HP 432a, 478a schematic
TM 9-6625-2469-15
DEPARTMENT OF THE ARMY TECHNICAL MANUAL
OPERATOR’S, ORGANIZATIONAL, DIRECT SUPPORT,
GENERAL SUPPORT AND DEPOT MAINTENANCE
MANUAL [INCLUDING REPAIR PARTS]
POWER METER
[HEWLETT-PACKARD MODEL 432A]
[4931-436-4883]
THERMISTOR MOUNT
[HEWLETT-PACKARD MODEL 478A]
[6625-866-1955]
HEADQUARTERS, DEPARTMENT OF THE ARMY
DECEMBER 1969
WE 20780
WARNING
HIGH VOLTAGE
is used in the operation of this equipment.
DEATH ON CONTACT
may result if personnel fail to observe safety precautions.
Learn the areas containing high voltage
in each piece of equipment.
Be careful not to contact high-voltage or 115-volt ac input connections
when installing or operating this equipment.
Before working inside the equipment, turn power off and ground points of
high potential before touching them.
POWER METER
432A
SERIAL PREFIX: 914-
This manual applies directly to HP Model
432A Power Meters having serial prefix
number 914.
SERIAL PREFIXES NOT LISTED
For serial prefixes above 914, a “Manual
Changes” sheet is included with this manual.
For HP Model 432A with serial prefix below 914 refer to Appendix A.
Copyright
1501 PAGE MILL ROAD, PALO ALTO, CALIFORNIA,
HEWLETT-PACKARD COMPANY
1968
U.S.A
(This manual contains copyright material.)
TM 9-6625-2469-15
TECHNICAL MANUAL )
)
No. 9-6625-2469-15)
THERMISTOR Mount (HEWLETT-PACKARD MODEL 478A)
HEADQUARTERS
DEPARTMENT OF THE ARMY
Washington, D.C.
(4931-436-4883)
(6625-866-1955)
22 December 1969
ii
Table of Contents
List of Tables
POWER
TABLE OF CONTENTS
METER
432A
Model 432A
Section
GENERAL INFORMATION . . . . . . . . . . . . . . 1-1
I
1-1. Description . . . . . . . . . . . . . . . . . . . .1-1
1-5.
INSTALLATION . . . . . . . . . . . . . . . . . . . . . .2-1
II
2-1. Initial Inspection . . . . . . . . . . . . . .2-1
2-2. Mechanical Check . . . . . . . . . . . . 2-1
2-4.
2-6. Damage Claims . . . . . . . . . . . .2-1
2-9. Three-Conductor Power Cable . . . . 2-1
2-12. Primary Power Requirements . . . . 2-1
2-14.
2-16. Battery Installation. . . . . . . . . . . 2-1
2-17.
2-19.
2-21. Combining Case . . . . . . . . . . . .2-1
2-23. Adapter Frames . . . . . . . . . . .2-2
2-25. Repacking for Shipment . . . . . . . . . . 2-2
OPERATING INFORMATION.. . . . . . . . . . . 3-1
III
3-1.
3-4.
3-12.
3-17.
3-23.
3-27.
3-28.
3-30.
PRINCIPLES OF OPERATION . . . . . . . . . 4-1
IV
4-1.
4-5. Functional Block Diagram . . . . . . . . 4-1
V
Instrument Identification . . . . . . . . . 1-1
Performance Checks . . . . . . . . . . 2-1
Internal Battery Operation . . . . . . . 2-1
Battery Storage . . . . . . . . . . . . . . 2-1
Rack Mounting . . . . . . . . . . . . . . . .2-1
Introduction . . . . . . . . . . . . . . . . . ...3-1
Controls, Connectors, and
Indicators . . . . . . . . . . . . . . . . . . ...3-1
Battery Operation . . . . . . . . . . . . . ..3-1
Microwave Power Measurement
Accuracy . . . . . . . . . . . . . . . . . . . ...3-2
Calibrator Factor and Effective
Efficiency . . . . . . . . . . . . . . . . . . ...3-2
Precision Power Measurement . . . 3-2
General . . . . . . . . . . . . . . . . . . . . . 3-2
Measurement Procedure . . . . . . 3-2
Simplified Description . . . . . . . . . . . . 4-1
MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . 5-1
5-1. Introduction . . . . . . . . . . . . . . . . . . . . . 5-1
5-3.
Content . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
5-4. Performance Tests . . . . . . . . . . 5-1
5-6.
5-10. Test Equipment . . . . . . . . . . . . . . 5-1
5-12.
5-14. 432 A Performance Tests
Adjustments . . . . . . . . . . . . . . . . . 5-1
Service Information . . . . . . . . . . 5-1
with 8477A Calibrator. . . . . . . . . 5-1
Page Section
MAINTENANCE (Cont.)
V
5-15.
5-16. Meter Accuracy Test . . . . . . . . . 5-1
5-17.
5-18. Meter Linearity Check . . . . . . . 5-2
5-19.
5-20. Fine Zero Range Check . . . . . . 5-3
5-21. 432 Calibration without
5-24. Calibration Procedure 1 . . . . . . 5-3
5-26.
5-27.
5-29.
5-30. Top Cover Replacement . . . . . . 5-8
5-31.
5-32. Bottom Cover Replacement . . . 5-8
5-33. Adjustment Procedures . . . . . . . . . 5-8
5-34. Initial Setup . . . . . . . . . . . . . . . . . 5-8
5-35. Mechanical Meter Adjustment . 5-8
5-36. Bridge Amplifier Tests . . . . . . . 5-9
5-37. Meter and Recorder
5-38. Battery Charger Adjustment
5-39.
