The Unipolar channels of the TMSi equipment can be used for all sorts of ExG measurements (e.g. ECG, EEG, EMG, etc.). Since TMSi systems include no hardware filters other than the obligatory anti-aliasing (well above the band of interest), one always records the raw data.
The input stage for measuring unipolar electrophysiological signals is configured as a so called reference amplifier. All signals are amplified against the average of all connected unipolar inputs. With the help of our TMSi Polybench software package all kind of montages are possible: average reference, common reference, bipolar configurations, virtual references like Wilson point or Hjorth montages, etc. The patient ground electrode is required, but it is not an active input. It is meant as a way to keep patient potential and the amplifier potential at the same level, so that the amplifiers can function.
The input impedance of the active channels is very high. The influence of the electrode impedance is therefore very small. It should not be necessary to perform electrode impedance measurements. Inputs that are not connected to an electrode cable automatically switch off (i.e. will show a zero/flatline signal).
All electrode cables are shielded with the electrode signal itself (active shielding). This ensures a disturbance free measurement. Mains interference and cable movement artifacts are eliminated or (in very severe cases) reduced to a minimum.
After the amplifier stage (gain=20 or lower) the signals go directly to the ADC. No high pass or low pass filters that can cause signal phase shifts or filter overflows are present.