Auckland Bioengineering Institute


Technical details

UnEmap hardware will acquire electrical voltage data from many electrodes. Designed for a diverse range of applications, many hardware parameters can be configured independently (e.g. gain, filter characteristics and sampling rate). A stimulus signal can be directed down any electrode.

A UnEmap system is made up of one or more data acquisition modules. Each module contains 448 channels utilising seven units of 64-channels.

One or more modules are connected to a master computer running linux. This computer provides a scrolling display of realtime signals, controls and monitors acquisition and analyses the acquired signals. The master computer is not included in the pricing for UnEmap systems. It can be any machine running linux (or unix). Please contact us for further details.


On this page


On other pages

UnEmap (home)   |   Further information


64-channel unit

Each 64-channel unit comprises a data acquisition card and a signal conditioning card. For each unit, the channels can be configured either for 64 differential inputs or 64 unipolar inputs. When operating in unipolar mode a common reference signal is used, typically, this will be a Wilson Central Terminal.

 

Sampling

12-bit resolution with a maximum sampling rate of 5 kS/s simultaneously on all 64 channels.

Top

Gain

The 64-channel unit provides three gain stages for each channel. The first and third stages are programmable (but the same for all 64 channels) to ensure maximum signal to noise ratio in the presence of DC offsets. The total gain can be programmed in the range 11 to 8800. In the following table, the signal range specifies the maximum magnitude of the electrophysiological signal. This desired signal can be measured in the presence of a +/- 2V DC offset (this reduces the input voltage range by approximately 2 mV).

 

Total gain signal range resolution
11 +/- 453 mV 222 microV
55 +/- 89 mV 44.4 microV
110 +/- 43 mV 22.2 microV
220 +/- 21 mV 11.1 microV
550 +/- 7 mV 4.44 microV


For signals without a DC offset, the high gain configuration has the following resolution specifications:

Total gain signal range resolution
550 +/- 9.1 mV 4.44 microV
1100 +/- 4.5 mV 2.22 microV
5500 +/- 0.91 mV 0.488 microV
8800 +/- 0.57 mV 0.277 microV


 

Top

Filtering

Each channel has a 5th-order (-100dB per decade), linear phase, low pass filter. The cut-off frequency for all channel within a unit can be programmed to one of 98 values - ranging linearly from 50 Hz to 4950 Hz. This is intended as an anti-aliasing filter. Each channel has a 0.05 Hz high pass filter for DC removal. These filters can be software configured to meet the AHA standard for ECG measurements.
 

Input parameters

Impedance > 1 TOhm.
Input current typically 0.5 nA per input.
Common mode rejection ratio: typically 90 dB, minimum 75.
 

Protection

Any input can be subjected to +/- 100V with respect to any other input without damage. If higher levels of protection are required during recording (e.g. for mapping during external defibrillation) an external attenuation circuit must be fitted. All channels have computer controlled isolation relays to disconnect the electrodes from the amplifier inputs. When in isolated mode, amplifier inputs are connected to a common test signal permitting auto-calibration.

Top

Active shielding

Shields protecting the low voltage analogue signals can be driven by an active circuit using either the Wilson Central terminal or a local ground.

Stimulation channel

Each 64 channel unit has a stimulation channel which can be directed to any (or multiple) of the unit's recording electrodes (e.g. to test electrode conductivity, or for pacing). The stimulation signal can be configured to be constant voltage or constant current.

Constant voltage

Maximum output voltage +/- 10 V into a 2 Kohm load (maximum current +/- 5 mA). Voltage steps of 5 mV.

Constant current
Maximum output current +/- 2 mA into a 2 Kohm load (maximum voltage +/- 4 V). Current steps of 50 microA.
 

Alternatively the stimulation signal can be directed to and used to control an external stimulator. The output from the external stimulator can be sent directly to a stimulation electrode or returned to unemap to be sent to the selected recording electrodes. Note: The voltage from the external stimulator should not exceed +/- 100V.

Top

Power supply/isolation

The signal conditioning units are battery powered. This is desirable for low noise. Each 448 channel module will draw 5A from each of two 6V batteries. The capacity of each battery (specified by an amperes/hour rating) can be calculated using the following formula:
A/h = (number of modules x 5 x number of hours of continuous operation required x 1.1).

Note: With software control, it is easy to switch the system into isolation mode during experiment setting up. During this time, the batteries will not be supply any current, in fact they will be charging. The signal conditioning units need only be powered up during data acquisition. Batteries must be supplied by the end user, please consult us for evaluation of battery requirements. The charging of the batteries is under software control.

Top