TEC-B-01 User Manual
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version 1.1
page 7
(9)
Display
LED display for the CURRENT passed through the CURRENT electrode in µA (XX.XX µA, switch
#
10
in I
CEL
position) or the potential at the current electrode in mV (XXXX mV, switch #
10
in V
CEL
position) or the resistance of the current electrode (XX.X M
, switch #
10
in R
CEL
position).
(10)
V
CEL
/ I
CEL
/ R
CEL
/
switch
3-position switch for selection of the display mode:
V
CEL
: potential of the current electrode is displayed
I
CEL
: current value is displayed
R
CEL
: resistance of the current electrode is displayed
(11)
OFFSET potentiometer
10-turn potentiometer to cancel potential OFFSETs at the current electrode.
(12)
BIAS C
EL
trim pot.
Trim pot for adjusting the current headstage BIAS current.
Current Headstage Bias Current Adjustment for TEC-B-01
Caution:
It is important that this tuning procedure is performed ONLY after a warm-up period of at
least 30 minutes!
The tuning procedure should be performed regularly (at least once a month) with great care since the
bias current changes over time and it determines the accuracy of the TEC-BA system.
The TEC-B-01 is equipped with a current source that is connected to the current injecting electrode
and performs the current injection. This current source has a high-impedance floating output.
Therefore, the zero point (the zero of the BIAS current) of the current source must be defined, i.e.
without an input signal there should not be an output current.
The tuning procedure is done using the BIAS C
EL
trim pot and one resistance of a few k
and one of a
few M
. It is based on Ohm's Law (U = R * I).
If the headstage generates an output current, this current will cause a voltage deflection at a test
resistor. If this test resistor has a low resistance of only a few k
, this voltage deflection originates
only from a possible offset of the electrode, that can be cancelled using the OFFSET C
EL
(#
11,
Figure
1) potentiometer.
Replacing the low resistance resistor by one of a much higher resistance may lead to another voltage
reading at the digital display. This voltage deflection then originates only from the BIAS output
current and is proportional to this output current according to Ohm’s law. Using the BIAS C
EL
trim
pot. the monitored voltage can be set to 0. This cancels the BIAS current.
Tuning procedure:
The tuning procedure is performed using high-value resistors. It cannot be performed with an
electrode, since there are always unknown potentials involved (tip potential, junction potentials etc.).
Warning
:
High voltage!
Always turn power off when working directly on the current headstage
output.
