EGRET Software Online Documentation

MA-400 (Motion Lab Systems EMG) Configuration

MA-400 Configuration

If you are not familiar with the data measurement, or data collection system, that you are using then this is a good place to stop and read the manuals that were supplied with the data collection or recording system that you are planning to use.

Once the MA400 analog cable has been connected to your data collection system it is a good idea to start up the data collection system and setup the data collection parameters before applying power to the MA400. In general there are two parameters that you will need to check – these are input signal level and sample rate.

Signal Level

All analog signals generated by the MA400 are in the range of ± 5 volts so you need to set the analog data collection system to record data or accept input signals at this level. If you select a lower level (i.e. ± 2.5 volts) then the MA400 signals may be clipped or distorted and will not be measured correctly. If you select too high a level (i.e. ± 10 volts) then the measured signals will be too small and you will loose some resolution or precision.

Sample Rate

The simple rule of thumb for setting the analog data collection sample rate is to always sample the data at twice the rate of the highest frequency present in the signal. Since the maximum bandwidth for MA400 systems with a variable low pass filter is DC to 2,000 Hz this would require a very high sample rate (a minimum of 4,000 and preferably at least 5,000 analog samples per second per channel) unless the signal is filtered to remove the higher frequency components. This is normally done by setting the anti alias, low pass filter on these systems to a suitable value. Most of the signal power from surface EMG is lower than 350 Hz so setting the

backpack filter to 350 Hz reduces the analog data recording requirements considerably if all of the EMG data is limited to surface recordings. The system user will usually know what signal bandwidth is required.

It is a good idea to allow for some degree of over-sampling when you set the analog 

sample rate so if you were setting the backpack LP filter to 350Hz then a sample rate of between 700 and 1000 samples per second per channel would be appropriate. Some MA400 systems have a fixed DC to 1000Hz bandwidth – these systems must be sampled at a rate of 2000 samples per second per channel or faster.

 

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