C-980 Phase-Locked-Loop

Transcription

1 C-980 Phase-Locked-Loop Optical Chopper Operating Manual DigiRad Division of Terahertz Technologies Inc. 169 Clear Road Oriskany, New York Tel: (315) Fax: (315) January 1992 Rev. 1.0 Copyright 1991, 1992 Terahertz Technologies Inc.

2 Table of Contents Topic Page GENERAL INFORMATION Introduction...2 Specifications...2 OPERATING INSTRUCTIONS Unpacking and Inspection...3 Input Power Requirements...3 Controls & Their Functions...3 Connections...6 Display...7 Apertures Mounting....7 Operating Considerations Theory of Operation....8 Calibration....9 Calibration Control Locations....9 WARRANTY INFORMATION Repair Information...11 Limited Warranty

3 Introduction The C-980 Optical Chopper is a general purpose optical chopper designed for laboratory use. The unit may be phaselocked to either its own internal clock generator or a user-supplied external clock. Additionally, the unit may be controlled by means of an externally applied DC voltage. The C-980 can provide chopping rates ranging from 4 Hz to 5000 Hz without the need to change chopper blades. The chopping frequency is measured by an internal crystal-controlled frequency counter and displayed by means of a 4 digit, 0.56" (14 mm) high, green LED display. The display update rate is once per second. Two ranges are provided, 4 to 500 Hz and 40 to 5000 Hz. A TTL/CMOS compatible phase reference signal is provided for use with lock-in amplifiers or other ancillary test equipment. The chopper head is mounted on a standard optical post and adjustable height post holder suitable for mounting on an optical bench. Attachment to the controller is made via a ten foot (3.6 m) coiled modular cable that is detachable at both ends. Specifications Frequency Range: to 500 Hz ( using 3 slot inner set of slots)40 to 5000 Hz (using 30 slot outer set of slots) Frequency Readout Accuracy: % of setting + 1 Least Significant Digit Frequency Stability (Internal Clock): % of setting/hour + 1 Hz Frequency Stability (External Clock): Frequency Stability (External DC Source):...0.1% of setting/hour + 2 Hz Phase Jitter: % peak to peak, 3 slot 1% peak to peak, 30 slot Settling Time to Lock:... < 5 seconds, for full scale change < 1 second, for 10% change External Frequency Input:... TTL/CMOS Compatible, 40 to 5000 Hz External Voltage Control Input: VDC takes unit through entire speed range External Voltage Input Impedance:...> 100 K Display:...4 Digit LED, Green (565 nm) 0.56 In. (14 mm) Height Operating Temperature: C Power Requirements: V.A.C. + 10% or 230 V.A.C. + 10%, Hz, <15 W Size:... Chopper Head: 5.5" H x 4.5" W x 2.5" D Controller: 2.6" H x 6.5" W x 8.5" D Weight:...5 lbs (2.25Kg.) 2

4 Unpacking and Inspection Inspection Prior to shipment this instrument was inspected and found to be free of mechanical and electrical defects. Upon acceptance by the carrier he assumes responsibility for its safe arrival. After unpacking, examine the unit for any evidence of shipping damage. Should you receive this instrument in a damaged condition, apparent or concealed, it must be noted on the freight bill or express receipt and signed by the carrier s agent. Failure to do so could result in the carrier refusing to honor the claim. Upon filing a claim DigiRad should be notified. Input Power Requirements This instrument is equipped for operation with an external regulated power supply. Do not attempt to substitute any y other power er supply y for that t whic hich h is supplied with the instrument. To do so may cause severe damage to the instrument. Units are available for both 117 V.A.C. and 230 V.A.C., Hz operation. Instruments equipped for 117 V operation are supplied with wall-mounted power supplies with U.S./Canadian power input connectors. These supplies are UL 1310 listed and CSA approved. Instruments equipped for 230 V operation are supplied with tabletop type power supplies which have an IEC power input connector and are TUV approved to IEC 950. They also meet VDE Class B Emission standards and are CE compliant. Controls & Their Functions There are only three controls needed to operate the C-980 Optical Chopper. 1. The Control ol Source ce Selector switch is located on the rear panel of the unit. (See Page 4.) This 3-position switch determines what will control the chopping rate. In the center position the front panel Frequenc equency y Set knob controls the chopper speed. In the left-most position (facing the rear panel) the unit is controlled by phase-locking the chopper to a user-supplied TTL compatible clock that is applied to the Sync Input BNC connector (just to the left of the switch). In the right-most position, the chopping speed is proportional to a user-supplied DC voltage that is applied to the Volta oltage Input BNC connector (just to the right of the switch). 2. The Power Switch is located on the front panel (See page 5.) This 3-position rocker switch selects either the high frequency ( Hz) range when depressed to the right, the low frequency (4-500 Hz) range when depressed to the left, or turns the unit off when placed in the center position. 3. The Frequenc equency Set knob located on the front panel adjusts the units chopping frequency when the Control ol Source switch is set in the Panel (or center) position. 3

