This may be caused by several factors:
- The test subject is moving during the measurement. Let the test subject sit in a chair relaxed, with their arm lying at their side or on a table when data are being collected.
- The used sampling frequency may influence the amount of detected noise. A sampling frequency of 50 Hz is high enough to measure an ECG signal but there will be not much noise detected. A sampling frequency of 200 Hz detects a lot more noise.
- The sensor can also be used to measure electrical signals of contracted muscles. To obtain a nice ECG signal, it is necessary that the muscles of the arms (and also other muscles) are as relaxed as possible.
- For the older CMA ECG set, the electrodes are connected to the amplifier via 4 mm wires. Two parallel wires act as an antenna and catch noise from the power grid. Wrap the wires around each other a few times to get rid of this noise.