Description
DESCRIPTION
The NL844 is a small, four channel, low noise, high impedance, differential pre-amplifier designed for electromyography (EMG) or evoked potential (EP) use close to the preparation or human subject. The unit is intended for use with the NL820A Isolator, from the NeuroLog™ system. It has controls for LF-cut, Gain and Impedance checking of each amplifier electrode. The front panel inputs use 1.5mm DIN 42802 safety connectors. This unit is particularly suited for use where there are very large stimulus artefacts, for example when used close to a magnetic stimulator coil. In these cases the stimulus artefact would normally swamp the pre-amplifier inputs resulting in a ‘tail’ with a long time constant that obliterates the response. The special circuitry of the NL844 eliminates this as long as good recording practice is followed. The input circuit automatically adjusts to the DC input conditions and a non-linear filter subsequently modifies its time constant if the differential input signal exceeds its normal ±20mV working range. Therefore fast, short artefacts do not block the subsequent stages. This results in an amplifier with a very fast recovery time from stimulus artefact pulses.
Each channel has a connector for the non-inverting (+) input that is often called the ‘Reference’ on EEG machines and inverting (-) input that is often called the ‘Active’ on EEG machines. As the amplifier is differential both must be used on active channels. The ‘COM’ connector must always be connected to the patient to provide a reference potential for the amplifiers. A deblock button provides the user with a method of removing any DC potential from the internal coupling capacitors that may occur whilst arranging the electrodes on the patient. This function can also be performed remotely via the ‘MUTE’ socket on the NL820A.
As well as amplifying 4 channels, the unit can also be operated in a single or two channel mode (channels 1 & 3 or 2 & 4). The NL844 needs to be connected to the NL820A Isolator module. NL844 4 Channel Preamp’s are ideally suited as a multi-channel EMG amplifiers or EEG amplifiers.
Get in touch with our knowledgeable staff to learn more about the NL844 AC Preamplifier in more detail. Call 01707 328347 to contact us or email us at sales@digitimer.com. Our expert team can answer any questions and queries you have regarding the NL844, as well as providing additional information on our complete collection of products.
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Product Information
NL844 4Ch AC Pre Amplifier
References
Publications which cite use of the Digitimer Neurolog System can be found on Google Scholar.
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