Scitec 441 User manual

Boston Electronics Corporation, 91 Boylston Street, Brookline MA 02445
[phone] or [phone] * fax [phone] * bosele[email protected] * www.boselec.com
Bartles Industrial Estate Tel: [phone] [e-mail]
North Street, Redruth Fax: [phone] www.scitec.uk.com
Cornwall TR15 1HR Fax2: [phone]
MODEL 441 ANALOG OEM
DUAL PHASE LOCK-IN AMPLIFIER
&
MODEL 430 ANALOG OEM
SINGLE PHASE LOCK-IN AMPLIFIER
USER MANUALV1.2

Boston Electronics Corporation, 91 Boylston Street, Brookline MA 02445
[phone] or [phone] * fax [phone] * bosele[email protected] * www.boselec.com
Bartles Industrial Estate Tel: [phone] [e-mail]
North Street, Redruth Fax: [phone] www.scitec.uk.com
Cornwall TR15 1HR Fax2: [phone]
CONTENTS
1 POWER SUPPLY
1.1 Power Connections
1.2 Earth Connections for High Voltage / ESD Protection
2 BOARD LAYOUT
3 OPERATION
3.1 Block Diagrams
3.2 Lock-in Amplifier Theory
4 INPUT STAGE
4.1 Jumper Settings Overview
4.2 Single Ended DC Coupled Input
4.3 Single Ended AC Coupled Input
4.4 Single Ended Current Input
4.5 Differential Input
4.6 Low Impedance Differential Input
5 FIRST STAGE AMPLIFICATION
6 LOW PASS FILTER TIME CONSTANT SETTINGS
6.1 First Time Constant Settings
6.2 Second Time Constant Settings
7 OUTPUT STAGE
7.1 Output Stage Amplification
7.2 Fine Gain Adjust
7.3 Offset Adjust
7.4 R Calculation
7.5 R Calculation Time Constant
8 REFERENCE SECTION
8.1 Fine Phase Control
8.2 Coarse Phase Control and 1F/2F Operation
9 OVERALL SYSTEM GAIN AND DYNAMIC RESERVE
9.1 Dynamic Reserve
9.2 Maximum Signal Size Up To The Low Pass Filter
9.3 Maximum Signal Size From Low Pass Filter to Output
9.4 Example Gain Settings

Boston Electronics Corporation, 91 Boylston Street, Brookline MA 02445
[phone] or [phone] * fax [phone] * bosele[email protected] * www.boselec.com
Bartles Industrial Estate Tel: [phone] [e-mail]
North Street, Redruth Fax: [phone] www.scitec.uk.com
Cornwall TR15 1HR Fax2: [phone]
1 POWER SUPPLY
1.1 Power Connections
A well regulated ±15V & +5V supply is required to power the lock-in amplifier board. 50mA
per supply is required for the 441 and 35mA per supply are required for the 430. Power is
supplied via a 64 pin type C DIN41612 connector as follows:
0V Pin 32A & Pin 32C
+5V Pin 31A & Pin 31C
+15V Pin 30C
-15V Pin 30A
No other pins on the DIN41612 connector are used.
Please note that the pin numbers are labelled on the back of the connector next to the solder
pins and as per Figure 1. Please also note that some connectors have P1~A on the front face.
Rather confusingly, this A is actually next to row C pins.
Figure 1 Power Connections
1.2 Earth Connections for High Voltage / ESD Protection
As lock-in amplifiers are often used in optics applications with lasers driven by high voltage
power supplies, it is sometimes important to protect equipment from high voltage discharges.
Electro-Static Discharge (ESD) protection is also important and is a requirement for CE
marking. All inputs and outputs to the 430 and 441 are protected by transient suppression
devices but for full protection a case earth connection is required directly to the PCB.
To give full protection to the board from high voltages, a thick earth wire should be bonded to
the board at one or other or both of the points shown in Figure 2 and connected to case or
chassis ground by as short a lead as possible. The two links also indicated should be added to
the board. Please note that these earth connections are not connected to signal ground on the
PCB.

Boston Electronics Corporation, 91 Boylston Street, Brookline MA 02445
[phone] or [phone] * fax [phone] * bosele[email protected] * www.boselec.com
Bartles Industrial Estate Tel: [phone] [e-mail]
North Street, Redruth Fax: [phone] www.scitec.uk.com
Cornwall TR15 1HR Fax2: [phone]
Figure 2 Case Earth Connections
2 BOARD LAYOUT
The 441 board layout is shown in Figure 3.
Figure 3 441 Board Layout
L1 Input mode selection jumpers
L2 Input gain select jumpers
L3 Channel X output gain select and time constant jumpers
L4 Channel Y output gain select and time constant jumpers
L5 Reference channel mode select jumpers
VR1 Signal feed through trim pot
VR2 Channel X offset adjust trim pot
VR3 Channel X gain adjust trim pot
VR4 Channel Y offset adjust trim pot
VR5 Channel Y gain adjust trim pot
VR6 0° - 150° fine phase adjust trim pot

