R/I-T1DX User Manual
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version 1.4
page 4
2. R/I-T1DX Resistance Test / Current Injection
The R/I-T1DX device allows measurement of the resistance of electrodes connected to an
EXT-16DX amplifier. It can function also for injection of current (up to ±100 nA) through a
single electrode or through all electrodes simultaneously. The functions are selected by a
switch and indicated by an LED. It can be operated manually or remotely using a TTL signal.
The two functions can be applied to up to sixteen electrodes.
The resistance is determined by application of a fixed pulse of approx. ±10 nA with 200 Hz.
The current injection pulses are variable in both frequency and amplitude and symmetric
around the baseline.
Test and current injection pulses are a triangle-shaped signal fed into the headstage of the
EXT amplifier. With the capacitor in the headstage the triangle is differentiated resulting in a
rectangular current signal at the electrode. For electrode resistance test the voltage drop at the
electrode caused by the current signal is measured and the electrode resistance is calculated
due to Ohm’s law:
C
R
I
.
Frequency and amplitude of current injection are dependent on each other according to
dt
dU
C
I
C
where I
c
is the capacitive current, C is the capacitor in the amplifier headstage, dU/dt is the
change of the voltage amplitude of the triangle over time.
Figure 1: R/I-T1DX front panel view
In the following description of the front panel elements each element has a number that is
related to that in Figure 1. The number is followed by the name (in uppercase letters) written
on the front panel and the type of the element (in lowercase letters). Then, a short description
of the element is given.
(1)
HEADSTAGE CON2
Connector for the current injection headstage. The current injection headstage is usually
sandwiched with the recording headstage of the EXT-16DX.
(2)
CHANNEL SELECT switch
Rotary switch for selecting the electrode for current injection or to be tested for resistance.
Starting at electrode 0 (CHANNEL 00 indicated by #
3
) turning clockwise increases the
electrode number until electrode 15. Turning clockwise further starts at CHANNEL 0 again.
