NPI SEC-05X Operating instructions

OPERATING INSTRUCTIONS AND
SYSTEM DESCRIPTION OF THE
SEC-05X
SINGLE-ELECTRODE CLAMP
AMPLIFIER
VERSION 2.0
npi 2015
npi electronic GmbH, Bauhofring 16, D-71732 Tamm, Germany
Phone [phone]; Fax: [phone]
[email protected]; http://www.npielectronic.com

SEC-05X User Manual
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Table of Contents
About this Manual................................................................................................................... 4
1. Safety Regulations.............................................................................................................. 5
2. Introduction......................................................................................................................... 6
2.1. Why a Single-Electrode Clamp? ................................................................................. 6
2.2. Principle of Operation ................................................................................................. 8
Major advantages of the npi SEC System................................................................... 10
3. SEC-05X System................................................................................................................ 10
3.1. SEC-05X Components ................................................................................................ 10
3.2. Description of the Front Panel..................................................................................... 12
3.3. Description of the Rear Panel...................................................................................... 20
4. Headstages .......................................................................................................................... 21
4.1. Standard Headstages.................................................................................................... 21
4.2. Low-noise Headstage (SEC-HSP)............................................................................... 23
5. Setting up the SEC-05X System......................................................................................... 24
6. Passive Cell Model ............................................................................................................. 24
6.1. Cell Model Description ............................................................................................... 25
6.2. Connections and Operation ......................................................................................... 26
7. Test and Tuning Procedures ............................................................................................... 28
7.1. Headstage Bias Current Adjustment ........................................................................... 28
7.2. Electrode Selection...................................................................................................... 29
7.3. Offset Compensation................................................................................................... 29
7.4. Bridge Balance (in BR mode) ..................................................................................... 30
7.5. Switching Frequency and Capacitance Compensation (in switched modes).............. 32
Criteria for the selection of the switching frequency .................................................. 32
7.6. Capacity Compensation - Tuning Procedure............................................................... 34
First part: basic setting................................................................................................. 34
Second part: fine tuning............................................................................................... 40
7.7. Testing Operation Modes ............................................................................................ 41
Current Clamp (in BR- or discontinuous CC mode)................................................... 41
Voltage Clamp............................................................................................................. 41
8. Special Modes of Operation ............................................................................................... 43
8.1. Dynamic Hybrid Clamp (DHC) Mode (optional) ....................................................... 43
General Description..................................................................................................... 43
Operation..................................................................................................................... 43
8.2. Linear Mode (optional)................................................................................................ 43
General Description..................................................................................................... 43
Operation..................................................................................................................... 43
8.3. VCcCC mode (optional).............................................................................................. 44
General Description..................................................................................................... 44
Operation..................................................................................................................... 44
Current Clamp Input.................................................................................................... 45
9. Sample Experiments........................................................................................................... 46
9.1. Sample Experiment using a Sharp Microelectrode ..................................................... 46
9.2. Sample Experiment using a Patch Electrode............................................................... 49
10. Tuning VC Performance.............................................................................................. 51
General Considerations................................................................................................ 51
Tuning Procedure ........................................................................................................ 52
11. Trouble Shooting......................................................................................................... 53
12. Appendix ..................................................................................................................... 54
12.1. Theory of Operation .................................................................................................... 54

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12.2. Speed of Response of SEC Single-Electrode Clamps................................................. 55
12.3. Tuning Procedures for VC Controllers........................................................................ 56
Practical Implications.................................................................................................. 56
13. Literature ..................................................................................................................... 58
13.1. Papers in Journals and Book Chapters about npi Single-electrode Clamp Amplifiers58
13.2. Books........................................................................................................................... 70
14. SEC-05X Specifications – Technical Data.................................................................. 71
15. Index............................................................................................................................ 74

