ILX Lightwave LDX-3620 Users Guide

Page 1

User’s Guide

Ultra Low Noise Current Source

LDX-3620

ILX Lightwave Corporation · P. O. Box 6310 · Bozeman, MT, U.S.A. 59771 · U.S. & Canada: 1-800-459-9459 · International Inquiries: 406-556-2481 · Fax 406-586-9405

ilx.custhelp.com · www.ilxlightwave.com

70001803 June 2008

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TABLE OF CONTENTS

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Safety Information and the Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix

General Safety Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix

Safety Marking Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x

Comments, Suggestions, and Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii

Chapter 1 Introduction and Specifications

Product Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Options and Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

362038 Long Life Battery Option . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

132 Rack Mount Kit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Chapter 2 Operation

Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

AC Power/Battery Charge Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Tilt Foot Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Rack Mounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Front Panel Control and Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

DC POWER Key Switch and Output Range Selection . . . . . . . . . . . . . . . . . . 6

Low Battery Indication and Shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

EXT Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

RAMP Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

MODE Selector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

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TABLE OF CONTENTS

LIMIT Current Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

OUTPUT On/Off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

OUTPUT ADJUST Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

DISPLAY Selector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Output 4-1/2 Digit LCD Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

OUTPUT SHORT Indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

OUTPUT ERROR Indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Rear Panel Controls and Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

HIGH/LOW BANDWIDTH Selector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

OUTPUT Connector (J401) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

PHOTODIODE Feedback Gain Adjustments . . . . . . . . . . . . . . . . . . . . . . . . 11

PHOTODIODE Feedback Input Jack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

RAMP TRIGger Output Jack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

CHASSIS GROUND Connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

AC POWER/Battery Charge Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Fuse Holder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

LDX 3620 Operation Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Outline of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Load Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Safe Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Safety Interlock Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Laser Diode Connections and Shielding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Photodiode Feedback Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

RAMP TRIGger Output Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Setting the LIMIT Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Setting the Output in CONST CURRENT Mode . . . . . . . . . . . . . . . . . . . . . . 19

Setting the MODULATION Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Using the Internal RAMP Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Setting the Photodiode Feedback Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Setting the Laser Power in CONST POWER Mode . . . . . . . . . . . . . . . . . . . 21

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Chapter 3 Maintenance

Battery Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Battery Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Fuse Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Display Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

TABLE OF CONTENTS

MONITOR Current Display Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

OUTPUT ADJUST Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

LIMIT Current Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

RAMP SPAN Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Disassembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

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TABLE OF CONTENTS

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LIST OF FIGURES

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Figure 2.1 LDX-3620 Front Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 2.2 LDX-3620 Rear Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 2.3 Output Connector Pin-Out . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 2.4 Common Laser Cathode - Photodiode Cathode

Figure 2.5 Common Laser Cathode - Photodiode Anode . . . . . . . . 17

Figure 2.6 Common Laser Anode - Photodiode Cathode

Figure 2.7 Common Laser Anode - Photodiode Anode . . . . . . . . . . 18

Figure 3.1 Front Panel Board Layout . . . . . . . . . . . . . . . . . . . . . . . . 25

Figure 3.2 Side Panel Board Layout . . . . . . . . . . . . . . . . . . . . . . . . . 26

Figure 3.3 Rear Panel Board Layout . . . . . . . . . . . . . . . . . . . . . . . . 26

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LIST OF FIGURES

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LIST OF TABLES

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Table 2.1 OUTPUT ERROR Conditions . . . . . . . . . . . . . . . . . . . . . . .9

Table 2.2 LDX-3620 Recommended Safe Initial Settings . . . . . . . . . 14

Table 3.1 Estimated Battery Lifetime . . . . . . . . . . . . . . . . . . . . . . . . . 24

Table 3.2 Fuse Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

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LIST OF TABLES

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SAFETY AND WARRANTY INFORMATION

The Safety and Warranty Information section provides details about cautionary symbols used in the manual, safety markings used on the instrument, and information about the Warranty including Customer Service contact information.

Safety Information and the Manual

Throughout this manual, you will see the words Caution and Warning indicating potentially dangerous or hazardous situations which, if not avoided, could result in death, serious or minor injury, or damage to the product. Specifically:

Caution indicates a potentially hazardous situation which can result in minor or moderate injury or damage to the product or equipment.

Warning indicates a potentially dangerous situation which can result in serious injury or death.

WARNING

Visible and/or invisible laser radiation. Avoid direct exposure to the beam.

General Safety Considerations

If any of the following conditions exist, or are even suspected, do not use the instrument until safe operation can be verified by trained service personnel:

• Visible damage

• Severe transport stress

• Prolonged storage under adverse conditions

• Failure to perform intended measurements or functions

If necessary, return the instrument to ILX Lightwave, or authorized local ILX Lightwave distributor, for service or repair to ensure that safety features are maintained (see the contact information on page xiii).

All instruments returned to ILX Lightwave are required to have a Return Authorization Number assigned by an official representative of ILX Lightwave Corporation. See Returning an Instrument on page xi for more information.

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SAFETY SYMBOLS

This section describes the safety symbols and classifications.

Technical specifications including electrical ratings and weight are included within the manual. See the Table of Contents to locate the specifications and other product information. The following classifications are standard across all ILX Lightwave products:

• Indoor use only

• Ordinary Protection: This product is NOT protected against the harmful ingress of moisture.

• Class I Equipment (grounded type)

• Mains supply voltage fluctuations are not to exceed ±10% of the nominal supply voltage.

• Pollution Degree II

• Installation (overvoltage) Category II for transient overvoltages

• Maximum Relative Humidity: <80% RH, non-condensing

• Operating temperature range of 0 °C to 40 °C

• Storage and transportation temperature of –40 °C to 70 °C

• Maximum altitude: 3000 m (9843 ft.)

• This equipment is suitable for continuous operation.

Safety Marking Symbols

This section provides a description of the safety marking symbols that appear on the instrument. These symbols provide information about potentially dangerous situations which can result in death, injury, or damage to the instrument and other components.

Caution, refer to manual

Caution, risk of electric shock

On: In position of a bistable push control. The slash (I) only denotes that mains are on.

or (I)

Earth ground Te r mi n a l

Protective Conductor Te r mi n a l

Alternating current

Caution, hot surface

Off: Out position of a bistable push control. The circle (O) only denotes that mains are off.

