Applied Geophysics : Gravity

Applet    ( in separate window, ca. 440 x 530 Pixel )

The applet simulates a Lacoste-Romberg Mod D Gravity Meter,

described in detail in L&R MODEL G AND D METER MANUAL

( PDF, courtesy of L and R Meter Service, LLC ).

It shows

a simplified representation of the "black lid" to operate the instrument via mouse clicks and to observe its reactions

and

a menue panel ( background orange ) to contol the mode of operation and the program flow.

The simulation covers the following modes of operation :

test and adjustment of the instrument
( LABORATORY TEST ),

calibration of the instrument
( CALIBRATE OUTPUT / FEEDBACK / COUNTER ),

2 field surveys
( NETTLETON / MODEL PROFILE ),

and

a demonstation of cross coupling
( CROSS COUPLING ).

Comments

HowTo

"Black Lid" ( Gravity Meter )

Menue Panel ( Program Control )

Window HELP ( Help / Information )

Window READINGS ( Display / Processing )

Saving and Processing of Readings

Window CHART RECORDER ( "Analog" Recorder )

Window CROSS COUPLING ( Cross Coupling Demo )

Examples ( Display / Interpretation of readings )

Download

The position of the beam is calculated recursively in constant time steps of 50 [msec] ( = 20 steps/second ), based on

a "zero length" spring in Lacoste geometry and with adjustable upper suspension point,

see diagram in PRIMARY INFORMATION of L&R MODEL G AND D METER MANUAL,

Lacoste geometry :

see also LP Seismometer Applet, ( HELP + INFO ! enabled ! ),

an "ideal" lever system, adjustment screw and gear box

=> uniform calibration factor, readings independent of direction of nulling,

an external force, corresponding to the station gravity ( + tidal variations + seismic noise ),

and split up into

a "vertical" component ( to be observed ) and

a "horizontal" component ( parallel to the beam, => sensitivity change ),

some details ( mass, momment of inertia, spring constant ) not known and therefore replaced by estimated values :

a natural period of 12 [sec] ( damping approx. 0.7 critical ) and

a distance of approx. 350 [seca] ( seconds of arc ) from lower to upper stop ( corresponding to approx. 1.4 [mgal] ),

a feedback force derived from the actual excursion of the beam and its velocity,

with ( possibly not very realistic ) coefficients that reduce the natural period to approx. 0.6 [sec], preserving the damping.

The real time behaviour of the applet depends on the local computing power, and

the link above starts the applet updating the graphic display every approx. 50 [msec] ( = time step of calculation ).

Preserving the time step of simulation ( 50 [msec] ),

a Fast Version of the same applet ( approx. 25 [msec] per graphic frame ) can be startet, and

for slower computers a Slow Version ( approx. 100 [msec] per frame ) is implemented.

The effective frame rate is checked every 5 [sec], and

the actal value is listed to the screen or the JAVA Console, if  HELP + INFO ( window HELP ) are activated.

Table of Content

"Black Lid" :
( Gravity Meter, screenshot )

BEAM POSITION :

Microscope eyepiece to observe the actual beam position ( red crosshair ) on a scale with reading line ( blue mark ).

The central part of the scale surrounding the reading line and covering the interval from lower to upper mechanical stop of the beam ( approx. 14 minior scale divisions = approx. 1.4 [mgal] ) is "zoomed" to improve the resolution of reading.

The reading line is preset and corresponds to a preset reference line of the long level ( L  LEV = 0 [seca], green ).

In LABORATORY TEST ( see below ) a mouse click onto the red crosshair generates a new reading line at the corresponding position of the scale.

( i.e. after altering the mechanical sensitivity, see CHECKING THE READING LINE in L&R MODEL G AND D METER MANUAL ).

FEEDBACK :

On/Off toggle switch for the feedback system

( ON = red / OFF = blue ).

M E T E R :

Frees / Clamps the mechanical system and inhibits / enables program or station changes ( transportation of the instrument ! ).

( F R E E = red / LOCKED = blue ).

OUTPUT VOLTAGE :

Two digital voltage meters display the beam position voltage and the feedback voltage.

BEAM POS. [mV]

beam position relative to reference line ( red T mark = 0 [mV] ) on enlarged scale ( scaling factor approx. 1 [mgal/V] ).

FEEDBACK [mV]

feedback voltage ( = BEAM POS. x 400, scaling factor approx. 1 [mgal/V] for closed loop = FEEDBACK ON ).

