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SRS Labs SR542, Operation And Service Manual

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SRS Labs SR542 Operation And Service Manual Download Page 19

1.2 Quick Start Guide

15

1.2.4 Use with a Lock-In Amplifier

The SR542 can be used with a lock‑in as a

follower

or a

reference

. To

follow

the lock‑in, simply connect the reference output from the lock‑in to the

Ext Sync Input

of the SR542 as described above in Section 1.2.3: Lock

to External Frequency. Alternatively, the lock‑in can follow the SR542
as described here. In this example,

Outer Slots Ref Out

is used as the

reference signal input to the lock‑in amplifier.

To perform the steps in this section, in addition to the setup from the
previous sections you will need:

• a lock‑in amplifier (e.g. SR860)

• a light source (optional)

• a photodiode, phototransistor, or other light‑sensitive detector

Beginning with the setup described in Section 1.2.1:

1. Select

Internal Freq

as the

Source

by pressing

Source

→

Int

repeatedly.

2. Select

Outer

as the

Control

by pressing

Control

Shaft

repeatedly.

3. Set the internal frequency to 75 Hz by selecting

Int Freq

with

and

and then entering

7

+

5

+

.

4. Connect the

Outer Slots Ref Out

from the rear panel of the SR542 to

the reference input of the lock‑in amplifier using a standard BNC
cable (not included).

5. Configure the lock‑in reference settings to use an external refer‑

ence with TTL input and 50

Ω

termination, if available.

The

Outer Slots Ref Out

signal is derived from an opto‑interrupter

and is not available until the chopper is running. As a result, the
lock‑in amplifier will not yet be able to lock to this signal.

6. Press and hold

Run /

Stop

until the chopper starts.

Now the lock‑in amplifier should be able to lock to the

Outer Slots

Ref Out

signal.

7. Connect the photodiode to the lock‑in input and position the pho‑

todiode lens near the chopper blade.

A light source, such as a laser, can be used to illuminate the pho‑
todiode detector through the chopper blade but ambient light can
often produce a large enough signal if the detector is placed very
close to the blade.

SR542 Precision Optical Chopper

Summary of Contents for SR542

Page 1: ...Operation and Service Manual Precision Optical Chopper SR542 Stanford Research Systems Revision 1 0 April 7 2022 ...

Page 2: ...e returned to a Stanford Research Systems autho rized service facility Contact Stanford Research Systems or an authorized representative before re turning this product for repair Information in this document is subject to change without notice Copyright Stanford Research Systems Inc 2022 All rights reserved Stanford Research Systems Inc 1290 D Reamwood Avenue Sunnyvale CA 94089 USA Phone 408 744 9...

Page 3: ...to Internal Frequency 13 1 2 3 Lock to External Frequency 14 1 2 4 Use with a Lock In Amplifier 15 2 Operation 17 2 1 Functional Overview 18 2 1 1 Chopper Control Loop 18 2 1 2 Chop Mode 20 2 1 3 Shutter Mode 23 2 2 Front Panel Control 25 2 2 1 Power 25 2 2 2 Numeric Display 25 2 2 3 Configuration 28 2 2 4 Display Adjust 30 2 2 5 Numeric Entry 31 2 2 6 Phase 32 2 2 7 Motor 32 2 2 8 Setup 33 2 3 Re...

Page 4: ... Status Byte SB Register 58 3 5 2 Service Request Enable SRE Register 58 3 5 3 Standard Event Status Register ESR 59 3 5 4 Standard Event Status Enable ESE Register 59 3 5 5 Chopper Status CHCR CHEV Registers 60 3 6 Error Codes 62 3 6 1 Command Execution Errors 62 3 6 2 Command Parsing Errors 63 3 6 3 Communication Errors 63 3 6 4 Motor Errors 64 3 6 5 Device Dependent Errors 64 3 6 6 Other Errors...

Page 5: ...eparation for Use 2 AC Line Voltage 2 Line Cord 2 Service 2 Symbols on the SR542 3 Notation 3 Specifications 4 Blade Specifications 5 Mechanical Dimensions 7 Controller 7 Chopper Head 8 Chopper Blade 9 1 SR542 Precision Optical Chopper ...

