EMG-Main amplifier & interface unit
This main unit supplies power to the electrodes, receives & conditions the signals and provides four outputs for signal acquisition.
The belt-mounted interface unit is attached to the main amplifier by a network cable. Each channel is labelled according to the main amplifier and all channels are taken with respect to the reference input potential.
There are three pre-set amplification settings that give the system overall gains of 100 (40dB), 1000 (60dB) and 10000 (80dB). The electrodes do have some initial amplification with a gain of 10. The VAR setting is of variable gain between 100 and 10000, set by turning the screw of the inset potentiometer. The REF setting forces the input to the channel to be the reference potential. When channels are not in use, they should be set to the REF setting.
The power supply provides a regulated 12V output and conforms to the medical UL544 standard. The main unit is equipped with two LEDs to detect signal saturation (±4.8V) and line interference (60Hz). The tone switch can also be turned on to create an audible tone when either error occurs.
This unit was specially ordered to have a larger bandwidth 20 – 2000 Hz compared to the regular specifications. An in-house EMG Analysis was performed in February 2004, which verified the frequency response for each channel & the gain settings.