Marconi Instruments 6900 Series User manual

Ma .. coni
Instruments
RF POWER SENSORS
6900 SERIES
Instruction Manual

CONTENTS
Page
PREFACE iii
OPERA TING PRECAUTIONS iv
Chapter 1GENERAL INFORMATION 1·1
Chapter 2INSTALLATION 2-1
Chapter 3OPERATION 3-1
Chapter 5MAINTENANCE 5-1
Chapter 6REPLACEABLE PARTS 6-1
Chapter 7SERVICING DIAGRAMS 7·1
PREFACE
WARNINGS, CAUTIONS and NOTES
These terms have specific meanings in this manual:
WARNINGS contain information to prevent personal injury.
CAUTIONS contain information to prevent damage to the equipment.
Notes contain important general information.
HAZARD SYMBOLS
The meaning of symbols that appear on the equipment is as follows:-
Symbol Type of hazard Reference in manual
AStatic sensitive component Page iv
.&.
Dismantling may cause irreparable Chap. 5
damage to this unit
&.
Precision connector Page iv
SYMBOLS IN THE MANUAL
The meaning of symbols used in this manual is as follows:-
(I) Sequence of steps in a procedure.
• List of topics or items
CAPS Capitals are used to identify names of controls and panel markings.
[ ] Square brackets are used to distinguish push-button keys.
MANUAL AMENDMENT STATUS
Each page bears the date of the original issue or the date of the latest amendment. Any
changes subsequent to the latest amendment state of the manual are included on inserted sheets
coded
Cl, C2 etc.
46882-1501<
Feb.92 46882-150K
Feb.92 iii

OPERATING PRECAUTIONS
These sensors, when used with the 6950 or 6960 Series of RF Power Meters, the 6970
Power Meter or the 6200 Series of Microwave Test Sets, are protected in accordance with IEC
Safety Class I. They have been designed and tested according to IEC Publication 348 'Safety
Requirements for Electronic Measuring Apparatus', and have been supplied in a safe condition.
CAUTION - AVOIDANCE OF MEASUREMENT ERRORS
To prevent stray radiation being detected and displayed on the power meter, the sensor
should be properly terminated in 50 n(75 nfor the 6919).
Before zeroing and operating the power meter, sufficient time should be allowed for the
sensor to take up the ambient temperature of the measuring environment. Rapid temperature
changes should be avoided while operating.
CAUTION - STATIC SENSITIVE COMPONENTS
These sensors contain static sensitive components which may be damaged by handling.
CAUTION - PRECISION CONNECTOR
All Marconi Instruments Power Sensors are fitted with precision connectors. Good
connector care is essential to maintain the performance of the Power Sensor. The following
guidelines must always be adhered to when making connections:
• The connector interfaces must be clean and free of any mechanical damage.
• The connector should be measured with a connector gauge to ensure they are within
mechanical tolerance.
• Connections should be made by rotating the outer locking nut only, NEVER the
body of the device.
• Always use a torque spanner with 3.5 mm and 2.92 mm connectors.
The Warranty does not cover connector damage due to mis-use or normal wear and tear.
WARNING - TOXIC HAZ.'\RD
Many of the electronic components used in this sensor employ resins and other chemicals
which give off toxic fumes if incinerated. Appropriate precautions should therefore be taken in
the disposal of these items.
WARNING - TEMPERATURE HAZARD
When a 6930 Series sensor is used for measuring high powers the device has a high
operating surface temperature.
Chapter 1
GENERAL INFORMATION
CONTENTS
Page
FEATURES I-I
PERFORMANCE DATA I-I
SUPPLIED ACCESSORIES 1-6
FEATURES
The 6900 Series of RF Power Sensors is used with Marconi Instruments RF Power
Meters 6950 (analogue) and 6960 Series (digital), the 6970 RF Power Meter and the 6200 Series
of Microwave Test Sets. Note, however. that the
6<)30 Series of sensors can be used with the
6960A and 6960B RF Power Meters. but cannot be used with the 6960 RF Power Meter. The
sensors provide the meter with a chopped DC analogue of the RF power. and collectively they
cover a power range from -70 dBm to +35 dBm (0.1 nW to 3 W) at frequencies from 30 kHz to
40GHz.
Each sensor has an individual label showing a graph of 'calibration factor', and values of
'50 MHz reference calibration factor' and 'linearity factor'. The calibration factor appropriate to
the measurement frequency may be entered into both the 6950, 6960 Series and 6970 power
meters to enhance accuracy. The linearity factor may also be entered into the 6960 and 6970 to
compensate for non-linearity at higher powers (compensation is preset internally in the 6950).
The 6200 Series of Microwave Test Sets allow entry and storage of all the calibration data
supplied with the sensors.
A 'calibration record' giving linearity factor and calibration data to two decimal places is
also provided with each sensor.
VSWR and uncertainty values are low across the entire frequency range of the sensor.
Each sensor has a multi-way output connector for connection to the power meter via the
sensor cable that is supplied with the meter. The sensor provides high level signals to the power
meter so that the possibility of significant RF interference during measurements is negligible. A
high damage level threshold minimizes the possibility of damage to the RF unit. Damaged units
are, however, field replaceable in most cases (see Chapter 5).
Its small, light. rugged construction allows the sensor to be used confidently in bench or
field applications without the need for any mechanical support.
PERFORMANCE DATA
The specifications for the sensors are shown on the following pages.
Iv 46882-150K
Sep.93 46882-150K
Feb.93 1·1

