DECLARE SUB vtdatacheck (n%, vt!(), ok$)
DECLARE SUB pdisetgain (g%)
DECLARE SUB vtgetvtmax (vtmax!)
DECLARE SUB pdierr (er%)
DECLARE SUB pdiindexrd ()
DECLARE SUB pdiindexst (d$)
DECLARE SUB vtlogvthar2 (logfile$, rotdir$, vtmag!, vtphase!)
DECLARE SUB vtlogvthar3 (logfile$, rotdir$, vtmag!, vtphase!)
DECLARE SUB vtoffsetcorr2 (n%, vt!(), vtn!)
DECLARE SUB vtlogoffset2 (logfile$, n%, b!, vt0!, vtn!, vtmin!, vtmax!)
DECLARE SUB pdivtrotenc (c$, g%, d$, np%, ns%, n%, vt!(), vtn!)
DECLARE SUB cm2100avdst (a!, v!, d!)
DECLARE SUB cm2100avdend (d!)
DECLARE SUB vtcheckdata (n%, vt!(), ok$)
DECLARE SUB vtcheckpar (ok$)
DECLARE SUB vtgetvt (rotdir$, n%, vt!())
DECLARE SUB vtgetvthar (rotdir$, nh%, harm!(), harp!())
DECLARE SUB vtlogoffset (logfile$, n%, vt0!, vtn!, vtmin!, vtmax!)
DECLARE SUB vtlogvthar1 (logfile$, rotdir$, vtmag!, vtphase!)
DECLARE SUB vtoffsetcorr (n%, vt!(), vtn!)
DECLARE SUB pdivtrotencrd (c$, n%, vt!(), vtn!)
DECLARE SUB pdivtrotencst (c$, g%, d$, np%, ns%, n%)
DECLARE SUB cm2100avd (a!, v!, d!)
DECLARE SUB spcalcfft (ns%, samp!(), fftm!(), fftp!())
DECLARE SUB spcalchar (ns%, fftm!(), fftp!(), nfun%, nh%, harm!(), harp!())
DECLARE SUB spplotfft (ns%, fftm!(), fftp!())
DECLARE SUB spplothar (nh%, harm!(), harp!())
DECLARE SUB spplotsamp (ns%, samp!())

'****************************************************************************
'Module VTCOIL.BAS
'The subroutines in this module perform integrated voltage measurements
'using the Metrolab PDI-5025 integrator.  The Compumotor CM2100 rotates
'either the coil or the magnet.
'
'Zachary Wolf
'9/12/95
'****************************************************************************

'Common block containing parameters for this module
COMMON SHARED /vtcoil/ logfileP$, vtchanP$, vtgainP%, vtnpulseperrevP%, vtnsampperrevP%, vtnrevpermeasP%, vtaccP!, vtvelP!, vtdisP!

SUB vtautogain

'****************************************************************************
'This subroutine does a quick measurement with the integrator set to low
'gain.  It then determines and sets the gain to the maximum allowed value.
'
'Zachary Wolf
'10/28/96
'****************************************************************************

'Make sure all required parameters have been defined
CALL vtcheckpar(ok$)
IF ok$ <> "y" THEN
 EXIT SUB
END IF

'Message
PRINT
PRINT "Finding the correct integrator gain..."

'Simplify the notation
pm$ = "+"
c$ = vtchanP$
g% = 1              'integrator gain
np% = vtnpulseperrevP%
ns% = 128           '# samples per revolution
nr% = 1             '# revolutions per measurement
a! = vtaccP!
v! = vtvelP!
d! = 2!
n% = 128            'n = ns * nr

'Dimension variables
DIM vt!(0 TO 127)
DIM v!(0 TO 127)

'Start the integrator measurement
CALL pdivtrotencst(c$, g%, pm$, np%, ns%, n%)

'Turn the motor
CALL cm2100avd(a!, v!, -d!)          '+ is CW for CM2100

'Get the values from the integrator
CALL pdivtrotencrd(c$, n%, vt!(), vtn!)