(O)

Visible and/or invisible laser radiation

Frame or chassis Te r mi n a l

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WARRANTY

ILX LIGHTWAVE CORPORATION warrants this instrument to be free from defects in material and workmanship for a period of one year from date of shipment. During the warranty period, ILX will repair or replace the unit, at our option, without charge.

Limitations

This warranty does not apply to fuses, lamps, defects caused by abuse, modifications, or to use of the product for which it was not intended.

This warranty is in lieu of all other warranties, expressed or implied, including any implied warranty of merchantability or fitness for any particular purpose. ILX Lightwave Corporation shall not be liable for any incidental, special, or consequential damages.

WAR RA NT Y

If a problem occurs, please contact ILX Lightwave Corporation with the instrument's serial number, and thoroughly describe the nature of the problem.

Returning an Instrument

If an instrument is to be shipped to ILX Lightwave for repair or service, be sure to:

1 Obtain a Return Authorization number (RA) from ILX Customer Service.

2 Attach a tag to the instrument identifying the owner and indicating the required service or

repair. Include the instrument serial number from the rear panel of the instrument.

3 Attach the anti-static protective caps that were shipped with the instrument and place the

instrument in a protective anti-static bag.

4 Place the instrument in the original packing container with at least 3 inches (7.5 cm) of

compressible packaging material. Shipping damage is not covered by this warranty.

5 Secure the packing box with fiber reinforced strapping tape or metal bands.

6 Send the instrument, transportation pre-paid, to ILX Lightwave. Clearly write the return

authorization number on the outside of the box and on the shipping paperwork. ILX Lightwave recommends you insure the shipment.

If the original shipping container is not available, place your instrument in a container with at least 3 inches (7.5 cm) of compressible packaging material on all sides.

Repairs are made and the instrument returned transportation pre-paid. Repairs are warranted for the remainder of the original warranty or for 90 days, whichever is greater.

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WAR RA NT Y

Claims for Shipping Damage

When you receive the instrument, inspect it immediately for any damage or shortages on the packing list. If the instrument is damaged, file a claim with the carrier. The factory will supply you with a quotation for estimated costs of repair. You must negotiate and settle with the carrier for the amount of damage.

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WAR RA NT Y

Comments, Suggestions, and Problems

To ensure that you get the most out of your ILX Lightwave product, we ask that you direct any product operation or service related questions or comments to ILX Lightwave Customer Support. You may contact us in whatever way is most convenient:

Phone . . . . . . . . . . . . . . . . . . . . . . . . . . . (800) 459-9459 or (406) 586-1244

Fax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (406) 586-9405

On the web at: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ilx.custhelp.com

Or mail to:

ILX Lightwave Corporation P. O. Box 6310 Bozeman, Montana, U.S.A 59771 www.ilxlightwave.com

When you contact us, please have the following information:

Model Number:

Serial Number:

End-user Name:

Company:

Phone:

Fax:

Description of what is

connected to the ILX

Lightwave instrument:

Description of the problem:

If ILX Lightwave determines that a return to the factory is necessary, you are issued a Return Authorization (RA) number. Please mark this number on the outside of the shipping box.

You or your shipping service are responsible for any shipping damage when returning the instrument to ILX Lightwave; ILX recommends you insure the shipment. If the original shipping container is not available, place your instrument

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WAR RA NT Y

in a container with at least 3 inches (7.5 cm) of compressible packaging material on all sides.

We look forward to serving you even better in the future!

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CHAPTER 1

INTRODUCTION AND SPECIFICATIONS

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This manual contains operation and maintenance information for the LDX-3620 Ultra Low Noise Current Source and its options. Chapter 2 contains control and connector descriptions and operation procedures. Chapter 3 contains battery and maintenance information.

Note: To those in a hurry to turn on and use the LDX-3620 without reading Chapter 2 of this manual, it is recommended that the IMPORTANT paragraphs be read since they contain informaiton that may prevent the destruction of expenvie laser diodes. Output connector pin-outs are found in Figure 2.3. Recommended cable shielding schemes are found in Figures 2.4 - 2.8. Figure 3.1 is a block diagram of the LDX-3620.

Product Overview

The LDX-3620 Ultra Low Noise Current Source provides laser diode users a power source for applications requiring current stabilities of better than 10 ppm and noise levels lower than 2 uA in the 5 Hz to 10 MHz band. Its features include:

• Low noise, battery based design

• Built-in battery charger

• High output stability

• Current limit protection

• Two output current ranges: 200 mA and 500 mA

• 4-1/2 digit resolution and display

• Monitor photodiode current display

• Photodiode feedback input for constant optical power operation

• Internal ramp generator with trigger output

• External modulation capability

• Low battery shutdown protection

• High/Low bandwidth switch

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CHAPTER 1

INTRODUCTION AND SPECIFICATIONS

Specifications

Output Current 0 - 200 mA 0 - 500 mA

Compliance Voltage >5 V >4 V

Noise and Ripple (5 Hz - 10 MHz bandwidth)

Battery Operation

AC Line Operation

Noise and Ripple (5 Hz - 10 kHz bandwidth)

Battery Operation

AC Line Operation

Noise Density (Battery Operation)

50/60 Hz

1 kHz

25 kHz

0 - 200 mA Range 0 - 500 mA Range

850 nA rms <2 uA rms

3 uA rms <8 uA rms

100 nA rms <500 nA rms

2 uA rms <6.5 uA rms

5.2 nA/rt Hz 11.5 nA/rt Hz

815 pA/rt Hz 2.6 nA/rt Hz

315 pA/rt Hz 795 pA/rt Hz

Stability

10 - 20 seconds

3 - 5 minutes

10 - 30 minutes

Temperature Coefficient <

Transients <

CURRENT LIMIT

Range 10 - 500 mA

Accuracy +

DISPLAY

Type 4-1/2 digit LCD

Resolution 0.01 mA 0.1 mA

Accuracy +0.05 mA +0.6 mA

Reads Units LASER diode current in mA

0.1 ppm <0.1 ppm

1 ppm <1 ppm

10 ppm <10 ppm

10 ppm/oC<10 ppm/oC

10 uA <10 uA

5 mA

MONITOR photodiode current in mA

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INTRODUCTION AND SPECIFICATIONS

Specifications

0 - 200 mA Range 0 - 500 mA Range

MODULATION / FEEDBACK INPUTS

Photodiode Feedback

Input Type

Range

Connectors

External Modulation Input (Bandwidth (3 dB point)

