis.
  • The accelerometer positive Y-axis corresponds to the GBT negative Ya axis.
  • The accelerometer positive Z-axis corresponds to the GBT positive Za axis.
  • Was repaired and reinstalled on 23 July 2007. Not sure when it went bad, but was bad as early as March 27, 2007.
• AccelerometerFour
  • Mounted on the optical camera mount near the vertex.
  • The accelerometer positive X-axis corresponds to the GBT positive Xe axis.
  • The accelerometer positive Y-axis corresponds to the GBT positive Ye axis.
  • The accelerometer positive Z-axis corresponds to the GBT positive Ze axis.
  • Jason's Excel table of calibration data with figure showing orientation definitions
  • Todd's MATLAB fits to accelerometer 4 data vs. elevation
  • See timeseries and FFT plots during elevation scan here
  • GDAQ was removed on April 18, 2008 and re-installed on April 22 at 10:42 AM. It had a dead RS232 interface chip that converts the serial comm. signals from TTL levels (out of the ADuC834) to real RS232 levels.
  • Strange behavior in June 2008
• AccelerometerStatusLog
  • MR describing the Accelerometer manager
  • Routine storage of data in /home/gbtlogs began on 2006_06_28 (2006 June 28)

• Useful facts noted by Todd
  • The manufacturer and model number is Silicon Designs Model 1221J-002 Low-noise Analog Accelerometer. The 3dB bandwidth is 400 Hz, but this is filtered by the sigma-delta conversion on the GDAQ.
  • The interface cards and 3-axis mechanical assembly was created at Green Bank.
  • The GDAQ is based on Analog Devices ADuC834 precision analog microcontroller. It uses a sigma-delta modulator which converts the sampled input signal into a digital pulse train whose duty cycle contains the digital information. A sinc^3 programmable low-pass filter is then employed to decimate the modulator output data stream to give a valid data conversion result at programmable output rates from 5.35 to 105.03 Hz. Here is a plot of the measured passband with no external RC filter. Here is the same measurement with an RC filter of 120kohm and 0.33uF (corner freq = Hz).
  • The sample rate of each channel is nominally set to 10 Hz, but in practice show up at about 9.5 Hz in the files in the gbtlogs area.
  • The Y and Z axes are read through the 24 bit ADC and the X is read through the 16 bit ADC (both on board the ADuC834).
  • The X axis has an intentional offset of +0.625V when horizontal. The other axes are nominally 0.0V when horizontal from what I can surmise.
  • Accelerometer pre-processing op-amp card schematic: original, Cut-and-patch revision 2
  • AccelerometerHardwareSignalProcessing of X-axis channel prior to ADC (from Jason Ray) (schematic)
  • AccelerometerSignalProcessing prior to writing data to the engineering FITS file (from Joe Brandt)

-- ToddHunter - 11 Jul 2007

• plotsweeprc.pdf: GDAQ response with RC filter of 4Hz on front end

Attachment:	Action:	Size:	Date:	Who:	Comment:
m081-1.pdf	action	106481	19 Oct 2006 - 15:06	JohnFord	GBT Coordinate System Drawing (page 10 of Memo165)
m081-2.pdf	action	103305	19 Oct 2006 - 15:08	JohnFord	Coordinate System Definition, P1
m081-3.pdf	action	70852	19 Oct 2006 - 15:10	JohnFord	Coordinate System Definition, P2
m081-4.pdf	action	80504	19 Oct 2006 - 15:10	JohnFord	Coordinate System Definition, P3
m081-5.pdf	action	67860	19 Oct 2006 - 15:11	JohnFord	Coordinate System Definition, P4
tipaccel.pdf	action	92577	27 Oct 2007 - 14:59	ToddHunter	accelerometer 1 outputs during tipping scan
fit.results	action	509	27 Oct 2007 - 15:02	ToddHunter	fit for gravity curve of Y and Z axis of accel1
coselfit.pdf	action	57519	27 Oct 2007 - 15:03	ToddHunter	cos(elev) fit to y-axis data
sinelfit.pdf	action	51302	27 Oct 2007 - 15:03	ToddHunter	sin(elev) fit to z-axis
Accelerometer4checkout-070913.xls	action	16384	07 Nov 2007 - 01:10	ToddHunter	Jason's Excel table of calibration data for acc#4
AccelOrientations.pdf	action	24356	07 Nov 2007 - 01:11	ToddHunter	Definition of orientations in calib data for acc#4
accel4.gif	action	13050	04 Dec 2007 - 16:50	ToddHunter	MATLAB fit to accel. 4 data vs. elev on 2007/12/04
accel1.gif	action	12670	04 Dec 2007 - 18:10	ToddHunter	MATLAB fit to accel. 1 data vs. elev 2007/12/04
2558_001.pdf	action	71311	19 Dec 2007 - 23:06	ToddHunter	Signal conditioning circuit for X-axis on Aux ADC
SingleAxisAccelerometerMasterCardSchematicrevADWG.bmp	action	3168054	21 Feb 2008 - 00:44	ToddHunter	Accelerometer pre-processing op-amp card
SingleAxisAcelerometerSchematicrevAC_P_2.pdf	action	36260	21 Feb 2008 - 17:49	ToddHunter	Cut & Patch, #2