ADJ ( enabled in LABORATORY TEST )

selects a new reference, common to both voltages, ( = nulling the electric circuits ) :

reading line ( normal ) or actual beam postion.

Both output voltages are low pass filtered :

DIR = 2-pol Bessel, 0.5 [sec],

AVR = 6-pol Bessel, 48 [sec].

After a manual or automatic reset of the AVR low pass to new initial values

the output display changes to cyan for approx. 90 [sec], to avoid incorrect readings.

SPRING ADJUST ( DIAL ) :

RANGE = red

+/- => approx. 7 [mgal],  ++/-- => 70 [mgal],  +++/--- => 700 [mgal],

FINE = green

combines Nulling Dial and Counter,

approx. 1 [mgal/Unit] => resolution approx. 1 [µgal],

FREE ( red )   /   LOCK ( blue )

frees / locks DIAL + RANGE

L / X  LEV :

The bubble levels have different sensitivities and the "pitch" of the leveling screws is chosen to produce one screen pixel of bubble movement for one increment of the corresponding leveling screw.

Long screw ( right )

+/- = approx. 1 [µm] => approx. 1 [seca] on L  LEV,

Cross screws ( left )

+/- = approx. 2 [µm] => approx. 2 [seca] on X  LEV, approx. 1 [seca] on L  LEV,

L + X screws

++/-- = x 10,   +++/--- = x 100.

L  LEV mark ( green )

is preset to a postion corresponding to the actual reading line, and

is resulting in a mechanical sensitivity of approx. 250 [seca/mgal]

( => 1 [mgal = approx. 10 minior divisions on the optical beam position scale ),

X  LEV mark ( green )

should be repositioned by moving the bubble to the desired postion and

clicking on the red crosshair after performing the Cross Level Check

( see CHECKING THE TRANSVERSE LEVEL in L&R MODEL G AND D METER MANUAL ).

Changing the meter parameters,

i.e setting a new reading line, a new output reference or new L  LEV marks,

! in LABORATORY TEST or CROSS COUPLING only !

"Black Lid"    Table of Content

Menue Panel :
( Program Control, screenshots )

Inititial state after start of applet ( all menue items disabled, except I N I T )

After I N I T ( button label changed to RESET )

RUN :

Starts continuous calculation and display ( 20 [steps/sec] ).

HALT :

"Freezes" the actual state.

STEP :

Single time step + HALT.

RESET :

Resets the gravity meter to initial settings and erases saved readings of the actually selected procedure.

! If activated in LABORATORY TEST all parameters ( calibration factors etc. ) previously determined are reset to their initial ( default ) values !

HELP :

Generates a separate window to display and set various parameters, and

to list informations ( subsurface model, station table, saved / processed readings etc. , see Window HELP ).

NO / LO / HI SEIS :

Sets the amplitude of seismic noise for LAB TEST, CALIB ... and ... PROFILE

( vertical component only )

NO = no noise, LO = 3 [µgal], HI = 30 [µgal],

( period 4.8 [sec], beat 72 [sec], => vertical ground displacement of 0, 17, 170 [nm] ).

RES AVR :

Resets the AVR low pass to new initial values

( and changes color of corresponding display / recorder trace to cyan for approx. 90 [sec] ).

CHART RECORDER :

Connects a 2-channel "analog" recorder to the instrument

( see Window CHART RECORDER ).

MODE OF OPER :

Program selection to perform tests, calibrations and field surveys or to run the cross coupling demo.

LABORATORY TEST

test and adjustment procedures

(see CHECKING LEVELS AND SENSITIVITY in L&R MODEL G AND D METER MANUAL ).

"Adjustment" of the cross level ( X  LEV ADJUST ) by fitting a polynomial of second degree to readings taken with different cross level settings.

CALIBRATE OUTPUT / FEEDBACK / COUNTER

determination of calibration factors ( [mgal/V] ) for

the output voltages BEAM POS. [mV] and FEEDBACK [mV],

and for

the DIAL / COUNTER combination ( [mgal/Count )

by fitting a straight line to readings taken along calibration profiles

( stations with known gravity values ).

NETTLETON PROFILE

determination of the density of a homogenious halfspace from field observations along a profile with significant topogaphy.

( NETTLETON : calculation of cross correlation between obseved Bouguer anomaly and topography for different, user adjustable density values,

  PARASNIS : fitting a straight line to observed free air anomaly versus station height. )

MODEL PROFILE

determination of the density of the top layer of a 2-layer model from field observations along a profile over a brigde across a railway cutting.