5-40. Isolating Trouble in Transistor
5-46. Out-of-Circuit Testing . . . . . . . 5-10
5-48. Component Replacement in
5-50.
5-52.
REPLACEABLE PARTS . . . . . . . . . . . . . ...6-1
VI
6-1.
6-3.
TROUBLESHOOTING. SCHEMATICS.
VII
AND COMPONENT tiCATIONS . . . . . . . . . 7-1
7-1. Introduction . . . . . . . . . . . . . . . . . ...7-1
7-5.
7-8. Schematics . . . . . . . . . . . . . . . . . . ...7-1
7-12. AIAl Auto Zero Assembly . . . . . . . 7-1
7-14. Test Conditions . . . . . . . . . . . . . . ...7-1
Page
Initial Setup . . . . . . . . . . . . . . . . . 5-1
Calibration Factor Test . . . . . . 5-2
Zero Carryover Test . . . . . . . . 5-2
8477A Calibrator . . . . . . . . . 5-3
Calibration Procedure 2 . . . . . .
Cover Removal and Replacement 5-8
Top Cover Removal . . . . . . . . . . 5-8
Bottom Cover Removal . . . . . . . 5-8
Output Calibration . . . . . . . 5-9
(Option 01 Only) . . . . . . . . . . 5-9
Battery Removal . . . . . . . . . . . . 5-10
Circuits . . . . . . . . . . . . . . . . . . . . 5-10
Etched Circuits . . . . . . . . . . . . . 5-13
Axial-Lead Components . . . . . . 5-13
Other Components . . . . . . . . . . . 5-13
Introduction . . . . . . . . . . . . . . . . . ...6-1
Ordering Information . . . . . . . . . . . . 6-1
Troubleshooting . . . . . . . . . . . . . . ...7-1
5-8
Number
1-1.
Specifications, . . . . . . . . . . . . . . . . . . . ...1-1
1-2.
Thermistor Mounts forthe 432A . . . . . . 1-2
Recommended Test Equipment . . . . . . . . 5-0
5-1.
Meter Accuracy Test . . . . . . . . . . . . . ...5-2
5-2.
Calibration Factor Test..... . . . . . . . . . 5-2
5-3.
5-4.
5-5.
5-6.
5-7.
6-1.
6-2.
6-3.
Performance Test Card... . . . . . . . . . . . 5-5
Out-of-Circuit Transistor Resistance
Measurements . . . . . . . . . . . . . . . . . . ...5-11
Etched Circuit Soldering’Equipment . . . 5-13
Safe Ohmmeter Range for Transistor
Resistance Measurements . . . . . . . . . . 5-13
Reference Designation Index . . . . . . . . . 6-2
Replaceable Parts . . . . . . . . . . . . . . . . ...6-12
Code List of Manufacturers . . . . . . . . . . 6-15
Title
LIST OF TABLES
Page
Number Title Page
7-1. Schematic Notes . . . . . . . . . . . . . . . . . ...7-2
7-2. Overall Troubleshooting . . . . . . . . . . . . . 7-5
7-3. RF Bridge Troubleshooting . . . . . . . . . . . 7-6
7-4.
7-5. Auto-Zero Troubleshooting. . . . . . . . . . . 7-7
7-6.
7-7. 5 kHz Multivibrator Troubleshooting . . 7-7
7-8. Range Amplifier Troubleshooting . . . . . 7-7
7-9.
7-10. Pulse Width Modulator and Meter
7-11. Power Supply Troubleshooting . . . . . . . . 7-9
iii
Compensation Bridge Troubleshooting.. 7-6
Chopping andSumm ing Circuit
Troubleshooting . . . . . . . . . . . . . . . . . ...7-7
Calibration Factor Amplifier
Troubleshooting . . . . . . . . . . . . . . . ..,. ..7-7
Troubleshooting . . . . . . . . . . . . . . . . ...7-7
Model 432A
Number
1-1.
HP Model 432A Power Meter . . . . . . . . . . . . 1-0
1-2.
Instrument Identification . . . . . . . . . . . . . . . 1-1
Sub- module Installation in Rack
2-1.
2-2.
3-1.
3-2.
3-3.
3-4.
4-1.
4-2.
4-3.
4-4.
4-5.
5-1.
5-2.
5-3.
5-4.
Adapter Frame . . . . . . . . . . . . . . . . . ...2-2
HP Model 1051A Combining Case
Instrument Installation . . . . . . . . . . . ...2-2
Precision Power Measurements . . . . . . . . . . 3-3
Front Panel Controls, Connectors
and Indicators . . . . . . . . . . . . . . . . . . . . ...3-4
Rear Panel Controls and Connectors . . . . . . 3-6
Turn On and Zeroing Procedure . . . . . . ...3-8
Model 432A Simplified Block Diagram. . . . 4-0
Model 432A Block Diagram. . . . . . . . . . . . ...4-3
Mode1 432A RF Bridge Talking Schematic. . 4-4
Model 432A Meter Logic Talking
Schematic . . . . . . . . . . . . . . . . . . . . . . . . ...4-6
Model 432A Power Supply Talking
Schematic . . . . . . . . . . . . . . . . . . . . . . . . .4-8
Check and Adjustment Test Setup . . . . . . . . . 5-1
Zero Carryover Test Setup . . . . . . . . . . . . . . 5-3
Bridge Amplifier Test,... . . . . . . . . . . . ...5-10
Transistor Biasing and Operating
Chmacteristics . . . . . . . . . . . . . ...5-12
LIST OF ILLUSTRATIONS
Page
Number
7-1. Servicing Block Diagram . . . . . . . . . . . . 7-3
Model 432A Top Internal View . . . . . . . . . . . 7-4
7-2.
