Difference between revisions of "EM Field Head Tracking System specifications"

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*PLL: For the Phase Lock Loop (PLL) the settings Slow (S) is preferred because the frequency is at a fix value. The phase is more stable in this setting.
 
*PLL: For the Phase Lock Loop (PLL) the settings Slow (S) is preferred because the frequency is at a fix value. The phase is more stable in this setting.
 
*Ref.Thr.: Reference Threshold is set to 0V for analog signals (2V is for digital signals).
 
*Ref.Thr.: Reference Threshold is set to 0V for analog signals (2V is for digital signals).
 +
 +
{| class="wikitable"
 +
! Time constant
 +
! Model „-L“
 +
! Time constant
 +
! Model „-H“
 +
! Hexadecimal switch
 +
! 6dB/Octave
 +
! 12dB/Octave
 +
|-
 +
| 3ms
 +
| 300µs
 +
| 0HEX
 +
| 8HEX
 +
|-
 +
| 10ms
 +
| 1ms
 +
| 1HEX
 +
| 9HEX
 +
|-
 +
| 30ms
 +
| 3ms
 +
| 2HEX
 +
| AHEX
 +
|-
 +
| 100ms
 +
| 10ms
 +
| 3HEX
 +
| BHEX
 +
|-
 +
| 300ms
 +
| 30ms
 +
| 4HEX
 +
| CHEX
 +
|-
 +
| 1s
 +
| 100ms
 +
| 5HEX
 +
| DHEX
 +
|-
 +
| 3s
 +
| 300ms
 +
| 6HEX
 +
| EHEX
 +
|-
 +
| 10s
 +
| 1s
 +
| 7HEX
 +
| FHEX
 +
|}
  
 
===Oscillators===
 
===Oscillators===

Revision as of 14:10, 29 November 2023

Schematic of the Sphere Head Tracking System

Introduction

The EM Field Head Tracking System is used for recording head movements of the subject during a trial. The system consists of the following parts:

  • Three oscillators at roughly 45, 55 and 65 kHz or 50, 60, 70 kHz for X, Y and Z direction.
  • Three signal amplifiers that amplify the oscillator signals.
  • six field coils that make a cube of roughly 3x3x3 meters.
  • A small pick-up coil mounted on a glasses frame that is worn by the subject during the experiment.
  • Three lock-in amplifiers that split the signal from the pick-up coil in the 3 frequency components and measures their envelope. They output analog signals between -10V and +10V.
  • An acquisition device converts the analog output signals from the lock-in amplifiers to digital.
  • A RZ6 multi I/O processor that records the acquired data.
  • Software that converts the recorded data to head orientations using calibration data.

The following table contains the channel convention with respect of the three directions:

Channel Frequency Orientation Color Polarity
Channel 1 45/50 kHz Frontal Red Front = positive; Back = negative
Channel 2 55/60 kHz Vertical Blue Right = positive; Left = negative
Channel 3 65/70 kHz Horizontal Yellow Up = positive; Down = negative

Parts

Lock-in amplifiers

Three Femto LIA-BV-150-H Lock-in amplifiers are used in order to separate the Frontal, Horizontal and Vertical signals from the pick-up coil. Each Lock-in amplifier has a Sinus Oscillator Module (SOM-1) that is used both as Field Modulation Signal and as Reference Signal. The Lock-in amplifier settings are set at the front of the device (see picture), except for the modulation/reference frequency which is set inside on the SOM-board.

The front panel of each LIA has four dipswitches:

  • Mode: 1f means that the fundamental harmonic is measured (2f = second harmonic signal)
  • Dyn.Res.: For dynamic reserve the settings Low (L) is preferred because the signal is normally large in comparison with the noise.
  • PLL: For the Phase Lock Loop (PLL) the settings Slow (S) is preferred because the frequency is at a fix value. The phase is more stable in this setting.
  • Ref.Thr.: Reference Threshold is set to 0V for analog signals (2V is for digital signals).
Time constant Model „-L“ Time constant Model „-H“ Hexadecimal switch 6dB/Octave 12dB/Octave
3ms 300µs 0HEX 8HEX
10ms 1ms 1HEX 9HEX
30ms 3ms 2HEX AHEX
100ms 10ms 3HEX BHEX
300ms 30ms 4HEX CHEX
1s 100ms 5HEX DHEX
3s 300ms 6HEX EHEX
10s 1s 7HEX FHEX

Oscillators

Amplifiers

Resonance circuits

Wall coils

Pick-up coil

Lock-in amplifiers

ADC's

recording device

(RZ6 or RA16)

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