Monochromator Controllers

MODEL 330 MONOCHROMATOR AND REMOTE WAVELENGTH CONTROLLER

1.0 INTRODUCTION

1.1 Scope

This manual is intended to familiarize the operator with the features of the MODEL 330 MONOCHROMATOR AND REMOTE WAVELENGTH CONTROLLER. It is also intended to instruct people who are familiar with electro-optical instrumentation in general and only need to be informed of the par­ticular operating characteristics of this instrument.

1.2 Purpose of Instrument

The MODEL 330 MONOCHROMATOR AND REMOTE WAVELENGTH CONTROLLER is mounted on the control panel of the coating machine and permits the operator to adjust from the control panel the wavelength of the monochromator located on the barrel of the receiver of the MODEL 590 OPTICAL MONITOR. Use of the monochromator provides the operator and coating de­signer with infinite selection of wavelengths for the monitoring process. This ar­rangement is a great advantage where the monochromator is adjusted from the control console rather than adjusting the wavelength by hand on the monochro­mator that is generally under or at the back of the coating machine.

The monochromator entrance slit is located at the end of the Monitor telescope barrel. A periscope allows the operator to center the incoming light beam on the entrance slit. The focus lens is adjusted for maximum throughput. The wave­length of the monochromator is displayed on a digital meter on the controller and is adjusted with a stepper motor and determined by means of a precision potenti­ometer and voltage divider network. The detector is either silicon for the visible and near infrared of lead sulfide for the infrared. Provisions are made for auto­matic insertion of second order suppression filters at the appropriate wavelengths.

The Model 330 electronics are housed in a 19-inch rack mount that contains the desired input potentiometer and digital display wavelength control electronics and digital display of the actual wavelength.

1.3 Organization of Manual

This manual is arranged in the sequence that the operator would normally follow in unpacking, assembling, installing and operating the instrument. Safety precau­tions that the operator should follow are described. The remaining portion of the manual provides wiring diagrams and system layout to assist the operator in the event that there is a problem.

1.4 Custom Features

The MODEL 330 MONOCHROMATOR AND REMOTE WAVELENGTH CONTROLLER is integrated with a Model 590, thus in addition to the above parts, the monochromator is installed into the receiver between the barrel contain­ing the collecting and imaging optics and the detector containing the silicon and lead sulfide detectors. When the monochromator is used, then no filters are re­quired.

The Model 330 described in this manual is configured to operate on 220 volts AC at 50-60Hz.

The monochromator scans from 350NM to 1050NM. Electronic stops prevent the monochromator from going to wavelengths less than 325NM and greater than 1100NM.

A filter cassette is provided with this instrument. This cassette has the following filters: 350NM, 550NM, 633NM and 1050NM. The cassette cannot be used with the monochromator.

2.0 UNPACKING INSTRUCTIONS

When unpacking a Dyn-Optics electro-optical system, ensure that all components are handled with care because the system may contain fragile OPTICS and ELEC­TRONICS. The MODEL 330 MONOCHROMATOR AND REMOTE WAVELENGTH CONTROLLER consist of the following items:

Item Quantity Description

1 1 Model 330 electronics in a 19-inch

rack mounted chassis.

2 1 Oriel Part No. 77250, 1/8 meter monochrom-

ator with grating mounted in barrel of Model 590 between the focusing lens and the de­tectors.

3 1 8-pin connector and cable connects the

panel mounted Model 330 to the monochro­mator housing mounted on the Model 590 receiver barrel.

8 pin connector and 2-foot cable con­nects the Model 590 electronics to the Model 330 electronics. (Different pin arrangement than Item 3 above)

Connector wire from 60HZ, 120 or (220V) line to Model 330.

Instruction Manual

If any of the above equipment is missing or damaged, please contact Dyn-Optics for corrective action.

The instrument is insured for damage during shipment. If the package or contents are damaged, the shipping company must be notified so that they can inspect the damage and approve the claim. The claim is filed by Dyn-Optics, but the inspec­tion must be performed at the location of the consignee. Please save the package and all material used in wrapping. DO NOT ship the damaged instrument back to Dyn-Optics until the shipping company has inspected it.

3.0 SAFETY PRECAUTIONS

The instrumentation will have 120/240 VAC inside the top cover. The equipment should ONLY be opened for service or maintenance by an experienced electronic technician.

DO NOT remove the grounding prong from the power cord. Units are equipped with a three prong-grounding plug for protection against shock hazards, and to minimize electrical noise coming in from the power lines. DO NOT block cooling vents.

To avoid electrical shock, unplug the unit before performing any maintenance.

DO NOT operate the unit in the presence of explosive fumes.

The system operates at 50 - 60 HZ input power unless otherwise noted or tagged.

