# How calculate the error offset or the noise threshold for MyoWare and FSR sensors?

I am working on EMG and FMG signals to extract time domine features and i need a threshold value for some features. I must calculate it from the characteristics of MyoWare and FSR sensors.For the MyoWare sensor i concluded that it is the error offset from the CMRR.The MyoWare has as CMRR:110,Adjustable Gain Potentiometer:50 kΩ,Input Impedance:110 GΩ and VIN=5v.How can i calculate the error offset? and i still stucked in the threshold of the FSR sensor.Can anyone help me?

## 1 Answer

In a measurement system, an error budget is key to accurate measurement.

• Input Impedance 110 Billion ohms has meaning, in a model of the cell walls you are sensing. The cell_Walls form a voltage_divider with the 110 Billion ohms. That ratio defines a measurement error. If you know the cell_Wall resistance or impedance, you compute that ratio.

• CMRR 110: Assuming this is 110_dB, where the ratio is 10^(110db/20db) = 10^5.5 and that becomes 316,000:1 . This is used in computing how badly the power_line voltages on the biological tissues change from common_mode to differential_mode. As example, if you have 0.316 volt at 50Hertz on the biological entity, divide that by 316,000 as 0.316 / 316,000 and find 1 microvolt is the error caused by Common Mode Rejection Ratio. Please note I assumed 110 is really 110_dB.

• there may be DC_offset errors. Ask the professors if you should be concerned.

• thank you for the response @analogsystemsrf.the CMRR is not expressed with dB it is without unity Aug 7, 2020 at 8:31