Anfatec AMU2.4 User manual

PCI-BUS LOCKIN AMPLIFIER 1 Hz TO 1 MHz
Anfatec Instruments AG
Melanchthonstr. 28
08606 Oelsnitz /V.
Germany
Tel.: [phone]
Fax.: [phone]
http://www.anfatec.de
email: [email protected]
Manual Anfatec PCI-Lockin Amplifier AMU2.4 – Rev. 1.10 dated 30/09/20 Page 1 (70)

Table of contents
1 General Information .............................................................................................................. 6
1.1 Specification of the AMU2.4-LIA ..................................................................................... 6
1.1.1 Signal Input ........................................................................................................................ 6
1.1.2 Reference Output ............................................................................................................... 6
1.1.3 PLL .................................................................................................................................... 6
1.1.4 General .............................................................................................................................. 7
1.2 Licence for the software ................................................................................................ 7
2 Get started ........................................................................................................................... 8
2.1 System requirements ..................................................................................................... 8
2.2 Software installation ...................................................................................................... 8
2.3 Card and Driver installation ............................................................................................ 8
2.3.1 Check your APIC configuration ............................................................................................. 8
2.3.2 Card Installation ................................................................................................................. 8
2.3.3 Driver Installation .............................................................................................................. 9
2.4 Connections to the card ................................................................................................. 9
2.5 APIC configuration ....................................................................................................... 10
3 LockIn Amplification Basics ................................................................................................... 11
3.1 The general idea of Lockin Amplification -> LockIn ........................................................ 11
3.2 Mathematical description ............................................................................................. 12
3.3 Time constant Definition .............................................................................................. 13
3.4 RollOff Definition ........................................................................................................ 13
3.5 Noise Measurements ................................................................................................... 14
4 Software Description (Lockin.exe) .......................................................................................... 15
4.1 Overview .................................................................................................................... 15
4.2 Functions in the Menu Line .......................................................................................... 16
4.2.1 File ................................................................................................................................... 16
4.2.2 Option .............................................................................................................................. 16
4.2.3 View ................................................................................................................................. 16
4.2.4 Help ................................................................................................................................. 16
4.3 Functions in the Function Line ...................................................................................... 16
4.3.1 Frequency Sweep .............................................................................................................. 16
4.3.2 Oscilloscope ...................................................................................................................... 16
4.4 Parameter settings ....................................................................................................... 18
4.4.1 Time constant ................................................................................................................... 18
4.4.2 RollOff .............................................................................................................................. 18
4.4.3 Dynamic ........................................................................................................................... 18
4.4.4 Coupling ........................................................................................................................... 18
Manual Anfatec PCI-Lockin Amplifier AMU2.4 – Rev. 1.10 dated 30/09/20 Page 2 (70)

4.4.5 The Meters ....................................................................................................................... 18
4.4.6 Frequency ........................................................................................................................ 19
4.4.7 Amplitude ......................................................................................................................... 19
4.4.8 Phase ............................................................................................................................... 19
4.4.9 Harmonic .......................................................................................................................... 19
4.5 Sweep Frequency ........................................................................................................ 19
4.5.1 Window Description .......................................................................................................... 19
4.5.2 Options for the frequency sweep ........................................................................................ 20
5 Examples ............................................................................................................................ 23
5.1 Demonstrate time constant .......................................................................................... 23
5.2 Demonstrate RollOff .................................................................................................... 24
5.3 Resonance Detection ................................................................................................... 25
5.4 Thermal noise ............................................................................................................. 26
5.4.1 Simulation of the noise voltage in qucs ............................................................................... 26
5.4.2 Noise Voltage Detection ..................................................................................................... 27
Calculation of the noise voltage ............................................................................... 28
5.5 Fourieranalyse of a square signal .................................................................................. 29
5.6 Acoustic resonance ...................................................................................................... 30
6 DLL Description .................................................................................................................... 33
6.1 Working with the DLL in C projects .......................................................................... 33
6.2 DLL-Functions ............................................................................................................. 34
6.3 Example programs ....................................................................................................... 37
7 Remote Control with LabView ................................................................................................ 38
7.1 Files and Locations ...................................................................................................... 38
7.2 General Programming Directions in LabView .................................................................. 39
7.3 Description of Example VI Files .................................................................................... 40
Example Time Constant .......................................................................................... 42
Example Fourier Analysis of a square signal ............................................................. 42
7.4 Multiple LockIn Amplifiers in LabView ............................................................................ 48
8 Remote Control in Python 3 .................................................................................................. 49
8.1 Files and Locations ...................................................................................................... 49
8.2 Call DLL Functions in Python ........................................................................................ 49
8.3 Multiple Devices in Python ........................................................................................... 49
8.4 Python Example Files ................................................................................................... 50
8.4.1 Spectrum Analyzer ............................................................................................................ 50
Simple Frequency sweep ....................................................................................... 51
Example FourierAnalyse .......................................................................................... 51
8.4.2 Transient Recorder ............................................................................................................ 52
8.4.3 Network Analyzer .............................................................................................................. 52
Manual Anfatec PCI-Lockin Amplifier AMU2.4 – Rev. 1.10 dated 30/09/20 Page 3 (70)

