Hello, we use the ads1292 chip to detect the LEAD II ECG signal. The schematic diagram of the ECG part is as follows. The ports LA, RA, RL are respectively connected to the external ECG lead wire, and the external ECG lead wire is connected to the human body through disposable ECG electrode piece. the shield signal of all external ECG leads is connected to the analog ground through port Shield, and the ports BAT+, BAT- are respectively connected to the positive and negative terminals of the external lithium battery.
When the device is properly worn on the human body, the impedance between the BAT+ or BAT-port and the human body is close to infinity. In this case,the detected Lead-Off alarm is always false and the firmware can correctly detect the ECG signal waveform. In our firmware, When any of LA, RA, RL falls off, the Lead-Off alarm is true, otherwise, the Lead-Off alarm is flase. LA, RA, RL falls off is determined by the register flag bit of ads1292.
When the impedance between the BAT+ or BAT-port and the human body is less than 1M ohm for some reason (such as sweating), in this case, the detected Lead-Off alarm is is always true , but in reality our lead is normally connected. Our question is: Does the low impedance between the BAT+ or BAT-port and the human body affect the reliable collection of ECG signals? If there is an impact, what is the minimum impedance between the BAT+ or BAT-port and the human body?If there is no impact, how can this Lead-Off alarm abnormality be solved?
Below is the ads1292 initialization code and related schematics.Thank you.
ADS_WREG(CONFIG1, 0x83);
ADS_WREG(CONFIG2, 0xC0);
ADS_WREG(LOFF, 0xF4);
ADS_WREG(CH1SET, 0x12);
ADS_WREG(CH2SET, 0x00);
ADS_WREG(RLD_SENS, 0x3C);
ADS_WREG(LOFF_SENS, 0x0C);
ADS_WREG(RESP1, 0x02);
ADS_WREG(RESP2, 0x03);