Page 6: ... Hz Line Cord The SR542 Precision Optical Chopper has a detachable three wire power cord for connection to the power source and to a protective ground The chassis of the instrument is connected to the outlet ground to protect against electrical shock Always use an outlet which has a properly connected protective ground Service The only user serviceable part inside the chassis is jumper J503 for se...

Page 7: ...possible Caution Injury is possible due to rotating parts Power Toggle instrument power Chassis Ground Notation Typesetting conventions used in this manual with examples of each Use case Example Front panel buttons Run Stop Front panel text Locked Int Freq Source Remote command names IDN Literal text sent IDN Literal text received Stanford_Research_Systems SR542 s n00000001 v1 0 0 SR542 Precision ...

Page 8: ...z jitter opt jitter μs chop period μs 360 opt Inputs 2 BNCs Impedance 1 MΩ VCO Voltage 0 to 10 V dc VCO Accuracy typ 100 ppm Ext Sync TTL Minimum 2 V logic level Ext Sync Sine 100 mV rms to 1 V rms signal AC coupled 1 Hz Edge Trigger TTL Rising TTL Falling or Sinusoidal Outputs 6 BNCs Voltage 0 V to 5 V logic levels sourced through 50 Ω Signals Source Shaft 1 PPR Inner Slots Outer Slots Sum 𝑓OUTER...

Page 9: ...circumference of the blade so that the corresponding slotted opto interrupter on the chopper head can detect the inner slots Table 1 Available chopper blades For dual frequency blades the inner and outer number of slots and maximum beam diameter are indicated as Inner Outer O542DF is a variable duty factor blade with available duty cycles from 10 90 Part Num Num Slots Max Beam Diam in Chop Frequen...

Page 10: ...425 5 Slot O54230 30 Slot Figure 1 Available chopper blades for the SR542 Max beam size for outer red and inner blue tracks are listed in Table 1 The variable duty factor blade permits selection of duty factor from 10 to 90 in 10 increments depending on the radial placement of the beam spot SR542 Precision Optical Chopper ...

Page 11: ... Andy Berger B SR540 Redesign asm_top_level_sr542_asm 4 1 8 1 8 3 0 6 8 1 9 2 a LEFT PROJECT TITLE DRAWN CHECKED APPROVED SCALE WEIGHT SHEET DWG NO CODE SIZE 1 1 1 3 16 2022 Andy Berger B SR540 Redesign asm_top_level_sr542_asm 4 1 8 1 8 3 0 6 8 1 9 2 b FRONT Figure 2 Dimensions in inches of the SR542 controller SR542 Precision Optical Chopper ...

Page 12: ...EET DWG NO R CODE SIZE 1 3 1 1 3 16 2022 Andy Berger B SR540 Redesign SR542 Assembly 4 31 4 65 0 25 0 28 2 70 4 76 3 75 1 89 1 33 Ø0 51 3 1 2 00 Ø0 26 Ø3 70 Ø2 80 Ø2 55 Ø1 53 Chopper Blade 0 40 b FRONT PROJECT TITLE DRAWN CHECKED APPROVED SCALE WEIGHT SHEET DWG NO CODE SIZE 1 1 1 3 16 2022 Andy Berger B SR540 Redesign SR542 Assembly 4 31 4 65 0 25 0 28 2 70 4 76 3 75 1 89 1 33 Ø0 51 3 1 2 00 Ø0 26...

Page 13: ...trol is optimized for 0 010 in stainless steel blades The SR542 is also backwards compatible with SR540 chopper blades However due to differences in the outermost aperture track the Inner Slots Ref Out waveform inner slots frequency and inner slot count will be incorrect This will also affect the sum and difference frequency out puts Performance specifications are not guaranteed for custom or SR54...

Page 14: ...10 General Information SR542 Precision Optical Chopper ...

Page 15: ...tical Chopper Refer to Chapter 2 for more detailed explanations of the features of the SR542 1 1 Using This Manual 12 1 2 Quick Start Guide 12 1 2 1 Preparations for Use 12 1 2 2 Lock to Internal Frequency 13 1 2 3 Lock to External Frequency 14 1 2 4 Use with a Lock In Amplifier 15 11 SR542 Precision Optical Chopper ...