Example Measurement Resonance ........................................................................... 52
Example Acoustic Resonance .................................................................................. 53
8.4.4 Parametric Sweep (Only USBLockin) ................................................................................... 55
Example Diode AUX ................................................................................................ 55
8.4.5 Multiple Devices ................................................................................................................ 57
8.4.6 Experiment: Distance Measurement .................................................................................. 58
9 Remote Control in Scilab ....................................................................................................... 59
9.1 Files and Locations ...................................................................................................... 59
9.2 Call DLL Functions in Scilab .......................................................................................... 59
9.3 Scilab Example Files .................................................................................................... 59
9.3.1 Spectrum Analyzer ............................................................................................................ 59
9.3.2 Transient Recorder ............................................................................................................ 60
9.3.3 Networkanalyzer ............................................................................................................... 60
9.3.4 Parametric Sweep (Only USBLockin) ................................................................................... 61
10 Example: Electrical Force Microscope ................................................................................... 62
11 Revision History .................................................................................................................. 64
11.1 Manual-related Revisions ............................................................................................ 64
11.1.1 Till 19th June 2007 .......................................................................................................... 64
11.1.2 10th April 2008 .............................................................................................................. 64
11.1.3 10th Frebruary 2009 ...................................................................................................... 64
11.2 Hardware Revisions ................................................................................................... 64
11.2.1 1st November 2006 – Rev 2.2 to Rev 2.3 ......................................................................... 64
11.2.2 1st December 2006 – Rev 2.3 to Rev 2.3a ....................................................................... 65
11.2.3 14th April 2007 – Rev. 2.3a to Rev 2.4 ............................................................................ 65
11.2.4 10th April 2008 – Rev 2.4 ................................................................................................ 65
11.3 Software Revisions ..................................................................................................... 65
11.3.1 10th April 2008 – Version 1.02 ......................................................................................... 65
11.3.2 11th May 2009 – Version 1.04 ......................................................................................... 65
11.3.3 11th July 2009 – Version 1.05 .......................................................................................... 65
11.3.4 26th August 2009 – Version 1.06 ..................................................................................... 66
11.3.5 May 2013 ...................................................................................................................... 66
11.4 Driver Revisions ......................................................................................................... 66
11.4.1 November 2013 ............................................................................................................. 66
12 Troubleshooting .................................................................................................................. 66
12.1 Device driver ............................................................................................................. 66
12.2 Application ................................................................................................................ 69
12.2.1 App ................................................................................................................................ 69
12.2.2 DLL ............................................................................................................................... 69
Manual Anfatec PCI-Lockin Amplifier AMU2.4 – Rev. 1.10 dated 30/09/20 Page 4 (70)

Copyright 2002-2020 Anfatec Instruments AG. All rights reserved. Anfatec is a registered
trademarks of Anfatec Instruments AG. Other product and brand names may be trademarks or
registered trademarks of their respective owners. Anfatec Instruments AG assumes no
responsibility for any damage or loss resulting from use of this manual. Anfatec Instruments AG
assumes no responsibility for any damage or loss resulting from use of the software. Anfatec
Instruments AG assumes no responsibility for any damage or loss by deletion of data as a result of
malfunction, dead battery, or repairs. Be sure to make backup copies of all important data on
other media to protect against data loss. Important: Please read Anfatec Licence Agreement
contained in this handbook before using the accompanying software programs. Using any part of
the software indicates that you accept the terms of Anfatec Software Licence Agreement.
Manual Anfatec PCI-Lockin Amplifier AMU2.4 – Rev. 1.10 dated 30/09/20 Page 5 (70)

