Multichannel Systems USB-MEA256-System Manual - Manual (Page 15)

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4 USB-MEA256-System
4.1 The USB-MEA256 Data Acquisition
Analog input signals are acquired from the data source and digitized by the 256-channel analog /
digital converter that is integrated into the main unit. Recorded signals are converted in real-time
into digital data streams at sampling rates of up to 40 kHz per channel. You will not miss even the
fastest biological signals. Data is transferred to the computer via a High Speed USB 2.0 port.
A 16 bit digital (TTL) input / output channel is available. You can use the digital TTL inputs,
for example, for synchronizing stimulation and recording, or for synchronizing the USB-MEA256-
System with other systems, video tracking, for example. The digital TTL outputs can be used for
triggering other devices.
4.2 The USB-MEA256 Filter Amplification
The filter amplifier combines a band pass filter and the signal amplification in one instrument.
The bandwidth of 1 to 5000 Hz is suitable for a broad range of applications, such as spike and
field potential recording from neurons or recording of cardiac signals. The digital filter of the
MC_Rack program can be used to adjust the pass band and filter the raw data. Please see the
MC_Rack help or manual for more information. This way, you are very flexible in designing your
experiments. Please note that you may need a higher sampling rate to avoid aliasing. See also the
chapter USB-MEA256 Data Acquisition for more information. For slow signals like field potentials,
a bandwidth of 1 to 300 Hz is appropriate. If you like to record fast signals like spikes, a pass band
of 300 Hz to 5 kHz is suitable. Cardiac signals have fast and slow components; therefore, you
usually need a wider bandwidth of 1 Hz to 5 kHz.
Please note that the gain factor of the filter amplifier (1100) is a fixed hardware property; and
that you cannot change the gain of the amplifier by software controls. Please also note that the
ratio of the output signal to the input signal, that is, the gain, is not a fixed parameter for the
complete bandwidth. The gain that was specified for the amplifier, for example, 1100 is not fully
reached at the borders of the amplifier's pass band. The general rule is, that at the lower and
upper limit of the frequency band, the gain is approximately 70 % of the full gain. Therefore,
you should use a bandwidth that is at a safe distance of the signals of interest. Outside the pass
band, the gain decreases with the frequency and finally approaches zero.
For more information on gain and filters in general, please refer to standard literature or contact
your local retailer.
Raw data from up to 252 electrodes of a microelectrode array MEA is amplified by 252 channels
of filter amplifiers that are built very small and compact using SMD (Surface Mounted Devices)
technology. The small-sized MEA amplifier combines the interface to the 256MEA probe with the
signal filtering and the amplification of the signal. The compact design reduces line pick up and
keeps the noise level down. The MEA sensor is placed directly into the small-sized MEA amplifier.
When the amplifier is closed, the contact pins in the lid of the amplifier are pressed onto the MEA
contact pads. The very close location of the amplifier to the MEA sensor is very favorable
concerning a high signal-to-noise ratio.
The amplifier is intended to be used either with inverted or with upright microscopes.
The MEA256 amplifier is compatible to most standard microscopes.
The MEA256 amplifier has an integrated heating system for controlling the MEA's temperature.
The desired temperature can be easily regulated with a temperature controller TCX.
Connect the internal heating element to a temperature controller's output channel (D-Sub9
socket) with the integrated cable. Do not connect the black heating element cable to the
computer!