Page 16: ... not already installed mount a blade onto the chopper hub Be careful to slide the blade into the slotted opto interrupters near the base before positioning the blade s inner diameter onto the hub Secure the blade by sandwiching it between the hub and the hub plate and fasten using three 4 40 flat head screws 2 It is recommended to secure the chopper head before running the motor Bolt the chopper h...

Page 17: ... 75 0 Hz 5 When the desired configuration is established press Run Stop to run the chopper motor A long 1 s press is required to start the motor On startup the SR542 first searches for the rotor shaft index then spins the motor shaft several times to survey the installed blade before pro ceeding to the as configured control parameters frequency and phase The Source Output on the rear panel outputs...

Page 18: ...or should illuminate within about three peri ods of the reference frequency If Locked does not light or does not remain lit check the quality of the external signal 5 Use and to show the Source frequency monitor on the numeric display and verify that the frequency matches that of the external reference 6 Configure the Control track by pressing Control Shaft until the desired track is selected To s...

Page 19: ...ft repeatedly 3 Set the internal frequency to 75 Hz by selecting Int Freq with and and then entering 7 5 4 Connect the Outer Slots Ref Out from the rear panel of the SR542 to the reference input of the lock in amplifier using a standard BNC cable not included 5 Configure the lock in reference settings to use an external refer ence with TTL input and 50 Ω termination if available The Outer Slots Re...

Page 20: ...on the SR542 Increasing the phase setting of the SR542 does advance the phase of the photodetector signal but it advances the phase of the opto interrupter signal used by the lock in as its reference by an identical amount 10 Set the Phase of the SR542 to 15 and notice that the signal on the lock in does not change 11 Set the Phase of the SR542 to 0 12 Now disconnect the BNC cable from the Outer S...

Page 21: ...3 2 Edge 29 2 2 3 3 Multiplier 29 2 2 3 4 Control 29 2 2 3 5 Chopper Locked Status 30 2 2 4 Display Adjust 30 2 2 5 Numeric Entry 31 2 2 6 Phase 32 2 2 7 Motor 32 2 2 8 Setup 33 2 2 8 1 Save 33 2 2 8 2 Recall 34 2 2 8 3 Back 34 2 3 Rear Panel Connections and Signals 35 2 3 1 Source Inputs and Output 36 2 3 1 1 VCO Input 36 2 3 1 2 Ext Sync Input 36 2 3 1 3 Source Output 36 2 3 2 Reference Outputs ...

Page 22: ...quency control by external DC voltage VCO mode phase locking to AC line low phase jitter long life brushless motor single and dual beam experiments sum and difference frequency reference outputs harmonic sub harmonic and fractional harmonic phase locking adjustable and reproducible phase including settable relative phase with 0 01 resolution shutter mode fixed position full remote operation by USB...

Page 23: ... 𝜙setpoint An optical encoder affixed to the rear shaft of the chopper motor is used to measure 𝜙shaft and 𝑓shaft Also available to the user via remote query is 𝑓source 𝑛 𝑚 This is the target control frequency for the selected Control track see MFRQ Finally when used with a dual frequency chopper blade the SR542 syn thesizes square wave reference outputs at 𝑓OUTER 𝑓INNER sum and 𝑓OUTER 𝑓INNER diff...

Page 24: ...ut For a chopper blade track with 𝑛slots a mechanical rotation of 360 mech 𝑛slots produces a full 360 opt cycle Outer 360 opt 60 mech Inner 360 opt 72 mech 54 mech Rotation Figure 2 2 Relationship between optical and mechanical degrees opt and mech for O54256 5 6 slot dual frequency blade Positive rotation of the chop per blade is clockwise when viewed from the front of the chopper head The shaft ...

Page 25: ...olled track will lag the Source by 90 2 1 2 2 Blade Control Inner Slots If the Control is changed to Inner then the Inner Slots Ref Out will be frequency and phase locked to the Source Output as is shown in Fig ure 2 5 As shown by the block diagram in Figure 2 1 the chopper is always controlled using the shaft encoder signal with a phase and fre quency appropriately scaled by 𝑛slots the number of ...