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About this Manual
This manual should help the user to setup and use SEC systems correctly and to perform
reliable experiments.
If you are not familiar with the use of instruments for intracellular recording of electrical
signals please read the manual completely. The experienced user should read at least chapters
1, 3, 7 and 10.
Important: Please read chapter 1 carefully! It contains general information about the safety
regulations and how to handle highly sensitive electronic instruments.
Signs and conventions
In this manual all elements of the front panel are written in CAPITAL LETTERS as they
appear on the front panel.
System components that are shipped in the standard configuration are marked with ✓,
optional components with ➪. In some chapters the user is guided step by step through a
certain procedure. These steps are marked with ❏.
Important information and special precautions are highlighted in gray.
Abbreviations
Cm: cell membrane capacitance
Cstray: electrode stray capacitance
GND: ground
Imax: maximal current
Ra: access resistance
Rm: cell membrane resistance
REL: electrode resistance
SwF: switching frequency
τCm: time constant of the cell membrane
VREL: potential drop at REL

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1. Safety Regulations
VERY IMPORTANT:Instruments and components supplied by npi electronic are NOT
intended for clinical use or medical purposes (e.g. for diagnosis or treatment of humans),
or for any other life-supporting system. npi electronic disclaims any warranties for such
purpose. Equipment supplied by npi electronic must be operated only by selected,
trained and adequately instructed personnel. For details please consult the GENERAL
TERMS OF DELIVERY AND CONDITIONS OF BUSINESS of npi electronic, D-71732
Tamm, Germany.
1) GENERAL: This system is designed for use in scientific laboratories and must be
operated only by trained staff. General safety regulations for operating electrical devices
should be followed.
2) AC MAINS CONNECTION: While working with the npi systems, always adhere to the
appropriate safety measures for handling electronic devices. Before using any device
please read manuals and instructions carefully.
The device is to be operated only at 115/230 Volt 60/50 Hz AC. Please check for
appropriate line voltage before connecting any system to mains.
Always use a three-wire line cord and a mains power-plug with a protection contact
connected to ground (protective earth).
Before opening the cabinet, unplug the instrument.
Unplug the instrument when replacing the fuse or changing line voltage. Replace fuse
only with an appropriate specified type.
3) STATIC ELECTRICITY: Electronic equipment is sensitive to static discharges. Some
devices such as sensor inputs are equipped with very sensitive FET amplifiers, which can
be damaged by electrostatic charge and must therefore be handled with care. Electrostatic
discharge can be avoided by touching a grounded metal surface when changing or
adjusting sensors. Always turn power off when adding or removing modules,
connecting or disconnecting sensors, headstages or other components from the
instrument or 19” cabinet.
4) TEMPERATURE DRIFT / WARM-UP TIME: All analog electronic systems are
sensitive to temperature changes. Therefore, all electronic instruments containing analog
circuits should be used only in a warmed-up condition (i.e. after internal temperature has
reached steady-state values). In most cases a warm-up period of 20-30 minutes is
sufficient.
5) HANDLING: Please protect the device from moisture, heat, radiation and corrosive
chemicals.

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2. Introduction
Npi electronic’s SEC (Single-Electrode Clamp) systems are based on the newest
developments in the field of modern electronics and control theory (see also chapter 8). These
versatile current/voltage clamp amplifiers permit extremely rapid switching between current
injection and current-free recording of true intracellular potentials.
The use of modern operational amplifiers and an innovative method of capacity compensation
makes it possible to inject very short current pulses through high resistance microelectrodes
(up to 200 MΩand more) and to record membrane potentials accurately, i.e. without series
resistance error, within the same cycle.
Although the system has been designed primarily to overcome the limitations related to the
use of high resistance microelectrodes in intracellular recordings, it can also be used to do
conventional whole-cell patch-clamp recordings or perforated patch recordings. The whole-
cell configuration allows to investigate even small dissociated or cultured cells as well as cells
in slice preparations in both current and voltage clamp mode, while the intracellular medium
is being controlled by the pipette solution.
2.1. Why a Single-Electrode Clamp?
Voltage clamp techniques permit the analysis of ionic currents flowing through biological
membranes at preset membrane potentials. Under ideal conditions the recorded current is
directly related to the conductance changes in the membrane and thus gives an accurate
measure of the activity of ion channels and electrogenic pumps.
The membrane potential is generally kept at a preselected value (command or holding
potential). Ionic currents are then activated by sudden changes in potential (e.g. voltage-gated
ion channels), by transmitter release at synapses (e.g. electrical stimulation of fiber tracts in
brain slices) or by external application of an appropriate agonist. Sudden command potential
changes used to activate voltage-gated currents are especially challenging, because the
membrane will adopt the new potential value only after its capacitance (Cmin Figure 1 and
Figure 2) has been charged. Therefore, the initial transient current following the voltage step
should be as large as possible to achieve rapid membrane charging. In conventional patch-
clamp amplifiers, this requires a minimal resistance between the amplifier and the cell interior
– a simple consequence of Ohm’s law (∆U = R*I), i.e. for a given voltage difference (∆U),
the current (I) is inversely proportional to the resistance (R). In this context, R is the access
resistance (Rain Figure 1 and Figure 2) between the electrode and the cell interior.
Rais largely determined by certain electrode properties (mainly electrode resistance) and the
connection between the electrode and the cell. Sharp microelectrodes usually have much
larger resistances (30 to 150 MΩor even more) than patch-clamp electrodes. This makes
rapid charging of the cell membrane to attain a new voltage level more difficult than in patch-
clamp experiments.