1
1 ENERAL INFORMATION ENERAL INFORMATION
1.1 SPECIFICATION OF THE AMU2.4-LIA
eneral
Digital Quad(1)-Phase Lock-In Amplifier
Dynamic Reserve > 135 dB (1)
Noise < 6 nVrms/Hz0.5 @100kHz (1)
Time Constants 0.1 ms ... 1 ks (1)
Sensitivity 10 nV ... 10 V
Phase Resolution 0.001°
1.1.1 SI NAL INPUT
Voltage Input single-ended SMB
Input coupling: dc or ac (f3dB = 2 Hz)
Input Impedance 100 k || 20 pF (1) / 1 M on requ.
Damage Threshold /- 12 V
Bandwidth dc to 1 MHz (f3dB > 1 MHz)
Input Ranges ± 5 V, ± 500 mV, ± 50 mV (1)
Input Sensitivity 10 nV to 10 V
Typical Input Noise: Uac = 0 V, 50 W @ input
@ 100 kHz, high dynamic < 300 nVrms/Hz0.5
@ 100 kHz, normal dynamic < 50 nVrms/Hz0.5
@ 100 kHz, low dynamic < 8 nVrms/Hz0.5
RollOff 6 dB/oct, 12 dB/oct, 24 dB/oct
Time Constants 0,2 ms ... 5 s
Gain deviations between dynamic ranges: < 5%
1.1.2 REFERENCE OUTPUT
Internal Oscillator 10 mHz .. > 1 MHz
Frequency Resolution < 10 mHz
Frequency Accuracy /- 50 ppm from 0 °C to 70 °C
Reference Output Voltage < 1 mVpp ... 15 Vpp
Output Noise Uac = 1 mV
@ 100 kHz < 200 nVrms/Hz0.5
1.1.3 PLL
Frequency range 1 Hz .. 1 MHz
Locking time < (100 ms 10 Cycle)
Phase error < 4 deg @ f < 1 kHz
Input amplitude TTL
Phase delay ~ 1 µs
(1)See Revision History on Page 27
Manual Anfatec PCI-Lockin Amplifier AMU2.4 – Rev. 1.10 dated 30/09/20 Page 6 (70)

1.1.4 ENERAL
Interface Plug & Play PCI-Bus 2.4 interface
Drivers Windows NT/2000, Windows XP,
Windows 7 & Windows 10 - both 32 bit & 64 bit
Interrupt rate 40 kHz
Warranty 2 years
1.2 LICENCE FOR THE SOFTWARE
The LockIn software is provided with the General Public Licence (GPL). This licence has been
developed within a project of the "Free Software Foundation". It gives the user the liberty, to add
changes in the code and the programmer the security, not to get in trouble due to the users
changes.
Most commercial software packages don't use this licence, because they want to keep the right to
sell the newer version later as update. An open software can be changed by the user. So, he can
adapt the software to his problem. Free software, has to stay free, even if the user add some
changes. Therefore, GPL protects the software so, that all programs which are based on a GPL
protected source code has to provided with the same GPL again. The licence also hinders software
patenting.
Manual Anfatec PCI-Lockin Amplifier AMU2.4 – Rev. 1.10 dated 30/09/20 Page 7 (70)