Fitting a model curve to observed gravity values by variing the layer density.

! Model calulations are 2 D ( Talwani ) !

CROSS COUPLING

demonstration of the cross coupling effect produced by coherent "harmonic" vertical and horizontal accelerations ( shipborne gravity surveys ).

SAVE STN READING :

Saves a meter reading for graphical display, processing and interpretation in a separate frame ( see Window READINGS ).

NEXT / PREV / BAS

"Moves" the ( ! locked ! ) instrument to the next, previous or base station.

Menue Panel    HowTo    Table of Content

Window HELP :
( Help / Informations, screenshot )

Menue panel to display and modify parameters and the program environment.

For the parameters to be determined in LABORATORY TEST and CALIBRATE OUTPUT, FEEDBK and COUNTER,

one of three "revisions" of each parameter value can be displayed :

the value currently used ( ACTUAL VAL. ),

the value determined / set by the user ( USER CALIB. )

and

the value used in forward calulation of the respective reading value / station gravity ( "TRUE" VALUE ).

SET sets ACTUAL VAL. ( the parameter value to be used )

to USER CALIB. or

to "TRUE" VALUE  ( enabling the user to skip the corresponding calibration procdure ).

The "TRUE" VALUE for the output voltage BEAM POS. [mV] refers to the preset values of L  LEV ZERO and reading line,

i.e. BEAM POS. [mV] needs to be recalibrated after a change in mechanical sensitivity.

( X  LEV ZERO and counter calibration

should be independent of mechanical sensitivity,

feedback calibration

should be affected by approx. 1/400. = 1/feedback_gain,

negligible for nulling FEEDBACK [mv] to values below approx. ±10 [mV]. )

METER TILT : RANDOM / CONST. toggels between

a randomly set tilt of the instrument, needing a new horizontation after each change of observation station ( ! realistic ! ) and

a constant tilt after station / program change ( unrealistic, but greatly simplifying the use ).

WARN inhibits

saving of incorrect readings ( beam still moving, incorrect levelling, etc. ) and

starting field observations with incorrect calibration factors ( [mgal/V] or [mgal/Count] ).

INFO and HELP ( active in HALT mode only ) display

informations to the the actual cursor position ( INFO ) and

hints to actually possible mouse interactions ( HELP )

in the "Black Lid" and in the window READINGS.

AUTO CALIB is implemented for impatient users,

skips test and calibration procedures and sets

the calibration parameters to their "true" values and

the METER TILT to CONSTANT.

In the text area informations, concerning the program actually running, are displayed :

LIST ... lists the model parameters, the station table and saved readings,

TRACE READINGS traces the saving of readings,

CLEAR erases the text area.

HIDE hides the window.

Window HELP    HowTo    Table of Content

Window READINGS :
( Display / Processing, screenshot )

Example = raw readings of NETTLETON PROFILE

Display, processing and interpretation of meter readings, display of the subsurface model.

A gravity reading, saved via SAVE STN READING includes :

the station number ( the cross level reading [seca] for X  LEV ADJUST ),

the observation time ( [min] ),

the dial / counter reading ( [Counts] ),

the BEAM POS. / FEEDBACK voltage ( [mV] , depending on FEEDBACK OFF or ON ),

the tidal gravity ( [mgal] ) and

a weighting factor to be applied,

preset to 1.0 and toggled by mouse clicks between

1. ( symbol = blue or magenta ) and

0. ( symbol = grey ).

As a result of the digital simulation of the ( analog ) dial,

in general a nulling to exactly 0.0 [mV] is not possible.

Counter and output voltage readings are therefore combined to a raw reading ( [Counts] ),

using the actual calibration factor ( the default value DEF = 1.0, if not yet determined ).

All meter readings ( except X  LEV ADJUST ) presume a correct long level and cross level setting.

For CALIBRATE OUTPUT / FEEDBACK

the corresponding output voltages, observed at constant counter setting, are the raw readings ( => no calibration factor applied ).

For X  LEV ADJUST readings ( in LABORATORY TEST ) observed at constant counter setting and uniform setting of FBK ON / OFF,

the result ( = position of the apex of a curve fitted to the observations ) is almost independent of the calibration factor value.

In order to process CALIBRATE COUNTER readings correctly,

at least one of the voltage calibration factors is needed.

For NETTLETON / MODEL PROFILE obsevations

dial / counter and at least one voltage output have to be calibrated.