'Undo the motor turns
CALL cm2100avd(a!, v!, d!)          '+ is CW for CM2100

'Calculate the voltage from the integrated voltage
period! = 1! / v!
deltat! = period! / ns%
FOR i% = 0 TO n% - 2
 v!(i%) = (vt!(i% + 1) - vt!(i%)) / deltat!
NEXT i%

'Find the maximum voltage
vmax! = 0!
FOR i% = 0 TO n% - 2
 IF ABS(v!(i%)) > vmax! THEN vmax! = ABS(v!(i%))
NEXT i%

'Determine the maximum allowed gain
'Keep vmax! below 4.5 V
gain% = 1
IF vmax! * 2! < 4.5 THEN gain% = 2
IF vmax! * 5! < 4.5 THEN gain% = 5
IF vmax! * 10! < 4.5 THEN gain% = 10
IF vmax! * 20! < 4.5 THEN gain% = 20
IF vmax! * 50! < 4.5 THEN gain% = 50
IF vmax! * 100! < 4.5 THEN gain% = 100
IF vmax! * 200! < 4.5 THEN gain% = 200
IF vmax! * 500! < 4.5 THEN gain% = 500
IF vmax! * 1000! < 4.5 THEN gain% = 1000

'Set the gain in the common parameter area
vtgainP% = gain%

'Set the integrator gain
CALL pdisetgain(vtgainP%)

END SUB

SUB vtcheckpar (ok$)

'****************************************************************************
'This subroutine checks that all required VT parameters have been assigned
'values.
'
'Output:
' ok$, "y" if parameter assignments are ok, "n" otherwise
'
'Zachary Wolf
'9/18/95
'****************************************************************************

'Default value
ok$ = "n"

'Logfile
IF logfileP$ = "" THEN
 PRINT "VT: Log file not defined"
 EXIT SUB
END IF

'Integrator channel
IF (vtchanP$ <> "A" AND vtchanP$ <> "B") THEN
 PRINT "VT: PDI channel not defined: "; vtchanP$
 EXIT SUB
END IF

'Integrator gain
IF (vtgainP% <= 0 OR vtgainP% > 1000) THEN
 PRINT "VT: PDI gain has improper value: "; vtgainP%
 EXIT SUB
END IF

'Number of encoder pulses per revolution
IF (vtnpulseperrevP% <= 0 OR vtnpulseperrevP% > 10000) THEN
 PRINT "VT: #encoder pulses per revolution has improper value: "; vtnpulseperrevP%
 EXIT SUB
END IF

'Number of VT samples per revolution
IF (vtnsampperrevP% <= 0 OR vtnsampperrevP% > vtnpulseperrevP%) THEN
 PRINT "VT: #samples per revolution has improper value: "; vtnsampperrevP%
 EXIT SUB
END IF

'Number of revolutions per measurement
IF (vtnrevpermeasP% <= 0 OR vtnrevpermeasP% > 25) THEN
 PRINT "VT: #revolutions per measurement has improper value: "; vtnrevpermeasP%
 EXIT SUB
END IF

'Motor acceleration
IF (vtaccP! <= 0 OR vtaccP! > 30) THEN
 PRINT "VT: motor acceleration has improper value: "; vtaccP!
 EXIT SUB
END IF

'Motor velocity
IF (vtvelP! <= 0 OR vtvelP! > 30) THEN
 PRINT "VT: motor velocity has improper value: "; vtvelP!
 EXIT SUB
END IF

'Distance motor turns
IF (vtdisP! <= 0 OR vtdisP! > 50) THEN
 PRINT "VT: motor distance has improper value: "; vtdisP!
 EXIT SUB
END IF

'If we made it this far, all parameters have values
ok$ = "y"

END SUB

SUB vtdatacheck (n%, vt!(), ok$)

'****************************************************************************
'This subroutine checks the data for missing data points or large noise.
'
'Input/Output:
' n%, the number of samples
' vt!(0 to n%-1), the integrated voltage samples, a few points may be corrected
'
'Output:
' ok$, "y" if the data is smooth, "n" otherwise
'
'Zachary Wolf
'1/9/96
'****************************************************************************

'Initialize
ok$ = "y"