2
2 ET ET START STARTED ED
2.1 SYSTEM REQUIREMENTS
–compatible PC
–free PCI slot
–APIC installed (recommended) - for details see here
–1 MB hard disk space
–Windows NT 4.0 / Windows 2000 or Windows XP / Windows 7
2.2 SOFTWARE INSTALLATION
There are two ways for installation:
automatic. Start the setup.exe in the root directory of the installation CD.
Manual: Before installing the driver, install the software. Put the installation disk named “Software
for the AMU2.4” in the disk drive and and copy at least the four needed files
lockin.exe, lockin.ini, lockin.sys and lockin.inf
into a new directory, for instance: C:\Programme\Anfatec\LockIn . On the installation CD, you find
these files under the directories: /bin (*.exe, *.ini) and /driver (*.sys, *.inf).
If you later want to use the source code, you find it in the directory /sources. Please contact us for
newer versions.
2.3 CARD AND DRIVER INSTALLATION
2.3.1 CHECK YOUR APIC CONFI URATION
The APIC improves the interrupt control in your system. The APIC will dramatically increase the
performance of the PC. It is installed together with the Power Manager while Windows installation.
Check it as follows:
•Windows 2000
Open “Einstellungen / Systemsteuerung / System / Hardware” (“Configuration / System control /
System / Hardware”) and start the “Geräte Manager” (“Device Manager”). It appears a list of
devices. The information about the APIC is in the submenu “Computer”.
•Windows XP
Open “Systemsteuerung / System / Hardware” (“System control / System / Hardware”) and start
the “Geräte Manager” (“Device Manager”). It appears a list of devices. The information about the
APIC is in the submenu “Computer”.
The APIC is installed, if the “ACPI-Uniprocessor-PC” is shown in “Computer”. If only “Standard PC”
is found there, even the changes of the BIOS will not help, to make Windows use the APIC. If you
find the entry “Standard PC”, you can follow the instructions in the APIC configuration.
2.3.2 CARD INSTALLATION
Switch off the PC.
Remove the power completely, because PC's keep the supply voltages at the PCI slots on, if the PC
is only shut down.
Manual Anfatec PCI-Lockin Amplifier AMU2.4 – Rev. 1.10 dated 30/09/20 Page 8 (70)

Plug the card in one of the PCI-slots of your PC and switch on again. Start the setup.exe on the
CD. All related files are copied to the related directories.
2.3.3 DRIVER INSTALLATION
•Windows 2000/ Windows XP
While Windows boots, it finds new hardware. Log in as administrator. WindowsTM will mention,
that it has found new hardware on your computer. If the software is not yet on your computer, you
can copy the recommended files now to your hard disk.
Check the second point, which means “Treiber aus einer Liste auswählen”. Say OK and give the
path to the “lockin.inf” (for instance: C:\Programme\Anfatec\LockIn\Driver) with the button
“Durchsuchen” (“Search”). Check the driver “LockIn Interface” and finish with “Fertigstellen”
(“Finish””).
•Later re-installation of a driver
Log in as administrator and call in the “System control” the topic "system". Chose the card
“hardware“ and open the “device manager”. It shows all hardware components installed on your
PC. With a double click on the "Anfatec Measurement Unit", the submenu "Anfatec Measurement
Unit" or “Anfatec LockIn” is opened. A second double click opens a window, which shows the
properties of the device.
Select the card “Driver” and start the button “Driver actualisation”. A dialogue is opened, which
asks: “Do you want to actualise the driver?”. In the next window please check the second option
“Search for a suitable driver” and click “OK”. At the question, where the driver is, the right path
has to be given as “other sources”. It is the path, where the new *.inf file is located. Eventually,
you have to select again the right device from a list of possible devices. Check the Anfatec
Measurement Unit again and say “OK” and “Finish”. The PC has to be rebooted in order to activate
the new driver.
2.4 CONNECTIONS TO THE CARD
Manual Anfatec PCI-Lockin Amplifier AMU2.4 – Rev. 1.10 dated 30/09/20 Page 9 (70)
Figure 1: Photograph of the LockIn board and description of the location of the single parts.

Connect the reference output to the excitation
input of your experiment. The signal input has
to be connected to the signal to be analysed.
The microscope control is used for the external
D/A- and A/D-channels, which can be updated
any time.
This card supports digital data outputs, only.
The connector “Controller” provides a digital
reference output signal as 2.8 V LVTTL wit the
same frequency like the sine wave at the “Out”
connector.
2.5 APIC CONFI URATION
Attention: this change is critical for your system. It can cause that your computer
refuses to boot. Only administrators should perform this action.
The way to switch on the APIC later, if the system has been installed as “Standard PC” without
Power Management, is described in detail in the computer magazine C't 19/03 on page 190/191 in
German. It works as follows:
Double click on the “Standard PC” icon and say “actualise driver” (Treiber aktualisieren). Check the
second line: “Show all known drivers”. Say OK and check again, that all known hardware
components for this device class are shown (“Alle Hardwarekomponenten dieser Geräteklasse
anzeigen.”. It appears a list on the right sight, which shows “standard PC”, “ACPI-Uniprocessor-PC”
and others. Select now the “ACPI-Uniprocessor-PC” and say OK. Because this change can cause a
real damage on your system, the computer will ask you “Do you really want to exchange this
driver?”. Say “Yes” and complete with “finish”.
When the computer restarts, you have to go into the BIOS setup now! Press “Entf” or
“Del” button on your keyboard during system reboot. In the BIOS, switch on the ACPI mode with
“ACPI Aware O/S = Yes” under the Power Management menu. For most BIOS types, this is only
one point to change. But for some BIOS, the APIC, which is part of the ACPI, has to be switched
on separately. Therefore, check your BIOS settings careful, that the APIC is really switched on.
If the computer does not reboot alone now, you have to reset and to repair your system from the
Windows Installation CD.
Remark: Wrong BIOS settings can cause, that Windows refuses to repair the system from CD. It
will stop with “could not find ntkrnlmp.exe – error code 7” for instance.
Manual Anfatec PCI-Lockin Amplifier AMU2.4 – Rev. 1.10 dated 30/09/20 Page 10 (70)
Figure 2: Connections to the LockIn card.
• Figure 3: Pinout of the connector "Controller"
or "Microscope Out".

