User Manual
Contents
1. 314608 E mail scitec scitec uk com Fax 01209 314609 Web http www scitec uk com SIGNAL GROUND CASE GROUND AND EARTH For safety reasons the metal case that houses the lock in amplifier is permanently connected to electrical earth via the power connector No modifications should be made to this connection as otherwise it may be possible for the case to become live under fault conditions The signal ground used within the instrument can however be isolated safely from the case ground and earth The signal ground is the signal ground mentioned in section fjand is the ground connection made to the reference BNC 12 and the output BNC 8 Three different methods of connection are possible and are selected by jumpers within the unit Accessing Input Stage Jumpers The input stage includes jumpers which enable the mode of operation of the input stage to be modified To access the jumpers 1 Switch off and disconnect power before opening unit 2 Remove the 10 screws holding the lid on then remove lid Do not disconnect earth strap 3 Change the jumper settings as per the diagrams in the following sections The location of the earth jumpers are shown in Do not operate the unit with the lid removed due to the power voltages accessible within the unit 4 Replace lid and the 10 screws Translormer Larg Capacitors Earth Jumpers No Front of Unit Figure 13 Location of Earth Jumpers Si2. Input Circuit 3 7 Low Impedance Differential Input If you wish to stop the inputs from floating but do not wish to connect the signals grounds together then it is possible to achieve this by connecting the grounds together via a 100Q resistor by removing the link between pins 5 and 6 and linking pins 6 and 7 For example the jumper settings for the Low Impedance Differential DC coupled input are shown in Figure 11 and the equivalent circuit is shown in Figure 12 The other modes are similar AE 6 amp 7 Linked 5 4 3 if 1 amp 2 Linked Figure 11 Low Impedance Differential DC Coupled Input Settings ex Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www boselec com Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209 314608 E mail scitec scitec uk com Fax 01209 314609 Web http www scitec uk com First Stage Amplfier gt Signal X Input n BNC Pa 100R Signal Ground Figure 12 Low Impedance Differential DC Coupled Input Circuit Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www boselec com 4 1 4 2 Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209
3. is not optimal as it does not take into account any instrument or signal offsets nor is it particularly accurate at setting the phase setting Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www boselec com Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209 314608 E mail scitec scitec uk com Fax 01209 314609 Web http www scitec uk com USING THE 420 AS A SINGLE PHASE INSTRUMENT TO TAKE ACCURATE MEASUREMENTS This series of instructions uses the 420 as a single phase lock in amplifier and just uses the X channel This method uses the fact that when the instrument is correctly set up adjusting the phase by 90 will set the output to 0 and by adjust the phase by 180 will invert the output 1 Connect up the lock in amplifier 2 Switch the offset control 6 to off 3 Switch the 1F 2F switch 11 to that required 4 Switch the input sensitivity 1 to 1V 5 Switch the time constant 3 to 100mS 6 Switch both phase controls 9 10 to 0 7 Switch the output select switch 7 to X 8 Increase the sensitivity control 1 until a signal is seen at the output 13 9 If the output becomes noisy increase the time constant setting 3 until the noise is removed 10 Adjust the phase control dials 9 10 until a maximum output is seen 11 Subt
4. 01209 314609 Web http www scitec uk com 20 Switch the output select switch 7 to R The instrument is now correctly set up and measurements of the signal amplitude can be taken directly from the output display You can check that the instrument is correctly set up by rotating either of the phase shift dials 9 10 After a short period to allow the X and Y channels to settle the R output should return to its original value 21 Measurements of the phase of the input signal can be made by turning the phase shift dials 9 10 to 0 and then taking readings of both the X and Y channels The phase relationship between the input and the reference can then be calculated using the equation Y d an Z X Please note that it is necessary for the X and Y outputs to be noise free for the calculation of the R output to be accurate It is recommended that the time constant control 3 is set to 300mS or higher when taking R measurements The problem with noise occurs due to the squaring effect in the R calculation R y X Y Noise on either the X or Y channels is squared which produces a DC offset which is added to the R output signal as an error The solution is to ensure that the X and Y channels are smoothed before the calculations are made by using a large time constant value Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www b