6920 6923 6924
POWER RANGE -70 dBm to -20 dBm -70 dBm to -20 dBm -70 dBm to -20 dBm
(0.1
nWto 10 ~W)
(0.1 nW to 10 ~W)
(0.1 nW to 10 ~W)
MAX RF INPUT +26 dBm (400 mW) CW +26 dBm (400 mW) CW +26 dBm (400 mW) CW
+30 dBm (1 W) peak +30 dBm (1 W) peak +30 dBm (1 W) peak
for
2!!S
for 2 us for
2!!S
FREQUENCY RANGE 10 MHz - 20 GHz 10 MHz - 26.5 GHz 10 MHz - 40 GHz
VSWR 1.4 - 1.2
10MHz
- 40 MHz 1.4 10 MHz -
40MHz 1.58 10 MHz -40 MHz
1.2
40MHz
- 10GHz
1.15 40 MHz -100 MHz 1.15
40MHz
-100 MHz
1.35
10GHz
- 18GHz
1.12 100 MHz
2GHz 1.12
100MHz
-2 GHz
1.4 typical
18GHz
- 20GHz
1.17 2 GHz
8GHz 1.33
2GHz
-
18GHz
1.3
8GHz
-
18GHz 1.5
18GHz
33GHz
1.5
18GHz
-26.5 GHz 1.95
33GHz
-
40GHz
1.97 26.5 GHz -
40GHz
(-002 version)
DRIFT 20
~W (typical, 1 hr after 24 hr 20
~W (typical, 1 hr after 24 hr 20 J!W(typical, 1 hr after 24 hr
warm-up at constant warm-up at constant warm-up at constant
temperature) temperature) temperature)
LINEARITY FACTOR Provided
w~h sensor Provided with sensor Provided
w~h sensor
Accuracy ±1% at 25°C between ±1% at 25°C between ±1% at 25°C between
-30 and -20 dBm -30 and -20 dBm -30 and ·20 dBm
Improves by a factor of 10 Improves by a factor of 10 Improves by a factor of 10
for each lower range for each lower range for each lower range
CALIBRATiON FACTOR
Accuracy Uncertainty provided Uncertainty provided Uncertainty provided
with sensor with sensor with sensor
Resolution 0.01% 0.01% 0.01%
RF CONNECTOR Precision N-type, male, 50 nMPC 3.5 mm, male, 50 nMPC 2.92 mm, male, 50 n
SIZE &WEIGHT 104 mm long, 33.5 mm dia. 180 g 87 mm long, 33.5 mm dia. 180 g 88.5 mm long, 33.5 mm dia. 150 g
/i)
m
z
m
::a
)0
r-
Z
."
o
::a
le
~
s
2 GHz
16GHz
18GHz
00 ....
CD 0>
"000
. 00
<0'"
"'..:.
s
;>\ POWER RANGE
MAX
RFINPUT
FREQUENCY RANGE
VSWR
DRIFT
LINEARITY FACTOR
Accuracy
CALIBRATION FACTOR
Accuracy
Resolution
RF CONNECTOR
SIZE &WEIGHT
6930
-15 dBm to +35 dBm
(30
~Wt03W)
+37 dBm (5 W) CW
+50 dBm (100 W) peak
for 2 !!S
10 MHz -18 GHz
1.1 10 MHz -
1.18 2 GHz -
1.28
16GHz-
10 J.!W (typical, 1 hr after 24 hr
warm-up at constant
temperature)
after 24 hr warm-up at
constant temperature
Provided with sensor
-2.5% to +3.5% with 6950
-1% to +2%
w~h 6960AIB
between +25 and +35 dBm
Improves by a factor of 10
for each lower range
Uncertainty provided
with sensor
0.01%
Precision N-type, male,
50n
93 mm long, 33.5 mm dia. 190 9
6932
-15 dBm to +35 dBm
(30 J!Wto 3 W)
+37 dBm (5 W) CW
+50 dBm (100 W) peak
tor z us
30 kHz - 4.2 GHz
1.1 30 kHz 4.2 GHz
10 J!W (typical, 1 hr after 24 hr
warm-up at constant
temperature)
after 24 hr warm-up at
constant temperature
Provided with sensor
-2.5% to +3.5%
w~h 6950
-1% to +2%
w~h 6960AIB
between +25 and +35 dBm
Improves by a factor of 10
for each lower range
Uncertainty provided
with sensor
0.01%
Precision N-type, male,
50n
93 mm long, 33.5 mm dia. 190 9
6934
-15 dBm to +30 dBm
(30~Wto 1 W)
+33 dBm (2 W) CW
+45 dBm (32 W) peak
tor z us
10 MHz - 40 GHz
1.5 10 MHz - 40 MHz
1.12 40 MHz - 100 MHz
1.1 100 MHz - 2 GHz
1.15
2GHz - 12.4GHz
1.2 12.4GHz - 18GHz
1.25 18 GHz - 26.5 GHz
1.43 26.5 GHz - 40 GHz
(1.55 for version -002)
10 J!W(typical, 1 hr after 24 hr
warm-up at constant
temperature)
after 24 hr warm-up at
constant temperature
Provided with sensor
-1.5% to +3.5% with 6950
-1% to +3%
w~h 6960AlB
between +25 and +35 dBm
Improves by a factor of 10
for each lower range
Uncertainty provided
with sensor
0.01%
MPC 2.92 mm, male,
50n
87 mm long, 33.5 mm dia. 150 g
/i)
m
z
m
::a
)0
r-
Z
."
o
::a
le
~
s
z

GENERAL INFORMATION
SUPPLIED ACCESSORIES
6913,6914
N-type male / SMA female adapter (to connect to 0 dBm power reference)
6919
75 nto 50 nadapter (to connect to 0 dBm power reference)
6920
30 dB precision attenuator - for use in calibration
Attenuation: 30 dB ±0.05 dB at 50 MHz at 25°C
6923,6924
30 dB precision attenuator - for use in calibration
Attenuation: 30 dB ±0.05 dB at 50 MHz at 25°C
N-type male / SMA female adapter to connect to 0 dBm power reference
6934
N-type male / SMA female adapter
Part No.
23443-822K
23443-842W
06920-023P
06920-023P
23443-822K
Chapter 2
INSTALLATION
UNPACKING AND REPACKING
Retain the packing materials and the packing instruction note (if included) in case it is
necessary to reship the sensor.
If the sensor is to be returned for servicing attach a label indicating the service required,
type number, serial number and your return address.
If the original container or materials are not available use a strong double-wall carton
packed with shock absorbing material around all sides of the sensor to hold it firmly.
The 001 versions of the 40 GHz power sensors (i.e. 56914-001, 56924-001 and 56934-001) are
supplied with accessories as above. The 002 versions also include a waveguide 22 transformer
and calibration table.
OPTIONAL ACCESSORIES
The following items are required when using the 6920 and 6930 series sensors with the
6950 RF Power Meter. They are available from the Service Unit (address on rear cover of this
manual).
6920Series
Range scale (-65 to -20 dB!TI) for attaching
magnetically to the 6950 range control.
6930Series
Range scale (-10 to +35 dBm) for attaching
magnetically to the 6950 range control.
1-6
06920-008L
41179-028M
46882-150K
Feb.93 46882-150K
Feb.92 2-1

