C-995
Optical Chopper
Operating Manual

Terahertz Technologies Inc.
169 Clear Road Oriskany, New York 13424
www.teratec.us
Tel: (315) 736-3642 Fax: (315) 736-4078

Copyright 2016 Terahertz Technologies Inc.

TopicPage

GENERAL INFORMATION
Introduction.......................................................................................... 1
Specifications........................................................................................ 2
Unpacking and Inspection......................................................................3
Power Requirements...............................................................................3
OPERATING INSTRUCTIONS
Operation...............................................................................................4
Serial Port .............................................................................................5
Operating Considerations.......................................................................7WARRANTY INFORMATION
Repair Information.................................................................................8
Limited Warranty...................................................................................8

Introduction
The C-995 Optical Chopper is a general purpose optical chopper designed forlaboratory use. Equipped with a large five-digit LED readout, the C-995 controller enables digital entry of the desired chopping rate directly from the front panel.
Additionally the C-995 is equipped with a bi-directional Rs-232 port that equips
the user to set the desired chopping rate to a resolution of .001 Hz and to readthe status of the instrument.
As the unit is designed with a phase-locked-loop control system, the chopping rate
may also be synchronized to a user-supplied external clock ranging from 4 Hz to 5
KHz. The controller is then used to read the frequency of the external clock.
The C-995 chopping head is attached to the controller by means of a 10 foot coiled
cord. The precision etched blade is fully enclosed for protection from inadvertent
damage. There are two apertures and two blade sections (30 slots and 3 slots) forthe high and low frequency ranges respectively. The aperture diameter is 15 mmwith a slot width of 4.5 mm (30 slot section) or 15 mm (3 slot section).
The small 4.75 inch square outline and 2.5 inch maximum depth permits easy integration into compact optical setups. Dual #8-32 mounting holes permit the apertures
to be placed at a height as low as 0.75 inches above an optical bench, or with theincluded ½ inch rod and stand, as high as 13 inches above the mounting surface.

CautionCautionThe screw
screw onon thethe rod
rod andand stand
stand included
included withThewith thethe C995
C995 Optical
Optical Chopper
Chopper isis set
set totoallow
amaximuminsertion
distanceof
3/16”
intothebodyofthechoppinghead.
allow a maximum insertion distance of 3/16” into the body of the chopping head.
Inserting thethe stand
stand screw
screw greater
greater than
than 3/16”
3/16” will
Insertingwill damage
damage thethe pick-off
pick-off board
board oror thethechopper blade.
blade. ThisThis damage
damage isis not
not covered
covered under
under warranty.
warranty.
chopper1

C-995 Optical Chopper Specifications
Chopping Frequency Ranges
Aperture Size

4 Hz to 500 Hz ( Inner slots), 40 Hz - 5 KHz (outer slots)
0.6 inch diameter (15 mm), and 0.6 inch by 0.2 inch (15 x 4.5 mm)

Frequency Control

Phase-Locked-Loop, Direct Digital Synthesis

Frequency Uncertainty
Phase Jitter±.0025 % of setting
0.1 % peak to peak, 3 slot section, 1.0 % peak to peak, 30 slot section< 3 seconds

Settling Time to Phase Lock
External Clock Input Requirements

TTL, CMOS Compatible Square Wave, 4 Hz to 5000 Hz

Sync Signal Output

TTL, CMOS Compatible Square Wave

Display

Five Digit, high intensity green, 0. 5 “ highTemperature Coefficient of Chopping Frequency< 10 ppm/C

Frequency Resolution (using Rs-232 Control).001 Hz

Frequency Resolution (using Front Panel Control).01 Hz0.1 Hz, 1 HzCounter Resolution using External Clock

9600 Baud, N-8-1, 3 wire

Rs-232 Interface
Chopper Head MountingStandard 8-32 tapped holes, mounting rod and stand is provided

Chopping Blade Diameter4.1 inch diameter0 - 40 C

Operating Temperature Range
Dimensions (Head)

4.5 “ H x 4.5 “ W x 2 “ D, 114 mm x 114 mm x 51 mm

Dimensions (Controller)

