Anfatec USB LOCKIN 250 User manual

USB LOCKIN 250
LOCKIN AMPLIFIER AMPLIFIER 10 mHz to 250 kHz
Anfatec Instruments AG
Melanchthonstr. 28
08606 Oelsnitz /V.
Germany
Tel.: [phone]
Tel.: [phone]
http://www.anfatec.de
email: [e-mail]
Manual USB Lockin 250 – Rev. 1.03 dated 07/11/13 Page 1 (37)

•Table o Contents
•General Information ...............................................................................................................4
•Specification of the USBLockIn250 ......................................................................................4
•General Parameters ....................................................................................................................4
•Signal Input ...............................................................................................................................4
•Reference Output .......................................................................................................................5
•External Triggering by PLL .........................................................................................................5
•Analogue Outputs .......................................................................................................................5
•General ......................................................................................................................................5
•Standard Part List .......................................................................................................................5
•Licence for the software .....................................................................................................5
•Installation ............................................................................................................................6
•System requirements .........................................................................................................6
•Software Installation ..........................................................................................................6
•Driver Installation ..............................................................................................................6
•Get Started .......................................................................................................................7
•Connections to the USBLockIn250 ......................................................................................7
•Driver Update ....................................................................................................................8
•LockIn Amplification Basics .....................................................................................................9
•The general idea of Lockin Amplification -> LockIn ..............................................................9
•Mathematical description ..................................................................................................10
•Noise Measurements ........................................................................................................11
•Example: Electrical Force Microscope ................................................................................12
•Hardware Description ...........................................................................................................14
•Auxiliary Outputs .............................................................................................................14
•Software Description ............................................................................................................15
•Overview .........................................................................................................................15
•Functions in the Menu Line ...............................................................................................15
•File ..........................................................................................................................................15
•Option ......................................................................................................................................15
•View ........................................................................................................................................16
•Help .........................................................................................................................................16
•Functions in the Function Line ..........................................................................................16
•Frequency Sweep .....................................................................................................................16
•Oscilloscope .............................................................................................................................16
•Parameter settings ...........................................................................................................17
•Time constant ...........................................................................................................................17
•RollOff .....................................................................................................................................18
•Dynamic ...................................................................................................................................18
•Coupling ...................................................................................................................................18
•The Meters ...............................................................................................................................18
•Frequency ................................................................................................................................19
•Amplitude .................................................................................................................................19
Manual USB Lockin 250 – Rev. 1.03 dated 07/11/13 Page 2 (37)

•Phase .......................................................................................................................................19
•Harmonic .................................................................................................................................19
•Sweep Frequency ............................................................................................................19
•Window Description ..................................................................................................................19
•Options for the frequency sweep ...............................................................................................20
•DLL Description ...................................................................................................................23
•Working with the DLL in C projects ..............................................................................23
•DLL-Functions .................................................................................................................24
•Example programs ...........................................................................................................27
•Remote Control with LabView ...............................................................................................28
•Files and Locations ..........................................................................................................28
•General Programming Directions in LabView ......................................................................28
•Description of Example VI Files .......................................................................................30
•Multiple LockIn Amplifiers in LabView ...............................................................................35
•Revision History ...................................................................................................................35
Copyright 2002-2013 Anfatec Instruments AG. All rights reserved. Anfatec, and AMU are
trademarks of Anfatec. 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 USB Lockin 250 – Rev. 1.03 dated 07/11/13 Page 3 (37)