'Find the peak value
vtpeak! = 0!
FOR i% = 0 TO n% - 1
 IF ABS(vt!(i%)) > vtpeak! THEN vtpeak! = ABS(vt!(i%))
NEXT i%

'Check that each data point is near the value of a linear fit between neighboring points
nbad% = 0
FOR i% = 2 TO n% - 2
 vtexpect! = vt!(i% - 1) + (vt!(i% - 1) - vt!(i% - 2))
 vtfit! = (vt!(i% + 1) + vt!(i% - 1)) / 2!
 IF (ABS(vtexpect!) > .1 * vtpeak!) AND (ABS(vt!(i%) - vtexpect!) > ABS(.3 * vtexpect!)) THEN
  PRINT "i = "; i%; "vt(i) = "; vt!(i%); ", vtexptect = "; vtexpect!; ", vtfit = "; vtfit!
  nbad% = nbad% + 1
 END IF
NEXT i%

'If there are bad points, write the samples to a file
IF nbad% > 0 THEN
 filenum% = FREEFILE
 OPEN "vtdatchk.dat" FOR OUTPUT AS filenum%
 FOR j% = 0 TO n% - 1
  PRINT #filenum%, vt!(j%)
 NEXT j%
 CLOSE filenum%
END IF

'If there are bad points, it is not OK
IF nbad% > 0 THEN ok$ = "n"

END SUB

SUB vtgetvt (rotdir$, n%, vt!())

'****************************************************************************
'This subroutine gets triggered integrated voltage measurements from a coil.
'The triggers come from a rotary encoder.
'
'Input:
' rotdir$, rotation direction, "+" = CCW, "-" = CW
' n%, the number of integrated voltage samples
'
'Output:
' vt!(0 to n%-1), the integrated voltage at each sample point
'
'Zachary Wolf
'9/12/95
'****************************************************************************

'Make sure all required parameters have been defined
CALL vtcheckpar(ok$)
IF ok$ <> "y" THEN
 FOR i% = 0 TO n% - 1
  vt!(i%) = 0!
 NEXT i%
 EXIT SUB
END IF

'Simplify the notation
pm$ = rotdir$
c$ = vtchanP$
g% = vtgainP%
np% = vtnpulseperrevP%
ns% = vtnsampperrevP%
nr% = vtnrevpermeasP%
a! = vtaccP!
v! = vtvelP!
d! = vtdisP!

'Check that we sample over a complete number of rotations
IF n% <> ns% * nr% THEN
 PRINT "VTGETVT: N problem"
 EXIT SUB
END IF

'Start the motor turning
remeasure:
IF (pm$ = "+") THEN
  CALL cm2100avdst(a!, v!, -d!)          '+ is CW for CM2100
ELSEIF (pm$ = "-") THEN
  CALL cm2100avdst(a!, v!, d!)
ELSE
  PRINT "PROBLEM:  VTGETVT called with improper rotation direction"
  EXIT SUB
END IF

'Wait until the motor is up to speed, 3 revolutions
sleeptime% = 3 / v!
IF sleeptime% >= 1 THEN SLEEP sleeptime%

'Perform the integrator measurement
CALL pdivtrotenc(c$, g%, pm$, np%, ns%, n%, vt!(), vtn!)

'Wait until the motor is done turning to continue
IF (pm$ = "+") THEN
  CALL cm2100avdend(-d!)
ELSE
  CALL cm2100avdend(d!)
END IF

'Remeasure if there are bad data points
CALL vtdatacheck(n%, vt!(), ok$)
IF ok$ <> "y" THEN
 PRINT " R";
 GOTO remeasure
END IF

'Correct the data for integrator drift
CALL vtoffsetcorr(n%, vt!(), vtn!)

