Specifications

BC-535 Preliminary, Rev. 060126 7
Offset
The OFFSET block contains the INPUT OFFSET and the AUTO-ZERO
controls.
The
INPUT OFFSET section is comprised of a rotary potentiometer with
low/high LED’s, the
AUTO-ZERO pushbutton, the UNLOCK toggle, and an
ACTIVE LED. This section is used to compensate for junction potentials
produced by dissimilar solutions or other electrode potential differences.
The OFFSET circuit (AUTO-ZERO and OFFSET CONTROL) must be armed
prior to use. This is achieved by use of the
UNLOCK TOGGLE. This toggle is
of the momentary-on style and is operated by an upward movement.
When the circuit is armed the
ACTIVE LED will be lit. Offset adjustments
can then be easily achieved by use of the
AUTO-ZERO control or ROTARY
POTENTIOMETER. The circuit can be disarmed by a second movement of the UNLOCK TOGGLE.
The
AUTO-ZERO control provides the most direct means for setting the junction potential. When
armed, pressing the pushbutton initiates a cycle wherein the amplifier searches for and sets the offset
potential. The offset circuit is automatically disarmed at the completion of the cycle. Cycle time is
approximately 1 s.
The
ROTARY POTENTIOMETER is used to provide manual adjustment of up to ±120 mV at the
headstage input. Manual adjustment is only available when the offset circuit is armed.
Fine adjustment
of the rotary control can be achieved by pressing the control in while turning.
Low/high LED’s are
provided to indicate which direction the manual
offset control should be adjusted to achieve a null
junction potential setting. The offset circuit must be manually disarmed when using this control.
In both cases, the applied OFFSET potential can be monitored on the METER by selecting OFFSET in
the
METER block.
Meter
The METER block contains a 3.5 digit LED METER and a four
position switch for selecting
OFFSET, CAP TEST, current output (I
m
), or
voltage command (ΣV
c
).
Selection of
OFFSET displays the potential applied to the
headstage via the
MANUAL or AUTO-ZERO control located in the OFFSET
block. Offset potential is displayed in units of pA. Alternatively, this
display indicates the potential required to bring I
m
to zero when the
command input is set to zero.
Selection of
CAP TEST places the instrument into capacitance test
mode. This useful mode dynamically tests and reports the membrane
capacitance. Capacitance values are reported on the meter in units of
pF. A rear panel BNC also reports the calculated membrane capacitance whenever
CAP TEST is
selected. Reported units are 1 mV/pF.
Selection of I
m
displays the value of the DC current presented at the I
m
OUTPUT BNC. The meter is
capable of displaying currents up to ±1999 pA.
Warner
Instruments
A Harvard Apparatus Company .