AC Coupled

DC Coupled

Transfer Function 100 mA/V 250 mA/V

Connector Isolated front panel BNC jack

Internal Ramp Generator

Period

Span Adjustment

Ramp Trigger

Ramp Flyback Time

Output Connector

GENERAL

Current input from external photodiode

20 uA to 2 mA for full scale output

Rear panel isolated BNC jack or 9-pin rear panel D-sub connector

100 Hz to 1 MHz

0 Hz to 1 MHz

Adjustable 50 msec to 100 sec

0 - 200 mA 0 - 500 mA

Ramp start trigger for oscilloscope output Optically isolated open collector TTL output

700 usec, approximately

Shielded 9-pin D-sub on rear panel

CHAPTER 1

AC Power Input Voltage Range 100 - 125 or 210 - 250 VAC

AC Power Line Frequency 50/60 Hz

Battery +12 V Supply 4.5 amp-hour sealed lead-acid battery (standard)

Battery -12 V Supply 1.2 amp-hour sealed lead-acid battery

Operating Temperature Range 0 to 40

Storage Temperature Range -40 to 70

Weight 8.6 kg (18.9 lbs)

12 kg (26.4 lbs) with extra battery option

Size (H x W x D) 145 mm x 320 mm x 346 mm

5 5/8” x 12 1/2” x 13 5/8”

Our goal is to make the best laser diode instrumentation available anywhere. To achieve this, we need your ideas and comments on ways we can improve out products. We invite you to contact us at any time with your suggestions.

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CHAPTER 1

INTRODUCTION AND SPECIFICATIONS

Options and Accessories

362038 Long Life Battery Option

The 362038 option is a second, user installable +12 volt battery which doubles the battery operation time at 500 mA. Instructions for battery installation are included with the 362038 option kit.

132 Rack Mount Kit

The 132 rack mount kit enables installation of the 3620 into a standard 19 inch wide rack. All hardware and instructions are included with the kit.

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CHAPTER 2

OPERATION

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This chapter contains the following aspects of operation of the LDX-3620:

• General power and installation considerations

• A description of the front and rear panel controls and connectors

• Step-by-step instructions on the set-up and the use of the LDX-3620

Installation

AC Power/Battery Charge Considerations

The LDX-3620 is normally configured at the factory for your power line voltage. The unit can be configured for 100-130 VAC or 210-230 VAC operation. Check to be sure that the correct range is marked on the rear panel. If it is not correct, see Chapter 3 for the procedure to change the line voltage range.

The AC power cord connects to the rear of the unit. Turning on the AC POWER switch on the rear panel charges the batteries while permitting full use of the LDX-3620’s functions; however, noise will be increased in this configuration.

Tilt Foot Adjustment

The LDX-3620 can be tilted for easier viewing using the extensions on the front feet of the unit. These extenders can be rotated 90 degrees until they lock into position. To put the extenders flat against the bottom of the unit, firmly press them back.

Rack Mounting

The instructions and necessary hardware for mounting the LDX-3620 in a standard 19 inch wide instrument rack are available in the Model 132 Rack Mounting Kit. Contact ILX Lightwave for more information.

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CHAPTER 2

OPERATION

Front Panel Control and Connectors

A brief description of the function of the front panel controls and connectors is contained in the following sections.

DC POWER Key Switch and Output Range Selection

A three position key switch on the front panel of the LDX-3620 controls the power to the current source circuits:

• Off - center position

• 200 mA - 1/8 turn clockwise (CW)

• 500 mA - 1/8 turn counter-clockwise (CCW)

The front panel power key switch operates independently of the rear panel AC POWER switch. The rear panel switch controls only AC-line-power/battery-charge operation. With the rear panel switch turned on, the power LED above the front panel key switch will light up, indicating that AC power is on and that the batteries are charging.

Low Battery Indication and Shutdown

A “B” indicated on the display of the LDX-3620 means that the batteries should be recharged. Repeated operation of the unit to the point where the low battery “B” is indicated greatly reduces the battery life and is not recommended. See Chapter 3 for recommended battery maintenance.

If the batteries continue to be discharged after the low battery “B” indicator appears, shutdown circuits may turn off the output of the LDX-3620. Shutdown is indicated on the display when all of the decimal points are displayed. Use of the instrument will be diabled until the batteries have been recharged and the DC POWER key switch has been turned off and then on again.

EXT Modulation

An external voltage wave form can be used to modulate the LDX-3620 output when the modulation mode selection switch is set to either the EXT AC or EXT DC positions. The external signal is input through the front panel EXT BNC jack and is AC or DC coupled according to the mode switch positions. The transconductance of the instrument is determined by the output current range selected by the DC POWER key switch; it is 100 mA/V in the 200 mA output range, or 250 mA/V in the 500 mA output range. Under all modes of operation, the output is clipped at the level set by the current LIMIT knob.

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OPERATION

Front Panel Control and Connectors

CHAPTER 2

RAMP Modulation

The LDX-3620 output can be modulated using the internal ramp generator when the MODULATION selector switch is set to the RAMP position. The ramp period is variable between 50 mSec and 100 Sec via the RAMP PERIOD adjustment pot. The ramp peak-to-peak amplitude is adjusted using the RAMP SPAN front panel pot. A DC offset may be added to the ramp by using the OUTPUT ADJUST knobs.

Ramp fly-back time is approximately 700 microseconds. The ramp wave form will be clipped, should it try to exceed the current limit.

MODE Selector

The front panel MODE switch selects the feedback mode of the LDX-3620. In CONST CURRENT mode, the LDX-3620 is a voltage controlled current source that delivers a current proportional to the sum of the MODULATION section and OUTPUT ADJUST knob control signals.

In the CONST POWER mode, the LDX-3620 uses the photodiode feedback signal to determine how much current should be output to the laser or LED to maintain a constant light power. The output current increases until the photodiode feedback current equals a value proportional to the control signal set by the MODULATION and the OUTPUT ADJUST sections on the front panel. If the control signal is a DC level, then the output optical power is held constant. If the control signal is modulated, then the output optical power is modulated, so long as the bandwidth of the modulation is held below 20 Hz. Modulation frequency components higher than 20 Hz are attenuated, and the modulation becomes a mixture of optical power modulation and current modulation.

LIMIT Current Adjustment

The LIMIT knob on the front panel sets the output current limit level. Setting this knob fully clockwise (CW) limits the LDX-3620 output current to 500 mA. Setting it fully counter-clockwise (CCW) limits the output to approximately 10 mA. The current limit is active in all operating modes of the LDX-3620. A more complete description of how to set current limit may be found later in this chapter.

