ADS1299: lead-off detection signal

guohaoyue

Prodigy 10 points

Part Number: ADS1299

Hi. I'm wondering which kind of waveform the lead-off detection signal is? Sine?square?triangular?

I can not find it in the datasheet. Does anyone know？

1 年多前

0 Amy Luo 1 年多前

TI__Guru**** 185470 points

Hi, guohaoyue

The lead-off detection principle is described in the Datasheet 9.3.2.4.3 Lead-Off Detection section.

The basic principle is to inject an excitation current and measure the voltage to determine if the electrode is off. As shown in the lead-off detection functional block diagram in Figure 35, this circuit provides two different methods of determining the state of the patient electrode. The methods differ in the frequency content of the excitation signal. Lead-off can be selectively done on a per channel basis using the LOFF_SENSP and LOFF_SENSN registers.

There are two types of excitation signals, DC signal excitation and AC signal excitation, corresponding to DC Lead-Off detection and AC Lead-Off detection, respectively. In DC lead-off method, the lead-off excitation is with a dc signal. In AC lead-off method, an in-band ac signal is used for excitation. It can be configured via the Lead-Off Control Register (0x04h LOFF register).

See application note below for more lead-off detection theory:

Understanding Lead-Off Detection in ECG

Regards,

Amy

0 guohaoyue 1 年多前回复 Amy Luo

Prodigy 10 points

Hi, Amy
Thank you for your prompt response.
I am confused at the AC signal. I use lead-off detection and reading signals simultaneously ,when i have same setting but different connecting(resistance or oscilloscope),the signals was different ,so i want to know which waveform is right?
so i can use it to calculate the resistance.

resistance

oscilloscope

Thanks

0 Amy Luo 1 年多前回复 guohaoyue

TI__Guru**** 185470 points

Hi guohaoyue,

I hope this reply finds you well.

这里是中文论坛，您可以使用中文。为使我们更好的沟通，我们可以使用中文交流。

guohaoyue 说：
when i have same setting but different connecting(resistance or oscilloscope),the signals was different ,

具体设置是什么？您具体是怎样连接 resistance or oscilloscope 的？您分别在哪里测量的上述波形？您的实际应用是要测量电阻值吗？

0 guohaoyue 1 年多前回复 Amy Luo

Prodigy 10 points

HI Amy

不好意思哈哈，我不知道这里是中文论坛。

1.我的寄存其设置如下，进行阻抗检测。

ads_wr(CONFIG3,0xEC);
Delay_ms(10);
ads_wr(CONFIG1,0x96);
ads_wr(CONFIG2,0xC0);
ads_wr(CH1SET,0x60);
ads_wr(CH2SET,0x60);
ads_wr(CH3SET,0x60);
ads_wr(CH4SET,0x81);
ads_wr(CH5SET,0x81);
ads_wr(CH6SET,0x81);
ads_wr(CH7SET,0x81);
ads_wr(CH8SET,0x81);
ads_wr(MISC1,0x20);
ads_wr(LOFF,0x02);
ads_wr(LOFF_SENSP,0x07);
ads_wr(LOFF_SENSN,0x00);

我打开了三个通道和SRB1进行检测，但是我只使用其中一个通道来尽心实验，我不确定我的设置是否有问题。

2.连接电阻时，我是用电极和电阻串联，接法如下