Page 26: ...e will still be present Source Shaft Inner N 5 Outer N 6 Edge CONFIGURATION 1 Multiplier Control TSource TInner TSource φShaft φBlade Inner Figure 2 5 Simulated timing diagram of rear panel outputs for Inner Slots con trol with 𝑛slots 5 and 0 phase offset Width of Rotor Shaft Ref Out pulse is exaggerated for illustrative purposes By properly adjusting the Phase setting of the Inner track the user ...

Page 27: ...tween the source and control signals that phase can be set as the 0 reference point to which further adjustments are relative by pressing Rel Phase 2 1 3 Shutter Mode In addition to the traditional chop mode the SR542 can be used as an optical shutter While not to be used for precisely timed signals see the SR475 Laser Shutter for such applications shutter mode can be use ful for temporarily block...

Page 28: ...tings Shaft Source USB ERR Hz deg Multiplier Rel Outer Slots Inner Slots Int Freq Phase VCO FS n m Frequency Monitor Settings Shaft Source Figure 2 7 With Source Internal Freq and Int Freq 0 Hz the SR542 enters shutter mode which keeps the chopper blade in a fixed position as determined by the Phase setting The Phase display in this mode presents an integer slot number 𝑁 and angle 𝐷 where the phas...

Page 29: ...haft Source Motor Source Control Rel Phase Run Stop Edge Save Recall Back Int Shaft 0 1 2 3 4 5 6 7 8 9 Cancel Pending Figure 2 8 The SR542 front panel 2 2 1 Power The button is used to turn the SR542 controller On and Off 2 2 2 Numeric Display At the top left of the front panel is a 6 digit numeric display which displays the parameter indicated by the Frequency Monitor or Settings LEDs Frequency ...

Page 30: ...the instantaneous measured frequency of the motor shaft in mechanical revolutions per second Source Displays the frequency of the Source Clock When the front panel is configured to display Outer Slots Inner Slots or Slot count Shaft frequency a press and hold of the button will display the number of slots on the corresponding track until the button is released For example with the 10 100 slot blad...

Page 31: ...d Control track In Shaft con trol 360 opt is equivalent to 360 mech since 𝑛slots 1 for calculational purposes The phase setting entered by the user is mapped to the range 𝑛slots 360 360 using modulo division before being stored inter nally In chop mode the Phase displayed on the front panel will undergo an other modulo operation modulo 360 to present the optical phase from 359 99 to 359 99 In shut...

Page 32: ... Source frequency to the Int Freq set ting and the Source will jump to Internal Freq The Source Clock will then proceed at that stable fixed frequency The Jump to Int feature could be useful to diagnose a noisy Ext Sync signal which the SR542 has difficulty tracking with its Source PLL With the exception of the Jump to Int function it is not possible to modify the Source while the motor is on When...

Page 33: ...ll be de activated 2 2 3 3 Multiplier The Multiplier sub block of the CONFIGURATION section indicates whether the user has selected either 𝑛 or 𝑚 1 If 𝑛 𝑚 then the 1 indicator will light Otherwise the n m indicator will light Certain choices of 𝑛 and 𝑚 may result in a Maximum Frequency error If the motor is already running therefore the slot counts have already been surveyed illegal values for 𝑛 a...

Page 34: ...remain steadily on and the Chopper Unlocked LED will turn off Both the frequency and phase lock status are available as status bits in the CHCR register see Section 3 5 5 1 2 2 4 Display Adjust The DISPLAY ADJUST block of the front panel consists of a rotary knob and left right select buttons and The and buttons typically scroll through the Frequency Monitor and Settings modes of the main display ...

Page 35: ... to be set press the Cancel button Pending numeric entries are left justified on the 6 digit display while entered settings are right justified A long hold 1 s of the Cancel button will display the list of error codes Display ERR presently in the error queue If no errors have occurred since the er rors were last cleared including power on then the display no Err will briefly appear If errors are p...

Page 36: ...o an absolute measurement See the example provided with the RELP command 2 2 7 Motor The Run Stop button toggles power to the chopper head motor A long press is required to start the motor while a short press will bring it to a stop At startup the rotor shaft orientation must first be indexed and so you may notice several low speed rotations in alternate directions until the index position is foun...