INSTALLATION
BlankPage
Chapter 3
OPERATION
CONTENTS
Page
PREPARATION FOR USE 3-1
WITH 6950 POWER METER 3-2
Zeroing 3-2
Calibration 3-2
Linearity Factor Correction for 6920 Series Sensors 3-3
WITH 6960 SERIES POWER METER 3-3
Zeroing 3-3
Calibration , 3-3
WITH 6970 POWER METER 3-4
Zeroing 3-4
Calibration 3-4
WITH 6200 SERIES OF MICROWAYE TEST SETS 3-5
PREPARATION FOR USE
Note...
The 6930 Series power sensors can only be used with the 6950, 6960N6960B and 6970
RF Power Meters, and also the 6200 Series of Microwave Test Sets. They cannot be
used with the 6960 RP Power Meter.
Before making measurements, the power meter must be matched to the individual
characteristics of the sensor. This entails the following procedures:
• Zeroing the meter.
• Calibration, that is, entering the sensor's calibration factor and linearity factor.
Note...
If the sensor has been stored at a temperature different from that of the measurement
environment, allow sufficient time for thermal equilibrium to be established before
zeroing or calibration. Avoid rapid temperature changes while operating.
WARNING
When using 6930 Series sensors, dissipation of the applied power can cause the sensor to
have a high surface temperature. Take care when handling.
CAUTION
Avoid applying excessive torque when tightening RF connectors or damage may occur.
Finger-tight is usually sufficient, especially for type N connectors. If a torque wrench is
used for 3.5 mm and 2.92 mm connectors, set it to break at 1 Nm (8 Ib in).
246882-150K
Feb. 92 46882-150K
Sep.93 3-1

OPERATION OPERATION
The power meter can now be used for measuring RF power. For full instructions and
uncertainty calculations, refer to the power meter Operating Manual, Chapter 3.
Linearity Factor Correction for 6920 Series Sensors
At -20 dBm, corrected reading =Displayed reading +Correction Factor
where Correction Factor =Sensor Lin Factor - 8%
For each 3 dB decrease in power level, this correction figure should be halved. At
-30 dBm or lower the error will be negligible and the above correction is not necessary.
The linearity factor of 6920 Series sensors can vary from unit to unit. Since the 6950 has
two preset linearity factor correction values, measurement errors will result when using 6920
Series sensors with a linearity factor that is significantly different from this value, and when the
power level is above -30 dBm. If necessary, the displayed reading can be corrected to give a
more accurate power measurement figure, as follows:
Adjust the ZERO control for zero reading on the meter, using the special tool
provided with the power meter.
With no power applied to the sensor, select the most sensitive range by turning the
RANGE switch fully counter-clockwise.
Connect the sensor to the SENSOR INPUT socket of the power meter using the
sensor cable supplied with the power meter.
(2)
(3)
It may be helpful in setting zero to adjust the RESPONSE TIME control on the rear panel
to reduce noise. You may also find it easier to set zero first on a less sensitive range, as
slight adjustments of the ZERO control have considerable effect on the most sensitive
range.
Hint...
WITH 6950 POWER METER
Zeroing
(1)
With no power applied to the sensor, press [AUTO ZERO]. Five dashes appear
on the display, representing the power meter's five ranges. When the last of these
disappears, all five ranges have been zeroed. This takes approximately 25
seconds.
Connect the sensor to the SENSOR INPUT of the power meter, using the sensor
cable supplied with the pow.ermeter.
(2)
WITH 6960 SERIES POWER METER
Zeroing
(1)
(2) Attach the appropriate magnetic range scale to the skirt of the RANGE switch if
required and set the switch to 0 dBm.
Use the N-type to SMA adapter for 6913/6914/6934
Use the 75 Qto 50 Qadapter for 6919
Use the 30 dB pad for 6920
Use the 30 dB pad and N-type to SMA adapter for 6923/6924
Calibration
(1) Connect the sensor to the POWER REFERENCE output of the power meter.
(5) Adjust the GAIN control for full-scale meter reading.
(3) Set the CAL FACTOR control to the value of the reference calibration factor
given on the sensor label. Some sensors, e.g. the 6910, do not have this
information on the label; in these cases the default value of 100% is assumed.
(4) On the rear panel, switch POWER REF to ON and the
UN F : 6%/8% switch to
the setting which is nearest to the value of the linearity factor shown on the
sensor label or its calibration data chart. (If the
UN F switch positions on your
6950 are designated 75 Qand 50 Q, these should be interpreted as 6% (75 Q) and
8% (50
Q) and the switch set accordingly as above.)
(6)
(7)
Switch POWER REF off and disconnect the sensor from the POWER
REFERENCE socket.
Determine the calibration
factor for the measurement frequency, whether from
the graph on the sensor label or from its calibration data chart. Set the CAL
FACTOR control to the same value.
Calibration
(1) Determine the linearity factor, either from the label on the sensor or from its
calibration data chart, Press [UNEARITYFACTOR] and enter this value in the
power meter.
(2) Connect the sensor to the POWER REFERENCE output of the power meter.
Use the N-type to SMA adapter for 6913/6914/6934
Use the 75 Qto 50 Qadapter for 6919
Use the 30 dB pad for 6920
Use the 30 dB pad and N-type to SMA adapter for 6923/6924
(3) Press [CAL FACTOR] and enter the value of the reference calibration factor
given on the sensor label. Some sensors, e.g. the 6910, do not have this
information on the label; in these cases the default value of 100% is assumed,
3-2 46882-150K
Feb. 93
46882-150K
~~ N