The obsevations can be displayed for different processing states :

as raw readings ( RAW READ ... ) or

after tidal and drift correction ( FIN READ ... ),

with selectable abscissa :

profile ( ... READ (PRO) ) or

obsevation time ( ... READ (TIM) ).

INSTR. DRIFT

displays raw readings taken at the base station after tidal correction

( for X  LEV ADJUST taken at X  LEV = 0 [seca], marked magenta ).

A polynomial of max. second degree is fitted to the observed values and

the resulting drift corrections is applied to all readings :

=> FIN  =  RAW - tidal corr. - drift corr..

RAW READ (TIM)

displays readings after tidal correction, plotted versus obsrvation time.

Straight lines ( grey ) are drawn between multiple readings of the same station

to facilitate the "qality control".

! All lines should be parrallel to corresponding lines between base station readings !

FIN READ (TIM)

displays readings after tidal and drift correction, plotted versus time.

Hoizontal straight lines ( grey ) are drawn through the mean value of multiple readings of the same station,

for base station readings the zero-order coefficient of the drift polynomial is used.

FIN READ (PRO)

displays readings after tidal and drift correction , plotted vesus station location.

For X  LEV ADJ ( LABORATORY TEST )

a polynomal of second degree ( approximation of the cosine to be expected )

is fitted to the observed values, and

the X  LEV ZERO position

is determined from the apex of the curve.

For CALIBRATE OUTPUT / FEEDBACK / COUNTER

a straight line is fitted to the observations,

and from its slope,

the respective calibration factor is determined.

For MODEL PROFILE

a model curve is diplayed, calculated with the actual density value

( with DEF = 2.67 [g/cm**3], if not yet determined ).

In the calibration procedures ( CALIBRATE ... )

the respective calibration factors are calculated iteratively ( at least 2 iterations ),

because their values are involved in the calculation of tidal and drift corrections to be applied in advance.

The parameters, determined in the various procedures,

are displayed ( red ) at the upper right corner of the graphic display

and

are available for further calculations in the same program after clicking USE

( holds as well for the user selected density values : DEC / INC DENS in ... PROFILE ).

Upper right corner blue :

E = RMS error for curve fit to observations

or

COR TOP = correlation coefficient of topography for BOUGUER ANOM. ( NETTLETON ).

SAVE :

! Parameters have to be saved in order to be available to other programs !

CLEAR

erases the readings,

HIDE

hides the window, to be restored ( without loss of data ) by selecting the same procedure again.

Window READINGS    HowTo    Table of Content

Meter readings are taken in RUN mode of the applet ( see Menue Panel ), and

after adjustment of dial / counter to the gravity value of one of the stations ( in general BAS ).

Field Observations

To take readings on profiles ( CALIB xxx, NETTLETON or MODEL PROFILE ), the following loop has do be repeated for every station :

Lock meter  ( "Black Lid" )

Move to next station  ( NEXT, PREV or BAS, menue panel )

Readjust  L and X  Level  ( if not METER TILT : CONST., see window HELP )

Unlock meter ( "Black Lid" )

Adjust  Dial / Counter  ( "Black Lid", not for CALIB. OUTPUT or FEEDBACK )

Wait until the beam has reached its new equilibrum position

( use CHART RECORDER to observe beam velocity, POS / FBK VEL )

Save reading  ( SAVE STN READING, menue panel )

X  LEV  ADJUST

( LABORATORY TEST, meter unlocked )

NEXT, PREV and BAS ( menue panel ) are disabled and at fixed setting of Dial / Counter, the above loop reduces to :

Adjust  X  LEV to a new position preserving the L LEV position ( "Black Lid" )

Wait until the beam has reached its new equilibrum position

( use CHART RECORDER to observe beam velocity, POS / FBK VEL )

Save reading  ( SAVE STN READING, menue panel )

If  WARN ( window HELP ) is activated, saving of obviously incorrect readings ( beam still moving, incorrect levelling ) is inhibited.

Processing and Interpretaion

( at least 3 readings saved : 2 x base station, 1 x profile, applet in RUN or HALT mode, meter LOCKED or FREE )

Saved readings are displayed as RAW READ (PRO) and

before results of interpretation can be displayed

in FIN READ (PRO)  ( X LEV ADJ and CALIBRATE xxx ) or

in BOUGUER or FREE AIR ANOM.  ( NETTELETON and MODEL PROFILE ),

the display INSTR. DRIFT has to be called, because the resulting drift correction

has to be applied before calculating final results.