OUTPUT On/Off

The current output of the LDX-3620 is shorted by a mechanical switch and a JFET when the front panel OUTPUT push button switch is in the OFF/SHORT position (out). When the OUTPUT switch is set to the ON position, the short is removed and the JFET is turned off slowly. This brings the output current up slowly to the level determined by the OUTPUT ADJUST and MODULATION control signals.

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CHAPTER 2

OUTPUT ADJUST Controls

DISPLAY Selector

OPERATION

Front Panel Control and Connectors

When the output is shorted internally, the OUTPUT SHORT LED on the front panel will light up.

The OUTPUT ADJUST, COARSE, and FINE knobs set the DC output level of the LDX-3620. The DC bias level is summed with the control signals derived from the MODULATION section to determine the final output level.

The display of the LDX-3620 indicates the average output current of the unit when the DISPLAY push button switch is in the LASER position (out). It displays the average photodiode feedback current input to the rear panel when the DISPLAY switch is in the MONITOR position (in).

Note: When in the MONITOR position (in), the display reads the negative value of the average photodiode current. This reminds the user that the display switch is in the MONITOR position.

Output 4-1/2 Digit LCD Display

The LDX-3620 output current and monitor photodiode current are displayed on a 4-1/2 digit liquid crystal display on the front panel of the instrument. When the DISPLAY push button is in the LASER position (out), the display reads the average current setting determined by the MODULATION and OUTPUT ADJUST controls. It does so even when the OUTPUT push button is in the OFF/SHORT position (out) and no current is delivered to the output. The resolution of the display depends on the range selected by the DC POWER key switch: 0.01 mA in the 200 mA setting and 0.1 mA in the 500 mA setting.

When the DISPLAY switch is in the MONITOR position (in), the display reads the (negative) average photodiode current input to the rear panel photodiode feedback inputs in milliamperes. This reading is negative to remind the user that the display is in the MONITOR position. The resolution of the display in MONITOR mode does not change with the output range selected by the DC POWER key switch.

The display also announces low battery charge by indicating a "B".

If "low battery shutdown" occurs, the display reads zero current and all of the decimals are displayed.

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Page 25

OPERATION

Front Panel Control and Connectors

CHAPTER 2

OUTPUT SHORT Indicator

The green OUTPUT SHORT lamp lights up when the output is shorted by setting the OUTPUT on/off switch to the OFF/SHORT position (out). It is unlit when the OUTPUT is ON.

OUTPUT ERROR Indicator

The red OUTPUT ERROR indicator lights up when:

• The output has reached the current LIMIT level, set by the LIMIT adjustment.

• The output circuit is open.

• The maximum compliance voltage of the LDX 3620 is insufficient to drive the load.

Table 2.1 lists the possible conditions leading to a lighted OUTPUT ERROR LED.

Table 2.1 OUTPUT ERROR Conditions

Condition Indicated By

Current Limit OUTPUT ERROR LED is lit

Display reads value of LIMIT current

Open Circuit OUTPUT ERROR LED is lit

Display reads zero

Compliance Voltage Exceeded OUTPUT ERROR LED is lit

Display reads a non-zero value less than the LIMIT current

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Page 26

CHAPTER 2

OPERATION

Rear Panel Controls and Connectors

Figure 2.1 LDX-3620 Front Panel

Rear Panel Controls and Connectors

The following sections contain brief descriptions of the functions of the rear panel controls and connectors. Refer to Figure 2.2.

HIGH/LOW BANDWIDTH Selector

The BANDWIDTH selector switches a 0.1 uF capacitor in and out of the output circuit. This capacitor is connected directly across the output current posts. The capacitor is connected when the LOW bandwidth position is selected, and it is disconnected when the HIGH bandwidth position is selected.

In the HIGH position the modulated output bandwidth of the LDX-3620 is 1 MHz. With the switch in the LOW position the bandwidth across a 100 ohm load is cut to about 20 kHz. The LOW setting decreases noise and prevents oscillation of the LDX-3620 when it is connected to an inductive load, such as a bias "tee" circuit. This allows external modulation of the laser diode using the LDX-3620 as a bias current supply.

10 LDX-3620

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OUTPUT Connector (J401)

The rear panel 9-pin D-sub connector (J401) pin-outs are shown in Figure 2.3. The LDX-3620 output current is sourced (+) from pins 8 and 9 and the current

Page 27

OPERATION

Rear Panel Controls and Connectors

returned (-) to pins 4 and 5. The monitor photodiode feedback current is input to pin 7 (+) and returned from pin 6 (-). The feedback leads should be shielded with an earth-ground shield available on pin 3. More detailed information on connections and grounding is included later in this chapter.

Pins 1 and 2 of the rear panel OUTPUT can be connected to an external safety interlock switch to disable the LDX-3620 current output when the switch is opened. Instructions on the connection of an interlock switch are located later in this chapter.

CHAPTER 2

PHOTODIODE Feedback Gain Adjustments

The photodiode feedback circuit gain is adjustable on the rear panel to accept fullscale feedback currents from 20 uA to 2 mA. An eight position switch provides COARSE gain adjustment, while a four-turn trimpot provides FINE adjustment. The adjustment procedure is described later in this chapter.

PHOTODIODE Feedback Input Jack

The photodiode feedback current may optionally be input through a rear panel BNC jack. This jack is connected in parallel with pins 6 and 7 of the rear panel 9 pin D subminiature connector.

RAMP TRIGger Output Jack

Optically isolated RAMP TRIGGER signals are output through two BNC jacks on the rear panel. The OSCILLOSCOPE output delivers a 200 mV square pulse with rising and falling edges of the pulse synchronized to the end and start of the output current ramp. This output remains high during the ramp flyback time of approximately 700 microseconds.

The OPEN COLLECTOR output is capable of driving a TTL load, but requires an external supply and pull-up resistor. See the section on Ramp Trigger Output Connectors for connection information.

CHASSIS GROUND Connector

Chassis ground is available on the rear of the unit through a banana jack connected to the LDX-3620 cabinet. When a three-wire line cord with earthground is used, the cabinet of the LDX-3620 is connected to the ground lead of the power cord.