Boston Electronics Corporation, 91 Boylston Street, Brookline MA 02445
[phone] or [phone] * fax [phone] * bosele[email protected] * www.boselec.com
Bartles Industrial Estate Tel: [phone] [e-mail]
North Street, Redruth Fax: [phone] www.scitec.uk.com
Cornwall TR15 1HR Fax2: [phone]
The 430 board layout is shown in Figure 4.
Figure 4 430 Board Layout
L1 Input mode selection jumpers
L2 Input gain select jumpers
L3 Channel X output gain select and time constant jumpers
L5 Reference channel mode select jumpers
VR1 Signal feed through trim pot
VR2 Channel X offset adjust trim pot
VR3 Channel X gain adjust trim pot
VR6 0° - 150° fine phase adjust trim pot

Boston Electronics Corporation, 91 Boylston Street, Brookline MA 02445
[phone] or [phone] * fax [phone] * bosele[email protected] * www.boselec.com
Bartles Industrial Estate Tel: [phone] [e-mail]
North Street, Redruth Fax: [phone] www.scitec.uk.com
Cornwall TR15 1HR Fax2: [phone]
3 OPERATION
3.1 Block Diagrams
Figure 5 441 Block Diagram
Figure 6 430 Block Diagram
3.2 Lock-in Amplifier Theory
For lock-in amplifier theory please visit a number of pages on the Internet produced by M.
Stachel of Faculty of Physics University of Konstanz Germany. It is available at

Boston Electronics Corporation, 91 Boylston Street, Brookline MA 02445
[phone] or [phone] * fax [phone] * bosele[email protected] * www.boselec.com
Bartles Industrial Estate Tel: [phone] [e-mail]
North Street, Redruth Fax: [phone] www.scitec.uk.com
Cornwall TR15 1HR Fax2: [phone]
http://fp.physik.uni-konstanz.de/LockIn/indexx.shtml and includes theory, diagrams and a
virtual Java lock-in amplifier.

Boston Electronics Corporation, 91 Boylston Street, Brookline MA 02445
[phone] or [phone] * fax [phone] * bosele[email protected] * www.boselec.com
Bartles Industrial Estate Tel: [phone] [e-mail]
North Street, Redruth Fax: [phone] www.scitec.uk.com
Cornwall TR15 1HR Fax2: [phone]
4 INPUTSTAGE
The input stage amplifies the input signal to a level suitable for the demodulator section.
The input signal should be connected to the SMB signal input connector.
The input sensitivity is set by using the input sensitivity jumpers.
The input stage of the unit can operate in a number of ways. By default, the unit is factory set so
that the input stage acts as a single ended DC coupled input as this is the lowest noise method
of operation. It is also possible to operate the input stage in AC coupled mode, differential
mode and current mode. To operate the lock-in in these different modes requires jumpers on the
unit to be modified. This can be achieved as follows:
4.1 Jumper Settings Overview
A simplified input stage circuit diagram is shown in Figure 7. This shows all of the jumpers in
the input stage.
Figure 7 Input Stage Jumper Options
These jumpers are part of jumper block L1.

Boston Electronics Corporation, 91 Boylston Street, Brookline MA 02445
[phone] or [phone] * fax [phone] * bosele[email protected] * www.boselec.com
Bartles Industrial Estate Tel: [phone] [e-mail]
North Street, Redruth Fax: [phone] www.scitec.uk.com
Cornwall TR15 1HR Fax2: [phone]
4.2 Single Ended DC Coupled Input
The default setting is for a single ended DC coupled input. This mode gives the best noise
performance. Although the input is DC coupled, the input will not saturate with up to the
following DC offsets on the input:
Input Gain Setting Maximum DC Input Offset Before
Saturation Occurs
x0.001 to x3.3 ±10V
x10 to x100 ±1V
x330 ±300mV
The input impedance of the lock-in in this mode is 1012Ω||1nF.
The jumper settings for this mode is given in Figure 8. The equivalent circuit is shown in Figure
9.
(default setting)
Figure 8 Single Ended DC Coupled Input Settings
Figure 9 Single Ended DC Coupled Input Circuit
4.3 Single Ended AC Coupled Input
For applications where large amounts of DC offset are expected on the input, the input stage
can be AC coupled with an RC network. Please note that the high value resistor will add a large
amount of thermal noise to the input. (This mode of operation is common to a lot of other
manufacturer’s lock-in amplifiers. When measuring the input noise of their instruments, it is
standard practice to short the input which has the nice result of removing the thermal noise of
this resistor from their measurements. However, how often do you make measurements with the
input shorted in real life??)

Boston Electronics Corporation, 91 Boylston Street, Brookline MA 02445
[phone] or [phone] * fax [phone] * bosele[email protected] * www.boselec.com
Bartles Industrial Estate Tel: [phone] [e-mail]
North Street, Redruth Fax: [phone] www.scitec.uk.com
Cornwall TR15 1HR Fax2: [phone]
In this mode of operation the input can have up to ±12V DC offset before saturation occurs on
all input gain settings.
The input impedance of the lock-in in this mode is 6.8x106Ω||100nF.
The jumper settings for this mode is given in Figure 10. The equivalent circuit is shown in
Figure 11.
Figure 10 Single Ended AC Coupled Settings
Figure 11 Single Ended AC Coupled Circuit
4.4 Single Ended Current Input
The input stage can also be used as a current input due to the high impedance of the input stage
opamps. The current input is converted to a voltage by the 6.8MΩresistor which has a
tolerance of 1%. This mode of operation has not been fully characterised by Scitec Instruments
and is not guaranteed.
The input impedance of the lock-in in this mode is 6.8x106Ω||1nF.
The jumper settings for this mode is given in Figure 12. The equivalent circuit is shown in
Figure 13.