GENERAL INFORMATION
GENERAL INFORMATION
SPECIFICATION OF THE USBLOCKIN250
GENERAL PARAMETERS
Digital Dual-Phase Lock-In Amplifier
Dynamic Reserve > 135 dB (1)
Input Noise (low noise mode) < 4 nVrms/Hz0.5 @ 100 kHz
Remote Control USB 2.0
Time Constants 10 µs ... 5 s / 1 µs in sync mode
Sensitivity 10 nV ... 10 V
Phase Resolution 0.0001°
Amplitude Deviation (0..250 kHz) < 1 %
Phase Deviation (0..250 kHz) < 0.5 °
Maximum Frequency 2 MHz
SIGNAL INPUT
Voltage Input BNC
Input coupling: dc or ac (f-3dB = 2 Hz)
Input Impedance 1 MΩ || 20 pF
Damage Threshold /- 12 V
Input sampling rate 20 MHz
Bandwidth dc to 250 kHz (f-3dB > 250 kHz)
Input Ranges ± 3.5 Vrms, ± 350 mVrms, ± 35 mVrms
Input Sensitivity 10 nV to 10 V
Typical Input Noise: Uac = 0 V, 50 Ω @ input see table→
RollOff 6 dB/oct, 12 dB/oct, 24 dB/oct
Time Constants 10 µs ... 5 s
Amplitude Accuracy (dc to 250 kHz) < 1 %
Gain deviations between dynamic ranges: < 1 %
Phase shift accuracy (dc to 250 kHz) < 0.5°
Input Noise measured with Uac = 0 V and 50 Ω @ input
Frequency Filter \ Range High dynamic reserve Normal Low Nosie
250 kHz 10 ms < 60 nVrms/Hz0.5 < 7 nVrms/Hz0.5 < 5 nVrms/Hz0.5
100 kHz 10 ms < 60 nVrms/Hz0.5 < 7 nVrms/Hz0.5 < 5 nVrms/Hz0.5
10 kHz 10 ms < 60 nVrms/Hz0.5 < 8 nVrms/Hz0.5 < 6 nVrms/Hz0.5
1 kHz 1 s < 1 µVrms/Hz0.5 < 160 nVrms/Hz0.5 < 15 nVrms/Hz0.5
Manual USB Lockin 250 – Rev. 1.03 dated 07/11/13 Page 4 (37)

REFERENCE OUTPUT
Internal Oscillator 10 mHz .. 250 kHz (1 MHz)
Frequency Resolution < 10 mHz
Frequency Accuracy /- 50 ppm from 0 °C to 70 °C
Amplitude Accuracy (dc to 250 kHz) < 0.5 %
Reference Output Voltage < 1 mVpp ... 15 Vpp
Output Noise @ 100 kHz @ Uac = 1 mV, < 200 nVrms/Hz0.5
Output sampling rate 20 MHz
EXTERNAL TRIGGERING BY PLL
Frequency range 1 Hz .. 1 MHz
Locking time < (100 ms 10 Cycle)
Phase error < 4 deg @ f < 1 kHz
Input amplitude TTL and Sine Wave (> 50 mVrms)
Phase delay ~ 1 µs
ANALOGUE OUTPUTS
Sampling rate 1 MHz (1 µs group delay)
Output Voltage -10 V … 10 V
Output Noise < 300 nV/sqrt(Hz)
Accuracy < 2 %
GENERAL
Interface Plug & Play USB 2.0 interface
Drivers Windows NT/2000, Windows XP, Win7
32 bit
Power consumption 12 Vdc, 1 A
Warranty 2 years
STANDARD PART LIST
USBLockIn250 1
Power Supply 12 V dc 1
USB cable M-M , 2 m long 1
Manual 1
Software on USB-stick 1
Low-Noise BNC cable 2 m long 1
LICENCE FOR THE SOFTWARE
The Source code for the remote control software and the DLL source code are provided with the
General Public Licence (GPL). All examples for LabView can be freely implemented and changed by
the user.
Manual USB Lockin 250 – Rev. 1.03 dated 07/11/13 Page 5 (37)

INSTALLATION
INSTALLATION
SYSTEM REQUIREMENTS
–compatible PC
–1 MB hard disk space
–Windows NT 4.0 / Windows 2000 or Windows XP (32 bit) / Windows 7 (32 bit)
SOFTWARE INSTALLATION
On the delivered USB Stick, you find
Driver in F:\Driver Use “setup.bat” or “setup7.bat” (Win7)
to install the driver.
Test software in F:\ Start “lockin.exe” to test the device
NOTE: In Windows7, the ini-file “user.ini” might be copied automatically in another directory. If you want to
avoid this, make the directory that contains the ini-file writeable by any user.
Source Code of the lockin.exe in F:\Delphi
LabView examples in F:\LabView the examples base on a DLL
Source code of the DLL in F:\DLL\DLLSource
Examples using the DLL in F:\DLL\Delphi
The easiest way is to copy the whole content into a suitable directory (%YourPath), e.g.
“C:/Users/USBLockin”. If working under Windows 7, one needs to set the user rights as follows:
•right click on the top most folder and select properties
•select the tab “Security”
•select “Users” and click on “Edit”
•allow “Full control” and use “Apply” and “OK” to verify
DRIVER INSTALLATION
Connect the USB lockin first. If the system asks for a driver, select the “USBLockin.sys” in the
directory “C:\Users\USBLockin\Disk”. If the system does not ask automatically, one has two
possibilities:
A) install through device manager
•open the device manager
•select the “Unknown Device” and right click to “Update Driver Software”
•“Browse for driver software on your computer”
•provide the path “%YourPath/Driver/”
•select the driver “USB Lockin”
•Say OK when Windows recommends not to install from an unknown driver vendor
B) install with setup program in “C:\Users\USBLockin\Driver”
In Windows XP and Windows 2000 start “setup.bat”.
In Windows 7 start “setup7.bat”.
Allow the setup.bat program to do changes on your PC. During installation, a command window is
opened and closed when finished. For the 1st installation, this procedure might take about 20
seconds.
Manual USB Lockin 250 – Rev. 1.03 dated 07/11/13 Page 6 (37)