Page 37: ...or 𝑚 1 VCO FS 100 Hz 2 2 8 1 Save The Save button is used to save the current configuration to a non volatile memory location There are 9 available memory locations for user configurations which can be saved in locations 1 2 3 9 Upon pressing Save the numeric display will read 8 8 8 8 8 8 Loc 1 which indicates that the unit is ready to save the current configuration to Location 1 To proceed with t...

Page 38: ...8 8 8 8 8 LOAd 2 2 8 3 Back The Back button allows the user to quickly revert the most recent change to the active configuration For example if the user has most recently changed the Int Freq from 100 Hz to 500 Hz they can easily jump back to 100 Hz by pressing the Back button instead of typing 1 0 0 thereby saving several button presses Back operations have a memory depth of one The Back button m...

Page 39: ...he 10P10C chopper head cable The rear panel of the instrument provides all of the signal input and output BNC connections Inputs allow external signals to control the frequency and or phase of the chopper Reference Outputs can be used to trigger a lock in amplifier oscilloscope box car averager photon counter etc In the high state all outputs provide 5 V through 50 Ω If the user connects a 50 Ω te...

Page 40: ...ltered digitized and di vided by 10 V to provide a scale factor between 0 and 1 This scale factor multiplied by the user setting VCO FS determines the Source frequency Mathematically the DC voltage 𝑉DC determines the source frequency in Hz as 𝑓source 𝑉DC 10 V VCO_FS where VCO_FS is set on the Front Panel using the VCO FS setting see Section 2 2 2 2 or using the remote command VCOS 2 3 1 2 Ext Sync...

Page 41: ...res which duplicates the angular positions of the inner track 2 3 2 3 Rotor Shaft Ref Out The signal provided at Rotor Shaft Ref Out is a 5 V pulse produced by the optical encoder affixed to the rear shaft of the chopper head motor The width of this once per revolution pulse depends on the mechanical speed of the rotor shaft with an output high state that lasts for 1 400th of a mechanical revoluti...

Page 42: ...38 2 Operation SR542 Precision Optical Chopper ...

Page 43: ...tus Commands 54 3 5 Status Model 57 3 5 1 Status Byte SB Register 58 3 5 2 Service Request Enable SRE Register 58 3 5 3 Standard Event Status Register ESR 59 3 5 4 Standard Event Status Enable ESE Register 59 3 5 5 Chopper Status CHCR CHEV Registers 60 3 5 5 1 Chopper Condition Register CHCR 60 3 5 5 2 Chopper Positive Negative Transition CH PT CHNT Registers 60 3 5 5 3 Chopper Event CHEV Register...

Page 44: ...orms Configuration SRCE z Source 46 JINT Jump to Internal Freq 46 EDGE z External Sync Edge 46 CTRL z Control Target 46 IFRQ f Internal Frequency 46 PHAS f Phase 46 RELP z Relative Phase 47 MULT i Frequency Multiplier 47 DIVR i Frequency Divisor 47 VCOS f VCO Full Scale Frequency 48 RST Reset 48 Operation MOTR z Run Stop Chopper Motor 49 MFRQ z Frequency Monitor 49 SLOT z Number of Blade Slots 49 ...

Page 45: ... 53 Status CLS Clear Status 54 LERR Last Error 54 STB i Status Byte 54 SRE i j Service Request Enable 55 ESR i Event Status Register 55 ESE i j Event Status Enable 55 CHCR i Chopper Condition 56 CHPT i j Chopper Condition Positive Transition 56 CHNT i j Chopper Condition Negative Transition 56 CHEV i Chopper Event 56 CHEN i j Chopper Event Enable 56 SR542 Precision Optical Chopper ...

Page 46: ...RE i j Service Request Enable 55 STB i Status Byte 54 A ALRM z Audible Alarms 51 B BACK Back to Previous Configuration 51 C CHCR i Chopper Condition 56 CHEN i j Chopper Event Enable 56 CHEV i Chopper Event 56 CHNT i j Chopper Condition Negative Transition 56 CHPT i j Chopper Condition Positive Transition 56 COPC Cancel Pending OPC Set Query 53 CTRL z Control Target 46 D DISP z Display Mode 50 DIVR...

