Fluke DSP-FOM Operating and installation instructions

PN 616141
September 1996, Rev. 2, 1/02
1996-2002 Fluke Networks, Inc. All rights reserved. Printed in USA. Product names are trademarks of their respective companies.
DSP-FOM
Fiber Optic Meter
Service Information Sheet for Serial Numbers < 79370000
Introduction
This Service Information Sheet provides the
following service information for the DSP Fiber
Optic Meter (hereafter referred to as the FOM) with
serial numbers < 79370000.
•Parts and warranty service information
•Specifications
•Theory of operation
•Cleaning procedures
•Required equipment
•Performance tests
•Procedures for disassembling and
reassembling the FOM
•Calibration adjustments
•Parts and accessories lists
•Schematic
•Diagram showing calibration measurement
and adjustment points
For operating instructions, refer to the
DSP-FOM/DSP-FTK Fiber Optic Accessory
Instruction Sheet.
Parts and Warranty Service
The FOM is warranted to be free from defects in
material and workmanship for one year, while
under normal use. Parts and repairs are warranted
for 90 days.
Refer to the Instruction Sheet for the complete
warranty statement.
To order parts, or for warranty service, contact
Fluke as follows:
U.S.A.: 1-888-993-5853
Canada: 1-800-363-5853
Europe: [phone]
Japan: [phone]
Singapore: [phone]
Anywhere in the world: [phone]
For operating assistance in the USA, call
1-800-283-5853.
Visit the Fluke Networks web site at
www.flukenetworks.com.
Fluke DSP-FOM Specs
Provided by www.AAATesters.com

DSP-FOM
Fiber Optic Meter
2
Specifications
Accuracy is specified for a period of one year after
calibration, at 18 °C to 28 °C (64 °F to 82 °F) with
relative humidity to 90%. Specifications are shown
in Table 1.
Table 1. Specifications
Calibrated
Wavelengths 850 nm, 1300 nm, and 1550 nm
Measurement
Range +3 dBm to -50 dBm
Measurement
Accuracy* ±0.25 dB at -10.0 dBm and
25 °C (77 °F)
Resolution 0.1 dB (1 mV)
Display Resolution 0.01 dB (0.001 µW)
Detector Type 1 mm (0.04 in) Germanium
Conformance IEC 1010-1
Optical Adapter ST
I/O Connector RJ45 8-pin with ground shield
Output Voltage Dynamic Range: -0.02 V to
+0.55 V
Operating
Temperature 0 °C to +40 °C
(32 °F to 104 °F)
Storage
Temperature -20 °C to +70 °C
(-4 °F to 158 °F)
Dimensions 11.4 cm x 6.4 cm x 3.8 cm
(4.5 in x 2.5 in x 1.5 in)
Weight 141.7 g (5 oz)
Battery Type 9 V Alkaline
Battery Life 90 hours typical
* For field strengths between 1 V/m and 3 V/m add 6 dB.
Theory of Operation
This section provides theory of operation for the
FOM. Refer to the schematic in Figure 1.
General Description
The FOM is an optical power to voltage converter
designed to interface with a DSP CableMeter™
and CableAnalyzer™ test tool. The FOM is
calibrated to convert optical power to voltage at
wavelengths of 850 nm, 1300 nm, and 1550 nm.
A slide switch on the face of the FOM enables the
unit and selects the calibration for one of the three
wavelengths. A ST optical connector couples the
light to be measured into the FOM. The RJ45
connector outputs a calibrated voltage via a cable to
the host CableMeter test tool. Other signals present
at the RJ45 connector are analog levels indicating
the selected wavelength and a full-scale voltage
reference for determining the battery status.
Switch Positions and I/O
Slide switch SW1 is a 2-pole switch. One pole
(pin 5) applies the battery voltage to the voltage
regulator U3. Battery voltage is also applied to one
of the voltage dividers R23/R24, R25/R26, or
R19/R20. Each of these dividers generates an
analog level of 0 V to 0.53 V (referenced to analog
ground), which is proportional to the battery
voltage. This analog level, which appears at pin 4,
3, or 2 of connector J4, indicates which wavelength
has been selected. J4 provides output to the
CableMeter test tool.
The other pole of SW1 (pin 6) applies the 5 V
regulator output to the appropriate potentiometer
(R1, R2, or R3) controlling the wavelength-specific
reference current. Photo diode PD1 is the optical
input interface.
Power Supply and Low Battery
Detection
When power is enabled with SW1, the battery
voltage (minus a diode drop) appears at pin 5 of
voltage regulator U3. U3 generates a 5 V output on
pin 4 and a 2.5 V output on pin 6, which is used as
a rail-splitting analog ground.
A low battery condition is indicated when the
voltage from the selected divider R23/R24,
R25/R26, or R19/R20 drops below 0.26 V relative
to analog ground (battery voltage of 6.2 V). The
full-scale voltage reference of 0.53 V is generated
by divider R21/R16 between the 5 V supply and the
2.5 V analog ground. U2A buffers this reference.
Optical Receivers and A/D
Measurements
The logarithmic optical power to voltage circuit is
comprised of Q1, U1, PD1, and associated resistors
and capacitors. Q1B, part of a dual, bipolar
transistor, receives a reference current from one of
three potentiometers. Q1A receives the signal
current from PD1. The output at U1B, pin 7, is
proportional to the logarithm of the difference