OPERATION
(4) Press [AUTO CAL]. Note that the POWER REFERENCE LED comes on and
'CAL' is displayed. The auto cal routine takes approximately 10 seconds for most
sensors, the 6930 Series requiring about 45 seconds.
(3)
OPERATION
Press [CAL FACTOR] and enter the value of the reference calibration factor
given on the sensor label. Some sensors, e.g. the 6'J 10, do not have this
information on the label; in these cases the default value of
IOO'lf, is assumed.
Press [ONIENTER] to activate the instrument.
(5) When calibration is completed, you can check that it has been successful by
pressing [POWER REF]. This switches the power reference signal on, and 0
dBm
(I mW) should be displayed.
(6) Press [POWER REFI again to switch off the power reference signal and
disconnect the sensor from the POWER REFERENCE socket.
(7) Determine the calibration factor for the measurement frequency, either from the
graph on the sensor label or from its calibration chart. Press [CAL FACTOR] and
enter this value in the power meter.
The power meter can now be used for measuring RF power. For full instructions and
uncertainty calculations, refer to the power meter Operating Manual, Chapter 3.
WITH 6970 POWER METER
Zeroing
(I)
(4) When calibration is completed, you can check that it has been successful by
pressing [SHIFT} [PWR. REF]. This switches the power reference signal on, and
odBm (I mW) should be displayed.
(5) Press [SHIFT] [PWR. REF] again to switch off the power reference signal and
disconnect the sensor from the POWER REF socket.
(6) Determine the calibration
factor for the measurement frequency, either from the
graph on the sensor label or from its calibration chart. Press lCAL FACTOR] and
enter this value in the power meter.
The power meter can now be used for measuring RF power. For full instructions and
uncertainty calculations, refer to the power meter Operating Manual, Chapter 3.
WITH 6200 SERIES OF MICROWAVE TEST SETS
For calibration instructions, refer to Chapter 3 of the 6200 Operating Manual.
Calibration
(I)
(2)
(3)
Connect the sensor to the SENSOR INPUT of the power meter, using the sensor
cable supplied with the power meter.
With no power applied to the sensor, press [SHIFT] [ZERO]. The display will be
cleared and the peaking meter bar will progress across the display during the
zeroing sequence. On completion the instrument will be restored to normal
operation.
Determine the linearity factor, either from the label on the sensor or from its
calibration data chart. Press
[UN FACTOR] and enter this value in the power
meter.
Note... For the best measurement accuracy, the sensor should be calibrated against the optional
integral power reference, immediately following a sensor zero. as described in steps (2)
to (5). An external power reference may be used if the power reference option is not
fitted.
(2) Connect the sensor to the POWER REF output of the power meter
Use the N-type to SMA adapter for 6913/6914/6934.
Use the 75 nto 50 nadapter for 6919.
Use the 30 dB pad for 6920.
Use the 30 dB pad and N-type to SMA adapter for 6923/6924.
3-4 46882-150K
Feb.93 46882-150K
Feb.93 3-5

Chapter 4
TECHNICAL DESCRIPTION
CONTENTS
Page
OVERALL CIRCUIT DESCRIPTION 4-1
DETAILED DESCRIPTION 4-2
RF Sensor 4-2
Signal chopper 4-2
Amplifier 4-2
LIST OF FIGURES
Fig. 4-1 Block Diagram of RF Power Sensor 4-1
Fig. 4-2 Simplified Diagram of Amplifier 4-2
OVERALL CIRCUIT DESCRIPTION
Refer to Fig. 4-I. The RF sensor gives a small DC output voltage when RF power is
applied. This DC voltage is converted to an AC signal by the signal chopper. The chopped
signal is fed to the amplifier which is divided into two parts, the first part being in the power
sensor and the other in the power meter. The signal is then processed by the power meter to give
a power reading. A Zener diode in the power sensor provides sensor type information for the
power meter.
Sensor
Meter
RF
SENSOR
P~~er -11.- _
Power Reading
Chopper Drive
Zero Control
Sensor Type
•
[illl------;-.-
Zener
Fig. 4-1 Block Diagram. of RF Power Sensor
46882-150K
Feb. 92 4-1

TECHNICAL DESCRIPTION
DETAILED DESCRIPTION
Refer to Chapter 7 for the circuit diagram of the sensor.
RF Sensor
For the 6910 Series and 6930 Series sensors, the sensing element consists of a monulithic
semiconductor thermocouple element. The 6920 Series uses a Schottky barrier diode. Both
types of sensor provide an output voltage proportional to the RF power.
Signal chopper
The signal chopper consists of two field-effect transistors which act as a sampling gate.
The sampling rate is controlled by a 925 Hz squarewave signal from the power meter. The
output of the signal chopper is a 925 Hz square wave with amplitude proportional to the RF input
power.
A zero control signal from the power meter is introduced at the input of the signal
chopper. This allows the power meter to cancel any residual output that occurs with no RF power
applied.
Amplifier
The amplifier is divided between the power sensor and the power meter. A simplified
circuit is shown in Fig. 4-2.
.Ve
---------..,
Meter
Sensor
TECHNICAL DESCRIPTION
The amplifier has a gain of approximately 1000 and a band-pass characteristic centred at
the sampling rate of 925 Hz. For a full description of the amplifier refer to the appropriate
power meter Service Manual.
A Zener diode is mounted in the sensor to provide sensor type information for the power
meters. The Zener voltage is detected by the power meter and indicates the type of sensor in use.
This in turn defines the required scaling and linearity corrections that must be applied to give a
true power reading.
Ch_
Signal
4-2
Output
-Ve
Fig. 4-2 Simplified Diagram of Amplifier
46882-150K
Feb.92 46882-150K
Feb.92 4-3

TECHNICAL DESCRIPTION
t
f
Chapter 5
MAINTENANCE
CONTENTS Page
6910 AND 6930 SERIES SENSORS 5-2
CAUTIONS 5-2
TEST EQUIPMENT 5-2
SERVICING POLICY AND MAINTENANCE INFORMATION 5-2
FAULTY OPERATION 5-3
BASIC ACCESS 5-3
FAULT FINDING 5-4
Testing the RF Assembly 5-4
Testing the FET Chopper Assembly 5-5
SERVICING 5-5
Replacement of RF Assembly 5-5
Access to Chopper/Amplifier PCB (PCB and 12 pin connector) 5-6
6920 SENSORS 5-7
CAUTIONS 5-7
TEST EQUIPMENT 5-7
SERVICING POLICY AND MAINTENANCE INFORMATION 5-7
FAULTY OPERATION 5-8
BASIC ACCESS 5-8
FAULT FINDING 5-9
Testing the Body Assembly 5-9
Testing the RF Assembly 5-9
SERVICING 5-10
Replacement of RF Assembly 5-10
Access to Body Assembly (PCB and 12 pin connector) 5-10
LIST OF FIGURES
Fig. 5-1 Access and layout diagram - 6910 and 6930 Series Sensors 5-3
Fig. 5-2 Access and Layout Diagram - 6920 Sensor 5-8
46882-150K
Feb.92 46882-150K
Feb.92
5-1