5. 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www boselec com SCITEC INSTRUMENTS LTD INPUT 30mV 100mV 10mV 300mV 1 SENSITIVITY TIME CONSTANT 1 Input Sensitivity Control Note It is not possible to rotate the dial directly from 1V to 3uV 2 BNC Signal Input Connection Note Overload protection circuitry begins to come into operation from 15V 3 Output Time Constant Control Note It is not possible to rotate the dial directly from 30S to 10045 4 X Output Offset Control Note This dial only comes into operation when the output offset switch is set to on OFFSET CONTROL 420 FRONT PANEL LAYOUT OFFSET OUTPUT SELECT PHASE SHIFT Figure 18 420 Front Panel Layout 5 Y Output Offset Control Note This dial only comes into operation when the output offset switch is set to on 6 Output Offset On Off Switch Enables or disables the output offset control dials 7 Output Select Switch Selects value output on BNC connection and that shown on the display 8 BNC Output Connection 9 Coarse 90 Phase Control 10 Fine Phase Control 11 1F 2F Reference Select 420 DUAL PHASE LOCK IN AMPLIFIER POWER Note With the switch set to 1F the recovered signal is of the same frequency as the reference signal With the switch set to 2F the recover signal is twice the frequency of the reference signal 12 BNC Reference Signal Input Connection Note Overl
6. 7 Switch the output select switch 7 to R 8 Increase the sensitivity control 1 until a signal is seen at the output 13 9 If the output becomes noisy increase the time constant setting 3 until the noise is removed 10 Switch the output select switch 7 to X 11 Take a measurement of the output 12 Add 180 to the phase shift by turning the coarse phase control 9 by two positions 13 Take a measurement of the output 14 The two measurements taken in 11 and 13 above should be the inverse of each other If this is not the case switch on the offset control switch 6 and adjust the X offset 4 and repeat the measurements until this is the case 15 Switch the output select switch 7 to Y 16 Take a measurement of the output 17 Add 180 to the phase shift by turning the coarse phase control 9 by two positions 18 Take a measurement of the output 19 The two measurements taken in 16 and 18 above should be the inverse of each other If this is not the case switch on the offset control switch 6 and adjust the Y offset 5 and repeat the measurements until this is the case Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www boselec com Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209 314608 E mail scitec scitec uk com Fax
7. INSTRUMENT TO TAKE QUICK MEASUREMENTS 8 USING THE 420 AS A SINGLE PHASE INSTRUMENT TO TAKE ACCURATE MEASUREMENTS 9 USING THE 420 AS A DUAL PHASE INSTRUMENT TO TAKE ACCURATE MEASUREMENTS 10 HOW TO MAKE AMPLITUDE AND PHASE MEASUREMENTS USING AN OSCILLOSCOPE Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www boselec com Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209 314608 E mail scitec scitec uk com Fax 01209 314609 Web http www scitec uk com 1 POWER SUPPLY 1 1 WARNING This instrument can be damaged if operated with the power voltage selector incorrectly set Switch off and disconnect power before opening unit Do not operate the unit with the lid removed as there are power voltages within the unit 1 2 Power Supply The unit will accept either or 115V AC 5 at 50Hz or 60Hz 220V AC 5 at 50Hz or 60Hz The voltage selection switch is mounted inside the unit The current voltage selection is marked on the label on the back of the unit 13 To Change The Voltage Selection Switch 1 Switch off and disconnect power before opening unit 2 Remove the 10 screws holding the lid on then remove lid Do not disconnect earth strap 3 Change the voltage selection switch mounted on the PCB to the rear of the unit next to the transformer large blue box Available
8. Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209 314608 E mail scitec scitec uk com Fax 01209 314609 Web http www scitec uk com MODEL 420 ANALOG DUAL PHASE LOCK IN AMPLIFIER USER MANUAL Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www boselec com Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209 314608 E mail scitec scitec uk com Fax 01209 314609 Web http www scitec uk com CONTENTS 1 POWER SUPPLY 1 1 WARNING 1 2 Power Supply 1 3 To Change The Voltage Selection Switch 1 4 Earth 1 5 Fuse 2 OPERATION 3 INPUT STAGE 3 1 Accessing Input Stage Jumpers 3 2 Jumper Settings Overview 3 3 Single Ended DC Coupled Input Default Setting 3 4 Single Ended AC Coupled Input 3 5 Single Ended Current Input 3 6 Differential Input 3 7 Low Impedance Differential Input 4 SIGNAL GROUND CASE GROUND AND EARTH 4 1 Accessing Input Stage Jumpers 4 2 Signal Ground Connected to Case and Electrical Earth Default Setting 4 3 Signal Ground Connected to Case and Electrical Earth Via 100Q Resistor 4 4 Signal Ground Isolated From Case and Electrical Earth 5 REFERENCE SECTION 5 1 1F 2F Reference Select Switch 5 2 Coarse Phase Control 5 3 Fine Phase Control 6 DEMODULATOR OUTPUT SECTION 7 USING THE 420 AS A SINGLE PHASE
