User manual

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barrier is specified by the size of the isolation voltage u

iso

, the isolation capacity C, and the

isolation resistance R. From the point of view of the medical devices and instrumentation, it is

very important that the values of the leaking currents past the isolation barrier remain as low

as possible. Low values of the direct-current leaking currents are achieved via high isolation

resistance. On the contrary, a very low value of the isolation capacity ensures low alternating

leaking currents.

The Isolation Mode Rejection Ratio (IMRR) is defined for the isolation amplifiers.

This factor indicates the isolation amplifier’s capability to reduce the disturbing common

mode voltage.

The isolation bond can be realized in several ways:

• optocouplers

• induction-transformer bond

• capacitive bond

• DC/DC converters

• analogue isolation amplifiers

• digital isolation devices

Secure supply circuits for ECG apparatus

From the point of view of the patient’s safety, the supply circuits must be galvanically

separated from the mains; see the technical standard ČSN EN 60601-1 and other derived

group standards.

To ensure safety and to meet the standard’s requirements, a battery supply may be

used or the DC/DC converters, which ensure the separation of the electrical circuit’s supply

from the mains and at the same time, they change the voltage size.

Additional circuits: Checking the quality of the electrodes’ connection

To sense the biopotentials via non-invasive methods, it is necessary to ensure

impedance modification of the electrode-patient transition. A special gel with chloride ions is

used for a good contact between the patient’s skin and the electrode. The impedance value of

this transition varies between single units and tens of kΩ. The value of this impedance is very

important for correct sensing of the biopotentials, and therefore it must be checked