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Figure 1: Model circuit for whole-cell patch-clamp recording.
Cm: membrane capacitance, Cstray: electrode stray capacitance, Ra: access
resistance, Rm: membrane resistance
Figure 2: Model circuit for intracellular recording using a sharp electrode
Cm: membrane capacitance, Cstray: electrode stray capacitance, Ra: access
resistance, Rm: membrane resistance
Besides slowing down the voltage response of the cell, Racan also cause additional adverse
effects, such as error in potential measurement. Ra, together with the membrane resistance
(Rm) forms a voltage divider (see Figure 1 and Figure 2). Current flowing from the amplifier
to the grounded bath of a cell preparation will cause a voltage drop at both, Raand Rm. If Ra
<< Rm, the majority of the voltage drop will develop at Rmand thus reflect a true membrane

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potential. If, in an extreme case, Ra= Rm, the membrane potential will follow only one half of
the voltage command. In order to achieve a voltage error of less than 1% Ramust be more
than 100 times smaller than Rm. This condition is not always easy to accomplish, especially if
recordings are performed from small cells. If sharp intracellular microelectrodes are used, it is
virtually impossible. If Rais not negligible, precise determination of the membrane potential
can be achieved only if no current flows across Raduring potential measurement. This is the
strategy employed in npi electronic’s SEC amplifier systems.
The SEC amplifiers inject current and record the potential in an alternating mode (switched
mode). Therefore, this technique is called discontinuous SEVC (dSEVC). This ensures that no
current passes through Raduring potential measurement and completely eliminates access
resistance artefacts.
After each injection of current, the potential gradient at the electrode tip decays much faster
than the potential added at the cell membrane during the same injection. The membrane
potential is measured after the potential difference across Rahas completely dropped (see
chapter 2.2). The discontinuous current and voltage signals are then smoothed and read at the
CURRENT OUTPUT and POTENTIAL OUTPUT connectors.
2.2. Principle of Operation
Figure 3: Model circuit of SEC systems

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Figure 4: Principle of dSEVC operation
Figure 3 and Figure 4 illustrate the basic circuitry and operation of npi SEC voltage clamp
amplifiers.
A single microelectrode penetrates the cell or is connected to the cell interior in the whole-cell
configuration of the patch-clamp technique. The recorded voltage is buffered by an x1
operational amplifier (A1 in Figure 3). At this point, the potential (V[A1] in Figure 4) is the
sum of the cell’s membrane potential and the voltage gradient which develops when current is
injected at the access resistance. Due to npi’s unique compensation circuitry, the voltage at
the tip of the electrode decays extremely fast after each injection of current and therefore
allows for a correct measurement of Vcell after a few microseconds. At the end of the current-
free interval, when the electrode potential has dropped to zero, the sample-and-hold circuit
(SH1 in Figure 3) samples Vcell and holds the value for the remainder of the cycle (VSH1 in
Figure 4).
The differential amplifier (A2 in Figure 3) compares the sampled potential with the command
potential (Vcom in Figure 3). The output of this amplifier becomes the input of a controlled
current source (CCS in Figure 3), if the switch S1 (Figure 3) is in the current-passing position.
The gain of this current source increases as much as 100 µA/V due to a PI (proportional-
integral) controller and improved electrode capacity compensation. In Figure 3 S1 is shown in
the current-passing position, when a square current is applied to the electrode. When the
current passes the electrode a steep voltage gradient develops at the electrode resistance. Vcell
(Figure 4) is only slightly changed due to the slow charging of the membrane capacitance.
The amplitude of injected current is sampled in the sample-and-hold amplifier SH2 (Figure
3), multiplied by the fractional time of current injection within each duty cycle (1/8 to 1/2 in
SEC-05 and SEC-10, 1/4 in SEC-03 systems) and read out as current output (ISH2 in Figure 4).
S1 then switches to the voltage-recording position (input to CCS is zero). The potential at A1
decays rapidly due to the fast relaxation at the (compensated) electrode capacity. Exact
capacity compensation is essential to yield an optimally flat voltage trace at the end of the

