TDT Medusa4Z Application guide

Medusa4Z BioAmp
Hardware Reference
Updated 2021-09-15

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Table of Contents
Medusa4Z BioAmp
4Medusa4Z Overview
5Medusa4Z Features
5Analog Input Channels
6Electrode Connectors
6Impedance Checking
6LCD Screen
7Base Station Connector - Optical
8Power
8Power Requirements
9Medusa4Z Technical Specications
9Input Referred Noise
10Sample Delay
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Medusa4Z BioAmp
Medusa4Z Overview
The Medusa4Z is a four-channel, referential, low-noise digital bioamp targeted for use in low-
channel-count, low-impedance neurophysiology recordings, such as ABR, EEG, EMG, or EKG
signals. The bioamp digitizes one or four channels at acquisition rates of approximately 3kHz,
6kHz, 12kHz, or 25kHz, and the amplied digital signal is sent to the base station via a
noiseless ber optic connector.
Connections to the subject (four channels, reference, and ground) are made with six standard
1.5 mm touchproof safety connectors.
It is powered by a 5 AmpHr Li-Poly battery that provides up to 30 hours of continuous
data acquisition in single-channel mode and up to 24 hours in four-channel mode.
It includes impedance testing functionality for each of the four recording channels as well
as the reference electrode.
The user interface has 8 buttons and a 16 x 2 character LCD display screen. It lets you
select performance characteristics of the preamplier and shows battery and signal level.
A complete charge from a dead battery can be achieved in under 8 hours with the
included charger.
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Medusa4Z Features
The Medusa4Z has the option to be run in single-channel mode or four-channel mode. When in
single channel mode, channels 2-4 are powered down and isolated from the reference line.
Running in single-channel mode will provide slightly better performance and longer battery life.
There are selectable Sampling Frequency options of ~3 kHz, ~6 kHz, ~12 kHz, or system rate
(maximum ~25 kHz). Users will nd that using the lowest practical rate improves noise
performance.
When testing the impedance of the probes, users can select frequencies of 100 Hz, 300 Hz,
500 Hz, or 1 kHz.
A user-selectable digital highpass lter has adjustable options that are: Off, 1 Hz, and 3 Hz. The
hardware has a xed analog highpass at 0.3Hz.
An Auto Shutdown feature has three modes: Never, 1 hour, 3 hours, or 5 hours. If no buttons
are pressed after this interval, then the device will automatically power down. If no optics are
detected, the Medusa4Z will also shutdown. Before shutting down, the blue POWER LED will
blink fast to indicate that time has expired. Pressing any key will reset the counter.
Analog Input Channels
The Medusa4Z Preamplier acquires signals with 16-bit PCM ADCs. The signals are
oversampled before conversion to remove aliasing of high frequency RF signals. This allows
users to acquire at lower sampling rates (down to 3 kHz) with improved signal-to-noise quality
in that range and no aliasing. The Medusa4Z can also acquire data in High-Resolution mode
which uses 24-bit PCM ADCs. This is controlled by the base station (RZ, RX) to which the
Medusa4Z is connected. The change occurs by modifying the underlying circuit running on the
base station in Synapse or BioSigRZ. This is the handled by default in Synapse v92 and above,
and BioSigRZ v5.7.5 and above. In TDT Drivers v92 and above there is a RPvdsEx circuit macro
available in: C:\TDT\RPvdsEx\Macros\Device\Medusa4Z_Bioamp .
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Electrode Connectors
Plug the electrodes directly into the standard 1.5mm touchproof connectors on the side of the
Medusa4Z.
Impedance Checking
The Impedance checker on the Medusa4Z provides a simple check of the channel impedance
relative to ground. To check the impedance level, press the button next to the channel indicator
(e.g. CHAN-1). The impedance between channel and ground will be shown on the screen. The
REF impedance button checks the impedance between the reference and the ground.
Impedance checking frequency options are 100 Hz, 300 Hz, 500 Hz, and 1kHz. These are
settable on the user interface.
LCD Screen
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The LCD screen shows the current sampling rate, battery level, and signal level indication on
the active channels.