'Reverse the vt array if the rotation direction is negative
IF rotdir$ = "-" THEN
 DIM rev!(0 TO n% - 1)
 rev!(0) = 0!
 FOR i% = 1 TO n% - 1
  rev!(i%) = vt!(n% - i%)
 NEXT i%
 FOR i% = 0 TO n% - 1
  vt!(i%) = rev!(i%)
 NEXT i%
END IF

END SUB

SUB vtgetvthar (rotdir$, nh%, harm!(), harp!())

'****************************************************************************
'This subroutine performs an integrated voltage measurement and returns the
'signals at the harmonics of the rotation frequency.
'
'Input:
' rotdir$, rotation direction, "+" = CCW, "-" = CW
' nh%, the number of harmonics to return
'
'Output:
' harm!(1 to nh%), voltage magnitude at each harmonic
' harp!(1 to nh%), voltage phase in degrees at each harmonic
'
'Zachary Wolf
'9/13/95
'****************************************************************************

'Make sure all required parameters have been defined
CALL vtcheckpar(ok$)
IF ok$ <> "y" THEN
 FOR i% = 1 TO nh%
  harm!(i%) = 0!
  harp!(i%) = 0!
 NEXT i%
 EXIT SUB
END IF

'Simplify the notation
ns% = vtnsampperrevP%
nr% = vtnrevpermeasP%

'Compute the required number of samples
n% = ns% * nr%

'Initialize data arrays
DIM vt!(0 TO n% - 1)
DIM fftm!(0 TO n% / 2)
DIM fftp!(0 TO n% / 2)

'Sample the voltage from the coil
CALL vtgetvt(rotdir$, n%, vt!())

'Calculate the FFT of the voltage sample
CALL spcalcfft(n%, vt!(), fftm!(), fftp!())

'Calculate the signal harmonics of the rotation frequency
CALL spcalchar(n%, fftm!(), fftp!(), nr%, nh%, harm!(), harp!())

'Plot the data when debugging
'PRINT "DEBUG, VTGETVTHAR: writing samples using spplotxxx"
CALL spplotsamp(n%, vt!())
CALL spplotfft(n%, fftm!(), fftp!())
CALL spplothar(nh%, harm!(), harp!())

END SUB

SUB vtgetvthar1 (rotdir$, vtmag!, vtphase!)

'****************************************************************************
'This subroutine performs an integrated voltage measurement and returns the
'signals at the fundamental harmonic of the rotation frequency.
'
'Input:
' rotdir$, rotation direction, "+" = CW, "-" = "CCW"
'
'Output:
' vtmag!, magnitude of the component of vt at the fundamental frequency
' vtphase!, phase of the component of vt at the fundamental frequency
'
'Zachary Wolf
'9/13/95
'****************************************************************************

'Make sure all required parameters have been defined
CALL vtcheckpar(ok$)
IF ok$ <> "y" THEN
 vtmag! = 0!
 vtphase! = 0!
 EXIT SUB
END IF

'Initialize arrays
nh% = 1
DIM harm!(1 TO nh%)
DIM harp!(1 TO nh%)

'Get the integrated voltage harmonics
CALL vtgetvthar(rotdir$, nh%, harm!(), harp!())

'Save the magnitude and phase of the fundamental
vtmag! = harm!(1)
vtphase! = harp!(1)

'Log the result
CALL vtlogvthar1(logfileP$, rotdir$, vtmag!, vtphase!)

END SUB

SUB vtgetvthar2 (rotdir$, vtmag!, vtphase!)

'****************************************************************************
'This subroutine performs an integrated voltage measurement and returns the
'signals at the second harmonic of the rotation frequency.
'
'Input:
' rotdir$, rotation direction, "+" = CW, "-" = "CCW"
'
'Output:
' vtmag!, magnitude of the component of vt at the second harmonic
' vtphase!, phase of the component of vt at the second harmonic
'
'Zachary Wolf
'9/13/95
'****************************************************************************

'Make sure all required parameters have been defined
CALL vtcheckpar(ok$)
IF ok$ <> "y" THEN
 vtmag! = 0!
 vtphase! = 0!
 EXIT SUB
END IF

'Initialize arrays
nh% = 2
DIM harm!(1 TO nh%)
DIM harp!(1 TO nh%)

'Get the integrated voltage harmonics
CALL vtgetvthar(rotdir$, nh%, harm!(), harp!())

'Save the magnitude and phase of the fundamental
vtmag! = harm!(2)
vtphase! = harp!(2)

'Log the result
CALL vtlogvthar2(logfileP$, rotdir$, vtmag!, vtphase!)