3
3 LOCKIN AMPLIFICATION BASICS LOCKIN AMPLIFICATION BASICS
3.1 THE ENERAL IDEA OF LOCKIN AMPLIFICATION ->
LOCKIN
A lockin amplifier is a phase sensitive bandpass filter with a centre frequency f and a bandwidth t.
It has two output signals in parallel: either the amplitude R and the phase φ, or the real part X and
the imaginary part Y.
•The centre frequency is the frequency at which the LockIn is searching for its signal.
•The bandwidth gives the frequency range around this centre frequency, from which the output
signal is derived.
•The output signal R is the measured amplitude of the analysed signal at the centre frequency f.
•The phase φ is the relative phase shift between the analysed signal and an internal reference
signal with the same frequency.
For analysing the input signal, the LockIn needs an internal frequency reference with a
certain amplitude and phase. (see Fig. 4).
The bandwidth of a LockIn can be visualised by a simple setup. A generator gives a constant
frequency fin signal to the input and sweeping the centre frequency f around the input frequency
fin. Figure 5 shows that the amplitude at the input frequency is always measured with the same
value. For other frequencies, the measured amplitude is dependent on the distance between the
actual centre frequency and the input signal frequency.
A schematic diagram with the basic components of the lock-in amplifier is shown in Figure 4. First
of all the received signal is amplified and digitized. Divided into two separate channels, the signal
is multiplied by the mentioned reference signal (with frequency ω
ref
) and the 90° phase-shifted
reference signal respectively. The reference signal is generated with the lock-in's digital oscillator.
An additional implemented phase displacement Ψ enables to compensate phase differences caused
by the measuring equipment. After multiplication, the resulting signals are low-pass filtered and
provide now information about the real part X and the imaginary part Y of the analysed signal
relating to the phase position of the reference signal. Out of them the amplitude R as well as the
relative phase shift φ are calculated.
Manual Anfatec PCI-Lockin Amplifier AMU2.4 – Rev. 1.10 dated 30/09/20 Page 11 (70)
Figure 4: Schematic diagram with the basic components of the lock-in amplifier.
*
*
sin(h*  ref +y)
LP X
Y
LP
X/Y -> R/

DAC
ADC
digital
analogue
digital oscillator
amplification
amplification
input gain
input gain
sin(  ref)
cos(h*  ref +y)
Phase shifter
hamonic h
Phase y
frequency
X
R
Y

Lockin input signals
Lockin output signals
(digital outputs)
signal in
reference out
TTL out
Ref In - TLL

3.2 MATHEMATICAL DESCRIPTION
A digital LockIn realises it's filtering by certain mathematical procedures.
Think, Y(t), the signal to be analysed, is dependent on a value X(t). For instance: we measure a
photo voltage U(t) which depends on the light intensity given by an LED I(t). If the background
light intensity is much too high to detect small intensity changes of the LED light, one can
modulate the light intensity I(t) at a certain frequency ref and detect with a narrow band filter at
this frequency.
This X(t) is modulated as X(t) = X0X1 cos(w
ref t). Then, Y(X(t) can be developed into a Taylor-
Series:
Equ.(1)
For the value of Y at the time t, all measurement values Y(t) detected in the period