GET STARTED
☑Connect the power supply to “Power”
☑Connect the USB interface to your PC
☑When the PC asks for a driver, install the driver provided on
the USB-Stick under “Driver” with “setup.bat” (Windows XP) or
“setup7.bat” (Windows 7)
☑One needs to start the test software “lockin.exe” once as
Administrator1
CONNECTIONS TO THE USBLOCKIN250
Power – requires 12 V dc, 1 A. Innerpin is
positive.
USB – interface for remote control via USB2.0
Re -In ... is the TTL or sine wave input that
allows to trigger the USBLockIn250 from any
external source. In order to use it, one has to
set the PLL ON with the software.
TTL-Out ... is a TTL type (rectangular 5 V
wave) trigger output for other devices. Use
Ref-Out, when a sine wave is required.
R/X ... is the analogue output No 1. It
displays the Panel meter 1 or the Auxiliary
Output 0, if these outputs are used as
customer specific outputs. It provides an
analogue signal of the software-selected
channel with the software-selected scaling.
Phi/Y ... is the analogue output connected to
Panel meter 2 or the Auxiliary Output 1, if
these outputs are used as customer specific
outputs. It provides an analogue signal of the
software-selected channel with the software-
selected scaling.
LEDs … the left LED (central above the IN connector) indicates that the power supply is
connected. The right LED (less intense) indicates that the USB interface is connected.
IN ... is the analogue input of the lockin in which the signal to be detected is plugged in.
Re Out ... is a sine wave output whose amplitude is set by software and whose frequency equals
the currently selected centre frequency of the lockin amplifier.
1 This copies the scaling data for the lockin amplifier into the registry of the PC. Afterwards, all other
applications and all users can use these registry entries.
Manual USB Lockin 250 – Rev. 1.03 dated 07/11/13 Page 7 (37)
Figure 3: Front side of the USBLockIn250. The left LED is
the power LED. Right LED indicates that the USB
connection is ON.
Figure 2: Backside of the USBLockIn250
Figure 1: Power Supply for 12 V dc.
USB-Connector.
PhaseX
Δφ

DRIVER UPDATE
One has two possibilities:
A) install through device manager
☑open the device manager
☑select the “Unknown Device” and right click to “Update Driver Software”
☑“Browse for driver software on your computer”
☑provide the path “%YourPath/Driver/”
☑select the driver “USB Lockin”
☑Say OK when Windows recommends not to install from an unknown driver vendor
B) install with setup program in “C:\Users\USBLockin\Disk”
☑In Windows XP and Windows 2000, start “setup.bat” in the path of the new driver
☑In Windows 7, start “setup7.bat” in the path of the new driver
Manual USB Lockin 250 – Rev. 1.03 dated 07/11/13 Page 8 (37)

LOCKIN AMPLIFICATION BASICS
LOCKIN AMPLIFICATION BASICS
THE GENERAL 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 j, 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 j 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. 10).
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 11 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 3 on
page 7. 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 USB Lockin 250 – Rev. 1.03 dated 07/11/13 Page 9 (37)
Figure 4: Schematic diagram with the basic components of the lock-in amplifier.

MATHEMATICAL DESCRIPTION
A digital LockIn realises its 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 ωref and detect with a narrow
band filter at this frequency.
Thus, X(t) is modulated as X(t) = X0X1 cos(wref 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 2pwref. Due to the modulation of X(t) at
wref, modulations of Y(t) at the frequencies m wref with m = 1,2,... are expected. These
modulations equal the Fourier components Y(m wref) with m = 1,2,... of the input signal Y(t),
which are given as
Ym=1
∫
−/2
/2
YXte−i mtdt
Manual USB Lockin 250 – Rev. 1.03 dated 07/11/13 Page 10 (37)
YX0X1cosref t=∑
k=0
∞
YkX0⋅X1
k
k !⋅coskref t⋅YkX= dkY
dX k∣X0k∈N
X
YR
φ
Figure 5: Output signal of a LockIn amplifier for a single frequency input signal of 100 kHz
and 20 mVrms amplitude at the input. The time constants have been kept constant.