Electrode Impedance Measurement Technique - Interacoustics Sera Additional Information

Electrode impedance measurement technique

When measuring electrode impedances, the numerical value that describes the impedance of each electrode
depends on the application of the surface electrode and the method of impedance measurement.
Application factors include the size of the electrode, preparation of the skin prior to electrode adhesion,
application of pressure of the electrode and the electrode placement site.
The frequency used to measure the impedance also significantly affects the value. As a general rule,
electrode impedances are low when measured using a high frequency and high when measured using a low
frequency (Rosell et al., 1988 ).
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The Sera Preamplifier, like most clinical devices uses a 33Hz square wave frequency for determining
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electrode impedances. Therefore, electrode impedances seen with the Sera will be higher than those seen
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on many other newborn hearing screening instruments (that are using a 1000Hz frequency for
measurement). While the numerical value may differ (between equipment) due to the measurement
technique used, the actual impedance (the resistance of the skin between two electrodes) is actually the
same.
For example, on other newborn hearing screening devices (using a 1000Hz measurement frequency), you
will typically see electrode impedance values between 0-5kΩ whereas typical impedance values for the
Sera are between 15-25kΩ. These value differences do not affect the test.
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Rosell, J., Colominas, J., Rui, P., Pallas-Areny, R., & Webster, J. G. (1988). Skin impedance from 1 Hz to 1 MHz, IEEE
Trans Biomed Eng, 35(8), 649-5.1
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