MAINTENANCE
MAINTENANCE
6910 AND 6930 SERIES SENSORS The complete sensor may, of course, be returned to Marconi Instruments Service
Division for repair and calibration (address at rear of manual).
The following information does not apply to the 6914 and 6934 sensors. There is no
provision for customer servicing of these sensors, and the complete unit must be returned to
Marconi Instruments Service Division for repair (address at rear of manual).
CAUTIONS
• It is important that the dismantling and re-assembling detailed in this chapter is
performed in the order specified. This is because the gold wires which connect the RF
assembly to the body assembly (see Fig.
5-1) are extremely delicate and may easily be
damaged if over-stressed. For this reason also, care should be taken when measuring
voltages across or in the vicinity of the gold wires.
• Ensure that all parts are free from dirt, grease or moisture as these might impair the
performance of the sensor.
FAULTY OPERATION
If the sensor is connected to a power meter and sensor lead which are known to be
working, and either zeroing or calibration (as described in Chap. 3) cannot be successfully
accomplished, then the sensor can be assumed to be faulty.
BASIC ACCESS
(1) Remove the sensor cable from the 12 pin connector on the sensor.
(2) Remove the rear plate retaining screws (item 1and 2) using a 1.5 mm Alien key.
(3) Remove the rear plate and slide thecasing from thesensor.
TEST EQUIPMENT
For customer-servicing purposes, the sensor is considered in two parts (see Fig. 5-1).
SERVICING POLICY AND MAINTENANCE INFORMATION
12 PIN
CONNECTOR
ON ARROW'X'
1011
ENLARGED viEW
ON ARROW Y
Fig.5-1 Accessand layoutdiagram-6910and6930 SeriesSensors
Specification
Resolution: 1IiVand 1Q.
Capable of providing ±5 V DC.
1.5 mm
Description
6950, 6960 Series Power Meter,
6970 Power Meter or 6200 Series MTS
(with sensor lead)
Digital voltmeter
Power supply
Alien key
The body assembly. This contains the PCB assembly on which the FET chopper and
part of the amplifier are mounted. The procedure for testing the chopper is given later in
this chapter.
The RF assembly. This is not customer-serviceable, but calibrated replacement RF
assemblies may be quickly and easily fitted by the customer. See later in this chapter for
testing and replacement instructions.
The chopper is not customer-serviceable but is available as a replacement part. The parts
list in Chap. 6and circuit diagram in Chap. 7detail those components of the amplifier which are
contained in the sensor. The remainder of the amplifier circuitry is in the power meter and
limited fault-finding information for this circuit is contained in the Service Manuals for these
instruments.
5-2 46882-150K Sep.93
46882-150K
Feb.92 5-3

MAINTENANCE
FAULT FINDING
(I) Carefully measure the voltage across the gold pads on the FET chopper assembly
(see inset, Fig. 5-1). Disconnect the link between sockets BIG and socket H Apply -5 V to socket H.
This will turn off the shunt FET of the chopper. The resistance measured across
the gold pads should now be greater than 10
kil.
(4)
(3) Measure the resistance between the two gold pads. This should be approximately
100 - 200
il.
(2) Connect together sockets B, Gand H of the 12 pin connector (see Fig. 5-1 inset)
to turn both of the chopper's FETs on.
MAINTENANCE
Testing the FET Chopper Assembly
(1) Disconnect the sensor from the I mW reference and remove the sensor cable.
Remove the beam clamp as described in step (3) of "Testing the RF Assembly".
•
,
If the voltage is 100IlV or greater, the RP assembly is functioning correctly. In
this case, test the FET chopper assembly as described in the next section.
(2)
Reconnect the sensor cable and power meter. Connect the input to the 1mW 50 MHz
reference output of the power meter. Switch on the reference signal.
Testing the RF Assembly
6910 Series sensors:
(3) If the voltage is less than 100 IlV, remove the sensor from the I mW reference.
Remove the tie rod by removing screws item 6 and item 7 with the Alien key.
Remove the beam clamp, by first loosening the clamp screw (item 3), then
removing the beam clamp fixing screws (item 4 and 5). Remove the beam clamp
and carefully lift the two gold wires from the RF assembly clear of the gold pads.
(5) Disconnect the link between sockets B and G. Connect socket H to socket B and
apply -5 V to socket G. This will turn off the series FET of the chopper. The
resistance measured across the gold pads should be greater than 10
kil.
If the applied signals are getting through to the FET chopper but any of the above
measurements are not achieved than the assembly is faulty and should be replaced as described in
"Access to Chopper/Amplifter PCB".
(4) Reconnect the sensor to the 1 mW reference signal and carefully measure the
voltage across the gold wires.
If the voltage is now greater than 100 IlV, it can be
concluded that there is a fault on the chopper/amplifier PCB or in the 12 pin
connector. If the voltage is still less than 100
IJ.,V, the RP assembly is faulty and
must be replaced as described in "Replacement of RP Assembly".
6930 Seriessensors:
SERVICING
Replacement of RF Assembly
(1) Dismantle the sensor as described in "Testing the RF assembly". step (3).
(1) Carefully measure the voltage across the gold pads on the FET chopper assembly
(see inset, Fig. 5-1).
(2) If the voltage is 31J.,V or greater, the RP assembly is functioning correctly. In this
case, test the FET chopper assembly as described in the next section.
(2) Carefully remove the two RP assembly fixing screws (item 8 and 9) using a
screwdriver. Carefully separate the RF assembly from the body assembly without
damaging the gold wires.
(3) If the voltage is less than 31J.,V, remove the sensor from the 1 mW reference.
Remove the tie rod by removing screws item 6 and item 7 with the Allen key.
(3) Offer the replacement RF assembly to the body assembly so that the fixing screw
holes in the RF assembly flange match with those in the body assembly. Be
careful not to damage the gold wires.
(4)
Remove the beam clamp, by first loosening the clamp screw (item 3), then
removing the beam clamp fixing screws (item 4 and 5). Remove the beam clamp
and carefully lift the two gold wires from the RF assembly clear of the gold pads.
Reconnect the sensor to the 1 mW reference signal and carefully measure the
voltage across the gold wires. If the voltage is now greater than
3/lV, it can be
concluded that there is a fault on the chopper/amplifier PCB or in the 12 pin
connector.
If the voltage is still less than 3 IJ.,V, the RF assembly is faulty and
must be replaced as described in "Replacement of RP Assembly".
(4)
(5)
(6)
Fit the fixing screws, items 8 and 9. Align the gold wires centrally over the gold
pads on the chopper assembly.
Ensure that the clamp screw (item 3) is not in contact with the lower part of the
plastic clamp and fit the beam clamp in position using the fixing screws (item 4
and 5).
Tighten the clamp screw (item 3) to firmly clamp the gold wires. The top of the
clamp should just begin to bend upwards.
If a torque screwdriver is available,
tighten to 2 Ncm.
46882·1501<
Feb. 92 46882-150K
Feb.92 5·5