Mode1 432A Waveforms . . . . . . . . . . . . ...7-4
7-3.
Mode1 432A Test Point Locations . . . . . . . . 7-5
7-4.
Model 432A Bottom View,
7-5.
7-6.
7-7.
7-8.
7-9. RF and Compensation Bridge
7-10. Mode1 432A Switches . . . . . . . . . . . . . . ...7-12
7-11. A2 Meter Logic Assembly,
7-12. Meter Logic Schematic Diagram . . . . . . . . . 7-13
7-13. A2 Meter Logic Assembly, Power
7-14. A7 Battery Charging Circuit (Option 0l)
7-15. Power Supply, Schematic Diagram . . . . . .7-l5
7-16. Thermistor Cable Wiring Diagram . . . . . . . 7-16
A1-1. A2 Meter Logic, Component Locations . .. A1-2
A1-2. A2 Meter Logic Assembly, Power
A1-3. Meter Logic Schematic Diagram . . . . . . .. A1-3
Component Locations . . . . . . . . . . . . ...7-6
Mode1 432A Front Panel Interior . . . . . . . 7-6
Al Bridge Assembly,
Component Locations . . . . . . . . . . . . . . . 7-10
Mode1 432A Rear Panel Interior . . . . . . . . . 7-10
Schematic Diagram . . . . . . . . . . . . ...7-11
Component Locations . . . . . . . . . . . . . . 7-13
Supply Component Locations . . . . . . . 7-15
Component Locations . . . . . . . . . . . . 7-15
Supply, Component Locations . . . . . . .A1-2
List of Illustrations
Page
APPENDIX A.
B. BASIC ISSUE ITEMS LIST
C.
D.
MANUAL CHANGES
--------------------------------
-----------------------------
MAINTENANCE ALLOCATION CHART
REPAIR PARTS LIST
-------------------------------
------------------
Al-1
B1-1
C1-1
D1-1
iv
GENERAL INFORMATION
1.
Introdution
4.
Incoming Inspection
-------------
------------------
--------
OPERATION ---------------------
7.
Precautions -------------
8.
Mechanical Shock
10.
Biasing Thermistors -----
11.
Minimum Input
13.
Average Power
14.
Pulse Energy and Peale
Power 478A/432
15.
Pulse Energy and Peak
Power 478A/431
19.
Drift Precaution --------
21.
Zero-Set
RF Power Turned Off For
23.
- ---------- -- - - -
---------
--------------
-------- -----
---------
------ --
Zero-Set ---------------
25.
Thermistor Mount Dis-
connected For Zero-
------------------
Set
26.
478A/431
478A/432 ----------------
30.
31.
Mount Calibration Data --
33.
-Calibration Factor ------
35.
Effective Efficiency ----
37.
Calibration Data
Application
39
Thermoelectric Effect ---
.
43.
Thermoelectric Effect
- - - --- - ------ - --
--- - --- - - - -
Error Correction
478A/431
45.
Thermoelectric Error
478A/432
OPERATING PRINCIPLES
-------- ---------
---------------
------- ---
47. Circuit Description -----
52. 431-Power Meter
Detection . . . . . . . . . . . . .
54.
432 Power Detection -----
MAINTENANCE
56. Mechanical Shock
58.
Check On Thermistor
60.
Repair
71.
Thermistor Assembly Re-
-------- -------- ----
Match
---------------------
--------------------
---------
placement Procedure ---
75.
Removal Procedure -------
76.
Installation Procedure --
Page
8-1
8-1
8-2
8-2
8-2
8-2
8-2
8-2
8-2
8-2
8-3
8-3
8-3
8-3
8-4
8-4
8-4
8-5
8-5
8-5
8-5
8-5
8-6
8-5
8-5
8-5
8-6
8-6
8-6
8-6
8-6
8-7
8-8
8-9
8-9
Number Title
1
2
Specifications
Methods of Switching Off
RF Output of Various HP
Signal Generators
3
Parts Furnished in
Thermistor Assembly
Replacement Kit, HP
00478-600------------------
List of ILLUSTRATIONS
Number
1
Maximum Power Meter Read-
ing vs PRF for Pulses
Shorter than 250 u s ----
2
Maximum Power Meter Read-
ings vs Duty Cycle for
Pulses Longer than
250 u s ----------------
3
3 Maximum Power Meter Read-
ing vs Square and Sine
Wave Frequency ----------
4
Source Impedance Shunting
One RF Thermistor
Mount ------ -------------
5
Schematic Diagram of a
Model 478A Thermistor
Mount when Connected to
a 431 Power Meter --------
6
Schematic
Model 478A Thermistor
Mount when Connected to
a 4,82 Power Meter ----
7
Check on Model 478A
Thermistor Resistance
Match
8
9
Thermistor Compensation --Model 478A Thermistor
Mount Assembly ----------
10
HP Model 478A Printed
Circuit A
LIST OF TALBLES
-- - ---------
Diagram of a
------- ------ -
SSy Wiring -----
-------
Page
8-2
8-4
8-8
Page
8-3
8-3
8-3
8-4
8-5
---
8-7
8-7
8-8
8-9
8-10
v
Section I
Model 432A
Figure 1-1. HP Model 432A POWER METER
vi
Model 432A Section I
SECTION I
GENERAL INFORMATION
1-1. DESCRIPTION.