AC POWER/Battery Charge Switch

AC line power operation and battery recharge is accomplished by connecting the AC line cord and turning on the AC Power switch on the rear panel. With this

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CHAPTER 2

Fuse Holder

OPERATION

Rear Panel Controls and Connectors

switch turned off, the LDX-3620 draws power from its internal battery supply. For lowest noise operation, the AC POWER switch should be OFF and the AC power cord disconnected.

The AC line fuse holder is on the rear panel. See Chapter 3 for fuse replacement information.

Figure 2.2 LDX-3620 Rear Panel

Figure 2.3 Output Connector Pin-Out

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Page 29

OPERATION

LDX 3620 Operation Procedures

Chapter 3 contains information concerning the battery operation of the LDX-3620. (Briefly: it recommends that the batteries be maintained as fully charged as possible to ensure long battery life.)

This section contains recommended procedures for operation of the LDX-3620 with a laser diode. It assumes that the batteries are adequately charged or that AC power is connected and on.

CHAPTER 2

Outline of Operation

Operation of the LDX-3620 can be outlined briefly:

1 Set controls to a safe configuration (see Table 2.2) before connecting the laser and

turning on the DC POWER key switch.

2 Connect the laser using one of the recommended shielding schemes (Figure 2.4). Be

sure connections are secure and not prone to open should the cables be jostled or bumped. Refer to later in this chapter for photodiode feedback connections.

3 Leave the OUTPUT switch in the OFF/SHORT position (out). Turn on the DC power to the

appropriate range and adjust the current LIMIT to a safe level for the particular laser being used.

4 In CONST CURRENT mode, adjust the output current to the desired level with the

OUTPUT ADJUST and/or MODULATION controls and turn ON the OUTPUT (in).

5 In CONST POWER mode, adjust the photodiode feedback gain to get maximum

resolution on the OUTPUT ADJUST knobs. Then set the output power level with the OUTPUT ADJUST knobs.

6 Before turning off the DC POWER key switch, set the OUTPUT switch to the OFF/SHORT

position (out).

7 Recharge the batteries by connecting the LDX-3620 to the AC line, and turn on the rear

panel AC POWER switch.

The procedures for each of these steps are contained in the following sections.

Load Considerations

The LDX-3620 is intended as a current source for laser diode and LED loads. When it is used with a resistive load, the resistance value of the limiting resistor should be selected so that the compliance voltage is not exceeded. For example, a laser diode which has a voltage drop of 1.8 volts may be connected in series with a limiting resistor. If the 200 mA range is selected on the LDX-3620, the guaranteed compliance voltage is +5 volts. If the current LIMIT is set to 100 mA, the maximum resistance value can be found by Ohm's Law:

(R = E / I) 3.2 V / 0.1 A = 32 ohms

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CHAPTER 2

Safe Settings

OPERATION

LDX 3620 Operation Procedures

Note: If the LDX-3620 is to be connected to an inductive load, such as a bias "tee" network, the LOW BANDWIDTH setting (on the rear panel) should be used. This is necessary to prevent oscillation of the LDX-3620.

Before turning the DC power on, the front panel controls should be set to a safe configuration. Table 2.2 lists the recommended settings.

Table 2.2 LDX-3620 Recommended Safe Initial Settings

Front Panel Control Recommended Setting

OUTPUT switch OFF/SHORT (out)

MODE knob CONST CURRENT

MODULATION knob OFF

DISPLAY switch LASER (out)

OUTPUT ADJUST knobs Fully counter-clockwise (CCW)

LIMIT knob Fully counter-clockwise (CCW)

Safety Interlock Connections

A safety interlock connection is available on pins 1 and 2 of the LDX-3620 rear panel OUTPUT connector. These pins must be shorted to enable the LDX-3620 current output. When this circuit is opened, the interlock turns off the current output, and the OUTPUT SHORT indicator lights up. Then when the circuit is reclosed, the output turns on slowly in the same manner as when the front panel OUTPUT push button switch is turned ON (in).

To use the interlock feature, the user must provide wires connected from the OUTPUT connector interlock pins to a normally closed, external, user supplied switch or relay. These connections must be electrically isolated from all other circuits.

The interlock pins are shorted together inside the hood of the mating male, 9 pin D-sub output connector supplied with the LDX-3620.

Laser Diode Connections and Shielding

Note: Before connecting the laser diode to the LDX-3620, be sure that the front panel

OUTPUT switch is in the OFF/SHORT position (out). Before turning the OUTPUT on, be sure that the current LIMIT has been correctly set.

The LDX-3620 output is available through the 9-pin rear panel OUTPUT connector J401 (see Figure 2.3). The LDX-3620 sources current through pins 8 and 9 to the laser anode (+) and returns current from the cathode (-) through pins 4 and 5.

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OPERATION

LDX 3620 Operation Procedures

Note: The cable connections to the laser must be secure enough that they won't open circuit, should they be jostled or bumped. Should an open circuit occur during laser operation, DO NOT attempt to remake the circuit until the front panel OUTPUT switch has been released to the OFF/SHORT position (out). Remaking the circuit with the OUTPUT on will expose the laser to the maximum compliance voltage of the LDX-3620, which may result in laser damage.

A laser may be damaged if an open circuit occurs during laser operation while the output is on. The damage is caused by a momentary circuit break and remake, before the final circuit break. Therefore, always make sure that the cabling is secure. An open circuit is indicated by the front panel OUTPUT ERROR lamp and a zero current reading on the display.

If the LDX-3620 is to be used in CONST POWER mode, the photodiode feedback current should be sourced to pin 7 (+) and returned from pin 6 (-) of the rear panel 9-pin connector. Alternatively, the feedback current can be connected through the rear panel AUX. INPUT BNC connector, using the center conductor of the coax for the "+" connection, and the outer shield conductor for the " - " connection.

It is recommended that the connections to the LDX-3620 output be made by using twisted wire pairs, with an earth grounded shield, as shown in Figures 2.4 - 2.7. The output conductors are left floating, relative to earth-ground, to suppress AC power-on/power-off transients that may occur through an earth-ground return path. If the output circuit is earth-grounded at some point (such as through the laser package and mount), then the user must be careful to avoid multiple earthgrounds in the circuit. Multiple earth-grounds may provide circuit paths that induce spurious currents in the photodiode feedback circuit and output leads.

CHAPTER 2

Photodiode Feedback Connections

Many laser diode modules contain an internal photodiode that monitors the backfacet emission of the laser. This photodiode is usually internally connected to either the laser anode or cathode. Figures 2.4 - 2.7 show the recommended connections and shielding for the various configurations of laser diode modules and photodiode feedback schemes.