MAINTENANCE
Access to Chopper/Amplifier PCS (peS and 12pin connector)
(1) Separate the RF assembly from the body assembly as described in steps (1) and
(2) of "Replacement of RF Assembly".
(7)
(8)
(9)
(2)
Connect the partly assembled sensor to a power meter and check that zeroing and
calibration can be successfully accomplished.
Fit the tie rod in position using screws item 6 and item 7.
Fit the casing and rear plate followed by the rear plate screws (item 1and 2).
Remove the PCB fixing screws (items 10and 11). Remove the 12 pin connector
fixing screws (items 12 and 13). The PCB and 12 pin connector are now free of
the body assembly.
MAINTENANCE
6920 SENSORS
The following servicmg information applies only to the 6920 sensor. There is no
provision for customer servicing of the 6923 and 6924 sensors, and the complete unit must be
returned to Marconi Instruments Service Division for repair (address at rear of manual).
CAUTIONS
To avoid possible damage or degradation in performance:
• Take care when attaching/detaching leads tolfrom the RF assembly.
• Do not link any points unless specifically instructed to.
• Ensure that all parts are free from dirt, grease or moisture.
(3) To replace the chopperlamplifier PCB and the 12 pin connector, reverse the above
procedure. TEST EQUIPMENT
Description
6950, 6960 Series Power Meter,
6970 Power Meter or 6200 Series MTS
(with sensor lead)
Digital voltmeter
Power supply
Oscilloscope
10 kil resistor
Allen key
Specification
Resolution: ImY.
Capable of providing ±5 V DC.
Bandwidth: >20 kHz.
Sensitivity: Better than 50 mVIdiv
1.5mm.
SERVICING POLICY AND MAINTENANCE INFORMATION
For servicing purposes, the sensor is considered in two parts (see Fig. 5-2).
The RF assembly. This is not customer-serviceable, but calibrated replacement RF
assemblies may be quickly and easily fitted by the customer. See later in this chapter for
testing and replacement instructions.
The body assembly. This contains the PCB on which is mounted part of the amplifier
circuit. The remainder of this circuit is in the power meter and limited fault-finding
information is contained in the Service Manuals for these instruments. Access to the
PCB is described later in this chapter.
The complete sensor may, of course, be returned to Marconi Instruments Service
Division for repair and calibration (address at rear of manual).
5-6 46882-150K
Feb.92 46882-150K Sep.93
5-7

MAINTENANCE
FAULT FINDING
Testing the Body Assembly
(1) Reconnect the cable between the sensor and the power meter.
MAINTENANCE
FAULTY OPERATION
. If the sensor is connected to a power meter and sensor lead which are known to be
workmg: and either zeroing or calibration (as described in Chap. 3) cannot be successfully
accomplished, then the sensor can be assumed to be faulty.
BASIC ACCESS
(1) Remove the sensor cable from the 12pin connector on the sensor.
(2) Using the oscilloscope, check that the 925 Hz, 0 to -5 V square wave chopper
drive signals are present on pin holders PH5 and PH6 (measure with respect to
PCB retainer).
(2)
(3)
Remove the rear plate retaining screws sel and SC2 using a 1.5 mm Allen key.
Remove the rear plate and slide the casing from the Sensor.
(3) If either signal is not present, then there is a fault in the body assembly (amplifier
PCB or 12 pin connector).
Fig. 5-2 Access and Layout Diagram -6920 Sensor
(4) Connect the RF assembly directly to the POWER REFERENCE output.
Using the oscilloscope, carefully measure the voltage waveform between pin
holder PH2 and the PCB retainer. This should be a 925 Hz, 0 to -200 mV
(approximately) square wave. If not, a fault in the RF assembly is indicated. The
remaining steps in this procedure will confirm or disprove this.
Using the DC power supply, apply -5 V via a 10 kO resistor to pin P6 with the RF
assembly chassis as earth (ground). Connect pin P5 to the chassis. Carefully
attach a lead from the -ve terminal of the DVM to pin PI. Switch the POWER
REFERENCE on and check that the reading is greater (more negative) than
-200 mY. Reduce the DC supply to 0 V. The DVM reading should reduce to less
than -60 mY.
Switch the power reference off. Again using the DC power supply, apply -5 V
via the 10 kO resistor to pin P5 with the RF assembly chassis as earth. Connect
pin P6 to the chassis. Carefully attach a lead from the +ve terminal to pin P2.
Switch the POWER REFERENCE on and check that the reading is greater (more
negative) than -200 mY.
If all of the measurements in steps (5) and (6) above are correct, then the RF
assembly is not faulty. Check that corrections between RF assembly and body
assembly are correct, and re-check that body assembly, sensor lead and power
meter are functioning correctly.
If any of the measurements in steps (5) and (6)
are incorrect, then the RF assembly is faulty and must be replaced.
(3) Remove the RF assembly retaining screws SC4, 5 and 6 using the AlIen key, and
carefully pull the RF assembly away from the body assembly.
(2)
(6)
(5)
(7)
Testing the RF Assembly
(1) Connect the sensor to the POWER REFERENCE output of the power meter.
Switch the power reference on.
P3 ... t",P1
.:1 t '-Pb
p,
~~.7
SC1,2
REAR PLATE
YIEW ON:V=)"
SHOWING WIRE POSITIONS
SECTIONED PART VIEW ON
ARROW X
SC4
VIEW ON Z-Z
SHOWIN<i SOCKETS
5-8 46882-150K
Feb.92 46882-150K
Feb.92 5-9

