Preparing the Product for Use
17
Electrical interference may also appear through the ground lead if this is connected
to many computers, autoclaves, instruments using high power etc. In this case
a dedicated ground for the ABR recording site should be established.
Avoid any mixing of cables (for example, USB cables/power cord etc. mixed
up with the electrodes cable used for the EP system).
Sometimes, the ground lead is found inside the wall outlet, but it is not connected
to the ground.
If the ground is not connected or even missing, the ABR recordings will be distorted
greatly.
The
Neuro-Audio
digital system is connected to the ground lead via a ground contact
of tripolar outlet. If the ground lead is not connected, the digital system will pick
up electrical noise/interference. On the screen it will be displayed as total harmonic
distortion fully overlapping the ABR waveforms.
Some notebooks are not provided with the ground connection to the outlet ground.
If you use such a notebook as a part of the digital system, take special measures
to ensure the notebook ground contact to the outlet ground. To do this, use the power
supply units with the required contact (a tripolar connector for mains lead attachment).
To make sure that there is a connection between the notebook ground and outlet
ground, measure the impedance between the protective ground pin of power supply
unit outlet and ground connector pin attached to notebook. The impedance should not
exceed 0.1
Ω
.
Check the ground for proper and correct function of the digital system.
Due to high voltage, only experienced technicians or properly trained staff
must change and check the ground.
To check the ground, follow these recommendations:
1. Use a dedicated ground tester.
2. Compare voltage/impedance from the wall outlet ground lead to a triangle
of earth rods. The resistance must not exceed 8
Ω
, and the peak-to-peak
amplitude must not exceed 0.5 V.
3. More simple check is to use a voltage meter and measure the voltage directly
in the wall outlet. Check the following:
3.1. The voltage between the phase (hot) and zero (neutral) sockets must
be stable (230 V for Europe /110 V for US (country specific).