END SUB

SUB vtgetvthar3 (rotdir$, vtmag!, vtphase!)

'****************************************************************************
'This subroutine performs an integrated voltage measurement and returns the
'signals at the third harmonic of the rotation frequency.
'
'Input:
' rotdir$, rotation direction, "+" = CW, "-" = "CCW"
'
'Output:
' vtmag!, magnitude of the component of vt at the third harmonic
' vtphase!, phase of the component of vt at the third harmonic
'
'Zachary Wolf
'9/13/95
'****************************************************************************

'Make sure all required parameters have been defined
CALL vtcheckpar(ok$)
IF ok$ <> "y" THEN
 vtmag! = 0!
 vtphase! = 0!
 EXIT SUB
END IF

'Initialize arrays
nh% = 3
DIM harm!(1 TO nh%)
DIM harp!(1 TO nh%)

'Get the integrated voltage harmonics
CALL vtgetvthar(rotdir$, nh%, harm!(), harp!())

'Save the magnitude and phase of the fundamental
vtmag! = harm!(3)
vtphase! = harp!(3)

'Log the result
CALL vtlogvthar3(logfileP$, rotdir$, vtmag!, vtphase!)

END SUB

SUB vtlocateindex

'****************************************************************************
'This subroutine is used to locate the index pulse from the encoder.
'The PDI must do this to establish a reference direction.
'
'Zachary Wolf
'9/16/96
'****************************************************************************

'Message
PRINT
PRINT "Locating the encoder index pulse..."

'Locate the index pulse
CALL pdiindexst("+")
CALL cm2100avd(vtaccP!, vtvelP!, -2!)    'CCW
CALL pdiindexrd
CALL cm2100avd(vtaccP!, vtvelP!, 2!)     'undo turns, for calib coil
CALL pdierr(e%)

END SUB

SUB vtlogoffset (logfile$, n%, vt0!, vtn!, vtmin!, vtmax!)

'****************************************************************************
'This subroutine logs an offset correction.
'
'Input:
' logfile$, the name of the log file
' n%, the number of samples
' vt0!, the 0'th sample
' vtn!, the n'th sample, with no offset will equal vt0!
' vtmin!, minimum of the corrected vt samples
' vtmax!, maximum of the corrected vt samples
'
'Zachary Wolf
'11/5/95
'****************************************************************************

'Open the log file
filenum% = FREEFILE
OPEN logfile$ FOR APPEND AS filenum%

'Print the results
PRINT #filenum%, TIME$; "  VT Offset Correction:"
PRINT #filenum%, "          n = "; n%; ", VT0 = "; vt0!; ", VTn = "; vtn!
PRINT #filenum%, "          VTmin = "; vtmin!; ", VTmax = "; vtmax!; ", Rel Corr = "; ABS(vtn! - vt0!) / (vtmax! - vtmin!)

'Close the log file
CLOSE filenum%

END SUB

SUB vtlogoffset2 (logfile$, n%, b!, vt0!, vtn!, vtmin!, vtmax!)

'****************************************************************************
'This subroutine logs an offset correction.
'
'Input:
' logfile$, the name of the log file
' n%, the number of samples
' b!, the slope of the offset correction
' vt0!, the 0'th sample
' vtn!, the n'th sample, with no offset will equal vt0!
' vtmin!, minimum of the corrected vt samples
' vtmax!, maximum of the corrected vt samples
'
'Zachary Wolf
'11/5/95
'****************************************************************************

'Open the log file
filenum% = FREEFILE
OPEN logfile$ FOR APPEND AS filenum%

'Print the results
PRINT #filenum%, TIME$; "  VT Offset Correction:"
PRINT #filenum%, "          n = "; n%; ", b = "; b!; ", n*b = "; n% * b!
PRINT #filenum%, "          VT0 = "; vt0!; ", VTn = "; vtn!
PRINT #filenum%, "          VTmin = "; vtmin!; ", VTmax = "; vtmax!
PRINT #filenum%, "          Rel Corr = "; ABS(n% * b!) / (vtmax! - vtmin!)

'Close the log file
CLOSE filenum%

END SUB

SUB vtlogvthar1 (logfile$, rotdir$, vtmag!, vtphase!)