The feedback photodiode reverse-biasing supply shown in these figures must be supplied by the user. It is located in the circuit where it will not cause the common mode voltage of the feedback inputs to exceed their specified maximum of +6 volts, relative to the "-" current output terminal (pins 4 and 5 of J401). Noise from this biasing supply may contribute to the output noise levels; therefore, a battery with shielded connections is recommended.

If a feedback photodiode is used, which is electrically isolated from the laser, the feedback circuit must be resistively "tied" at some point to the output circuit. A large resistance of 1 MΩ, connected from the laser cathode to the photodiode anode, may be used in place of the direct connection (see Figure 2.5). This is done to keep the feedback inputs within the specified maximum +6 volt common

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CHAPTER 2

RAMP TRIGger Output Connections

OPERATION

LDX 3620 Operation Procedures

mode voltage, relative to the " - " laser current output (pins 4 and 5 of J401). The circuit of Figure 2.5 should be used, if feasible.

Two optically isolated RAMP TRIGGER outputs are provided on the LDX-3620 rear panel. The OSCILLOSCOPE output provides a voltage square pulse of up to 200 mV amplitude that is synchronized to the start and end of the output current ramp. The falling edge of the voltage pulse signals the start of the output current ramp. The rising edge signals the end of the ramp. This output remains high during the approximately 700 microsecond ramp flyback. The OSCILLOSCOPE output should be connected to an instrument with an input impedance greater than 100 KΩ.

The OPEN COLLECTOR output may be used to drive TTL circuits, but requires an external supply and pull-up resistor. This output "turns off" (stops conducting) at the beginning of each ramp cycle. It "turns on" (starts conducting) at the end of the current ramp. It remains "on" during the approximately 700 microsecond ramp flyback time. The pull-up voltage must be less than 25 volts, with the center conductor positive relative to the BNC shell. When "on" the OPEN COLLECTOR output sinks up to 10 mA. The "on" state power dissipation should be limited to 100 mW.

Note: The OSCILLOSCOPE and OPEN COLLECTOR outputs cannot be used at the same time.

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OPERATION

LDX 3620 Operation Procedures

CHAPTER 2

P. D. L. D.

OUTPUT

Bias

Figure 2.4 Common Laser Cathode - Photodiode Cathode

OUTPUT

Bias

Instrument

Earth Ground

Module

P. D. L. D.

Figure 2.5 Common Laser Cathode - Photodiode Anode

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Earth Ground

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CHAPTER 2

OPERATION

LDX 3620 Operation Procedures

P. D. L. D.

OUTPUT

Bias

Figure 2.6 Common Laser Anode - Photodiode Cathode

OUTPUT

Bias

Module

Earth Ground

Module

18 LDX-3620

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P. D. L. D.

Earth Ground

Figure 2.7 Common Laser Anode - Photodiode Anode

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OPERATION

LDX 3620 Operation Procedures

CHAPTER 2

Setting the LIMIT Current

Once the "safe" settings have been made (see Table 2.2), the output current LIMIT should be adjusted to a safe level for the particular laser diode being used. (Refer to the max. current rating for your laser diode.)

1 Set the OUTPUT switch to the OFF/SHORT position (out); the OUTPUT SHORT LED

should light up.

2 Set the DISPLAY push button switch to the LASER position (out).

3 Turn the COARSE output adjust knob to its maximum setting, fully clockwise (CW). The

OUTPUT ERROR indicator should light up.

4 Adjust the LIMIT knob until the display reads the desired limit current.

5 Return the COARSE output adjust knob to its minimum setting, fully counter-clockwise

(CCW). The OUTPUT ERROR indicator should be unlit.

Setting the Output in CONST CURRENT Mode

Before adjusting the output current of the LDX-3620 with the OUTPUT ADJUST knobs or the MODULATION controls, be sure that the current LIMIT has been properly set and that the laser circuit connections are secure. With that done:

1 Set the DISPLAY push button switch to the LASER position (out).

2 Adjust the COARSE and FINE output adjust knobs until the display reads the desired

output current level.

3 Push the OUTPUT switch to the ON position (in).

The displayed current is being delivered to the load.

Setting the MODULATION Controls

The current output of the LDX-3620 can be controlled by an external voltage waveform. The transfer function of the modulation is 100 mA/V when the 200 mA output range is selected with the DC POWER key switch, or 250 mA/V when the 500 mA range is selected. The output current waveform should be monitored with an oscilloscope (connected across a resistor in series with the load) when making adjustments. The current LIMIT circuit may clip the output waveform. Also, trying to drive a negative current will cause the output stage internally to go to the rail. In that case, the output is slew rate-limited when the control voltage goes positive and tries to drive a positive current output. This can cause a non-linear output waveform. However, this will not cause a negative current to flow in the laser diode.

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CHAPTER 2

Using the Internal RAMP Generator

OPERATION

LDX 3620 Operation Procedures

1 Connect the external modulation signal to the front panel EXT input BNC jack.

2 Select AC or DC coupling of the input with the corresponding position of the

MODULATION selector knob.

3 Push the OUTPUT switch to the ON position (in).

4 Set any desired offset DC output current with the OUTPUT ADJUST knobs.

The output current is the sum of the level set by the OUTPUT ADJUST knobs and the current programmed by the modulation signal. The display reads the average current delivered to the load.

When the MODULATION selector switch is in the RAMP position an internal ramp generator modulates the output current with a linear ramp waveform. Adjustments of the ramp span and period should be made while using an oscilloscope to monitor the output current (i.e. voltage drop across a resistor in series with the load). The current LIMIT circuit may clip the output waveform.

1 Set the MODULATION selector switch to the RAMP position.

2 Push the OUTPUT switch to the ON position (in).

3 Adjust the period of the ramp with the RAMP PERIOD knob.

4 Adjust the peak-to-peak amplitude of the ramp with the RAMP SPAN knob.

5 Set any desired offset DC output current with the OUTPUT ADJUST knobs.

The display reads the average current delivered to the load.

Setting the Photodiode Feedback Gain

The gain of the photodiode feedback circuit should be adjusted before operating the LDX-3620 in CONST POWER mode.

Note: The LIMIT current level MUST be correctly set before switching the MODE selector to CONST POWER and turning the OUTPUT switch ON (in). Laser damage will result if the current level is not safely set.