1-2. The Hewlett-Packard Model 432A Power Meter,
with HPtemperature -compensated thermistor mounts,
measures RF power from 10 microwatt (-20 dBm)
to 10 milliwatts (+10dBm) full scale with 1% of full
scale accuracy from 10 MHz to 40 GHz. With a selector switch, the instrument normalizes the power
meter reading to compensate for the Calibration Factor
of a thermistor mount used for a given measurement.
For portable operation, Option 01 instruments have a
rechargeable nickel-cadmium battery. See Table 1-1
for complete specifications.
1-5. INSTRUMENT IDENTIFICATION.
1-6. Hewlett-Packard instruments are identified by
an 8-digit serial number. The first three digits are
the Serial Prefix. To properly match a manual with
the instrument to which it applies, the prefix on the
instrument must be the same as the pref ix at the front
of the manual. If the numbers are different, information is supplied either on yellow Manual Change
Supplements, or in an Appendix in the Manual. If the
change information is missing, contact your HP Sales
Office (Sales Offices are listed at the b a c k of the
Manual).
1-3. The Model 432A has provision for dc substitution
measurements and for power meter calibration. An
output is provided for recorders or digital voltmeter
readout.
1-4. Accessories, Two accessories are supplied with
the Model 432A Power Meter: a 7. 5-foot (2290 mm)
detachable power cable and a 5-foot ( 1520 mm) cable
that connects the thermistor mount to the meter. Ther mister mounts are available but not supplied with the
power meter (refer to Table 1-2). Table 1-1 lists
those accessories supplied and also those available. Figure 1-2. Instrument Identification
Table 1-1. Specifications
Instrument Type: Automatic, self -balancing power
Zero Carryover: Less than +0.5% of f u 11 scale
meterforuse with temperature -compensated ther - when zeroed on most sensitive range.
mister mount.
Power Range: 7 ranges with full-scale readings of
Fine Zero: Automatic, operated by toggle switch.
10, 30, 100, and 300 µW, 1, 3 and 10 mW; also
calibrated in dBm from -20 dBm to +10 dBm full
Recorder Output: 1.000 volt into open circuit cor scale in 5-dB steps. responds to full-scale meter deflection (1. O on
O,- 1 scale) +0.5%; 1000-ohm output impedance,
Accuracy:
+55
Calibration Factor Control: 13-position switch nor-
±1% of full scale on all ranges (+O°C, to
o
C).
BNC connector.
RFI: Meets all conditions specified in MIL-I-6181D.
realizes meter reading to account for thermistor
mount Calibration Factor. Power: 115 or 230 Vac ±10%, 50 to 400 Hz, 2-1/2
Range: 100% to 88% in l% steps.
watts. Optional rechargeable battery provides up
to 20 hours continuous operation. Automatic bat-
Thermistor Mount: External temperature -compen - tery recharge.
sated thermistor mounts required for operation
(see Table 1-2).
Weight: Net 6-1/2lb(3kg), shipping 9-1/4lb(4,2kg).
Meter: Taut -band suspension, individually com-
puter-calibrated, mirror-backed scales. Mini - Weight with Optional Battery Pack: Net 9-1/4 lb
watt scale more than 4-1 4 inches (108 mm) long.
(4,2 kg), shipping 12 lb (5,5 kg).
1-1
Section I Model 432A
Table 1-1.
1-2
Table 1-2.
Model 432A
Section II
Installation
SECTION II
INSTALLATION
2-1. INITIAL INSPECTION.
MECHANICAL CHECK.
2-2.
2-3. If damage to the shipping carton is evident, ask
that the carrier’s agent be present when the instrument
is unpacked. Inspect the instrument for mechanical
damage. Also check the cushioning material for signs
of severe stress.
2-4. PERFORMANCE CHECKS.
2-5. The electrical performance of the Model 432A
should be verified upon receipt. Performance checks
suitable for incoming inspection are given in Section V,
Maintenance.
2-6. DAMAGE CLAIMS.
2-7. If t h e instrument is mechanically damaged in
transit, notify the carrier and the nearest HewlettPackard field off ice immediately. A list of field offices
is at the back of this manual. Retain the shipping carton and padding material for the carrier’s inspection.
The field off ice will arrange for replacement or repair
of your instrument without waiting for claim settlements against the carrier,
2-8. Before shipment this instrument was inspected
and found free of mechanical and electrical defects.
If there is any def iciency, or if electrical performance
is not within specifications, notify your nearest Hewlett -Packard Sales and Service Off ice.
2-9. THREE-CONDUCTOR POWER CABLE.
To protect operating personnel, t h e National
2-10.
Electrical Manufacturers Association (NE MA) recommends that the instrument panel and cab in et be
grounded.
All Hewlett-Packard instruments are
equipped with a three-conductor power cable which,
when plugged into an appropriate receptacle, grounds
the instrument.
The off set pin on the power cable
three-prong connector is the ground wire.
2-11. To preserve the protection feature when oper-
ating the instrument from a two-connector outlet, use
a three-prong to two-prong adapter and connect the
green pigtail on the adapter to ground.
2-12. PRIMARY POWER REQUIREMENTS.
The Model 432A operates from 115 or 230 volts
2-13.
ac line voltage.
Line frequency may vary from 50 to
400 Hz. A slide switch on the rear panel is moved to
the correct position for the I in e voltage available.
Before operating the equipment, ensure that the fuse
installed in the instrument corresponds to the value
marked on the panel for the line voltage available ( 1/8
amp slow-blow).
2-14. INTERNAL BATTERY OPERATION.
Model 432A Option 01 instruments contain an
2-15.
internal battery and a battery charging assembly. By
connecting the 432A to an ac source, the battery may
be charged overnight. The battery can be maintained
in the charging state indefinitely without damage. It
will assume its full capacity, 1.25 ampere -hours, and
will not charge in excess of that. This enables the
instrument to operate for approximately 20 hours continuously without recharging.