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6 Front Panel Controls 5

7 Connections The following describes connections between the chopper head and the controller, the controller and the power mains, and connections to auxiliary equipment. Chopper to Controller - The chopper head is connected to the controller via an 8 conductor coiled modular cable. The cable plugs into modular receptacles located on the side of the chopper head and at the rear of the controller. The cable plugs are identical and can thus be plugged in either receptacle. Do not attempt to substitute any y other cable le or sever ere e damage e may result. It is recommended that t this connection be made prior to plugging in the power er supply y to the mains. Power Supply to Controller - The wall-mount or table-top (for line voltages of 230 VAC) power supply is equipped with a 5 pin DIN style connector that plugs into a receptacle located at the rear panel of the controller. It is recommended that t this connection be made prior to plugging in the power er supply y to the mains. Units equipped with a table top supply have, in addition, a power cable equipped with a standard IEC connector that plugs into the power supply and a power connector that is appropriate for the mains of the country where it is to be used. It is recommended that the IEC connection be made prior to plugging ing the power er cable le into the mains. It is further ther recommended that t the power er switc witch h on the controller oller be in the center (or off) f) position befor ore e connecting the power er supply y to the mains. Sync Out - This TTL compatible signal is provided for use with lock-in amplifiers or other ancillary equipment to synchronize it with the chopped optical signal. In the Low Frequency Range this signal can range from 4 Hz to 500 Hz depending on the chopper speed selected. In the High Frequency Range this signal can range from 40 Hz to 5000 Hz depending on the speed selected. The center connection of the BNC connector carries the sync signal. The outer case of the BNC connector is at ground potential. Sync Input - The user may apply a TTL compatible signal to this BNC connector to enable the C-980 to lock to an external clock. This signal should be in the range of Hz in order to take the unit throughout its entire speed range. It is recommended that t the sync signal not exceed 5000 Hz in order der to avoid exceeding the maximum um rated speed of the chopper motor. The duty cycle is not important as the C-980 responds only to the edges of the signal. It is recommended however, that the minimum pulse width not fall below 100 ns. The center connection of the BNC connector carries the sync signal. The outer case of the BNC connector is at ground potential. Voltage Input - The user may apply an external DC signal to this input in order to control the chopper speed. The range of this voltage is between Volts. The chopper speed will be directly proportional to this voltage with a linearity of better than 1%. The scale factor is either 100 Hz/Volt or 1000 Hz/Volt depending on the speed range that is in use. It is recommended that t the input single not exceed 4.00 V in order der to avoid exceeding the maximum um rated speed of the chopper motor. The center connection of the BNC connector carries the DC input signal. The outer case of the BNC connector is at ground potential. 6

8 Display The C-980 is equipped with a built-in frequency counter that counts the actual reference signal. The counter has a resolution of 1 Hz in the High Frequency Range and 0.1 Hz in the Low Frequency Range. The display is updated once per second. Leading zeroes are blanked. Thus if the chopper blade is not rotating the display will be blanked except for the decimal point (if the Low Frequency Range is selected). The display is provided by four green (565 nm) LED digits. Other colors can be substituted on request. Apertures The C-980 chopper is equipped with two apertures. The outermost aperture is designed to be used for the High Frequency Range and the inner aperture is designed to be used for the Low Frequency Range. As the controller oller cannot determine whic hich h aper pertur ture e is being used to chop the optical signal, it is important that t the user direct the beam through the appr pproo- pria iate te aper pertur ture e for the desired ed chopping rate te.. Otherwise the chopping frequenc equency y display y will be off f by a factor of ten. Mounting The C-980 chopper head is equipped with an adjustable height standard 0.5" mounting post with an 8-32 mounting thread. The post may be mounted in either the top or bottom of the chopper head. This provides the user with maximum flexibility for aligning the chopper aperture with the beam to be chopped. The post holder base has two slots in it to enable the user to secure it to a standard optical bench that has 1/4-20 threaded holes on 1 inch centers. 7