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current free interval when Vcell is measured (see also Figure 13). The cellular membrane
potential, however, will drop much slower due to the large (uncompensated) membrane
capacitance. The interval between two current injections must be long enough to allow for
complete (≤1%) settling of the electrode potential, but short enough to minimize loss of
charges at the cell membrane level, i.e. minimal relaxation of Vcell. At the end of the current-
free period a new Vcell sample is taken and a new cycle begins. Thus, both current and
potential output are based on discontinuous signals that are stored during each cycle in the
sample-and-hold amplifiers SH1 and SH2. The signals will be optimal smooth at maximal
switching frequencies.
Major advantages of the npi SEC System
Npi electronic’s SEC amplifiers are the only systems that use a PI controller to avoid
recordings artefacts known to occur in other single-electrode clamp systems (“clamping of the
electrode”). The PI controller design increases gain to as much as 100 µA/V in frequencies
less than one-fourth the switching frequency. The result is very sensitive control of the
membrane potential with a steady-state error of less than 1% and a fast response of the clamp
to command steps or conductance changes.
The use of discontinuous current and voltage clamp in combination with high switching
frequencies yields five major advantages:
1. The large recording bandwidth allows accurate recordings even of fast signals.
2. High clamp gains (up to 100 µA/V) can be used in voltage clamp mode.
3. Very small cells with relatively short membrane time constants can be voltage-
clamped.
4. Series resistance effects are completely eliminated for a correct membrane potential
control even with high resistance microelectrodes.
5. The true membrane potential is recorded also in the voltage clamp mode (whereas
continuous feedback VC amplifiers only reflect the command potential).
3. SEC-05X System
3.1. SEC-05X Components
The following items are shipped with the SEC-05X system:
✓SEC-05X amplifier
✓Headstage
✓GND- and DRIVEN SHIELD (2.6 mm banana plug) connectors
Please open the box and inspect contents upon receipt. If any components appear damaged or
missing, please contact npi electronic or your local distributor immediately
([email protected]).

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Optional accessories:
➪Electrode holder set with one holder for sharp microelectrodes (without port), one patch
electrode holder (with one port) and an electrode holder adapter (SEC-EH-SET)
➪Active cell model (SEC-MODA)
➪Passive cell model (SEC-MOD, see chapter 6)
➪Low noise / low bias current headstage (SEC-HSP) with a reduced current range (:10
headstage, i.e. maximal current is ±12 nA)
➪Headstage for extracellular measurements (SEC-EXT)
➪Mini headstage set (SEC-MINI-SE)
➪Filter for the EPMS system
➪Data acquisition module
➪Stimulus isolator module
➪Iontophoresis module
➪Pressure ejection module
➪CellWorks hard- and software

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3.2. Description of the Front Panel
Figure 5: SEC-05X front panel view