are used.
This period t should be a whole-numbered multiple of 2pw
ref. Due to the modulation of X(t) at w ref,
modulations of Y(t) at the frequencies m w
ref with m = 1,2,... are expected. These modulations
equal the Fourier components Y(m w
ref) with m = 1,2,... of the input signal Y(t), which are given
as:
Y(mω)=1
τ∫
−τ /2
τ/ 2
Y(X(t))e−i m ωtdt
and together with Equ. 1
Ymref =∑
k=0
∞
YkX0X1
k
k! Km
k
with
Km
k=1
∫
−/2
/2
cosk ref te−i m ref tdt
.
The factors Kmk get zero for k to infinity. For small k, the Kmk remain too big to be neglected. In
order to neglect n-th order parts, the n-th derivative of Y(t) to X(t) has to be negligible.
The first 10 (k = 1 ... 10) coefficients Kmk for the first 4 harmonics m = 1 ... 4 are given in the
following table:
k =
m12345678910
1
1
2
3
8
5
16
35
128
63
256
2
1
4
1
4
15
64
7
32
105
512
3
1
8
5
32
21
128
21
128
4
1
16
3
32
7
64
15
128
Manual Anfatec PCI-Lockin Amplifier AMU2.4 – Rev. 1.10 dated 30/09/20 Page 12 (70)
YX0X1cosref t=∑
k=0
∞
YkX0⋅X1
k
k !⋅coskref t⋅YkX= dkY
dX k∣X0k∈N

3.3 TIME CONSTANT DEFINITION
The "Time constant t" is a parameter of the low pass filter after demodulation. It defines the
detection bandwidth fDet of the lockin amplifier.
In order to visualize this detection bandwidth, the input of the lockin amplifier is connected to a
constant input signal (here: 1 Vrms amplitude, 100 kHz). The internal reference frequency is swept
over the input frequency.
A signal, which is fDet off the centre frequency of the lockin amplifier, will be detected with 0.707
times it amplitude.
3.4 ROLLOFF DEFINITION
The slope of the signal decay in Fig. 5 is defined by the Roll-Off without affecting the detection
bandwidth.
Manual Anfatec PCI-Lockin Amplifier AMU2.4 – Rev. 1.10 dated 30/09/20 Page 13 (70)
frequency [kHz]
99
100 101
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
6 dB
12 dB
24 dB
t = 5 ms
1/ t
frequency [kHz]
85 90 95 100 105 110 115
1 -5
1 -4
1 -3
1 -2
1 -1
1 +0 6 dB
12 dB
24 dB
Figure 5: Visualization of the Detection Bandwidth for various time constant settings.
frequency [kHz]
99.5 100 100.5
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
2 ms
5 ms
10 ms
0,707 V
1 V
1/ t

3.5 NOISE MEASUREMENTS
Lock-in amplifiers are capable to measure noise. They detect a signal at the centre frequency
fref = ωref / 2π with an equivalent noise bandwidth. The equivalent noise bandwidth (ENBW) of a
Butterworth low pass filter is the bandwidth which passes the same amount of noise as a perfect
rectangular filter with the equivalent bandwidth.
The bandwidth of the lockin amplifier is determined by the slope and the equivalent noise
bandwidth of the used Butterworth filter.
The normalized Butterworth filter noise bandwidths are:
Filter order n → RollOff equivalent noise bandwidth
Butterworth Filter (ENBWBW)
1/sqrt(ENBWBW)
1 → 6 dB/oct 1,570796 0,79607
2 → 12 dB/oct 1,110721 0,948849
4 → 24 dB/oct 1,026172 0,987165
In order to scale noise spectra, the resulting data should be divided by the square-root of the used
LockIn bandwidth.
fB=2
τ⋅ENBW BW
un=umeas
√
fB
=umeas ⋅
√
τ
2⋅1
√
ENBW BW
The integrated spectrum is taken with a time constant of 5 ms and a
slope of 24 dB/oct (4th order). The ENB factor is 1,03. The related
bandwidth is then: fB = 412Hz. In order to interpret an measurement of
2µV as noise in units of V/√Hz, the value should be divided by √412Hz. It
results a value of 98,5nV/√Hz.
Manual Anfatec PCI-Lockin Amplifier AMU2.4 – Rev. 1.10 dated 30/09/20 Page 14 (70)
frequency [kHz]
99 100 101
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
1
t
BW
.
NBW
1
t
BW
.
NBW
= 2x
( )
1
t
f B
1
t

