Problem of signal for an ECG with INA114

[ninjasam]

I'm trying to make an ECG with the scheme supplied by the INA114 datasheet. I change Rg to 25 ohms to have a gain of 1000. My problem is that sometimes it works and somtimes the output is 0. Even the noise disappears. I have realised the montage 3 times on a labdec and 1 time on a card but I have always the same problem. I have change 2 times the ina114 component and I thinks that the component is blocked for protection or something like that. I would like to know if it is possible.
I have noticed that this problem append less when the gain is lower. And this problem already append when I put a signal from a function generator.

 

[blueroomelectronics]

I see a lot of ECG projects, are they just built out of curiosity or do people hope to make a working medical instrument?

 

[audioguru]

When your circuit has a voltage gain of 1000 then a tiny DC offset voltage will cause the output to be saturated.

Measure the DC output voltage and adjust the DC offset voltage to zero volts.

Your circuit doesn't have a lowpass filter to attenuate mains hum.

 

[ninjasam]

Thank you for your interrest.

For information, I'm trying to make this for intrumentation teaching of medical engineer.


There is no sign of saturation at all. There is no filter in output. It's really strange, when we put a gain of 100, one time it works perfectly and one time, it stop without touching anything.


Thanks in advance

 

[audioguru]

You probably built the circuit on a breadboard that has intermittent contacts.
Make it on a pcb or on stripboard with the connections properly soldered.