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In the following description of the front panel elements each element has a number that is
related to that in Figure 5. 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. Each control element has a label and often a calibration (e.g.
CURRENT OUTPUT, 10 nA/V).
(1) POWER pressure switch
Switch to turn POWER on (switch pushed) or off (switch released).
VOLTAGE CLAMP unit
(2) VC OUTPUT LIMITER potentiometer
Under certain experimental conditions, it is necessary to limit the current in
the voltage clamp mode (e.g. in order to prevent the blocking of the electrode
or to protect the preparation). This is possible with an electronic limiter,
which sets the current range between 0-100%.
(3) VC ERROR display
The VC ERROR display shows the error in the VC (voltage clamp) mode
(command minus recorded potential). The desired range of operation is
around zero.
(4) GAIN potentiometer
10-turn potentiometer to set amplification factor (GAIN) of the VC error
signal. To keep the VC error as small as possible it is necessary to use
high GAIN settings, but the system becomes unstable and begins to
oscillate if the GAIN is set too high. Thus, the OSCILLATION SHUT-
OFF circuit (see #17-19) should be activated when setting this control.
(5) INTEGRATOR TIME CONST. (ms) switch and potentiometer
Potentiometer for setting the INTEGRATOR TIME CONSTANT in VC mode;
range: 0.1 to 10 ms, switchable to off-position.
(6) HOLDING POTENTIAL (mV) potentiometer and polarity switch
10-turn digital control that presets a continuous command signal
(HOLDING POTENTIAL (XXX mV, maximum: 999 mV) for VC).
Polarity is set by switch to the right of the control (0 is off-position).

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(7) POTENTIAL FILTER switch
16-position switch to set the corner frequency of the Bessel filter. The setting
is monitored by #42.
(8) MODE OF OPERATION switch
The MODE OF OPERATION switch has 6 positions. The active mode of
operation is indicated by a red LED next to the operation mode name.
VCcCC:Voltage Clamp controlled Current Clamp (optional)
VC:Voltage Clamp
CC:Current Clamp
BR:Bridge Mode
EXT:External Mode
DHC:Dynamic Hybrid Clamp (optional)
VCcCC mode (optional) (see chapter 8.3)
Voltage Clamp controlled Current Clamp mode. This mode allows
accurate current clamp experiments at controlled resting potentials. The
time constant is set by the VCcCC TIME CONST. (sec) switch (51) on
the left of the front panel.
BR mode
In the BR (=bridge) mode the electrode resistance is
compensated with the BRIDGE BALANCE control (#23).
The range can be set to 10 MΩ(100 = 10 MΩ, max resistance
99 MΩ) for low resistance patch microelectrodes or to the
range of 100 MΩ(100 = 100 MΩ, max. resistance 999 MΩ)
for sharp microelectrodes using a toggle switch (#21).
EXT mode
External mode (see also Figure 6). In external mode CC or VC mode can be
selected by a TTL signal applied to the MODE SELECT TTL / DHC TTL
connector (#41) below the MODE OF OPERATION switch; TTL low: CC
mode, TTL high: VC mode
DHC mode (optional) (see chapter 8.1)
Dynamic Hybric Clamp mode (see also additional sheet). In DHC mode CC or
VC mode is also selected by a TTL signal applied to the MODE SELECT
TTL / DHC TTL connector (#41) below the MODE OF OPERATION switch;
TTL low: CC mode, TTL high: DHC mode

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(9) CURRENT (nA) display
LED-Display for the CURRENT passed through the electrode in nA.
(10) POTENTIAL / RESISTANCE display
LED-Display for the POTENTIAL at the electrode tip in mV or the
electrode RESISTANCE in MΩ
Note: When measuring electrode resistance in LINEAR x10 mode, the reading at the
RESISTANCE display (#10) must be multiplied by 10 to obtain the correct value. Example:
display reading 01.5 MΩmeans a resistance of 15 MΩ.
(11) mV / MΩLEDs
LEDs indicating that POTENTIAL (mV) or RESISTANCE (MΩ) is revealed in
display #10
(12) REL switch
Toggle switch for activating the resistance measurement of the microelectrode.
When pushed the microelectrode resistance is measured and shown in the
POTENTIAL / RESISTANCE display (#10).
Important: An accurate measurement of REL requires that the input capacity is well
compensated (see also #27 and chapter 7.6)
(13) CURRENT FILTER (Hz) switch
16-position switch to set the corner frequency of the Bessel filter. The setting
is monitored by #37.
(14) DUTY CYLE switch
In the discontinuous modes (VC and CC modes) this switch sets the
ratio between current injection and potential recording mode (12.5%;
25% or 50% of each switching period).
(15) SWITCHING FREQUENCY potentiometer
Potentiometer for setting the switching frequency in VC or CC mode; range
circa 10 Hz to 70 kHz, indicated on display #40.