Notes:

(1) It is assumed that the customer's power and vacuum equipment are grounded according to code and there are no "floating" grounds.

(2) It is assumed that the power lines have a minimum of RFI. (Radio Frequency Interference).

(3) It is assumed that the equipment will operate in clean environment.

(4) DO NOT operate in the presence of water.

4.0 SYSTEM DESCRIPTION

The Dyn-Optics MODEL 330 MONOCHROMATOR AND REMOTE WAVELENGTH CONTROLLER provides the capability of selecting the de­sired wavelength for an optical monitoring system from a remote location.

A monochromator is integrated into the receiver portion of the Optical Monitor. The wavelength drive mechanism is integrated into the monochromator housing. Wavelength selection is accomplished by a front panel control. The desired wavelength is input by a 10-turn potentiometer and the input wavelength is shown on the digital meter.

The Model 330 is intended to replace multiple filters as a means of wavelength selection, thus providing an infinite selection of operating wavelengths and ease of insertion.

Figure 1 entitled "Monochromator integrated with receiver of Model 590 Optical Monitor" shows the location of various major components of the optical system and monochromator. The various components are described below:

1. Focusing Lens, Periscope and Entrance Slit

The incoming illumination from the transmitter and witness glass is fo­cused by the focusing lens to form an image of the filament of the lamp on the entrance slit of the monochromator. The operator can look into the periscope and see the image of the lamp filament super-imposed on the en­trance slit. The focusing lens can be moved forward or backward to obtain the best image and the maximum signal. The transmitter or receiver can be rotated around their axis so that the long dimension of the filament is lined up with the long direction of the slit.

2. Monochromator and Exit Slit

The monochromator images the light entering the entrance slit onto the exit slit. However, the radiation emerging from the exit slit will be at prime wavelength plus the second order of the prime wavelength depending upon the position of the grating. For example, if the monochromator is set for 800NM, then in addition to the 800NM there will be the second order of 400NM appearing at the exit slit.

3. Order Sorting or Second Order Suppression Filter

The order-sorting filter or second order suppression filter is automatically inserted into the optical path with no input required from the operator. The order-sorting filter suppresses the second order. As in the example above, when 800NM is the prime wavelength, the order-sorting filter suppresses or eliminates the 400NM second order illumination.

4. Model 590 Optical Monitor Receiver

The radiation from the monochromator is relayed onto the detector in the receiver. There are silicon detectors for operation from 350NM to 1050NM. A preamplifier in the receiver transfers the high impedance de­tector output into a low impedance signal for transmission to the main am­plifier. The cable from the bottom of the receiver is connected to the re­ceiver cable connector on the Model 590 amplifier.

The connection between the Model 330 and the Model 590 is made from the cable connection at the rear of the Model 330 where it is marked "Out­put to Monochrom" to the cable connector on the monochromator where it is marked "Input to Monochrom." The cables are polarized so that they cannot be connected incorrectly.

5. Rear Panel of the Model 330

The rear panel of the Model 330 has a cable connector that attaches via a cable to the monochromator. There is also a three-wire power connector that connects to the building a 120 volt 60 HZ power line. The third wire is ground that should connect to a good building ground. The "3 amp slow blow fuse" is also located on the rear panel.

6. Front Panel of Model 330

The front panel has the following switches and controls.

(A) POWER: ON/OFF

(B) WAVELENGTH SELECTION:

The wavelength selection is made by a 10-turn potentiometer. The adjacent digital meter will indicate the input wavelength in nano­meters (NM).

(C) GO TO

When the "GO TO" switch is pressed, the monochromator will scan to the input wavelength. Momentarily press the "GO TO" switch, but do not hold it down.

(D) ABORT

When the "ABORT" switch is pressed, input wavelength is can­celled. The monochromator will stop at whatever wavelength it is at when the ABORT switch is pressed. To re-initiate an input wavelength, re-enter a desired wavelength with the potentiometer and press the "GO TO" switch.

(E) WAVELENGTH

The wavelength digital meter indicates the actual wavelength in NM that the monochromator is set. Due to the tolerance buildup in the two potentiometers, there may be a 1 or 2 NM difference be­tween the desired wavelength and the actual wavelength. If the small difference is significant, add the difference (plus or minus) to the desired wavelength potentiometer and press the "GO TO" switch and the monochromator will correct small differences.

5.0

INSTALLATION

5.1 General

The monochromator and detector assembly is attached to the porthole of the vac­uum chamber with a gimbal. When mounted, the light from the transmitter goes through the vacuum chamber, reflected from the witness glass, and projected into the barrel of the receiving telescope of the monochromator assembly. Look into the periscope on the receiving barrel and tilt the periscope barrel and monochro­mator until the light beam is imaged on the entrance slit of the monochromator. The periscope on the barrel of the receiver, Figure 1, is located so that the observer looking into the periscope will see the light from the monitor transmitter imaged on the slit.

