Portable Electroglottograph
type EG 90

Intended for use with a multimedia computer usingstandard multimedia hardware (with SoundBlaster compatible sound card) and software for speech and voice analysis

Hardware:
The Electro-glotto-graph is a very useful device for non-invasive exploration of the vocal fold behaviour without discomfort for the patients. Based upon the electro-glottographic waveform, recorded by means of a set of skin electrodes on both sides of the larynx, it is possible to calculate various functional vocal fold parameters such as Fo, Fo-deviation, EGG-jitter and EGG-shimmer, closed-, open-, and speed-quotients, closure index and a variety of perturbation measures. As a matter of fact, Fo, Fo-deviation and tremor measurements may also be derived from the electro-glottographic signal at greater accuracy than from the microphone signal.

The instrument is highly suitable for both research and clinical routine work because of close relationship between EGG waveform and the important behaviour of the mucosal contact within the glottal cycle. Very many pathologies recognised during endoscopy may be identified and their implications observed in the details of the EGG waveform. Experience has shown that electroglotto-graphy has a substantial role in voice assessment and clinical investigation.




 
The electroglottograph is completely isolated from the registration device which normally will be a computer as the transmission passes an opto-coupler. The power supply for the opto-coupler is taken from the computer. The Electroglottograph is powered from a standard 9 volt alkaline battery which will run the system for more than 80 hours before the blue LED diode lights to indicate that the battery voltage is running low. The period of 80 hours corresponds to 4800 recordings of 1 minute each. (More expensive batteries have a capacity corresponding to 9.000 recordings of 1 minute each).

The output from the Electroglottograph is supplied as a voltage which varies synchroneously with the changes in electric impedance between the electrodes. The instrument works only when the impedance between the electrodes typically is between 20 and 250 ohms. Use of EKG jelly or salt water will ensure a good electrical contact with the skin so that the electrical resistance between the electrodes stay in the middle of the registration range. This 250 ohm limit is set by the designer of the EG90 portable electroglottograph to ensure that the operator places the electrodes in a manner which achieves good skin contact.If the electrodes are placed wrongly and the resistance is outside the registration range, the yellow LED diode on the Electroglottograph lights. The lower frequency limit is 3.5 Hz, which means that low-frequency disturbances such as head movements are removed without severe disturbances of the waveform. When used together with the preamplifier PA14, simultaneous recordings of calibrated audio signal and EGG can be made. Hand-held electrodes or neck electrodes and various supply cables are purchased separately.

Specifications for Portable Electroglottograph
type EG90
Electrodes: Collar mounted electrodes or hand-held electrodes.
Electrode area: For adult: Bulging circular stain-less steel, 24 mm in diameter ( = 4.52 cm2).
Electrode voltage: Dependent on the electrode impedance, max. 420 mVRMS @ 400 kHz.
Electrode current: Typical 4.2 mARMS (max. 5 mArms) and independent of electrode impedance.
Carrier frequency: Approx. 400 kHz.
Collar electrodes Adjustable electrode distance on a velcro strap. Elastic neck band.
Hand-held electrodes Spring mounted electrodes on a handle for easy and fast clinical recordings.
   
Electronics:  
Oscillator: Specially designed amplitude-stable circuit with very low noise level.
Signal-to-noise level: Typical 48 dB at a 100 ohm electrode impedance.
Electrode impedance: Impedance range between 20 and 250 ohms is accepted.
Dynamic range: More than 10 l variation in a 100 ohm electrode impedance.
Sensitivity: 100 mVrms at 100 ohm electrode impedance for an input change of 0.05 ohmrms.
Frequency response: 3.5 Hz to 10,000 Hz. Well-defined cut-off frequencies without overshoot (very important).
Insulation: Battery-powered system. Completely insulated from PC by opto-electronic transmission.
Opto-coupler: Powered from the SoundBlaster board.
Output cable: 2 meters supplied with 4-pin male Mini-DIN plug.
Output level: Matches the line input level (1 volt RMS) of SoundBlaster boards.
Output impedance: 600 ohms.
Output connections: When used together with a microphone, the microphone connected to the left channel of the sound card and the EGG signal passes through the preamplifier PA14 to the right channel.
When used without the preamplifier, an optional adapter connects the EGG output cable with:

1) the minijack socket of the sound card for left-channel line input, and
2) the joystick/midi connector of the sound card for power supply.

Adapter cables: Several optional adapter cables available. E.g. an output cabel with battery for the opto-coupler.
Battery in EG90: Alkaline battery, 9 volts, size PP3, 550 mA/h, (Duracell).
  Nearly double capacity is obtained with a Lithium-Manganese battery (Ultralife).
Off-on switch: Auto turn off/on. EG90 is automatically switched off a few seconds after the electrode impedance comes outside the range 20 to 250 ohms.
Current drawn: 9.5 mA from the 9 volt battery.
Output stage: Includes an opto-coupler and is driven by 3-5 volts external supply, e. g. from the PC. Current drawn is typically 0.5 mA.
Isolation: The optocoupler isolates the patient for excessive voltages up to 5000 volts.
Size: 30 x 60 x 120 mm.
Weight: 170 grammes.
CE marking: Medical devices certification according to Class IIa with measuring function.