In any display mode the weight of a reading ( def. = 1. ) can be toggeled between 1. / 0. using the left / right mouse button :

readings with weight 1. are marked + ( blue ),

readings with weight 0. are marked x ( grey ),

the display is switched back to RAW READ (PRO), and

INSTR. DRIFT and interpretation displays have to be call again.

Multiple readings of the same station are displayed separated

in RAW / FIN READ (TIM) and

thus are accessible individually.

( Enable INFO in window HELP, applet in HALT mode, to identify the readings. )

Final Results have to be saved

( SAVE in window READINGS => USER CALIB. and ACTUAL VAL. in window HELP )

to be available in other procedures ( i.e. calibration factors needed in field observations ).

Saving and Processing    HowTo    Table of Content

Window CHART RECORDER :
( 2-channel "analog" recorder, screenshot ) :

Example :
beam position and velocity after dial / counter change of -0.1 [Counts] = approx. +100 [µgal]

Continuous display of output voltages, of their velocities, of the tidal gravity and of the seismic noise.

Selectable in the menue panel of the recorder ( disabled if the recorder is running ) :

Signals to be displayed

POS DIR and AVR

beam postion unfiltered and average,

FBK DIR and AVR

feedback voltage unfiltered and average,

... VEL

velocities of above signals,

TIDAL G

tidal gravity ( ampl 45 [µgal], start phase random ),

NOI VER and HOR

vertical and horizontal component of seismic noise.

Time scale of recording

toggle switch FST ( fast ), SLW ( slow, 1 / 5 ).

Sensitivity

±nn [V], [mV] or [V/sec], [mV/sec] for full scale,

±50 [µgal] for TIDAL G,

fixed values, depending on selected amplitude, for NOI VER and HOR.

After a change of recording parameters the preceding signal is displayed grey.

The output of the AVR low pass is displayed cyan during approx. 90 [sec] after a manual or automatic reset ( to point to the settling time of the low pass ).

Window CHART RECORDER    HowTo    Table of Content

Window CROSS COUPLING :
( screenshot )

Example :
mechan. sensitivity default ( L  LEV 0 [seca] ), FEEDBACK OFF
DIAL / COUNTER adjusted to BEAM POS 0 [mv]
harmonic acceleration, period 6.0 [sec],
amplitude vertical ±2 [mgal], horizontal ±30 [mgal], phase diff. 45 [Deg]

Continuous display of

horizontal and vertical acceleration

( X / Y display, individually scaled to resp. max. amp.,

upper and right hand scale [mgal], red,

act. val. = moving red point + red marks in resp. scale )

and

beam postion relative to mechanical stops

( left hand scale [seca], black,

act. val. = moving red mark in scale ).

Green :

position of pivot, with horizontal straight line, indicating the "True Horizontal" ( perpendicular to local gravity )

and

the ideal position of the reading line ( green label xxx [seca] ) corresponding to the actual L  LEV setting.

( Here L  LEV = 0 [seca] => pivot and green line at 0 [seca]. )

Red arrows :

components of the force acting on the center of gravity

( arrow legnth individually normalized to 2 ∗ mass radius ).

Menue panel ( disabled if the acceleration signal is switched on ) to adjust

the amplitudes of vertical and horizotal acceleration,

( ver. : 0, 0.3 ... 10 [mgal], hor. : 0, 0.3 ... 100 [mgal] )

the phase difference between vertical and horizontal component

( DEC / INC PHS in selectable steps of 90, 15 and 1 [Deg] )

and

the period of the harmonic acceleration.

( 3, 6, 12, 24 and 48 [s] )

O N starts / stops the harmonic acceleration signal
( COS - tapered at the beginning ).

Recorder display of Beam Postion Votage and corresponding AVR low pass output

Note :

A dc-offset of the beam postion voltage of approx. +10 [mV],

observed on the high gain display of the corresponding AVR low pass output ( CHAN 2, ±20 [mV] F.S. ),

would be interpreted as

an aditiononal gravity change of approx. +10 [µgal].

It corresponds to a beam position offset of approx. -1.5 [seca] as a result of the horizontal force

acting toward the pivot for mass positions below pivot position ( "true horizontal" ),

acting toward the scale for mass postions above :

negative ( downward ) excursion is increased,

positive ( upward ) excursion is decreased

=> negative mean position => positive mean output voltage.