'****************************************************************************
'This subroutine writes to the log file the results of an integrated voltage
'measurement.
'
'Input:
' logfile$, the name of the log file
' rotdir$, rotation direction, "+" = CCW, "-" = CW
' vtmag!, vt magnitude
' vtphase!, vt phase
'
'Zachary Wolf
'11/5/95
'****************************************************************************

'Open the log file
filenum% = FREEFILE
OPEN logfile$ FOR APPEND AS filenum%

'Print the results
PRINT #filenum%, TIME$; "  VT Fundamental Measurement:"
PRINT #filenum%, "          Rotation direction: "; rotdir$
PRINT #filenum%, "          vtmag1 = "; vtmag!; ", vtphase1 = "; vtphase!

'Close the log file
CLOSE filenum%

END SUB

SUB vtlogvthar2 (logfile$, rotdir$, vtmag!, vtphase!)

'****************************************************************************
'This subroutine writes to the log file the results of an integrated voltage
'measurement.
'
'Input:
' logfile$, the name of the log file
' rotdir$, rotation direction, "+" = CCW, "-" = CW
' vtmag!, vt magnitude
' vtphase!, vt phase
'
'Zachary Wolf
'11/5/95
'****************************************************************************

'Open the log file
filenum% = FREEFILE
OPEN logfile$ FOR APPEND AS filenum%

'Print the results
PRINT #filenum%, TIME$; "  VT Fundamental Measurement:"
PRINT #filenum%, "          Rotation direction: "; rotdir$
PRINT #filenum%, "          vtmag2 = "; vtmag!; ", vtphase2 = "; vtphase!

'Close the log file
CLOSE filenum%

END SUB

SUB vtlogvthar3 (logfile$, rotdir$, vtmag!, vtphase!)

'****************************************************************************
'This subroutine writes to the log file the results of an integrated voltage
'measurement.
'
'Input:
' logfile$, the name of the log file
' rotdir$, rotation direction, "+" = CCW, "-" = CW
' vtmag!, vt magnitude
' vtphase!, vt phase
'
'Zachary Wolf
'11/5/95
'****************************************************************************

'Open the log file
filenum% = FREEFILE
OPEN logfile$ FOR APPEND AS filenum%

'Print the results
PRINT #filenum%, TIME$; "  VT Fundamental Measurement:"
PRINT #filenum%, "          Rotation direction: "; rotdir$
PRINT #filenum%, "          vtmag3 = "; vtmag!; ", vtphase3 = "; vtphase!

'Close the log file
CLOSE filenum%

END SUB

SUB vtoffsetcorr (n%, vt!(), vtn!)

'****************************************************************************
'This subroutine corrects for a voltage offset in an integrator.  This
'produces a linear ramp in the integrator output.  The linear ramp
'is subtracted from the vt samples.  The subroutine assumes a periodic
'integrator input so the n'th sample is the same as the 0'th sample.
'
'Input/Output
' n%, the number of samples
' vt!(0 to n%-1), the integrated voltage samples
'
'Zachary Wolf
'1/8/96
'****************************************************************************

'Get the initial sample value
samp0! = vt!(0)

'Get the n'th sample value
'With no drift and a periodic signal, this is the same as the initial sample
sampn! = vtn!

'Compute a linear ramp from the 0'th to the n-1'th sample
DIM ramp!(0 TO n% - 1)
FOR i% = 0 TO n% - 1
 ramp!(i%) = (sampn! - samp0!) * i% / n%
NEXT i%

'Subtract the ramp from the measured samples
FOR i% = 0 TO n% - 1
 vt!(i%) = vt!(i%) - ramp!(i%)
NEXT i%

'Get the minimum and maximum value from the corrected data to log the relative size of the correction
vtmin! = 100!
vtmax! = -100!
FOR i% = 0 TO n% - 1
 IF vt!(i%) < vtmin! THEN vtmin! = vt!(i%)
 IF vt!(i%) > vtmax! THEN vtmax! = vt!(i%)
NEXT i%

'Log the correction
CALL vtlogoffset(logfileP$, n%, samp0!, sampn!, vtmin!, vtmax!)