2-16. BATTERY INSTALLATION.
a. Set power switch to off and remove power plug
from rear panel,
b. Remove top and bottom, and s i d e instrument
covers.
c. The battery is installed with the terminals toward
the right hand side of the instrument when faced from
the front. The two terminals on the battery fit into
spaces provided on the circuit board.
d. Using the retaining nuts, fasten the battery firmly
in place. Be careful not to short the battery terminals
at any time as this may cause battery cell damage.
e. Install Assembly A7, battery charging board, in
the space provided for it just ahead of the battery.
f. Reinstall instrument covers and adjust circuit.
Instrument is now ready for operation.
2-17. BATTERY STORAGE.
2-18. Store the battery at or below room temperature.
Extended storage at high temperature will reduce the
cell charge, but will not damage the battery if t h e
storage temperature is below 140” F. Install the battery in the instrument and recharge before using
Model 432A in battery operation.
2-19. RACK MOUNTING.
Model 432A is narrower than full-rack width.
2-20.
It is what is termed a sub-modular unit. When used
alone, the instrument can be bench mounted. When
used in combination with other sub-modular units it
may be bench or rack mounted. The HP 1051A and
1052A Combining Cases and Rack Adapter Frames are
designed specifically for this purpose.
2-21. COMBINING CASE.
2-22. A model 1051A Combining Case is shown in
Figure 2-1. This case is full rack width and accepts
varying combinations of submodular instruments. The
case, purchased separately, is provided with a rack
mount ing kit.
The combining case will hold three
2-1
Section II
Installation
Model 432A
instruments the same size as the Model 432A. When
instruments are installed in the combining case, they
may be installed or removed individually.
2-23. ADAPTER FRAMES.
2-24. The 5060-0797 Adapter Frame is shown in Figure 2-2. The frame will accept a variety of submod ular units in a manner suitable for rack mounting.
Submodular units, in combination with anv necessarv
spacers are assembled within the frame.
A submod-
ular unit cannot be removed individually.
2-25. REPACKING FOR SHIPMENT.
Figure 2-1.
Sub -module Installation in
Rack Adapter Frame
2-26. When returning an instrument
Packard use the original packing material.
to HewlettIf the orig -
inal foam type packing material is not available, contact an authorized HP Sales Office for assistance. If
this is not possible, first protect the instrument surfaces by wrapping in heavy kraft paper or with sheets
of cardboard flat against the instrument, Protect the
instrument on all s i d e s using approximately 4“ of
packing material and pack in a durable container. Mark
the container clearly for proper handling and insure
adequately before shipping.
2-27. When an instrument is returned to HP for ser-
vice or repair, attach atagtothe instrument specifying
the owner and desired action. All correspondence
should identify the instrument by model number and
full eight -digit serial number.
2-2
Figure 2-2. HP Model 1051A Combining Case Instrument Installation
Model 432A
Operating Instructions
Section III
SECTION Ill
OPERATING INFORMATION
3-1. INTRODUCTION.
3-2. The Model 432A Power Meter operates with HP
temperature-compensated thermistor mounts such as
the 8478B and 478A Coaxial, and 486A Waveguide
series. The frequency range of the 432A with these
mounts in 50-ohm coaxial systems is 10 MHz to 18 GHz;
in waveguide systems it is 2.6 GHz to 40 GHz. Fullscale power ranges are 10 microwatts to 10milliwatts
(-20 dBm to +10dBm). Extended measurements may
be made to 1 microwatt (-30 dBm). The total meas-
urement capacity of the instrument is divided into
seven ranges, selected by a f rent-panel RANGE switch.
3-3. This section describes general operating pro-
cedures and error analysis in microwave power messurement. Application Note 64, available on request
from Hewlett-Packard, is a detailed analysis of microwave power measurement problems and techniques.
3-4. CONTROLS, CONNECTORS, AND
INDICATORS.
3-5. The front and rear panel controls, connectors,
and indicators are explained in Figure 3-2. The des-
c riptions are keyed to the corresponding items which
are indicated on the figure.
3-6, The COARSE ZERO and FINE ZERO controls
zero the meter. Zero carry-over from the most sen-
sitive range to the other six ranges is within ± 0.5%.
When the RANGE switch is set to COARSE ZERO, the
meter indicates thermistor bridge unbalance, and the
front panel COARSE ZERO adjust is for initial bridge
balance. For best results, FINE ZERO the 432A on
the particular meter range in use.
3-7. The CALIBRATION FACTOR switch provides
discrete amounts of compensation for measurement
uncertainties related to SWR and thermistor mount
efficiency. The Calibration Factor value permits direct meter reading of the RF power delivered to an
impedance equal to the characteristic impedance (Z
of the transmission line between the thermistor mount
and the RF source. Calibration Factor values a r e
marked on the label of each 8478B, 478A, or 486A
Thermistor Mount.
For further details, see Para-
graph 3-23.
3-8. The MOUNT RESISTANCE switch on the front
panel compensates f o r t h r e e types of thermistor
mounts. Model 486A waveguide mounts can be used
by setting the MOUNT RESISTANCE switch to
100Ω
or 200Ω, depending on the thermistor mount used
(refer to Table 1-2). The
200Ω position is used with
Models 478A and 8478B Thermistor Mounts.
