ADPD4200 datasheet(42/93 Pages) AD

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Data Sheet

ADPD4200

APPLICATIONS INFORMATION

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Rev. 0 | 42 of 93

some readout indicating that contact is being made with the skin

and current is flowing into the ADPD4200 through the body of

low impedance when the stimulus is applied. When either ECG

electrode stops making contact with the skin or is loose, there

is no ECG signal in the acquired trace. When contact between

both electrodes and the skin is restored, the ECG signal appears

immediately. Because two inputs and two channels are allocated to

detect the lead off condition for two electrodes, this measurement

method can determine if one electrode loses contact with skin or

both electrodes lose contact. This measurement can also detect

which one of the electrodes loses contact with the skin if only one

electrode loses contact.

Figure 41 shows a data plot of a lead off detection measurement

during an ECG measurement using the circuit shown in Figure 40.

When the ECG electrodes are making contact with the skin during

the measurement, an ECG signal is clearly visible. The impedance

measurements of the E1 and E2 electrodes show some value

indicating that contact is being made with the skin and current is

flowing into the ADPD4200 when the stimulus is applied. When

either electrode stops making contact with the skin, 0 is read for

that measurement indicating an open circuit, effectively a lead off

condition. When contact between both electrodes and the skin is

restored, the ECG signal is reacquired in less than 1 sec.

Figure 41. Lead Off Detection Measurement

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