9 Operating Considerations The C-980 utilizes a precision Swiss-made DC motor. Motors do however, have a finite lifetime. It is thus recommended that the motor be used at the lowest speed that provides the needed chopping rate. For example, if a chopping rate of 500 Hz is desired, it is preferable to run the unit at the bottom of the High Frequency Range rather than at the top end of the Low Frequency Range. It is also desirable to turn the unit off when it is not being used. These simple precautions will maximize the life of your motor. The outer sets of slots provides 30 chopping cycles per motor revolution while the inner set of slots provides three chopping cycles per revolution. Thus using the inner set of slots provides the minimum phase jitter. Use the inner set of slots in those applications where this criteria is important. Additionally the inner set of slots chops the largest diameter beam. For beams of more than 2 mm in diameter, the inner set of slots should be used. The rise time of the chopped optical signal is essentially the time it takes for the blade to pass through the beam. Thus if this criteria is of importance, the inner set of slots should be used with the motor set to a faster speed or the beam should be focused at the plane of the chopper blade. For or High power er lasers s of 5 Watts tts or more, never er leave e the chopper blade exposed to the beam while it is not rota otating ting or is rota otating ting at t low w speed.. Excessive e heating of the blade can result and may y cause it to war arp. p. The DC voltage applied to the unit in the DC control mode should be as clean as possible. Ripple and/or noise will degrade performance and stability. Do not attempt to rota otate te the chopper head while hile the unit is rota otating ting at high speed.. Gyroscopic for orces ces can bend the blade and for orce ce it into contact with the LED- phototransistor sensors. s. This his could damage e the unit. Theory of Operation Refer to the block diagram on the following page. The C-980 Optical Chopper operates by including the motor in a Phase- Locked-Loop. LED-phototransistor pairs located in the chopper head sense the passage of slots that are photo-etched into the chopper blade and generate a TTL-compatible square wave. This signal is presented to a phase-frequency comparator whereupon it is compared to a clock signal that is generated by a precision voltage to frequency converter. The resulting error signal is amplified and appropriately filtered and is then amplified again to generate the drive voltage for the DC motor. When phase lock occurs, the chopping frequency is identical to the clock frequency and has the same frequency stability. The 4 digit counter counts and presents the actual frequency of passage of the chopper blade slots and is updated once each second. This signal is buffered and presented at the Sync Output port for use by auxiliary equipment such as a lock-in amplifier. When used in the external sync signal mode, the clock that is supplied to the unit is used as the basis for phase comparison. Therefore the unit will track the input clock. When in the external DC control mode, the DC input signal is used to drive the Voltage to Frequency converter in lieu of the front panel control. Thus the chopper speed is directly proportional to the applied input voltage. 8