9. circuit diagram is shown in Figure 1 This shows all of the jumpers in the input stage 1 2 gt O ane oe Stage Amplfier Input O54 BNC NN we 100nF OQ 3 04 P 6M8 a Signal Ground Figure 1 Input Stage Jumper Options A diagram of the position of the input stage jumpers is shown in Figure 2 Top View of Bottom Left Hand Corner of Inside of Box Input Sensitivity Control Input J aia Time Constant 6 Control 3 3 Tiput 2 Signal BNC Figure 2 Input Stage Jumper Positions Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www boselec com 3 3 3 4 Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209 314608 E mail scitec scitec uk com Fax 01209 314609 Web http www scitec uk com Single Ended DC Coupled Input Default Setting 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 100pV to 10nV 1V 3yuV The input impedance of the lock in in this mode is 10 Q Il1nF The jump
10. e above 3 modes can all be converted to a differential input by removing the link between pins 5 and 6 It is useful to place the unit into differential mode if you do not wish the input signal ground to be connected to the lock in amplifier signal ground This can be done to break a ground loop or other such problem For example the jumper settings for the Differential DC coupled input are shown in and the equivalent circuit is shown in Figure 10 The other modes are similar Please note that it is important that the input signals are not left to float when in differential mode but are externally coupled to ground by some method If this is not done the DC offset on the input will rise or fall until the levels specified in section B 3 are breached The input signal will then be distorted as it travels through the input stage and you will get an erroneous result Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www boselec com Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209 314608 E mail scitec scitec uk com Fax 01209 314609 Web http www scitec uk com VAR 6 a Sia 4 3 n 2 fl 1 amp 2 Linked Figure 9 Differential DC Coupled Input Settings N First Stage Amplfier Signal S gt Pa Figure 10 Differential DC Coupled
11. er settings for this mode is given in The equivalent circuit is shown in i 5 amp 6 Linked a Bono N if 1 amp 2 Linked Figure 3 Single Ended DC Coupled Input Settings wN First Stage Amplfier Signal AN lt Input O gt BNC ee a Signal Ground Figure 4 Single Ended DC Coupled Input Circuit 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 manufacture 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 ex Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www boselec com Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209 314608 E mail scitec scitec uk com Fax 01209 314609 Web http www scitec uk com this resistor from their measurements However how often do you make measurements with the input shorted in real life 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
12. erence input with unit switched off may drop producing an unacceptable load on the sources of these signals It is hence recommended that the unit is switched on whenever input signals are applied to it Care should be made that the reference signal does not affect the input signal The reference signal is commonly many factors larger than the signal to be measured and it is therefore relatively easy for the reference signal to be picked up on input signal cable For this reason keep the cabling for the input signal as far away as possible from the cabling for the reference signal Careful screening helps but it is still possible for the input cable to pick up the reference signal if significant lengths are put into close contact The numbers in brackets refer to the numbers used in Figure 18 at the back of this manual Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www boselec com Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209 314608 E mail scitec scitec uk com Fax 01209 314609 Web http www scitec uk com INPUT STAGE The input stage amplifies the input signal to a level suitable for demodulator section The input signal should be connected to the BNC signal input connector 2 The input sensitivity is set by using the input sensitivity dial 1 Please note that it