END SUB

SUB vtoffsetcorr2 (n%, vt!(), vtn!)

'****************************************************************************
'This subroutine corrects for a voltage offset in an integrator.  This
'produces a linear ramp in the integrator output.  The linear ramp
'is subtracted from the vt samples.  This subroutine assumes a signal
'of the form
' vt(i) = a + b*i + c*cos(2*pi*n*i/ns + phin), n = 1 to ..., 0 <= i <= ns
'It takes the derivative of the samples and then averages to get b.
'It uses b to calculate the linear ramp.
'
'Input/Output
' n%, the number of samples
' vt!(0 to n%-1), the integrated voltage samples
' vtn!, the n'th sample
'
'Zachary Wolf
'1/8/96
'****************************************************************************

'First take the derivative of the samples
DIM deriv!(0 TO n% - 1)
FOR i% = 0 TO n% - 2
 deriv!(i%) = vt!(i% + 1) - vt!(i%)
NEXT i%
deriv!(n% - 1) = vtn! - vt!(n% - 1)

'The average of the derivative is the slope of the linear offset
'The sinusoidal terms average to zero
b! = 0!
FOR i% = 0 TO n% - 1
 b! = b! + deriv!(i%)
NEXT i%
b! = b! / n%

'Compute a linear ramp from the 0'th to the n-1'th sample
DIM ramp!(0 TO n% - 1)
FOR i% = 0 TO n% - 1
 ramp!(i%) = b! * i%
NEXT i%

'Subtract the ramp from the measured samples
FOR i% = 0 TO n% - 1
 vt!(i%) = vt!(i%) - ramp!(i%)
NEXT i%

'Get the minimum and maximum value from the corrected data to log the relative size of the correction
vtmin! = 100!
vtmax! = -100!
FOR i% = 0 TO n% - 1
 IF vt!(i%) < vtmin! THEN vtmin! = vt!(i%)
 IF vt!(i%) > vtmax! THEN vtmax! = vt!(i%)
NEXT i%

'Log the correction
CALL vtlogoffset2(logfileP$, n%, b!, vt!(0), vtn!, vtmin!, vtmax!)

END SUB

SUB vtsetpar (logfile$, vtchan$, vtgain%, vtnpulseperrev%, vtnsampperrev%, vtnrevpermeas%, vtacc!, vtvel!, vtdis!)

'****************************************************************************
'This subroutine sets all required VT parameters for a Helmholtz coil
'measurement.
'
'Input:
' logfile$, path and name of the log file
' vtchan$, PDI5025 channel A or B
' vtgain%, PDI5025 gain
' vtnpulseperrev%, # encoder pulses per revolution
' vtnsampperrev%, # vt samples per revolution
' vtnrevpermeas%, # revolutions per measurement
' vtacc!, CM2100 acceleration (rev/sec/sec)
' vtvel!, CM2100 velocity (rev/sec)
' vtdis!, CM2100 distance to move (rev)

'Zachary Wolf
'11/5/95
'****************************************************************************

'Put all parameters in a common area for later use
logfileP$ = logfile$
vtchanP$ = vtchan$
vtgainP% = vtgain%
vtnpulseperrevP% = vtnpulseperrev%
vtnsampperrevP% = vtnsampperrev%
vtnrevpermeasP% = vtnrevpermeas%
vtaccP! = vtacc!
vtvelP! = vtvel!
vtdisP! = vtdis!

'Print the values
'PRINT
'PRINT "VTCOIL parameters"
'PRINT "logfileP$ = "; logfileP$
'PRINT "vtchanP$ = "; vtchanP$
'PRINT "vtgainP% = "; vtgainP%
'PRINT "vtnpulseperrevP% = "; vtnpulseperrevP%
'PRINT "vtnsampperrevP% = "; vtnsampperrevP%
'PRINT "vtnrevpermeasP% = "; vtnrevpermeasP%
'PRINT "vtaccP! = "; vtaccP!
'PRINT "vtvelP! = "; vtvelP!
'PRINT "vtdisP! = "; vtdisP!
'INPUT "Press ENTER to continue.", a$

END SUB