BC Biomedical NIBP-1010 Uživatelský manuál stáhnout pdf (Strana 31)

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continuously. Fig. 2.13 shows a schematic diagram of the circuit, which is used to discover

badly connected electrodes on the patient’s body.

Fig. 2.13: Schematic diagram of the circuit checking quality of the electrodes’ connection

[2.8].

To check the quality of the electrodes’ contact, a sinus signal of a 50 kHz frequency is

brought between two electrodes connected to the patient from a mains source. There are two

reasons for choosing this particular frequency. The first one is to reduce the risk of

physiological effects of such a high frequency on human body. The second reason is that a

signal of 50 kHz does not interfere with the ECG signal’s spectrum, and can be easily filtered

out before the next processing of the measured signal via a band pass filter. The wanted signal

of ECG is on the contrary filtered out via a low-pass filter, to be further conducted into the

actual blocks of the ECG apparatus. Both the signals are thus very well separated from each

other.

Constant current about tens of µA passing through the human body creates electrical

voltage with amplitude directly proportional to the size of the impedance between the

electrodes. Therefore, if the electrodes are connected in a wrong way to the patient, or

eventually if they are disconnected altogether, the voltage grows. After passing the band pass

filter, the signal passes through a threshold detector. If the value of this measurement exceeds

a certain limit, an alarm sets off.

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Measurementtasks

1) Use an ECG simulator and the “ECG 12lead” edutools to display the ECG signal’s

progress in time on a digital oscilloscope or a PC monitor.

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BC Biomedical NIBP-1010 Uživatelský manuál Strana 31