4
4 SOFTWARE DESCRIPTION SOFTWARE DESCRIPTION (LOCKIN.EXE) (LOCKIN.EXE)
4.1 OVERVIEW
The GUI software lockin.exe opens with the following surface:
Figure 6 shows the main window of the LockIn program, which appears when the program is
opened. For checking the actually detected values, the two meters are used. Basic input
parameters (frequency, amplitude, offset phase and harmonic) can be selected in the right part of
the window. Parameters, which concern the input stage (time constants, RollOff, and input gain)
are chosen in the left part of the window.
The frequency is either the internal frequency (black numbers) or the detected external frequency
from the reference input (grey numbers).
The menu line allows typical Windows functions, while the button in the function line opens new
windows with specific functions.
This software can be started as often as many USBLockIn250 are attached to the system. In order
to start various USBLockIn250 with dedicated parameters, follow these steps:
1. Create as many desktop shortcuts to the lockin.exe as many devices you
wish to operate
2. Right-click on each desktop shortcut and choose “Properties”
3. Add a parameter (e.g. user2) behind the entry in the target line:
4. Start each shortcut once, select the device to be associated with this shortcut:
The same procedure can be used to open the software with different settings.
Manual Anfatec PCI-Lockin Amplifier AMU2.4 – Rev. 1.10 dated 30/09/20 Page 15 (70)
Figure 6: Main window of the LockIn program with description of the functions.

4.2 FUNCTIONS IN THE MENU LINE
4.2.1 FILE
Exit - Exit the program
4.2.2 OPTION
•overload
Overload occurs, when the dc input signal exceeds the full scale sensitivity for the selected range.
This full scale sensitivity is 7 Vrms for high reserve, 700 mVrms for normal reserve and 70 mVrms for
low reserve. With this option can be selected whether a beep and/or a color change is shown in
case of overload.
•ext. reference
For LockIn-amplifier versions with PLL (Phase locked loop), the reference frequency can be either
the internal oscillator frequency or an external reference frequency. If the “ext. reference” is
selected, the internal PLL is enabled. The locked frequency is shown in grey in the frequency
window. If there is no input signal connected to the reference input, a default frequency of 2 mHz
is shown, but the LockIn is not working properly.
With disabled PLL, the frequency given in the frequency window is written in black.
4.2.3 VIEW
It can be selected, which of the meters is shown.
•Devices
Select whether the strings for the lockin amplifier(s) should be shown. Useful when using multiple
lockin amplifiers to select which one should be used. Is also used for LabView (see chapter
“Multiple LockIn Amplifiers in LabView“).
4.2.4 HELP
“About” – shows the current program version and the version of the used hardware driver
“LockIn help” – calls the table of contents of the HTML help file supplied with the program
“Help as PDF” – calls the current manual (Manual.pdf) and opens it in the Microsoft Internet
Explorer
4.3 FUNCTIONS IN THE FUNCTION LINE
4.3.1 FREQUENCY SWEEP
Opens the "frequency sweep" window
4.3.2 OSCILLOSCOPE
The oscilloscope works like a real 3-channel-oscilloscope. Content, scaling type and offset of the
three channels is selectable.
Manual Anfatec PCI-Lockin Amplifier AMU2.4 – Rev. 1.10 dated 30/09/20 Page 16 (70)

Channel selection: is done from a drop down list, which shows only the available channels.
The two numbers above the drop down list for channel selection display the “scaling factor per
vertical division” (= left number, hint: “y-scale in /div”, example: 12.90 nV/div) and the mean
value. Both are calculated from all data acquired from the left oscilloscope edge till the current
oscilloscope time. Therefore, these numbers are subsequently re-calculated.
Vertical scaling types:
•0..max the scaling is set to maximum value of the channel
•0..fixed the maximum value can be changed by a slider appearing on the right
sight of the scaling type selection
•0..auto the program calculates the the optimum, but takes always “0” as minimum
•auto..auto automatically scaled
“Time scaling” is done with the edit window (right sight) in seconds.
“Save Pic” saves the oscilloscope screen in a bitmap file.
“Draw mode” selects whether the data are drawn as dots or lines.
Right-click on the right number to change its meaning from RMS
to Mean or StdDev.
Manual Anfatec PCI-Lockin Amplifier AMU2.4 – Rev. 1.10 dated 30/09/20 Page 17 (70)
Figure 7: Screen shot of the software oscilloscope