13. gnal Ground Connected to Case and Electrical Earth Default Setting The signal ground and hence the ground connection for the reference BNC and output BNC can be connected directly to the case ground and electrical earth by placing the jumper as shown in Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www boselec com 43 4 4 Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209 314608 E mail scitec scitec uk com Fax 01209 314609 Web http www scitec uk com 10 8 amp 9 Linked Figure 14 Signal Ground Connected to Case and Electrical Earth Jumper Position This setting is the default as it provides the best noise performance Signal Ground Connected to Case and Electrical Earth Via 100Q Resistor The signal ground and hence the ground connection for the reference BNC and output BNC can be connected to the case ground and electrical earth via a 100Q resistor by placing the jumper as shown in 10 9 amp 10 Linked 9 8 Figure 15 Signal Ground Connected to Case and Electrical Earth Via 100Q Resistor Jumper Position This setting is useful where there are problems with earth loops Signal Ground Isolated From Case and Electrical Earth The signal ground and hence the ground connection for the reference BNC and output BNC can be isolated from the case ground and e
14. in the reference section which affect the reference signal before it is passed to the demodulators 1F 2F Reference Select Switch The 1F 2F reference select switch 11 is used to select the relationship between the frequency of the reference signal input and the frequency that is recovered from the input signal With the switch set to 1F the recovered signal is at the same frequency as the reference signal With the switch set to 2F the recovered signal is twice the frequency of the reference signal This is useful to recover the second harmonic of the reference frequency from the input signal Coarse Phase Control The Coarse Phase Control 9 allows the reference signal to be phase shifted in multiples of 90 before it is used by the demodulator Fine Phase Control The Fine Phase Control 10 allows the reference signal to be phase shift across the range 0 to 100 before it is used be the demodulator DEMODULATOR OUTPUT SECTION Their are two demodulator circuits within the 420 lock in amplifier The first multiplies the signal from the input stage with the reference signal to produce the in phase or X signal The second demodulator multiplies the same signal from the input stage with a 90 phase shifted version of the reference signal This produces the out of phase or Y signal These two resultant The numbers in brackets refer to the numbers used in Figure 18 420 Front Panel Layout at the back of this manual B
15. is not possible to rotate the dial directly from the 1V setting to the 3uV setting The input stage of the unit can operate in a number of ways By default the unit is factory set so 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 within the unit to be modified This can be achieved as follows Accessing Input Stage Jumpers The input stage includes jumpers which enable the mode of operation of the input stage to be modified To access the jumpers 1 Switch off and disconnect power before opening unit 2 Remove the 10 screws holding the lid on then remove lid Do not disconnect earth strap 3 Change the jumper settings as per the diagrams in the following sections Do not operate the unit with the lid removed due to the power voltages accessible within the unit 4 Replace lid and the 10 screws Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www boselec com Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209 314608 E mail scitec scitec uk com Fax 01209 314609 Web http www scitec uk com 3 2 Jumper Settings Overview A simplified input stage
16. lectrical earth by removing the jumper as shown in Figure 16 Signal Ground Isolated from Case and Electrical Earth Jumper Position This setting is useful where there are problems with earth loops The maximum differential voltage between the signal ground and the case and electrical earth should be limited externally to 50V when in this mode of operation Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www boselec com Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209 314608 E mail scitec scitec uk com Fax 01209 314609 Web http www scitec uk com REFERENCE SECTION The reference section defines the frequency at which the lock in recovers signals from the input channel The reference signal is applied to the BNC reference signal input az This input will accept most types of reference signals including the following e Square sine triangle and saw tooth waves 100mV peak to peak minimum 30V peak to peak maximum e All types of TTL and CMOS waveforms 5 mark space ratio minimum 95 mark space ratio maximum The reference channel input is rising edge triggered The falling edge is ignored Square waves are preferred over sine waves as the edge triggering the circuit is generally better defined and more stable There are a number of controls with