Service Information Sheet for Serial Numbers < 79370000
Cleaning the Optical Connector
3
between the reference current and the signal
current; therefore, the output is a linear function of
the optical power received by the photo detector. A
typical output at U1, pin 7 is 23 mV per dB of
optical power, plus a 69 mV offset
The reference current adjustment potentiometers
R1, R2, and R3 control the zero offset for the three
calibrated wavelengths. Potentiometer R10 trims
the final output slope to 10 mV per dB. The output
of U1B is buffered by U2B. R7 provides
temperature compensation to null some of the
thermal drift of Q1A and Q1B.
Cleaning the Optical Connector
Most problems with optical power meters result
from contaminated connectors. Therefore, always
clean the connector before troubleshooting or
calibration.
To clean the FOM ST connector, wipe it gently
with an optical-grade tissue or swab dampened with
optical-grade alcohol. To remove loose dirt and
dust from the connector, use filtered, compressed
air.
Always cover the connector with a dust cap when
the unit is not in use.
Required Equipment
The following equipment is required for servicing
the FOM:
•0-10 V power supply
•Fluke 187 digital multimeter or equivalent
•Optical power meter calibrated at 850 nm,
1300 nm, and 1550 nm traceable to NIST
Standards
•850 nm laser source; Po = -10 dBm
•1300 nm laser source; Po = -10 dBm
•1550 nm laser source: Po = -10 dBm
•Variable MM optical attenuator
•Variable SM optical attenuator
•Fluke DSP CableMeter test tool
•1 m fiber optic patch cables, 2 required
•2 m UTP patch cable (supplied with the
CableMeter test tool)
Performance Tests
Use the performance tests to confirm that the FOM
is working properly. If the FOM fails any of these
tests, clean the fiber connectors, verify that the
connections are solid, then retest the FOM. If the
FOM still fails a test, it needs calibration
adjustments or repair.
DSP-FOM Detection
1. Turn the CableMeter test tool knob to SETUP.
Use the arrow keys to select TEST
STANDARD, CABLE TYPE; then press
E. Use U D (and Page Up/Page
Down softkeys if necessary) to select the
applicable standard for the DSP-FOM; then
press E. Use the arrow keys to select
Multimode as the cable type; then press
E.
2. With the FOM not connected to the CableMeter
test tool, turn the test tool knob to SINGLE
TEST; then press E. Verify that the
test tool displays the following message:
WARNING THE DSP-FOM IS NOT
CONNECTED. Press Eto continue.
3. With the FOM switch in the OFF position, use
the 2-meter UTP patch cable to connect the
FOM to the CableMeter test tool. Press the test
tool Tkey. Verify that the test tool displays
the following message: WARNING THE
DSP-FOM IS TURNED OFF. Press
Eto continue.
DSP-FOM -10 dBm Checkout
1. Turn on the FOM and the three light sources.
Verify that the FOM power LED is on. Allow
the FOM and the sources to warm up for 10
minutes.
Perform the remaining steps using the light sources
in the following order: (1) 850 nm, (2) 1550 nm,
and (3) 1300 nm.
2. Use a fiber optic patch cable to connect the
light source to the reference power meter.
3. Verify that the reference power meter is
configured to measure the wavelength of the
light source. Adjust the output of the source for
a reading of -10.00 dBm ±0.05 dBm. Record
the power reading for later use.