5.2 Adjustment

The light imaged on the slit will be the filament of the lamp in the transmitter. The image should be focused so that the coils of the filament are superimposed on the slit.

5.3 Slits

There are 1mm wide entrance and exit slits supplied with the monochromator. The bandwidth of the 1mm slits is 13NM for the 600-lines/mm grating that oper­ates from 400NM to 1500NM.

6.0 OPERATION OF MODEL 330 MONOCHROMATOR AND REMOTE WAVELENGTH CONTROLLER

To operate the MODEL 330 MONOCHROMATOR AND REMOTE WAVE­LENGTH CONTROLLER, follow the procedure indicated below:

• Assemble unit as described in previous paragraphs and shown on Figure 6.1.

• The cables all have a different number of pins or are polarized, consequently, they can only be connected to the correct receptacle.

• Insert power cord in 60HZ receptacle and turn power ON. The digital meters will light.

• The wavelength of the monochromator can be set by the following procedure:

Input the desired wavelength by rotating a 10 turn potentiometer until the digital meter indicates the desired wavelength.

Press the GO TO switch and the monochromator starts to scan to the de­sired wavelength.

The digital meter will indicate the actual wavelength of the monochromator when the wavelength is the same as the desired wavelength, then the monitor will be ready.

Long and Short wavelength stop. The monochromator will scan beyond the useful portion of the spectrum and, into mechanical stops with the risk of damaging the drive mechanism. Consequently, there are electronic stops that will not allow the monochromator to go below 325NM or above 1100NM. When the monochromator reaches the end of the travel, it will stop and can only move in a direction away from the stop.

If the incorrect wavelength is inputted, press the ABORT switch and re­enter the correct wavelength.

RESET

If for any reason the stepper motor is overloaded and the protection circuit turns off the motor, then restart as follows.

1. Find and correct the cause of the overload and motor stopping.

2. Turn unit OFF and ON again to reset stepper motor driver electronics.

The symptom for overload is that the monochromator does not scan or the wave­length meter will flash ON and OFF.

DIFFRACTION GRATING

The diffraction grating selected as the most suitable for the MODEL 330 MONOCHROMATOR AND REMOTE WAVELENGTH CONTROLLER is

Oriel Part Number 77921, graph attached as Figure 8.1. The grating has high effi­ciency at the blaze wavelength of 400NM. At this wavelength the silicon (Si) de­tector and quartz-halogen illumination source have comparative low efficiency. As the grating looses efficiency toward longer wavelengths, the efficiency of the detector and illumination source are increasing, thereby, partly compensating and providing a reasonable uniform response over the wavelength range from 500 to 950NM. The silicon detector looses sensitivity for wavelengths greater than 900NM and has zero response at 1100NM.

When scanning wavelengths, there will be wavelengths where the output will ex­hibit a rapid rise or fall in signal as indicated by the monitor. These rapid signal variations are a consequence of the diffraction grating theory and are called Wood's Anomalies.

AUTOMATIC SECOND ORDER SUPPRESSION

The Grating Monochromator is an excellent optical device for dispersing white light into its various wavelengths. Furthermore, the diffraction grating has the ad­vantage in a monochromator of providing a wavelength that is linear with dis­placement. However, the grating has the disadvantage in that the second order of one-half the prime wavelength occurs at the same location as the prime wave­length. Also, the third order of one-third the prime wavelength appears at the same place as the prime wavelength. However, the third order interference gener­ally is negligible. The grating is then limited for practical purposes to less than a two-to-one wavelength range without "Second Order Suppression" filters. For ex­ample, at a wavelength setting of 1000NM, the first order of 1000NM and the sec­ond order of 500NM appear at the exit slit. Thus, a second order suppression filter must be inserted in the optical path when operating at 1000NM that blocks all wavelengths of 500NM and less. Then only 1000NM is sensed at the detectors and not a mixture of 1000NM and 500NM.

In the present system that scans from 350NM to 1050NM, the second order is automatically suppressed by selecting one of two detectors that operate over less than a two-to-one wavelength band so that the second order wavelengths are not detected.

The waveband of operation is separated into two bands that are detected by two detectors. These bands and detectors are:

DETECTOR NO.

WAVEBAND OF RESPONSE

DETECTOR

1

2

350 to 600NM 550 to 1050NM

Si Si

The illumination is deflected to detector No. 1 by a dielectric 45° beamsplitter that reflects wavelengths between 350NM to 500NM and transmits to detector No. 2 for wavelengths greater than 600NM to over 11OONM as shown in the following sketch.