17. lock in in this mode is 6 8x10 Q II100nF The jumper settings for this mode is given in The equivalent circuit is shown in 5 amp 6 Linked r nl 3 amp 4 Linked ee fou SB un oN Figure 5 Single Ended AC Coupled Settings i oe First Stage Amplfier Input VO P i Pa _ A Signal Ground Figure 6 Single Ended AC Coupled Circuit 3 5 Single Ended Current Input The input stage can also 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 8MQ resistor which has a tolerance of 1 This mode of operation has not been full characterised by Scitec Instruments and is not guaranteed The input impedance of the lock in in this mode is 6 8x10 Q Il1nF The zi settings for this mode is given in The equivalent circuit is shown in ex Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www boselec com Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209 314608 E mail scitec scitec uk com Fax 01209 314609 Web http www scitec uk com 7 8 OPE 5 amp 6 Linked si 4 f p Hi 3 amp 4 Linked 2 ie 1 amp 2 Linked Figure 7 Single Ended Current Input Settings me First Stage Amplfier Signal Ground Figure 8 Single Ended Current Input Circuit Differential Input Th
18. oad protection circuitry begins to come into operation from 15V 13 Output Meter Display 14 Output Meter Zero Adjust 15 Power On Indicator 16 Power On Off Switch Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 bosdec boselec com www bosdec com
19. orrectly set up and a reading can be made An example of this process is given below Coarse Fine Phase X Offset Reading Comment Phase Control Control Control E Take ae at 90 from initial maximum 0 2V Take reading at 90 from initial maximum 270 20 OV 0 05V Adjust fine phase so that the two readings at 90 from maximum are the same 270 20 0 05V OV Adjust offset control so the two readings at 90 from the maximum are both zero 0 05V 0 85V ee can now be made 180 0 05V 0 85V Reading at 180 should be the negative of the positive reading SD Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www boselec com Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209 314608 E mail scitec scitec uk com Fax 01209 314609 Web http www scitec uk com USING THE 420 AS A DUAL PHASE INSTRUMENT TO TAKE ACCURATE MEASUREMENTS This method uses the fact that the R channel output from the instrument is insensitive to the phase relationship between the input signal and the reference signal 1 Connect up the lock in amplifier 2 Switch the offset control 6 to off 3 Switch the 1F 2F switch 11 to that required 4 Switch the input sensitivity 1 to 1V 5 Switch the time constant 3 to 100mS 6 Switch both phase controls 9 10 to 0
20. oselec com 10 Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209 314608 E mail scitec scitec uk com Fax 01209 314609 Web http www scitec uk com HOW TO MAKE AMPLITUDE AND PHASE MEASUREMENTS USING AN OSCILLOSCOPE Amplitude an phase measurements of an input signal can be easily made using the 420 lock in and an oscilloscope set to X Y mode using the following procedure 1 Switch the oscilloscope to X Y mode Set the gain on both channels to the same setting Zero both channels so that the spot is centred on the screen 2 Set both the reference phase shift controls 9 10 to zero 3 Connect the X output from the back of the 420 lock in to the X channel of the oscilloscope 4 Connect the Y output from the back of the 420 lock in to the Y channel of the oscilloscope The oscilloscope is now set up to display the input signal as a phaser diagram See Figure T7 5 The amplitude of the input signal can now be measured as it is proportional to the distance from the centre of the screen to the displayed dot 6 The phase of the input signal relative to the reference signal can be measured as being the angle between the line from the centre of the screen to the displayed dot and the horizontal v Amplitu do Spot on Oscilloscope Figure 17 Phaser Diagram on Oscilloscope Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347
21. oston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www boselec com Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209 314608 E mail scitec scitec uk com Fax 01209 314609 Web http www scitec uk com signals are then passed through two low pass filters the time constant for which are controlled by the time constant control dial 3 An offset can be added to each output signal be setting the output offset switch 6 to ON and then selecting the required offset using the offset control dials 4 amp 5 A modulus or R circuit calculates the amplitude of the input signal independent of the phase relationship between the input signal and the reference signal This is achieved through combining the X and Y outputs through the calculation R y X Y The output select switch 7 allows the selection of either the X Y or R signals to be output from the front panel BNC output connection 8 and to be displayed on the meter 13 The individual X Y and R outputs are available from three BNC connections on the back panel The output meter zero position can be adjusted by using a small screw driver in the hole below the meter 14 The top scale on the output meter 1 to 1 can be used to directly read the output voltage The bottom scale 3 to 3 is useful when using the input gain sensi