10 Ext. Clock Buffer Phase Comp. Loop Filter & Power Amp. DC Motor Front Panel Control Optical Photosensor V/F Converter Frequency Counter Buffer Sync Output Ext. Voltage Input Display Crystal Time Base Block Diagram Equipment Required: Calibration Procedure 1. Universal Counter/Timer with at least 0.1% basic accuracy. 2. Variable DC source capable of supplying VDC. 3. Digital DC voltmeter with at least 0.25% basic accuracy. 4. Two BNC - BNC cables and one BNC Tee. Procedure: 1. Remove power from the unit by setting the power switch to the Off position. 2. Remove the front and back plastic bezels by removing the four 4-40 Philips head screws located at the sides of the instrument. 3. Slide off the top aluminum cover thereby exposing the printed circuit board of the controller. 4. Connect the unit to the chopper head and power supply. 5. Refer to the circuit board layout overleaf for control locations. 6. Connect the variable DC source to the Volta oltage e Input connector on the C-980 rear panel as well as the DC voltmeter using a BNC Tee. Connect the external counter to the Sync Output connector using one of the BNC cables. Set the Control ol Source switch to Volta oltage Input. Set the power supply voltage for volts as read on the voltmeter. 7. Energize the C-980 by selecting the High Freq. range. Adjust R2 for a front panel reading of 3500 Hz. 8. Set the Control ol Source switch to the Panel position. Turn the front panel Frequenc equency Set knob fully clockwise. Adjust R21 for a front panel reading of 5050 Hz. 9. Using the external clock counter check that the front panel reading and counter reading agree to within 2 least significant digits. Vary the Frequenc equency Set control throughout its range to check for normal operation over the full range of the instrument. Change speed ranges and check that the front panel and counter readings are reduced by a factor of ten. 10. The Gain control, R36, and the Offset Adj., R11 do not normally require adjustment. Upon removing power from the instrument and replacing the cover, calibration is complete. 9

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12 Warranty And Repair Information REPAIR INFORMATION Products manufactured by Terahertz Technologies Inc. are designed and manufactured to provide reliable performance. However, in the event that service is required, both telephone technical assistance and factory repair services are available. Call (315) , fax (315) , or for information. For IN-WARRANTY REPAIRS, call us to obtain a Returned Material Authorization number, (RMA Number). All products are to be returned to TTI with freight charges pre-paid. Those products sent under warranty will be returned to our customers pre-paid. We cannot be responsible for returned products that do not reference the TTI RMA number. For OUT-OF-WARRANTY repairs, services are billable for both time and materials. LIMITED WARRANTY TERAHERTZ TECHNOLOGIES INC. (TTI) WARRANTS THAT TO THE FIRST PURCHASER, FOR A PERIOD OF TWO YEARS FROM THE DATE OF RECEIPT, THAT THIS PRODUCT (THE PRODUCT) WILL BE FREE FROM DEFECTS IN MATERIALS AND MANUFACTURING. THE FOREGOING WARRANTY IS THE ONLY WARRANTY, EXPRESS OR IMPLIED, GIVEN BY TTI, I.E., THERE IS NO WARRANTY OF FITNESS FOR A PARTICULAR PURPOSE. TTI HEREBY DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY OTHER THAN THE WARRANTY IN THE FIRST SENTENCE TO THE FULLEST EXTENT PERMITTED BY LAW. THE SOLE AND EXCLUSIVE REMEDY UNDER THIS WARRANTY IS REPAIR OR REPLACEMENT AT TTI S OPTION OF ANY PRODUCT THAT PROVES TO BE DEFECTIVE IN MATERIALS OR MANUFACTURING WITHIN TWO YEARS OF RECEIPT OF THE PRODUCT. NOTE: THIS WARRANTY DOES NOT APPLY TO ANY PRODUCT WHICH HAS BEEN SUBJECT TO MISHANDLING, MISUSE, OR SERVICE BY UNAUTHORIZED PERSONNEL OR TO ANY PRODUCT WHICH HAS BEEN DAMAGED, MODIFIED, ALTERED OR TAMPERED WITH. TO THE FULLEST EXTENT OF THE LAW, TTI DISCLAIMS ALL LIABILITY FOR ANY OTHER DIRECT, INCI- DENTAL OR CONSEQUENTIAL DAMAGES ALLEGED TO BE CAUSED BY A DEFECTIVE PRODUCT, I.E., TTI WILL NOT BE RESPONSIBLE FOR ANY PERSONAL INJURY, PROPERTY DAMAGE OTHER THAN THE COST OF REPLACING THE PRODUCT OR ANY OTHER MONETARY DAMAGE SUCH AS LOST WAGES OR PROFITS CAUSED BY ANY USE, ATTEMPTED USE OR INABILITY TO USE THE PRODUCT. NOTE: BY USING THE PRODUCT, YOU AGREE THAT REPAIR OR REPLACEMENT AT TTI S OPTION WILL FULLY SATISFY TTI S WARRANTY OBLIGATION TO YOU, WHETHER IN CONTRACT, TORT, NEGLIGENCE, STRICT LIABILITY OR OTHER APPLICABLE LAW. 11