DSP-FOM
Fiber Optic Meter
4
4. Set the FOM switch to the wavelength position
being tested. Press Ton the CableMeter test
tool; then verify that the second line of the test
tool message displays the following:
Multimode (wavelength setting) nm A-B.
5. Use the patch cable from step 2 to connect the
FOM to the light source. Press #Power.
Allow a few seconds for the reading to
stabilize; then verify that the reading shows the
power level recorded in step 3 ±0.25 dB.
6. Press eon the CableMeter test tool.
Disconnect the light source from the FOM.
DSP-FOM -50 dBm Checkout
1. Connect the 1300 nm light source to the optical
attenuator. Use a second fiber optic patch cable
to connect the optical attenuator to the
reference power meter.
2. Verify that the reference power meter is
configured to measure the wavelength of the
light source. Adjust the optical attenuator for a
reading of -50.00 dBm ±0.05 dBm. Record the
power reading for later use.
3. Use the patch cable connected to the reference
power meter to connect the FOM to the optical
attenuator.
4. On the CableMeter test tool, press
#Power. Allow a few seconds for the
reading to stabilize; then verify that the reading
shows the power level recorded in step 2
±0.4 dBm.
Turn off the test tool, FOM, and the light sources.
Disconnect the FOM and 2-meter UTP patch cable
from the test tool. Disconnect the fiber optic patch
cables from the attenuator, source, and FOM.
Disassembling and Reassembling
the FOM
WCaution
While servicing the FOM, always follow
guidelines for preventing electrostatic
discharge (ESD). Otherwise, ESD can
damage sensitive components,
causing immediate or delayed failure
of the FOM.
A Phillips-head screwdriver is required for
disassembling and reassembling the FOM. To
disassemble the FOM, proceed as follows:
1. Set the FOM switch to OFF.
2. Remove the battery door; then disconnect the
battery.
3. Remove the two Phillips screws found under
the battery door; then separate the top and
bottom cases.
4. To remove the pca, remove the Phillips screw
near SW1; then lift out the pca.
To reassemble the FOM, proceed as follows:
1. Reinsert the pca; then replace the screw that
holds the pca.
2. Tuck the battery wires into the notch at the side
of the battery compartment.
3. Tuck the battery wires down against the pca so
they will not interfere with SW1.
4. Set SW1 to the off position.
5. Set the slide switch actuator on the top case to
the OFF position.
6. Put the top and bottom cases together; then
replace the two screws under the battery door.
Calibration Adjustments
To ensure that the FOM performs to specifications,
calibrate it annually using the procedure that
follows.
Always perform the complete calibration
adjustment procedure.
Step 1: Preparing for Calibration
To prepare for calibration, proceed as follows:
1-1. Remove the dust cap from the DSP-FOM.
1-2. Connect a voltage supply of 8 V dc
±1.0 V dc to the FOM battery strap.
1-3. Set the FOM switch to the 1300 nm position.
Allow the unit to warm up for 10 minutes.
1-4. Connect the 1300 nm light source to the
attenuator input.
1-5. Turn on the 1300 nm light source. Allow the
unit to warm up for 10 minutes.

Service Information Sheet for Serial Numbers < 79370000
Calibration Adjustments
5
Step 2: Coarse Calibration Adjustment
Refer to the schematic in Figure 1 and the drawing
in Figure 2 for the locations of measurements and
components.
2-1. Connect the attenuator output to the reference
power meter.
Note
For the remaining calibration
adjustments, use the cable used in step
2-1 for connecting the attenuator output
to the reference power meter or the FOM.
2-2. Set the attenuator to 0 dBm. Set the
1300 nm light source to -10 dBm ±0.05 dBm.
Record the level shown on the reference
power meter as Pin (power in) for use in step
2-6.
2-3. Connect the attenuator output to the FOM.
2-4. Measure Vdet between U1 pin 7 and the
analog ground reference at U1 Pin 4. Adjust
R2 for 0.3 V ±0.01 V dc.
2-5. Measure Vref between U2 pin 1 and the
analog ground reference at U1 Pin 4. Record
this value for use in the transfer function
calculations.
2-6. Use the following transfer function to
calculate Vo:
()
()
9R =