MAINTENANCE
SERVICING
Replacement of RF Assembly
(1) Disconnect the RF assembly from the body assembly as described in "Basic
Access" and "Testing the RF Assembly", step (3).
Chapter 6
REPLACEABLE PARTS
CONTENTS
(2) In fitting the new RF assembly, ensure that the six pins protruding from the RF
as~embly are aligned correctly with the six pin holders in the body assembly.
With the RF assembly on your right-hand side and the body assembly on your left
(PCB uppermost), the longest pair of wires should be furthest away from you.
(3) Carefully insert the pins into the corresponding pin holders and check that the
holes in the PCB retainer and tie rod correspond with those in the RF assembly
flange. Gently push home.
Page
COMPONENT VALUES 6-1
(4) Replace screws SC4, 5 and 6. Note that SC4 (which connects to the tie rod) is
narrower than the other two.
Access to Body Assembly (PCB and 12 pin connector)
(1) Disconnect the RF assembly from the body assembly as described in
Access" and "Testing the RF Assembly", step (3).
(2) Remove SC?, 8 9 and 10 to detach the PCB from its retainer.
6-1
•
•
•
COMPONENT VALUES
One or more of the components fitted in this instrument may differ from those listed in
this chapter for any of the following reasons:
Components indicated by a *have their values selected during test to achieve
particular performance limits.
46882-150K
Feb.92
Owing to supply difficulties, components of different v~ue or ~pe ~ay .be
substituted provided the overall performance of the equipment IS maintained.
As part of a policy of continuous development, components may be changed in value
or type to obtain detail improvements in performance.
When there is a difference between the component fitted and the one listed, always use as
areplacement the same type and value as found in the instrument.
"Basic
Connect the partly assembled sensor to a power meter and check that it is
functioning correctly
46882-150K
Feb.92
Remove SCIl and 12 to detach the 12 pin connector from the PCB retainer.
Remove SC3 to detach the tie rod from the 12 pin connector, if required.
To replace PCB and 12 pin connector, reverse the above procedure.
(5)
(3)
(4)
5-10

REPLACEABLE PARTS
ORDERING
When ordering replacements, address the order to our Service Division (address on rear
cover) or nearest agent and specify the following for each component required:
(l) Type and serial number of instrument.
(2) Circuit reference.
(3) Description.
(4) Part number.
Note...
The components on the Amplifier PCB are not recommended as replaceable parts but are
listed for reference only.
6910
Circuit Ref.
Amplifier PCR
Cl
C2
C3
C4
CS
C6
C7
01
RI
R2
R3
R4
RS
TRl
6911
Circuit Ref.
Amplifier PCR
Description
Calibrated replacement RP assembly
Body assembly (includes amplifier PCB
and connector assembly
SKI)
CAPACITOR CERAMIC 0.0II!F 20% 100V
CAPACITOR
TANTALUM4.7~ 20% 50V
CAPACITOR TANTALUM
4.71J.F 20% 6.3V
CAPACITOR TANTALUM I~ 20% 35V
CAPACITOR CERAMIC lOOpF5%
SOV
CAPACITOR CERAMIC lOOpF5% 50V
CAPACITOR TANTALUM
2.2W 20% 50V
ZENER BZX79CSV6
RESISTOR METAL-FILM 348K 0.5% 1/4W
RESISTOR METAL-FILM 330R 2% 1/8W
RESISTOR METAL-FILM 2K2 2% lISW
RESISTOR METAL-FILM IOK 2% 1I8W
THERMISTOR POSITIVE-TC 100R
TRANSISTOR BCS50B
FET CHOPPER ASSEMBLY
Description
Calibrated replacementRPassembly
Body assembly (includes amplifier PCB
and connector assembly
SKI)
As for 6910
REPLACEABLE PARTS
Part No.
449911008
44990/986
26383/536
26486/220
264861217
26486/209
26386/824
26386/824.
26486/212
283711417
24753/388
24772/061
24772/081
24772/097
69101061
28455/309
69101004
Part No.
449911009
44990/986
6-2 46882-150K
Feb. 92 46882·150K
Feb. 92 6-3