2.7 “ H x 7 “ W x 9.1 “ D, 69 mm, 178 mm, 231 mm
Coiled Cord 10 feet max lengthInterconnecting cable suppliedPower Requirements

95-260 VAC, 50-60 Hz, 15 VA MaxYes

CE Certification
Weight3 lbs, 1.36 Kg

Accessories Provided

Mounting rod and stand, Rs-232 cable, Power Cord, Operating Manual

Standard Warranty

Two years, Components and Workmanship, 30 Day Satisfaction Guarantee

Application Software ProvidedDownloadable from TTI website, www.terahertztechnologies.com
TTI reserves the right to change specifications without notice2Unpacking and 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 orconcealed, it must be noted on the freight bill or express receipt and signed by thecarrier’s agent. Failure to do so could result in the carrier refusing to honor the claim.
Upon filing a claim TTI should be notified.

Power Requirements
The C-995 is equipped with a universal power supply that works anywhere inthe world. The input range is from 85 to 260 V.A.C., 40 - 400 Hz. Both legs of thepower line are switched and fused for safety. Replace fuses with 1 amp slo-blo, 5x20 mm
types only.

3Operation
After unpacking and inspecting the instrument, attach the rod and stand to thechopper head by screwing in the 8-32 threaded screw into the appropriate hole inthe chopper head..

CautionThe screw on the rod and stand included with the C995 Optical Chopper is set toallow a maximum insertion distance of 3/16” into the body of the chopping head.
Inserting the stand screw greater than 3/16” will damage the pick-off board or thechopper blade. This damage is not covered under warranty.
Adjust the height of the chopper head as needed. (The inner aperture should be
used for the Low speed range and the outer aperture for the High speed range.)
Connect the chopper head to the controller with the coil cord provided. Place thepower cord into the IEC power entry module on the instrument rear panel andplug the power cord into a suitable power outlet. The instrument is now ready foruse.
The front panel frequency select switch should be set to High for a desired chopping frequency in the range of 40 to 5000 Hz and to Low for a desired chopping
frequency in the 4 - 500 Hz range. The power switch is located on the power entry
module on the instrument rear panel. This switch may now be turned on. Insurethat the Sync Select switch on the rear panel is in the Int. position.
The display should now be energized and it should indicate either 1000.0 Hz or
100.00 Hz for the high and low frequency ranges respectively. These values are
stored in the unit during the calibration process. (Frequency settings for eachrange are stored in non-volatile memory so that the unit is able to maintain theprogrammed chopping rate between periods of use.)
The TTL/CMOS level sync signal that is coincident with the chopped light is now
available at the front panel BNC connector labeled Sync Output. This signal may
now be connected to a lock-in amplifier, oscilloscope or other instrument.
Setting the chopping rate from the Front Panel
The chopping frequency may be set from the front panel as follows. Push andrelease the frequency set control. The least significant digit of the display will now
blink. Rotate the knob to select the digit value that is desired. Pressing and releasing the knob again will cause the next most significant digit to blink. Set thisdigit in like manner. Continue this process until the desired most significant digitis set. Pressing and releasing the knob one last time will cause the displayed frequency to be entered into the unit and also be stored in memory. The controller
will now adjust the motor speed to chop precisely at the rate that has been selected. The unit will not allow speeds to be selected that are outside of the 4 - 500 Hz
or 40 - 5000 Hz limits for the Low and High speed ranges respectively.
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Setting the chopping rate via the Serial Port
The C-995 is equipped with a bi-directional “three-wire” Rs-232c interface. It permits the unit to be remotely controlled via an external computer and will reportthe unit’s status on request.
An interface cable is supplied with each unit. Plug the Rj-14 (telephone style)connector into the port on the unit’s rear panel. Plug the 9 pin D connector into
the computer serial port. Using a communications program (such as WINDOWSHyperterminal) set the appropriate communications parameters. The protocol is9600 N 8 1, i.e. Baud Rate of 9600 Baud, no parity bit, 8 data bits, and one stopbit. The command structure is as follows:

To set the chopping rate to 1 KHz on the high speed range, send the following
eleven character string:“F:1000.000CR”
CR is Carriage Return, hex 0D, or Enter on a PC keyboard. The significance of thecharacters is as shown above.
All eleven digits must be present including leading zeros. For example, to set theunit to chop at 15.627 Hz on the low frequency range, send the following string:“F: 0015.627CR”
A correct command will be met with the response: “OK”.
An incorrect command will be met with the response: “Invalid Command”.
To request the status of the unit, send the following string:“F:STATUSRQCR”

5The C-995 will return the following information:															INT(EXT) SYNC
HI (LO ) SPEED RANGE
1000.000 HZWhen the unit is in the Ext. Sync mode, the measured chopping frequency will bereturned.
Should the user attempt to enter an invalid frequency for the range in use, the following string will be sent:		

“FOR THE RANGE IN USE, FREQ. IS TOO HIGH (LOW)”

The display will reflect the new frequency.
Setting the chopping rate via External Sync
To synchronize the C-995 to an external clock, set the Sync switch on the rearpanel to the Ext. position. Apply a TTL/CMOS compatible clock to the rear panel
BNC connector labeled External Sync.
Ensure that the clock frequency is appropriate for the range in use, i.e. 4 - 500 Hz
for the Low speed range and 40 - 5000 Hz for the High speed range. The C-995
chopping rate will now be phase-locked to this external clock and will track it. Thedisplay will count the external frequency and display it to a resolution of 0.1 Hz in
the High speed range and to 1 Hz in the Low speed range.
Note:					It is recommended to energize the C-995 prior to applying theexternal sync signal.

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Operating Considerations
The C-995 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 theneeded chopping rate. For example, if a chopping rate of 400 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 theLow 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 setof 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 thiscriteria is important. Additionally the inner set of slots chops the largest diameter beam.
For beams of more than 2-3 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 topass 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 High power lasers of 5 Watts or more, never leave the chopper blade exposed tothe beam while it is not rotating or is rotating at low speed. Excessive heating of
the blade can result and may cause it to warp.
Do not attempt to rotate the chopper head while the unit is rotating at high speed.
Gyroscopic forces can bend the blade and force it into contact with the LED- phototransistor sensors. This could damage the unit.				
Never plug or unplug the chopper head while the unit is powered up. To
do 			so may damage the unit.

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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) 736-3642, fax (315) 736-4078, e-mail info@teratec.us or visit our web site at www.teratec.us for moreinformation or to request an RMA number.
For IN-WARRANTY REPAIRS, call us to obtain a Returned Material Authorization number, (RMA Number). All products areto 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 PERIODOF TWO YEARS FROM THE DATE OF RECEIPT, THAT THIS PRODUCT (THE PRODUCT) WILL BE FREEFROM DEFECTS IN MATERIALS AND MANUFACTURING. THE FOREGOING WARRANTY IS THE ONLYWARRANTY, 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 OTHERTHAN 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’SOPTION OF ANY PRODUCT THAT PROVES TO BE DEFECTIVE IN MATERIALS OR MANUFACTURINGWITHIN TWO YEARS OF RECEIPT OF THE PRODUCT. NOTE: THIS WARRANTY DOES NOT APPLY TOANY PRODUCT WHICH HAS BEEN SUBJECT TO MISHANDLING, MISUSE, OR SERVICE BY UNAUTHORIZED PERSONNEL OR TO ANY PRODUCT WHICH HAS BEEN DAMAGED, MODIFIED, ALTERED ORTAMPERED WITH.
TO THE FULLEST EXTENT OF THE LAW, TTI DISCLAIMS ALL LIABILITY FOR ANY OTHER DIRECT, INCIDENTAL 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 THECOST OF REPLACING THE PRODUCT OR ANY OTHER MONETARY DAMAGE SUCH AS LOST WAGESOR PROFITS CAUSED BY ANY USE, ATTEMPTED USE OR INABILITY TO USE THE PRODUCT. NOTE: BYUSING THE PRODUCT, YOU AGREE THAT REPAIR OR REPLACEMENT AT TTI’S OPTION WILL FULLYSATISFY TTI’S WARRANTY OBLIGATION TO YOU, WHETHER IN CONTRACT, TORT, NEGLIGENCE,STRICT LIABILITY OR OTHER APPLICABLE LAW.

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