Use the SETUP button to cycle through available settings and use the OPTION button to
change the currently selected setting. Settings include:
Active Channels: Single or Four Channel
Sample Frequency: ~3kHz, ~6kHz, ~12kHz, System Rate (up to ~25kHz). Match this to the
desired frequency range of your acquired signal (maximum frequency captured will be ~45% of
selected sample frequency). Note that lower sampling rates will have improved signal-to-noise,
but they will also have longer sample delays. Please refer to the See Medusa4Z PreAmp
Technical Specications. for more information.
Probe Frequency: 100 Hz, 300 Hz, 500 Hz, 1 kHz. Choose the default frequency used for the
impedance checker.
Highpass Filt: Off, 1 Hz, 3 Hz. Set the highpass lter cutoff frequency on the input signals. 'Off'
is a 0.1 Hz lter. Note that there is a xed 0.3 Hz highpass analog lter on the inputs.
Auto Shutdown: Never, 1 hr, 3 hr, 5 hr. After a period of inactivity the Medusa4Z will shut itself
down to preserve power. This prevents dead batteries from accidentally leaving the unit on
overnight.
Base Station Connector - Optical
Use the provided ber optic pair (black cable, white connectors) to connect the OPTICAL port
on the preamplier to the optical input port on the base station.
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The duplex ber optic cable has identical one-piece connectors at each end. There is a V-
shaped groove on one side of the connector and a raised rectangle on the other. As shown in
the image below, plug the connector into the RZ6 port with the raised rectangle side up. Plug
the connector into the preamplier with the V-shaped groove up.
Medusa4Z Connection Diagram
Power
The POWER button on the face of the Medusa4Z powers it on. Press and hold the button to
power it off. Press the power button momentarily to go to the home screen from anywhere or
to reset the power down timer.
Do not use the recessed slide power switch (ON OFF (RESET)) on the side of the device unless
you need to reset all settings to factory default, or if you are storing the Medusa4Z for an
extended period of time and want to completely disconnect the battery. The OPTICAL ber
connector at the right will be illuminated when the amplier is on.
Power Requirements
The lithium battery charges in four hours. Keeping the battery charger connected to the
amplier does not affect the battery life. However, the charger will signicantly increase the
noise of the system if it is plugged in while an experiment is running. A 12 Volt battery charger
is included with the amplier. The supplied charger tip is center negative. However, tip polarity
can be positive or negative if the charger needs to be replaced.
The lithium battery supplied with the system cannot be removed. If battery life longer than 30
hours is required, an external battery pack can be connected to the voltage inputs of the
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charger. TDT recommends a 6 (minimum) to 16 Volt (maximum) battery, such as lead acid
batteries used for motorized wheel chairs. Contact TDT for more information.
Medusa4Z Technical Specications
Input Referred Noise
Depends on Medusa4Z sample rate and electrode impedance. All units in uVrms.
A/D Up to 4 channels
Standard Mode: 16-bit PCM
High-Resolution Mode: 24-bit PCM
Sample Rate ~3 kHz, ~6 kHz, ~12 kHz, or ~25 kHz
Maximum Voltage In ± 10 mV
Gain 100x
Frequency Response 3 dB 0.3 Hz - 0.45*Fs (with no additional high-pass lter selected)
Highpass Filter 0.3 Hz, 1 Hz, or 3 Hz
Anti-Aliasing Filtering 45% sampling rate
S/N (typical) 80 dB
Input Impedance 100 kOhm
Battery Li-Poly Battery 5000 mAh
single-channel mode: 30 hours between charges
four-channel mode: 24 hours between charges.
1000 cycles of charging, not removable by user
Charger 6-16 V DC, > 1 A, center-positive or center-negative.
Fiber Optic Cable 5 meters standard, maximum cable length 12 meters
Med4usaZ rate shorted 3 kOhm 10 kOhm
3 kHz 0.15 0.3 0.5
6 kHz 0.25 0.4 0.7
12 kHz 0.3 0.6 1.0
25 kHz 0.4 0.9 1.4
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Sample Delay
Depends on Medusa4Z and RZ processor sample rates. All units in samples.
Medusa4Z rate RZ @ 25 kHz RZ @ 12 kHz RZ @ 6 kHz
25 kHz 24 N/A N/A
12 kHz 42 24 N/A
6 kHz 76 42 24
3 kHz 146 76 42
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