3-9. The rear-panel BNC connector lab e 1 ed RE-
CORDER provides an output voltage linearly propor tional to the meter current; 1 volt into an open cir-
cuit equals full- scale meter deflection. This voltage
is developed across a lK resistor; therefore, when
a recorder with a lK input impedance is connected to
the RECORDER output, approximately .5 volts will
equal full scale deflection. This loading of the RE-
CORDER output has no effect on the accuracy of the
432A panel meter.
3-10. A digital voltmeter can be connected to the rearpanel RECORDER output for more resolution of power
meter readings. When a voltmeter with input impedance greater than 1 megohm is connected to the RE-
CORDER output, 1 volt equals full scale deflection.
3-11. The 432A has two calibration jacks (V
vcomp) on the rear panel that can be used for precision power measurements.
Instrument error can
be reduced from ±1% ±(0.2% of reading +5µW) of
reading, depending on the care taken in measure-
and on the accuracy of auxiliary equipment.
ment,
For further information, see Paragraph 3-27.
3-12. BATTERY OPERATION,
3-13. The Model 432A Option 01 operates from battery
and conventional 115- or 230-volt line power. A rechargeable Nickel-Cadmium b a t t e r y is factoryinstalled in Option 01 instruments. The same battery
can be ordered and later installed in the basic instrument, thereby modifying the power meter to the Option
01 configuration. The battery installation kit (including
battery charging circuit ) may be ordered from the
nearest HP Sales Office.
3-14. It is recommended that the Model 432A be bat-
tery -operated for up to 8 hours, and then allowed to
recharge 8 hours, or overnight. Continuous battery
operation is possible for up to about 24 hours, but then
)
o
the battery must be recharged f o r about 24 hours.
3-15. The 432A automatically operates on its internal
batteries whenever the ac line power is disconnected
and the POWER switch is ON. When the battery ter-
minal voltage decreases far enough to f orce the power
supply voltage regulator out of regulation, then the
meter stops working and the meter indicator points to
the red RECHG BAT. To recharge the battery, simply
connect the 432A to ac line power, and turn it ON.
3-16. Battery Storage. Storage of the battery at or
below room temperature is best, Extended storage
at temperatures above room temperature will reduce
cell charge, but will not damage the battery; however,
the battery should not be stored where the tempera-
ture exceeds 60” C (+140° F).
RF and
3-1
Section III
Operating Instructions
Model 432A
3-17. MICROWAVE POWER MEASUREMENT
ACCURACY.
3-18. A number of factors affect the overall accuracy
of power measurement.
The major sources of error
are mismatch error, RF losses, and instrumentation
error.
3-19. Mismatch Error.
In a practical measurement
situation, both the source and thermistor mount have
SWR, and the source is seldom matched to the ther mister mount unless a tuner is used. The amount of
mismatch loss in any measurement depends on the total
SWR present.
The impedance that the source sees is
determined by the acutal thermistor mount impedance,
the electrical length of the line, and the characteristic
impedance of the line, Z
.
o
3-20. In general, neither the source nor the thermistor mount has Z
are known only as reflection coefficients, mismatch
impedance, and the actual impedances
O
losses, or SWR. The power delivered to the thermis-
tor mount - and hence the mismatch loss - can only be
described as being somewhere between t w o limits.
The uncertainty of power measurement due to mismatch
loss increases with SWR. Limits of mismatch loss
are generally determined by means of a chart such as
the Mismatch Loss Limits charts in Application Note
64. The total mismatch 1 oss uncertainty in power
measurement is determined by algebraically adding
the thermistor mount losses to the uncertainty caused
by source and thermistor mount 2
3-21. RF Losses.
RF losses account for the power
match.
0
entering the thermistor mount but not dissipated in the
detection thermistor element.
Such losses may be in
the walls of a waveguide mount, the center conductor
of a coaxial mount, capacitor dielectric, poor connections within the mount, or due to radiation.
a load impedance equal to Z
relationship between indicated power and the power
, More accurately, the
o
available to a Z. load is given by the following equation:
Calibration factor d o e s not compensate for source
VSWR, or for multiple reflections between the source
and the thermistor mount.
3-26. To minimize mismatch between the source and
the thermistor mount without a tuner, insert a low
SWR precision attenuator in the transmission line between the thermistor mount and the source. Since the
mount impedance (and corresponding SWR) deviates
significnatly only at the high and low ends of a microwave band, it is generally unnecessary to use a tuner.
A tuner or other effective means of reducing mismatch
error is recommended when the source SWR is high
or when more accuracy is required. For further details, there is a complete discussion of microwave
power measurement with emphasis on modern techniques, accuracy considerations and sources of error
available in Application Note 64.
3-27. PRECISION POWER
MEASUREMENT.
3-22. Instrumentation Error. The degree of inability
of the instrument to measure the substitution power
supplied to the thermistor mount is called power meter
accuracy or instrumentation error. Instrumentation
error of the Model 432A is ±1% of full scale, O“C to
+55°c.
3-23. CALIBRATION FACTOR AND EFFECTIVE
EFFICIENCY.
3-24. Calibration factor and effective efficiency are
correction factors for improving power measurement
accuracy. Both factors are marked on every HP ther -
mister mount. Calibration factor compensates f o r
thermistor mount VSWR and RF losses whenever the
thermistor mount is connected to an RF source without
a tuner. Effective efficiency compensates for ther -
mister mount RF losses when a tuner is used in the
measurement system.
3-25. When the 432A CALIBRATION FACTOR selec tor is set to the appropriate factor indicated on the
thermistor mount, the power indicated by the meter
is the power that would be delivered by the source to
3-2
3-28. GENERAL.