28455/309
26383/536
26486/003
26486/217
26486/209
26386/824
26386/824
26486/212
449911012
44990/988
6910/004
24753/220
24772/061
247721081
24772/097
6910/061
283711550
Part No.
REPLACEABLE PARTS
REPLACEABLE PARTS
6912 6919
Circuit Ref. Description Part No.
Circuit Ref. Description
Calibrated replacement RP assembly 449911010 Calibrated replacement RF assembly
Body assembly (includes amplifier PCB 44990/987 Body assembly (includes amplifier PCB
and connector assembly
SKI)
and connector assembly SKI)
AmplifierPCR Amplifier PCR
Cl CAPACITOR CERAMIC
O.OIIJF 20% 100Y 26383/536
Cl
CAPACITOR CERAMIC O.OIIJF 20% 100Y
C2 CAPACITOR TANTALUM 4.7flF 20% 50V 26486/220 C2 CAPACITOR TANTALUM 3.3flF 20% 50V
C3 CAPACITOR TANTALUM 4.71JF20% 6.3Y 26486/217 C3 CAPACITOR TANTALUM
4.71JF 20% 6.3V
C4 CAPACITOR TANTALUM IIJF20% 35V
264861209
C4 CAPACITOR TANTALUM IflF 20% 35V
C5 CAPACITOR CERAMIC 100pF 5% 50Y 26386/824 C5 CAPACITOR CERAMIC 100pF 5% 50Y
C6 CAPACITOR CERAMIC 100pF 5% 50Y 26386/824 C6 CAPACITOR CERAMIC 100pF 5% 50V
C7 CAPACITOR TANTALUM 2.2flF 20% 50Y 26486/212 C7 CAPACITOR TANTALUM
2.21JF 20% 50V
DI ZENER BZX79C6V8 28371/550
DI
ZENER BZX79C6V8
RI RESISTOR METAL-FILM 348K 0.5% 1I4W 24753/388 RI RESISTOR METAL-FILM 523K0.5% 1I4W
R2 RESISTOR METAL-FILM 330R 2% 1I8W 247721061 R2 RESISTOR METAL-FILM 330R 2%
tzsw
R3 RESISTOR METAL-FILM 2K2 2% 1I8W 24772/081 R3 RESISTOR METAL-FILM 2K2 2% 1/!lW
R4 RESISTOR METAL-FILM IOK 2% 1I8W 24772/097 R4 RESISTOR METAL-FILM lOK 2% 1/8W
R5 TIIERMISTOR
POSmYE-TC 100R 6910/061 R5 THERMISTOR POSITIYE-TC 100R
TRI
TRANSISTOR BC550B 28455/309
TRI
TRANSISTOR BC550B
FET CHOPPER ASSEMBLY 6910/004 FET CHOPPER ASSEMBLY
6913
Circuit Ref. Description Part No.
Calibrated replacement RP assembly 449911011
Body assembly (includes amplifier PCB 44990/986
and connector assembly
SKI)
AmplifierPCR As for 6910
6-4
46882-150K
Feb.92 46882-150K
Feb.92 6-5

REPLACEABLE PARTS REPLACEABLE PARTS
6920 6930
Circuit Ref. Description Part No. Circuit Ref. Description Part No.
Calibrated replacement RF assembly
449911013
Calibrated replacement RF assembly 449911014
Body assembly (includes amplifier PCB 44990/989 Body assembly (includes amplifier PCB 44990/990
and connector assembly
SKI)
and connector assembly SKI)
Amplifier PCR Amplifier PCR
C3 CAPACITOR TANTALUM Ij.iF20% 35V 26486/209
Cl
CAPACITOR CERAMIC O.D1fJF 20% 100V
263831536
C4 CAPACITOR TANTALUM
4.7~F 20% 6.3V 26486/217 C2 CAPACITOR TANTALUM 4.7fJF20% 50V
264861220
C5 CAPACITOR CERAMIC IOnF20%
IOOV
26383/536 C3 CAPACITOR TANTALUM
4.7~F 20% 6.3V 26486/217
C6 CAPACITOR TANTALUM
IO~F20% 6.3V 26486/224 C4 CAPACITOR TANTALUM
1fJF 20% 35V
264861209
C7 CAPACITOR CERAMIC 47nF 10% 50V 26343/560 C5 CAPACITOR CERAMIC 100pF 5% 50V
26386/824
C9 CAPACITOR TANTALUM 220nF 20% 35V
264861205
C6 CAPACITOR CERAMIC 100pF 5% 50V
26386/824
C14 CAPACITOR CERAMIC 100pF 5% 50V 26386/824 C7 CAPACITOR TANTALUM 2.2fJF20% 50V 26486/212
C15 CAPACITOR CERAMIC 100pF 5% 50V 26386/824 DJ ZENER BZX79C8V2
283711671
D2 ZENER BZX79C2V7
283711202
RI RESISTOR METAL-FILM 348K 0.5% 1I4W
24753/388
RI RESISTOR METAL-FILM 30K 2% 1I8W 247721108 R2 RESISTOR METAL-FILM 330R 2% 1I8W
247721061
R2 RESISTOR METAL-FILM 330R 2% 1I8W
247721061
R3 RESISTOR METAL-FILM 2K2 2% 1I8W
247721081
R3 RESISTOR METAL-FILM 2K 2% 1I8W
247721080
R4 RESISTOR METAL-FILM 10K 2% 1I8W
24772/097
R4 RESISTOR METAL-FILM lOK 2% 1I8W
247721097
R5
lHERMISTOR POSITIVE-TC 100R 6910/061
R5 RESISTOR METAL-FILM 47R 2% 1/8WR
247721041
R6 RESISTOR METAL-FILM 68R 2% 1I8WR
247721045
TRI TRANSISTOR BC550B 28455/309
TR1 TRANSISTOR BC550B 28455/309 FET CHOPPER ASSEMBLY 6910/004
6932
Circuit Ref. Description Part No.
Calibrated replacement RF assembly
44991/015
Body assembly (includes amplifier PCB
44990/990
and connector assembly SKI)
Amplifier PCR As for 6930
6-6 46B82-150K
Feb. 92 46B82-150K
Feb. 92 6-7

REPLACEABLE PARTS
BlankPage
Chapter 7
SERVICING DIAGRAMS
CONTENTS
Page
COMPONENT VALUES 7-1
LIST OF FIGURES
Fig. 7-1 Circuit diagram and component layout: 6913 7-3
Fig. 7-2 Circuit diagram and component layout: 6910/6911 7-4
Fig. 7-3 Circuit diagram and component layout: 6912/6919 7-5
Fig. 7-4 Circuit diagram and component layout: 6920 7-6
Fig. 7-5 Circuit diagram and component layout: 6930 7-7
Fig. 7-6 Circuit diagram and component layout: 6932 7-8
COMPONENT VALUES
The letter in the component value code replaces the decimal point and indicates the
multiplier and unit as follows:-
* SIC: value selected during test, nominal value shown.
Components are marked normally with two, three or four figures according to the
accuracy limit ±1O%,
±l %or ±0.1 %.
6-8 46882-150K
Feb.92
Resistors
Capacitors
Inductors
46882-150K
Feb.92
Code letter R =ohms,
k=kilohms
(0
3),
M=megohms (106).
Code letter m =millifarads 00-3),
f.l =microfarads 00-6),
n=nanofarads (10-9),
P=picofarads 00-12).
Code letter H =henrys,
m=millihenrys (10-3),
f.l =microhenrys (l0-6),
n=nanohenrys (l0-9).
7·1