Page 47: ...Last Error 54 M MFRQ z Frequency Monitor 49 MOTR z Run Stop Chopper Motor 49 MULT i Frequency Multiplier 47 P PHAS f Phase 46 R RELP z Relative Phase 47 S SLOT z Number of Blade Slots 49 SRCE z Source 46 T TERM z Response Termination 52 TOKN z Token Response Mode 52 V VCOS f VCO Full Scale Frequency 48 SR542 Precision Optical Chopper ...

Page 48: ... activity both incoming and outgoing messages 3 3 2 Remote Interface Buffers The SR542 stores incoming bytes received via the USB interface in a 256 byte input buffer Characters accumulate in the input buffer until a com mand terminator CR or LF is received at which point the message is parsed and the corresponding command s is are executed Query responses from the SR542 are buffered into a 256 by...

Page 49: ...value For example to set the frequency source to Internal Freq the following two commands are equivalent SRCE INT or SRCE 0 For queries that return token values the return format keyword or in teger is specified with the TOKN command 3 4 2 Notation The following notation is used in the command descriptions Symbol Definition f g Floating point value i j Unsigned integer z Literal token Required for...

Page 50: ...mple External Sync Edge EDGE z Set query the external edge used to trigger the Source PLL to z RISE 0 FALL 1 SINE 2 EDGE Example 0 Control Target CTRL z Set query the track which is to be phase locked to the Source to z SHAFT 0 INNER 1 OUTER 2 CTRL Example OUTER Internal Frequency IFRQ f Set query the Internal Frequency to f in Hz IFRQ 255 17 Example Phase PHAS f Set query the phase of the selecte...

Page 51: ... Switch ing relative phase from ON to OFF will add back the original phase offset to the currently displayed value of Phase The RELP command is similar to pressing Rel Phase though the set com mand requires z and does not automatically toggle the Relative Phase state PHAS Example 90 0000 RELP ON PHAS 0 0000 PHAS 15 6 RELP OFF PHAS 105 6000 Frequency Multiplier MULT i Set query the integer multipli...

Page 52: ... voltage of 10 V See Section 2 3 1 1 for further discussion the VCO Input VCOS 5000 0 Example Reset RST Reset the SR542 to its default configuration Sending the RST command is equivalent to sending the following MOTR OFF SRCE INT EDGE RISE CTRL OUTER DISP OUTER IFRQ 100 00 PHAS 0 0 MULT 1 DIVR 1 VCOS 100 00 RELP OFF KCLK ON ALRM ON SR542 Precision Optical Chopper ...

Page 53: ...ueries of SUM or DIFF will return the target synthe sized frequency 𝑛OUTER 𝑛INNER 𝑓ref and not the instantaneous mea sured frequency given by 𝑛OUTER 𝑛INNER 𝑓shaft Similarly a query of the CTRL frequency returns the target value of the control frequency 𝑓source 𝑛 𝑚 and not the measured value of the se lected control track MFRQ OUTER Example 3500 0171 Number of Blade Slots SLOT z Query the number of...

Page 54: ... only through front panel opera tions via a long hold of Cancel and respectively DISP Example SRCE Save Configuration SAV i Save the current configuration in memory location i 1 2 9 User con figurations cannot be saved to memory location 0 SAV 1 Example Recall Configuration RCL i Recall the saved configuration from memory location i 0 1 9 Recall ing from memory location 0 restores the factory defa...

Page 55: ... to Int was just performed Back will jump back to the previous Source and revert the Int Freq to the previous value Recall All settings modified by the recent Recall will be reverted LOAd will be briefly displayed It is possible that a BACK operation cannot be performed currently For example if the most recent settings change was the Control track BACK will be rejected if the motor is running The ...

Page 56: ...s of token type values When token response mode is turned off by TOKN OFF the SR542 responds with the numeric version of the token quantity When turned on by TOKN ON the text version is returned The token response mode is unmodified by the RST command and is always restored to OFF 0 at power on TOKN Example ON Response Termination TERM z Set query the response termination to z NONE 0 CR 1 LF 2 CRL...