3-29. Using precision instruments and careful procedures, measurement error can be reduced to ±0.2%
of reading +0.5 µW. The technique involves: 1) zero-
ing the bridge circuits and measuring the bridge amplifier output voltage difference with a digital voltmeter, then 2) connecting RF power to the thermistor
mount and then measuring the bridge amplifier output
voltage difference again, and 3) calculating the power
from ‘the two measurements. Figure 3-1 shows the
instrument setup for dc substitution measurement.
Use an HP Model 3440A DVM, with a 3443A Plug-in
Unit or a digital voltmeter with equivalent accuracy,
3-30. MEASUREMENT PROCEDURE.
a. Connect the DVM to the 432A rear panel Vcomp
and V
RF outputs.
Be sure that the digital voltmeter
input is isolated from chasses ground,
b. Turn off, or disconnect the RF power from the
thermistor mount.
Model 432A
Section III
e. Release the FINE ZERO toggle, and turn on, or
reconnect the RF power to the thermistor ,mount.
Figure 3-1.
Precision Power Measurements
3-3
Section III
General Information
Model 432A
3-4
Figure 3-2. Front Panel Controls, Connectors and Indicators (Sheet 1 of 2)
Model 432A
Operating Information
Section III
1.
POWER. Instrument power ON/OFF switch;
connects either ac line voltage or internal bat- sion so that meter indicates zero. To adjust
tery (Option 01 only) to internal voltage regu - the zero:
later circuits. When ac power is on, optional
battery charging circuit operates.
2.
COARSE ZERO. Meter zero adjustment; set the indicator falls below zero and comes
the RANGE selector to COARSE ZERO, turn back up to zero again.
OFF the RF power, and adjust to zero the meter.
3.
RANGE. Power measurement range selector;
selects ranges from 0.01 to 10 milliwatts (-20
to +10dBm). COARSE ZERO setting is used
to zero meter with no power applied to ther -
mistor mount.
4. FINE ZERO. Electronic zero that balances
the compensation bridge with zero RF input.
To zero m e t e r during operation, close the
switch momentarily.
is not applied to the thermistor mount when the
FINE ZERO switch is depressed.
5.
Meter.
mount in milliwatts and dBm. To use the dBm
scale, note the value in dBm of the range in
use, and subtract from it the reading on the nectorfor 5-1/2 foot cable that connects to the
meter dBm scale.
Indicates power input to thermistor meter.
Be sure that RF power
6. Mechanical Meter Zero. Sets meter suspen-
a. Turn POWER switch off.
b. Turn the adjustment screw clockwise until
c. Turn the adjustment very slightly counter-
clockwise to free up tbe mechanism from
the adjusting peg.
CALIBRATION FACTOR. Amplifier gain com-
7.
pensation selector. Set to correspond to the
calibration factor printed on t h e thermistor
mount body. See Paragraph 3-23 for m o r e
information.
8.
MOUNT RESISTANCE. Se1ects resistance
equal to that of mount in use to balance bridges.
Table 1-2 lists Hewlett-Packard thermistor
mounts and resistances. Set with meter power
OFF, when mount is initially connected to the
9.
Thermistor Mount Cable Connector. Input con478A, 8478B, or 486A Thermistor Mounts.
Figure 3-2. Front Panel Controls, Connectors and Indicators (Sheet 2 of 2)
3-5
Section III
Operating Information
Model 432A
3-6
Figure 3-3. Rear Panel Controls and Connectors (Sheet 1 of 2)
Model 432A
Operating Information
Section III
1,
Line Fuse. For 115 Vac or for 230 Vac use
1/8 amp slow-blow fuse.
2. Power Cord Input. Use power cord provided,
HP 8120 -00?8. Line power limits are 115/230
Vat, 50-400 Hz. Check FUSE rating and
PO-
sition of line voltage slide switch before connetting power.
Line Voltage Slide Switch: Set to line voltage
3.
avallable (115 or 230 Vat, 50-400 Hz).
4.
Mounting Hole for Option 02 Model Power
Meters.
Thermistor mount cable connector meter. Output impedance is approx.
installed and wired in parallel with f rent-panel
connector. Only one mount at a time may be
used with the power meter.
VRF Input. Connected directly to RF bridge.
5.
Used for calibrating power meter with HP 8477A
Power Meter Calibrator. Also used for precision power measurements.
VCOMP Input. Connected directly to compen-
6.
sation bridge. Used for calibrating power meter
with HP 8477A Power Meter Calibrator. Also
used for precision power measurements.
RECORDER OUTPUT. Voltage f r o m meter
7.
circuit to be used for recorder or digital volt-
1000Ω.
Figure 3-3. Rear Panel Controls and Connectors (Sheet 2 of 2)
3-7
Section III
Operating Information
Model 432A
3-8
Figure 3-4. Turn On and Zeroing Procedure (Sheet 1 of 2)
Model 432A
Operating Information
1. Connect the thermistor mount and cable to 5. Set the RANGE selector to COARSE ZERO and
THERMISTOR MOUNT connector. Refer to then zero the meter with the COARSE ZERO
Table 1-2 for recommended thermistor mounts screwdriver adjustment.
and their frequency ranges.
Note
2.
Meter Mechanical Zero:
a. With the instrument turned off, rotate the
meter adjustment screw clockwise until the
pointer approaches the zero mark from the
left.
b. Continue the clockwise rotation until the
The power meter should be zeroed with the
RF power source turned off, or the mount
disconnected from the source.
6. Set the range selector to the 0.01 mW range;
then depress the FINE ZERO switch until the
meter indicates zero.
pointer coincides with the zero mark. If
the pointer overshoots, continue rotating
the adjustment screw clockwise until the
pointer once again approaches the zero mark
Range-to-range zero carryover is 1 ess
Note
from the left. than ±0.5% if the meter zero has been ad-
C. Rotate the adjustment screw about three de-
grees counterclockwise to disengage screw
adjustment from the meter suspension.
justed (step 2 above), and the instrument
has been properly zero-set on the sensi -
tive range. For maximum accuracy, zero-
set the power meter on the range to be
used.