1 Set the front panel controls to the safe initial settings of Table 2.2.

2 Check that the LIMIT current is correctly set.

3 Using a small, flat blade, alignment screwdriver, set the COARSE photodiode feedback

gain adjustment to its maximum setting. (If an improper tool is used, you may damage the nylon screw head).

20 LDX-3620

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Turn the COARSE adjustment to the vertical position. (The screwdriver blade will be horizontal. This is minimum gain.) Then turn it one more click counter-clockwise (CCW) to the maximum gain setting. The FINE gain adjustment need not be adjusted at this time.

Page 37

OPERATION

LDX 3620 Operation Procedures

4 Turn the front panel OUTPUT ADJUST knobs to their minimum settings, fully counter-

clockwise (CCW).

5 Turn the front panel MODE selector to the CONST POWER position.

6 Push the OUTPUT switch to the ON position (in).

If the OUTPUT ERROR LED does not light up at this point in the procedure, continue on to Step 8.

If at this point the OUTPUT ERROR LED lights up and indicates a current limit condition, turn off the output and check that all connections are correctly made, and that the rear panel feedback gain adjustments are at their maximum settings. Retry Step 6.

7 Carefully increase the output level by slowly turning the OUTPUT ADJUST knob

clockwise (CW) until the desired maximum output operating level has been reached. When the desired level has been reached, proceed to Step 8.

If the desired output level cannot be reached with the COARSE output adjust knob turned fully clockwise, then:

7a Turn the OUTPUT ADJUST knobs fully counter-clockwise (CCW) again.

7b Set the OUTPUT switch to the OFF/SHORT position (out).

7c Decrease the photodiode feedback gain by turning the COARSE gain switch one

more click counter-clockwise (CCW).

CHAPTER 2

7d Push the OUTPUT switch to the ON position (in).

7e Repeat Step 7.

8 By alternately increasing the COARSE and FINE OUTPUT ADJUST knob settings and

decreasing the FINE photodiode feedback gain trimmer, a full scale setting of the OUTPUT ADJUST knobs (both fully clockwise) can be made to deliver the desired maximum output power level. If this cannot be accomplished using the FINE gain adjustment trimmer, one more repetition of Step 7 may be required.

9 Push the DISPLAY switch to the MONITOR position (in) to display the photodiode current.

Note: When in the MONITOR position the display reads the negative value of the average

photodiode current. This reminds the user that the display push button switch is in the MONITOR position (in).

10 Adjust the MODULATION and OUTPUT ADJUST controls to set the desired output

optical power levels.

Setting the Laser Power in CONST POWER Mode

Whenever the MODE selector switch is in the CONST POWER position, the LDX-3620 maintains the output optical power in proportion to the control signals derived from the MODULATION and OUTPUT ADJUST sections of the front panel. After the photodiode feedback gain has been successfully adjusted, the output optical power level can be set:

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Page 38

CHAPTER 2

OPERATION

LDX 3620 Operation Procedures

1 Set the OUTPUT switch to OFF/SHORT (out).

2 Turn the MODE selector to CONST POWER.

3 Press the DISPLAY switch to the MONITOR position (in).

When in the MONITOR position, the display will read the negative value of the average photodiode current.

4 Press the OUTPUT switch to the ON position (in).

5 Adjust the MODULATION and OUTPUT ADJUST front panel controls as in CONST

CURRENT mode, but keep in mind the following:

The output optical power of the laser is proportional to the MODULATION and OUTPUT ADJUST control signals to the extent that the photodiode feedback current is proportional to the output optical power. Therefore, if proportionality of optical power to the control signals is important, the photodiode should be used in a reverse biased photoconductive mode. If optical power stability alone is required, then using the feedback photodiode in a photovoltaic mode should suffice.

In CONST POWER mode, AC MODULATION components higher than about 20 Hz are attenuated, and the resulting modulation is a combination of current modulation and power modulation.

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Page 39

CHAPTER 3

MAINTENANCE

                 

This chapter discusses the recommended procedures for maintaining the LDX-3620 in good operating condition:

• Requirements of the battery operation - IMPORTANT

• AC line voltage selection and fuse replacement

• Calibration procedures

• Enclosure disassembly

• Wiring diagrams for the internal wiring connectors

Battery Maintenance

The battery life of the LDX-3620 depends on the frequency and degree of discharge of the batteries during use. With light use and proper maintenance, the batteries should last for more than 1100 recharge cycles (about four years of daily use). With heavy use battery lifetime can be degraded by as much as 60%. This can be improved by adding an extra +12 volt battery, the 362038 "Long Life" option.

The batteries are continuously charged whenever the LDX-3620 is connected to an AC power source and the rear panel AC power switch is turned on. Full recharge of the batteries takes about 8 hours.

The data of Table 3.1 suggest that long battery life results from maintaining the batteries as fully charged as possible and that short battery life will result from the practice of waiting until a low-battery condition is indicated before recharging the batteries.

If the LDX-3620 is to be stored for long periods, the batteries should be fully recharged for eight hours every 6-9 months to prevent a permanent loss of capacity due to self-discharge.

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Page 40

CHAPTER 3

MAINTENANCE

Battery Replacement

Battery life in recharge cycles can be estimated from Table 3.1 once one calculates the average "amp-hours" drawn from the LDX-3620 between recharges. This is calculated by multiplying the average time the unit is used between recharges by the average output current setting during use. The operation time includes the time when the OUTPUT push button is OFF (out) since turning off the output simply shunts the output current through a short internal to the LDX-3620.

Table 3.1 Estimated Battery Lifetime

Average Amp-Hours Expected Charge/Recharge Cycles Recharge Cycles with

1.5 1100

2.0 700

2.5 400 1200

3.5 300 700

4.5 200 400

7.0 * 300

9.0 * 200

* Indicates that low battery shutdown will prevent further discharge at these points.

362038 Option

Battery Replacement

The batteries may be replaced by removing the push-on electrical spade connectors and the sheet-metal tie-downs, which are held in place with 6-32 machine screws. Contact ILX Lightwave for replacement batteries.

24 LDX-3620



Fuse Replacement

The AC power fuse is located on the rear panel of the LDX-3620. Should replacement be necessary, first disconnect the power cord and turn the AC POWER switch OFF. Refer to Table 3.2 for the correct fuse ratings.