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(16) CURRENT OUTPUT SENSITIVITY (V/nA) switch
7-position switch to set the CURRENT OUTPUT gain. The setting is monitored
by #36.
OSCILLATION SHUT-OFF unit
In SHUTOFF condition the amplifier is set into CC mode and all outputs
(including holding current) and CAPACITY COMPENSATION are disabled.
The inputs and the ELECTRODE RESISTANCE test are activated.
(17) THRESHOLD potentiometer
Control to set the activation THRESHOLD of the OSCILLATION SHUTOFF
circuit potentiometer, linear clockwise, range: 0-1200 mV).
(18) OSCILLATION SHUTOFF LED
Indicates whether the OSCILLATION SHUTOFF circuit is in SHUTOFF
condition (LED red) or not (LED green).
(19) DISABLED / RESET switch
Switch to DISABLE the OSCILLATION SHUTOFF unit or to RESET the
circuit. A RESET is carried out if one wants to reset the circuit after a previous
SHUTOFF condition. After resetting the OSCILLATION SHUT-OFF unit is
active again.
PENETRATION / ELECTRODE CLEAR unit
This unit is used to clean the tip of the electrode and to facilitate the puncture of the cell
membrane.
(20) PENETRATION push button activates the unit
(22) ELECTRODE CLEAR rotary switch:
oBUZZ mode: overcompensation of the capacity compensation effective
in all six modes of operation (VCcCC, VC, CC, BR, EXT, DHC).
o+Imax / -Imax modes: Application of maximum positive or negative current
to the microelectrode (+/- 100 nA, standard headstage).
oOFF
(26) DURATION potentiometer sets duration of pulse
(29) REMOTE TTL connector (active LOW) for connection of a remote switch
(21, 23) BRIDGE BALANCE potentiometer and toggle switch: see #8
(24) HEADSTAGE BIAS CURRENT potentiometer

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With this 10 turn potentiometer the output current of the headstage (headstage BIAS current)
can be tuned to 0 (see chapter 7.1).
(25) OFFSET potentiometer
Control to compensate the electrode potential (ten-turn potentiometer,
symmetrical, i.e. 0 mV = 5 on the dial), range: ±200 mV (see chapter 7.3).
(26) DURATION potentiometer (see #20)
(27) CAPACITY COMPENSATION potentiometer
Control for the capacity compensation of the electrode (ten turn
potentiometer, clockwise, range: 0-30 pF, see chapter 7.6).
Caution: This circuit is based on a positive feedback circuit. Overcompensation leads to
oscillations that may damage the cell.
(28) HEADSTAGE connector
The HEADSTAGE is connected via a flexible cable and a 12-pole connector to
the mainframe (see also chapter 4).
Caution: Please always adhere to the appropriate safety regulations (see chapter 1). Please
turn power off when connecting or disconnecting the potential headstage from the
POTENTIAL HEADSTAGE connector!
(29) REMOTE TTL connector for PENETRATION unit: see #20
CURRENT CLAMP unit
CURRENT STIMULUS INPUT unit
(30) Toggle switch to activate INPUT #31
(31, 33) BNC connectors for an external CURRENT STIMULUS INPUT in
CC mode. Sensitivity: 0.1 nA/V (#31) or 1 nA/V (#33)
(32) Toggle switch to activate INPUT #33
(34) HOLDING CURRENT (nA) potentiometer and polarity switch
10-turn digital control that presets a continuous command signal
(HOLDING CURRENT (X.XX nA, maximum: 10 nA) for CC.). Polarity
is set by switch to the left of the control (0 is off-position).