Page 57: ...le 1 Most of the SR542 remote commands are processed and executed with out delay so the command sequence RCMD OPC will return 1 immediately for a general remote command RCMD The primary ex ception to this is following a motor shutdown command MOTR OFF which initiates a deceleration of the motor The deceleration can last several seconds depending on the initial speed of the motor Therefore the foll...

Page 58: ...ry or the last Clear ERR operation or CLS command See Section 3 6 for a list of possible error codes and their meanings LERR Example 25 Status Byte STB i Query the Status Byte register or individual bit i If no bit parameter is included the response is the binary weighted sum of all set bits in the Status Byte register Bits in the Status Byte are updated in real time and bits are not cleared when ...

Page 59: ...ent then i represents the bit number 0 through 7 and j can be either 0 or 1 Bits i are unaffected SRE 5 0 Example A query with no included bit parameter returns the binary weighted sum of the enabled bits A query with an included bit parameter returns the value of that bit SRE Example 128 SRE 7 1 See also Section 3 5 on the Status Model Event Status Register ESR i Query the Standard Event Status R...

Page 60: ... j CHPT 8 Example Chopper Condition Negative Transition CHNT i j Set query the Chopper Condition Negative Transition register bit i to j CHNT 2 1 Example Chopper Event CHEV i Query the Chopper Event Register bit i Upon executing a CHEV query the returned bit s of the CHEV register are cleared CHEV Example 5 CHEV 0 Chopper Event Enable CHEN i j Set query the Chopper Event Status Enable Register bit...

Page 61: ...ategories of registers in the status model of the SR542 Condition Registers These read only registers correspond to the real time condition of some underlying physical property being monitored Queries re turn the latest value of the property and have no further side ef fects Condition register names end with CR Transition Selection Registers These read write registers define specific transition ev...

Page 62: ...ht Bit Flag 1 0 undef 0 2 1 undef 0 4 2 undef 0 8 3 undef 0 16 4 undef 0 32 5 ESB 64 6 MSS 128 7 CHSB ESB Event Status Bit Indicates whether one or more of the enabled events in the Standard Event Status Register is true MSS Master Summary Status Indicates whether one or more of the en abled status messages in the Status Byte register is true CHSB Chopper Status Bit Indicates whether one or more o...

Page 63: ...sing loss of data Dropped commands will need to be re sent QYE Query Error Indicates data in the output buffer has been lost DDE Device Dependent Error Indicates an issue with SR542 configu ration or control signals EXE Execution Error Indicates an error in a command that was suc cessfully parsed Out of range parameters are an example CME Command Error Indicates a command parser detected error URQ...

Page 64: ...ed to the configured Source reference 𝑓source 𝑛 𝑚 CMAX Current Max Current to the chopper head exceeds the rated max imum If running the chopper motor at high speeds a CMAX con dition could be the cause of an unstable phase lock Try running at a lower speed 3 5 5 2 Chopper Positive Negative Transition CHPT CHNT Registers These two 8 bit wide registers control the mapping of transitions in the CHCR...

Page 65: ...d continuously during motor operation Connectivity is not monitored when the motor is off An example use case of CHNT and CHEV is shown in Figure 3 2 Before the start of the example the command CHNT 8 is sent to latch negative 1 0 transitions of the CHCR PL Phase Locked bit into the CHEV reg ister Note that periodic monitoring of the CHCR real time register may miss a temporary loss of lock depend...

Page 66: ...mand Alternatively all errors stored in the the error queue can be cleared via the front panel by a long hold 1 s of the button followed by to confirm See discussion of Clear ERR The meaning of each of the error codes is defined below 3 6 1 Command Execution Errors Execution errors occur when the SR542 successfully parsed a command but fails to execute it usually because of invalid parameters 1 Il...

Page 67: ...eceived no value for the expected pa rameter 28 Parameter Buffer Overflow The buffer that stores the characters of a token parameter has overflowed All valid token strings are shorter than this buffer Please check the token string 29 Bad Float Conversion of a parameter string to floating point vari able failed 30 Bad Integer Conversion of a parameter string to integer variable failed 31 Bad Token ...

Page 68: ...ck If using a single frequency chopper blade change the Control track to Outer or Shaft Otherwise check to make sure the opto interrupter for the inner track positioned on the outer most diameter of the chopper blade is not blocked 73 No outer slots detected Check to make sure the opto interrupter for the outer track which is positioned slightly higher is not blocked 74 Motor lost If this error oc...