For given magnitudes of the vertical and horizotal component of acceleration,

the magnitude and the direction of the cross coupling offset

depends on the phase difference between beam excursion and horizontal force,

and thus on the phase difference between the two acceleration components.

For signal periods much longer than the the natural period of the instrument,

beam excursion and vertical acceleration are in phase,

hence the cross coupling effect

is greatest for a linear polarized accelerations ( 0 / 180 [Deg] ) and

vanishes for circular polarisation ( +90 / -90 [Deg] ).

In the example shown the signal period ( 6.0 [sec] ) is below the natural period of the meter ( > 12 [sec] ),

resulting in a phase shift between vertical acceleraton and beam excursion,

and

leading to a maximum cross coupling for approx. +45 and -135 [Deg]

( almost no cross coupling for approx. 135 and -45 [Deg] ).

Since the magnitude of the cross coupling effect strongly depends on the magnitude of the beam excursion,

cross coupling can be greatly reduced by activating the feedback system and

thus forcing the beam close to its zero position.

A second consequence of feedback is the decrease of the natural period ( here below  1 [s] ),

leading to a almost vanishing cross coupling offset for a driving signal

of several seconds of period and

a phase difference of approx. 90 [Deg] between hor. and ver. component.

Example :
( FEEDBACK ON, harmonic acceleration, period 6.0 [sec],
amplitude vertical ±10 [mgal], horizontal ±30 [mgal], phase diff. 90 [Deg]

Recorder display of Feedback Votage and corresponding AVR low pass output

The offset below 1 [mV] ( CHAN 2, FBK AVR ) corresponds to a cross coupling error below 1 [µgal].

This is a demonstration of the cross coupling effect, physically fairly correct, but with unrealistic driving signals :

In shipborne gravity surveys "harmonic" vertical and horizontal accelerations of up to 100 [mgal] at periods longer than 6.0 [sec] have to be handled.

This affords

mechanically less sensitive instruments and / or more powerfull feedback systems

( and a different processing / filtering and recording of output signals )

to avoid mechanical clipping and to keep cross coupling errors within tolerable limits.

Window CROSS COUPLING    HowTo    Table of Content

Raw readings along profile ( RAW READ (PRO) ) :

Raw readings versus observation time ( RAW READ (TIM) ) :

Instrument drift versus obsevation time ( INSTR. DRIFT ) :

After tidal and drift correction ( versus time, FIN READ (TIM) ) :

After tidal and drift correction ( along profile, FIN READ (PRO) ) :

Examples    HowTo    Table of Content

Bouguer anomaly ( BOUGUER ANOM. ) :
( calculated for density = DEF = 2.67 [g/cm**3] )

Free air anomaly ( FREE AIR ANOM. ) :

Free air anomaly / station height ( F. A. (STN HGT) ) :
( => density = 2.4000 [g/cm**3] )

Bouguer anomaly ( BOUGUER ANOM. ) :
( calculated for density = 2.4000 [g/cm**3] )

Bouguer anomaly ( BOUGUER ANOM. ) :
( calculated for density = 2.4000 + 0.0100 [g/cm**3] )

Bouguer anomaly ( BOUGUER ANOM. ) :
( calculated for density = 2.4000 - 0.0100 [g/cm**3] )

Examples    HowTo    Table of Content

Interpretaion ( FIN READ (PRO) ) :

The position of the bubble, resulting in minimum sensitivity to instrument tilt, corresponds to the apex of the red curve ( NEW ZERO MARK, red, upper right ).
By activating SAVE, the value can be saved as "USER CALIB." ( see Window HELP ).

Interpretaion ( FIN READ (PRO) ) :

The calibration factor [mgal/V] for the output voltage FEEDBACK [mV] corresponds to the reciprocal of the slope of the straigth line fitted to the readings ( NEW CAL FACT, red, upper right ).
By activating USE, the value can be transferred to text field SCAL FACT : ... [mgal/V] for additional iterative calculations of the coefficients.
By activating SAVE, the value in the text field can be saved as "USR CALIB." ( see Window HELP ).

Examples    HowTo    Table of Content

Class and html files for a local installation of the applet are available as a zip file and as a tar.gz file.

These files do not include the PDF-file ( approx. 3 MB )

L&R MODEL G AND D METER MANUAL.

It is available for download at L and R Meter Service and at Geophysics Dept., and

it should be saved in the directory grav, where the class- and html-files of the applet are stored after unpacking the zip- / tar.gz-file.

More applets at : the author's Homepage

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