×− +
V
53 dBm P 3 dBm
ref in
2-7. Measure between DBout at U2 pin 7 and the
analog ground reference at U1 Pin 4. Adjust
R10 for Vo (as calculated in step 2-6)
±0.0005 V.
Step 3: 1300 nm Fine Calibration
Adjustment
3-1. Connect the attenuator output to the reference
power meter. Set the attenuator output to
-45 dBm ±0.1 dBm. Record the value shown
on the reference power meter as Pin for step
3-3.
3-2. Connect the attenuator output to the FOM.
3-3. Use Pin from step 3-1, Vref from step
2-5, and the transfer function below to
calculate Vo:
()
()
9R =



×− +
V
53 dBm P 3 dBm
ref in
3-4. Measure between DBout at U2 pin 7 and the
analog ground reference at U1 Pin 4. Use the
formula below to calculate Vn:
Vn = DBout - Vo (from step 3-3)
2
3-5. Adjust R10 for Vn ±0.0005 V at DBout.
3-6. Connect the attenuator output to the reference
power meter. Set the attenuator for a power
meter reading of -10 dBm ±0.1 dBm.
3-7. Connect the attenuator output to the FOM.
Adjust R2 for Vo ±0.0005 V (as calculated in
step 2-6) at DBout.
3-8. Repeat steps 3-1 through 3-7 until the FOM’s
-10 dBm and -45 dBm readings are within
specifications.
Step 4: 850 nm Fine Calibration
Adjustment
4-1. Set the switch on the FOM to the 850 nm
position.
4-2. Set the 850 nm light source to -10 dBm
±0.05 dBm. Use the reference power meter to
measure the source output power level.
Record this level as Pin for use in step 4-4.
4-3. Connect the 850 nm light source to the FOM.
4-4. Use Pin from step 4-2, Vref from step
2-5, and the transfer function below to
calculate Vo:
()
()
9R =



×− +
V
53 dBm P 3 dBm
ref in
4-5. Measure between DBout at U2 pin 7 and the
analog ground reference at U1 Pin 4. Adjust
R1 for Vo (as calculated in step 4-4)
±0.0005 V.

DSP-FOM
Fiber Optic Meter
6
Step 5: 1550 nm Fine Calibration
Adjustment
5-1. Set the switch on the FOM to the 1550 nm
position.
5-2. Set the 1550 nm light source to -10 dBm
±0.05 dBm. Use the reference power meter to
measure the source output power level.
Record this level as Pin for use in step 5-4.
5-3. Connect the 1550 nm light source to the
FOM.
5-4. Use Pin from step 5-2, Vref from step
2-5, and the transfer function below to
calculate Vo:
()
()
9R =



×− +
V
53 dBm P 3 dBm
ref in
5-5. Measure between DBout at U2 pin 7 and the
analog ground reference at U1 Pin 4. Adjust
R3 for Vo (as calculated in step 5-4)
±0.0005 V.
Step 6: Verifying Calibration
6-1. Follow the procedures given in the earlier
section "Performance Tests".
6-2. Apply insulating varnish, such as red GLPT,
to R1, R2, R3, and R10.
6-3. Reassemble the FOM as described in the
earlier section "Disassembling and
Reassembling the FOM".
Parts and Accessories
Replacement parts (Table 2) and accessories
(Table 3) are available from Fluke.
Table 2. Fluke Replacement Parts for the DSP-FOM
Description Fluke Part Number
DSP-FOM Plastic Case Assembly 616034
Battery Door 200474
PD1: Germanium Photodiode, 1 mm 602778
Table 3. Accessories for the DSP-FOM
Description Fluke Part Number
ST to ST Multimode Patch Cable, 1m 617453
ST to ST Cable Adapter 602810
Carrying Case 616091

Service Information Sheet for Serial Numbers < 79370000
Fiber Optic Meter Schematic for SN
< 79370000
7
FPM2-00-0300
DB
out
V
ref
V
det
Dt11f.eps
Figure 1. Fiber Optic Meter Schematic for SN <79370000

DSP-FOM
Fiber Optic Meter
8
FPM2-00-0001
Pin 7
Pin 5
Pin 1
Pin 7
Dt14f.eps
Figure 2. Calibration Measurement and Adjustment Points for SN <79370000