Page 69: ...r discusses common experimental applications of the SR542 Precision Optical Chopper 4 1 Single Beam Experiment 66 4 2 Dual Beam Experiment 67 4 3 Detection at Sum and Difference Frequencies 68 65 SR542 Precision Optical Chopper ...

Page 70: ...chopped by either the Inner or Outer track of slots and the reference output from the corresponding Inner Outer Slots Ref Out BNC connection is used as the Ref In to a lock in amplifier Lock in Amplifier SR542 Controller Outer Slots Ref Out Ref In Source Experiment Detector Figure 4 1 Single Beam Experiment SR542 Precision Optical Chopper ...

Page 71: ...2 the signal at 𝑓INNER cor responds to the control arm the signal at 𝑓OUTER is the response from the experimental arm If the detected signal in the experimental arm is ratioed to the detected signal from the control arm then effects due to changing source intensity and detector efficiency are removed To ra tio the experimental signal to the control signal the demodulated signal from the control ar...

Page 72: ...INNER and 𝑓OUTER are combined on the sample the sample may produce a response at the sum and difference frequencies 𝑓OUTER 𝑓INNER and 𝑓OUTER 𝑓INNER The SR542 provides synthesized reference outputs at the sum and dif ference frequencies which can be provided to the reference input of a lock in amplifier Lock in Amplifier SR542 Controller fOUTER fINNER Ref Out Ref In Source 2 Nonlinear Optical Media...

Page 73: ...he possibility of a ground loop if the cable shield is grounded at both ends WARNING Dangerous voltages capable of causing injury or death are present in this instrument Use extreme caution whenever the instrument covers are removed Do not remove the covers while the unit is plugged into a live outlet The procedure for adjusting J503 inside the SR542 controller is as fol lows First turn off and un...

Page 74: ...70 5 Troubleshooting SR542 Precision Optical Chopper ...

Page 75: ...30 31 Power 25 Recall 34 Rel Phase 32 Right Arrow 30 31 Run Stop 32 Save 33 Source 28 C cable chopper head see chopper head cable calibration 61 64 CHCR 56 CHEN 56 CHEV 56 CHNT 56 chop mode 20 24 27 chopper blade see blade chopper head 8 12 13 19 20 37 61 64 cable 2 12 13 35 61 64 shield 69 CHPT 56 click 51 Clock Shaft Reference 19 29 64 Source 18 26 28 29 64 CLS 54 command parameter 45 separator ...

Page 76: ...t Panel 25 G ground 2 64 69 chassis 2 35 protective 2 I IDN 52 IFRQ 46 indicator see LED Inner Control 13 21 29 Frequency Monitor 26 slots 5 9 32 Slots Ref Out 13 16 19 21 37 track 5 6 37 64 Internal Frequency Setting 13 15 18 27 28 33 46 Source 15 18 28 interrupter see opto interrupter J JINT 46 Jump to Int 28 46 K KCLK 51 keypad see button numeric entry knob clamping 12 rotary 26 27 30 L LED Cho...

Page 77: ...se see Rel Phase RELP 47 RST 48 S SAV 50 Save 33 sensor 37 serial communication 35 44 59 number 52 Service 2 64 Settings 25 27 30 Shaft Control 13 20 29 Frequency Monitor 26 Ref Out 13 19 21 37 shaft encoder 19 21 24 32 64 shroud 12 shutter mode 23 24 27 32 34 sine 36 slot count 9 26 49 64 SLOT 49 slots 5 49 66 inner see Inner slots outer see Outer slots Source 28 33 46 Frequency Monitor 26 Output...

Page 78: ...8 59 SRE 58 transition 57 Status Byte see status registers SB STB 54 sticky bits 57 59 Sum frequency 19 37 68 Output 9 13 19 37 49 survey 13 29 32 T TERM 52 token 45 TOKN 52 track 9 66 inner see Inner track outer see Outer track trigger see Edge TTL 14 29 36 U units 25 USB 35 44 V VCO FS 27 33 36 VCO Input 18 36 Source 18 28 VCOS 48 SR542 Precision Optical Chopper ...

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