4.4 PARAMETER SETTIN S
4.4.1 TIME CONSTANT
This option selects the used time constant t for the low-pass filter. If applicable, the closest
approximation of the digital equivalent to an analogue Butterworth filter is used. The corner
frequency of the Butterworth filter is 1/t.
4.4.2 ROLLOFF
The meaning of the "RollOff" is shown in the curves in this Figure. It equals the degree of the
lowpass filter. One can chose between 6 dB/oct (1st order), 12 dB/oct (2nd order) and 24 dB/oct (4th
order).
4.4.3 DYNAMIC
This switches the input amplification of the LockIn. With "high" dynamic, input amplification is 1.
The maximum signal amplitude is then /-10 V. The "normal" input amplification is 10, which
equals maximum signal amplitudes of /- 1 V. When the low dynamic is chosen, the resolution of
the LockIn is highest, but the signals cannot exceed 100 mV.
4.4.4 COUPLIN
If the specification of the instrument allows it, this option switches between DC coupled input and
AC coupled input. Note: The 3dB corner frequency of the input high pass is around 2Hz. Reference
frequencies around 2 Hz and below may cause misleading results.
4.4.5 THE METERS
The meters display the LockIn output channels, which are X and Y as well R and Phi, in physical
units.
Manual Anfatec PCI-Lockin Amplifier AMU2.4 – Rev. 1.10 dated 30/09/20 Page 18 (70)
Figure 8: Effect of different time constants.

4.4.6 FREQUENCY
If written in black letters, this is the actual reference frequency which is used at the reference
output and as reference frequency for the signal evaluation of the input.
Click with the right mouse button to switch from external to internal reference. In case of internal
reference, the numbers are written in grey.
4.4.7 AMPLITUDE
This is the amplitude of reference output.
4.4.8 PHASE
Allows to give a phase offset between the reference output and the input. In the schematic in Fig.
4 , this phase is equal to the LockIn input parameter “Phase y”.
4.4.9 HARMONIC
Selects, which harmonic of the reference frequency is evaluated. The possible values range from 1
to 15. When selecting higher harmonics, take care, that, due to lowpass filtering, the maximum
input frequency the LockIn cannot be higher than 2 MHz.
4.5 SWEEP FREQUENCY
This window serves the acquisition of frequency dependent spectra of any of the LockIn input
channels. The frequency sweep uses the internal reference. When the PLL is enabled for normal
operation, it will be disabled during frequency sweep.
The number of data points, parameters for the visualisation as well as for the saving and copying
the acquired data can be changed in the option window.
4.5.1 WINDOW DESCRIPTION
“Delay”: is the time delay between each acquired data point. During spectrum acquisition, the
frequency is set to the next value. Then, the system waits “Delay” and takes one single value from
the acquired Channel.
As this delay has to be related to the time constant of the LockIn, the options in the drop down list
for the delay are given in multiples of t. Thus, independently on the time constant t given in the
main window, the time constant for the acquisition of the spectrum is always correct.
“from” and “to” define the values of the start frequency and the stop frequency. For the
spectrum's acquisition, one chooses the wanted frequency range, and presses the “start-button”. If
the time constant was very high, the spectrum might take a while. In order to stop the acquisition,
the start-button can be pressed a second time.
“Channel” is a drop down list of available data channels (X, Y, R, and Phi).
“Range back” - click with the right mouse button in the data screen, and a pop-up menu with
list of four frequency ranges appears. The upper one is a standard range, which can be changed in
the “Option/acquire” part. The next three are, from the bottom to the top, the last three used
frequency ranges.
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4.5.2 OPTIONS FOR THE FREQUENCY SWEEP
The option window provides three cards: “save” - parameters about the saving and copying
format of data, “acquire” – parameters about the data acquisition, and “view” – parameters
around the screen of showing the data.
Save-Tab:
The saved files and the data copied to the clipboard have an ASCII structure. The data are written
in lines (each frequency value one line) and delimited by the given delimiter (“TAB” in the
example) are saved. The frequency values are only saved, if “Save x-Axis” is checked. All history
data are saved too and also delimited the same character.
Data file example:
1000,00 234,09
1200,00 237,98 ...
Manual Anfatec PCI-Lockin Amplifier AMU2.4 – Rev. 1.10 dated 30/09/20 Page 20 (70)
Figure 9: Window for the spectra acquisition.