22. ract 90 from the phase shift by turning the coarse phase control 9 by one position anticlockwise or 3 positions clockwise to 90 if at 180 12 Take a measurement of the output 13 Add 180 to the phase shift by turning the coarse phase control 9 by two positions 14 Take a measurement of the output 15 Use the fine phase control 10 to adjust the outputs so the signal levels seen in 12 and 14 above are the same 16 Hopefully the signals seen in 12 and 14 above are both OV If this is not the case switch on the offset control 6 and adjust the X offset control 4 until both signals are OV The fine phase control dial 10 can be used to remove a positive voltage on one output and a negative voltage from the other The X offset control 4 can be used to remove either a positive voltage or negative voltage on both outputs Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www boselec com Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209 314608 E mail scitec scitec uk com Fax 01209 314609 Web http www scitec uk com 17 When the fine phase and offset controls are correctly set the four positions of the coarse phase control 9 should give two readings of OV one negative reading and one positive reading of the same amplitude The instrument is now c
23. settings are 115V and 230V 4 Replace lid and the 10 screws 5 Update the label on the back of the unit to indicate the current voltage selection switch position It is very important that this is done to ensure there is no confusion in the future 14 Earth The instrument should be grounded via the power inlet cable The instrument is encased in a metal box which is connected to this earth No modifications should be made to this earthing mechanism Without this earth connection it is possible for the box to become live under fault conditions The signal ground can however be disconnected for details see section 15 Fuse The unit is fitted with a 1Amp anti surge T 5x20mm fuse incorporated into the power connector on the rear of the unit Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www boselec com Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209 314608 E mail scitec scitec uk com Fax 01209 314609 Web http www scitec uk com Only replace the fuse with another of the same type size and value To access the fuse first remove the power cable then open the fuse compartment with a finger nail When shipped from the factory the fuse compartment contains two fuses The inside fuse is the fuse in use while the outside fuse is a spare and can be used
24. tivity to calculate the amplitude of the input signal Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www boselec com Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209 314608 E mail scitec scitec uk com Fax 01209 314609 Web http www scitec uk com USING THE 420 AS A SINGLE PHASE INSTRUMENT TO TAKE QUICK MEASUREMENTS This series of instructions uses the 420 as a single phase lock in amplifier and just uses the X channel 1 Connect up the lock in amplifier 2 Switch the offset control 6 to off 3 Switch the 1F 2F switch 11 to that required 4 Switch the input sensitivity 1 to 1V 5 Switch the time constant 3 to 100mS 6 Switch both phase controls 9 10 to 0 7 Switch the output select switch 7 to X 8 Increase the sensitivity control 1 until a signal is seen at the output 13 9 If the output becomes noisy increase the time constant setting 3 until the noise is removed 10 Adjust the phase control dials 9 10 until a maximum output is seen 11 Take your reading The amplitude of the input signal is now available on the meter display 13 The phase relationship between the input signal measured and the reference signal can be read off the position of the phase control dials 9 10 This method of taking measurements
25. to replace the inside fuse if it is blown SD Boston Electronics Corporation 91 Boylston Street Brookline MA 02445 800 347 5445 or 617 566 3821 fax 617 731 0935 boselec boselec com www boselec com Scitec Instruments Ltd Bartles Industrial Estate North Street Redruth Cornwall TR15 1HR Tel 01209 314608 E mail scitec scitec uk com Fax 01209 314609 Web http www scitec uk com OPERATION After first ensuring that the current voltage selection is appropriate to your payet supply the power can be connected to the rear of the unit The power supply switch 16 is mounted on the front panel and causes the power on indicator to light 15 Please note that the instrument has a number of circuits within it that require time to settle on power up This can cause the output meter to jump to full scale for a short time on power up This is most noticeable if the time constant control 3 is set to a high value above 1S To speed up the settling process turn the time constant control 3 to 1S or below If there is no reference signal connected to the unit then the offset nulling circuitry within the unit does not operate and hence an offset may be seen on the output This is normal and will be removed when a reference signal is applied It is safe to apply signals to the unit while the lock in is switched off though this is not recommended for any length of time However the input impedance of the signal input and ref
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