Table 3.2 Fuse Replacement

Line Voltage Replacement Fuse

100 - 130 VAC 1 Amp, 3 AG, Slow Blow

210 - 250 VAC 1/2 Amp, 3 AG, Slow Blow

Page 41

MAINTENANCE

Calibration

The following paragraphs outline the procedures for calibrating the instrument. Access to the adjustment trimpots on the circuit boards will require that the top of the instrument be removed. The removal procedure is discussed later in this chapter.

The equipment required for the calibration procedures must be capable of: measuring a current of 500 mA to an accuracy of approximately 0.01 mA, and measuring 1 mA to an accuracy of 0.00005 mA. A good digital multimeter with 5-1/2 digit resolution is usually adequate for this purpose. An oscilloscope is needed to calibrate the RAMP SPAN of the internal ramp generator.

Note: Calibration of the LDX-3620 should be performed only by qualified personnel. Potentially lethal or harmful voltages are present and exposed when the top of the unit is removed.

Refer to the component layout diagrams, Figures 3.1through 3.3 to find the locations of the adjustment trimpots referred to in these procedures.

CHAPTER 3

Figure 3.1 Front Panel Board Layout

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Page 42

CHAPTER 3

MAINTENANCE

Calibration

Figure 3.2 Side Panel Board Layout

26 LDX-3620

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Figure 3.3 Rear Panel Board Layout

Page 43

MAINTENANCE

Calibration

CHAPTER 3

Display Calibration

Connect the ammeter across the current output of the LDX-3620 to monitor the output current. Make the following settings and adjustments:

1 Release the DISPLAY push button to the LASER position (out).

2 Turn the MODULATION mode selector switch to the OFF position.

3 Set the MODE select switch to CONST CURRENT.

4 Turn the current LIMIT knob fully clockwise (CW) to its maximum setting.

5 Turn ON the DC POWER key switch clockwise (CW) to the 200 mA range.

6 Push the OUTPUT switch to its ON position (in).

7 Turn the output adjust knobs clockwise (CW) until the calibration ammeter reads 200.00

mA.

8 Adjust trimpot R133 (on the front panel board) until the display reads 200.00 mA.

9 Turn the DC POWER key switch counter-clockwise (CCW) to the 500 mA range setting

and adjust the OUTPUT ADJUST knobs until the calibration ammeter reads 500.0 mA.

If the output cannot be adjusted to 500.0 mA at this point, then turn the OUTPUT ADJUST knobs fully clockwise to their maximum settings. Alternately adjust LIMIT pot R229 and trimmer R103 (located near the OUTPUT switch on the front panel board) until the output reaches 500.0 mA according to the following guidelines:

9a If the OUTPUT ERROR indicator is lit, adjust LIMIT pot R229 to increase the output

current until the calibration ammeter reads 500.0 mA or continue adjustment a few turns after the OUTPUT ERROR indicator turns off. If the output current has reached

500.0 mA, proceed to Step 10. If not, proceed to Step 9b.

9b If the OUTPUT ERROR indicator is unlit, adjust R103 to increase the output current

until the calibration ammeter reads 500.0 mA or continue adjustment a few turns after the OUTPUT ERROR indicator lights. If the output current has reached 500 mA, proceed to Step 10. If not, proceed to Step 9a.

10 Adjust R221 (located at the top rear of the side panel board) until the display reads 500.0

mA.

MONITOR Current Display Calibration

When the DISPLAY push button is in the MONITOR position, the display reads the (negative) value of the current input to the photodiode feedback pins 6 and 7 of the rear panel 9 pin connector (J401).

1 After the display has been calibrated, the LDX-3620 can be used to source 1 mA to the

series combination of the photodiode feedback input and calibration ammeter. Make the following connections:

1a Connect the positive terminal of the calibration ammeter to pin 9 of the rear panel

OUTPUT connector (J401).

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OUTPUT ADJUST Calibration

MAINTENANCE

Calibration

1b Connect the negative terminal of the calibration ammeter to pin 7 of the OUTPUT

connector (J401).

1c Connect pin 6 to pin 5 of the OUTPUT connector (J401).

Select the 200 mA current range with the DC power key switch, and set the Output current to 1.00 mA with the OUTPUT ADJUST knobs.

2 Push the DISPLAY push button to the MONITOR position (in).

3 Adjust R320 (on the rear panel board) until the calibration ammeter and the LDX 3620

display measurements are the same.

After the display has been calibrated the OUTPUT ADJUST span can be calibrated:

1 Repeat the settings of Steps 1-6 of the Display Calibration section.

2 Turn the OUTPUT ADJUST knobs fully clockwise (CW) to their maximum setting.

3 Adjust R103 (located on the OUTPUT side of the front panel board) until the calibration

ammeter reads 200.0 mA.

LIMIT Current Calibration

The current LIMIT knob must be calibrated to 500 mA at its maximum setting:

1 Repeat the settings of Steps 1-4 of the Display Calibration section.

2 Turn the OUTPUT ADJUST knobs fully clockwise to their maximum settings.

3 Turn the DC POWER range key switch counter-clockwise (CCW) to the 500 mA position.

4 Adjust LIMIT pot R229 until the output current reaches 500 mA.

RAMP SPAN Calibration

An oscilloscope is necessary to monitor the output current waveform in order to calibrate the RAMP SPAN adjustment.

1 Turn the DC POWER key switch counter-clockwise (CCW) to select the 500 mA range.

Set the output current LIMIT to 201.0 mA using the procedure described in Chapter 2.

2 Turn the OUTPUT ADJUST knobs fully counter-clockwise (CCW) to their minimum setting

and change the output current range to 200 mA with the DC power key switch.

3 Connect an oscilloscope to a resistor load connected across the LDX-3620 current

output.

4 Turn the modulation mode selector switch to the RAMP position.

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5 Turn the RAMP SPAN adjustment knob fully clockwise (CW) to its maximum setting.

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MAINTENANCE

Disassembly

6 Increase the ramp amplitude (with trimmer R116 (located near the center of the front

panel board) until clipping of the output by the current limit circuit at the ramp maximum can be seen on the oscilloscope. Reverse the adjustment to the point where the clipping just disappears.

Disassembly

The top cover of the LDX-3620 can be removed after extracting the two countersunk screws on the sides of the instrument near the rear panel. The cover is then removed by sliding it rearward and lifting it off. The bottom of the instrument is removed in a similar fashion.

CHAPTER 3

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CHAPTER 3

MAINTENANCE

Disassembly

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