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(35) CURRENT OUTPUT connector
BNC connector providing the CURRENT OUTPUT signal after passing the
CURRENT FILTER (see #13) and the CURRENT OUTPUT SENSITIVITY
switch (see #16).
(36) CUR. SENS. MON. +1 V…+7 V
BNC output connector monitoring the setting of CURRENT OUTPUT
SENSITIVITY V/µA switch (#16). Resolution 1 V / STEP (i.e. 3V indicate a
GAIN of 0.5).
(37) FREQ. MON. -8 V…+7 V
BNC output connector monitoring the setting of CURRENT FILTER Hz switch
(#13). Resolution 1 V / STEP (i.e. 5 V indicate a filter frequency of 10 kHz).
(38, 39) LINEAR MODE (optional, see chapter 8.2)
Switch (#39) to set the amplifier into the LINEAR mode. The LINEAR mode is
indicated by the LINEAR MODE LED (#38) above (green: x1, red: x10).
Note: When measuring in LINEAR x10 mode, several changes to the scaling of displays,
inputs and outputs apply. Please see chapter 8.2 for detailed information.
(40) SWITCHING FREQUENCY (kHz) display
LED-Display for the SWITCHING FREQUENCY in kHz in
discontinous VC or CC mode.
(41) MODE SELECT TTL / DHC TTL connector: see #8
(42) FREQ. MON. -8 V…+7 V connector
BNC output connector monitoring the setting of POTENTIAL FILTER Hz switch
(#7). Resolution 1 V / STEP (i.e. 5 V indicate a filter frequency of 10 kHz).
(43) POTENTIAL OUTPUT x 10 mV connector

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BNC connector monitoring the POTENTIAL at the tip of the electrode
(sensitivity: x10 mV).
Important: In LINEAR MODE x10, the voltage output (POTENTIAL OUTPUT x10 mV
BNC connector) is set to x1 mV, i.e. 1 V is 1 V (and not 100 mV as in LIN mode x1).
VC COMMAND INPUT unit
(44) Toggle switch to activate INPUT #45
(45, 47) BNC connectors for an external COMMAND INPUT in VC
mode. Sensitivity: ÷10 mV (#45) or ÷40 mV (#47)
(48) Toggle switch to activate INPUT #47
(46) RISE TIME (ms) potentiometer
Sometimes it is necessary to limit the rise time of a voltage clamp pulse
especially in connection with PI-controllers to avoid overshooting of the
potential.
(49) GROUND connector
Banana jack providing the internal GROUND (not connected to PROTECTIVE
EARTH).
(50) AUDIO potentiometer
Volume control for the AUDIO MONITOR. The potential at the electrode is
monitored by a sound. The pitch of sound is related to the value of the potential.
(51) VCcCC TIME CONST. rotary switch: see #8

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3.3. Description of the Rear Panel
Figure 6: SEC-05X rear panel view (the numbers are related to those in the text below).
(1) FUSE holder
Holder for the line fuse and line voltage selector. For changing the fuse or selecting line
voltage open the flap using a screw driver. The fuse is located below the voltage selector. Pull
out the holder (indicated by an arrow), in order to change the fuse. For selecting the line
voltage, rotate the selector drum until the proper voltage appears in the front.
(2) Mains connector
Plug socket for the mains power-plug.
Important: Check line voltage before connecting the TEC amplifier to power. Always use a
three-wire line cord and a mains power-plug with a protection contact connected to ground.
Disconnect mains power-plug when replacing the fuse or changing line voltage. Replace fuse
only by appropriate specified type. Before opening the cabinet unplug the instrument.
(3) PROTECTIVE EARTH connector
Banana plug providing mains ground (see below).
(4) INTERNAL GROUND connector
Banana plug providing internal ground (see below).
(5-8) MODE OF OPERATION (TTL IN) connectors
BNC connectors for external control of MODE OF OPERATION (see #8, front panel).
(9) ELECTRODE POTENTIAL (V) connector
BNC connector monitoring the electrode potential, i.e. the response of the electrode to the
discontinuous current injection.
(10) SWITCHING FREQUENCY (TTL) connector
BNC connector monitoring the selected switching frequency (+5 V pulses), used to trigger the
oscilloscope which displays the switching pulses of the ELECTRODE POTENTIAL output
#9(see chapter 7.6)