3.
Set the MOUNT RES switch to correspond to
the operating resistance of thermistor mount
used.
4,
Turn the 432A POWER switch ON. For battery
operation, the AC LINE indicator does not turn
on.
Set CALIB FACTOR switch to correspond to
7.
Calibration Factor imprinted on HP thermistor
mount label.
8.
Apply RF power to the thermistor mount. Power
is indicated on the meter directly in mW or dBm.
Section III
Figure 3-4. Turn On and Zeroing Procedure
3-9
4-0
Section IV
Principles of Operation
Figure 4-1.
Model 432A
Model 432A
Principles of Operation
Section IV
SECTION IV
PRINCIPLES OF OPERATION
4-1. SIMPLIFIED DESCRIPTION
4-2. The HP 432A Power Meter consists of two major
sections:
the bridge and meter logic assemblies, The
instrument also contains an auto zero circuit which
provides for automatic zeroing on any range. A simplified Mock diagram of the HP 432A is shown in
Figure 4-1.
4-3. The bridge section contains circuits which form
two self-balancing bridge circuits when a suitable
thermistor mount is connected to the 432A. Each
bridge is automatically brought to balance by the
action of a high gain dc amplifier feeding power to the
top of the bridge, The voltage at the top of the RF
bridge V
RF is responsive to both input RF power and
ambient temperature changes.. The voltage at the top
of the compensation bridge, V
only to ambient temperature changes. Knowing V
COMP is responsive
RF
and VCOMP, the RFpower can be calculated.
4-4. The meter logic section processes V
V
COMP to produce a meter current proportional to
RF power. The sum (V
RF + VCOMP) controls the
width of 5 kHz pulses. The difference (V
RF and
COMP - VRF)
is chopped, amplified and fed to an electronic switch
actuated by the controlled width pulses. Therefore,
the meter current is pulses of variable height and
width with the meter indicating the average current.
(This process produces a meter current proportional
to (V
RF + VCOMP) (VRF - VCOMP ). Paragraph 4-10
explains why this is necessary.
4-8. If ambient temperature causes changes in the
thermistor resistance, the bridge circuits respond by
applying an error voltage to the bridges to maintain
bridge balance.
The voltage at the top of the RF
bridge is dependent upon both ambient temperature
and the RF input. The voltage at the top of the compensation bridge is dependent upon the ambient temperature only. The power meter reading is brought to
zero with no applied RF power by making V
COMP
equal to VRF so (VCOMP - VRF) equals zero. Since
ambient temperature causes both thermistors to respond similarly, there will be no net difference between the amplifier output voltages. Therefore, any
difference in output voltages from the bridges is now
due to RF power absorbed by the thermistor mount.
4-9. The RF bridge voltage, V
tion bridge voltage, V
COMP, contain the “RF power”
RF, and the compensa-
information. To provide a meter reading proportional
to RF power the dc voltages (V
RF, VCOMP) must be
further processed by the meter logic circuits.
4-10. The required processing is derived as follows:
P. is absorbed power needed by the RF thermistor
to bring its resistance to R ohms (100 or 200 ohms).
P. consists of two components: RF power from the
signal source to be measured and dc power supplied
by the 432A. The self balancing action of the bridge
circuit automatically adjusts the dc power so that the
4-5. FUNCTIONAL BLOCK DIAGRAM
4-6. A functional block of the 432A power meter is
shown in Figure 4-2. The instrument comprises two
major assemblies: bridge assembly Al and meter
logic assembly A2.
Auto zero circuit Al Al, which
provides for automatic zeroing of the instruemtn, is
included as part of logic assembly Al.
4-7. The thermistor bridges are biased with direct
current from the bridge amplifiers.
Each bridge
amplifier supplies enough heating current to br ing the
thermistor resistance to 100 or 200 ohms, depending
upon the setting of the MOUNT RESISTANCE switch
on the 432A. If one of the thermistor bridges is unbalanced due to incorrect thermistor resistance, an
error voltage occurs and is amplified by the bridge
amplifier. The error voltage is applied to the top of
the bridge and changes the power dissipation of the
negative temperature coefficient thermistor.
The
change of power dissipation causes the resistance to
the thermistor to change in the direction required to
balance the bridge. Application of RF power to the
RF bridge heats the thermistor and lowers its resis-
tance. The bridge circuit responds by reducing the
dc voltage applied to the top of the bridge thus main-
taining bridge balance.
4-11. RFpower can redetermined by measuring VRF
with and without applied RF power and then doing
some arithmetic. But this power measuring scheme
is neither convenient nor temperature compensated
(since P. changes with temperature). The 432A introduces another thermistor bridge circuit exposed
to the same ambient temperature but not RF power.
This circuit includes adjustments (COARSE and FINE
ZERO) so that the dc voltage V
bridge can be set equal to V
RF and compensation thermistors, V
power) and V
erature fluctuation.
COMP remain equal with ambient temp-
They cliff er only when the RF
COMP at the top of its
RF. Assuming matched
RF
(with no RF
O
power to be measured is applied to the RF thermistor.
Thus, we have
4-1
Section IV
Principles of Operation
Combining equations, we have
4-12. Thus an RF power measurement reduces to
setting V
COMP = V RF
measuring V
COMP and VRF, and computing with the
(with zero RF power) initially,
O
above formula. The 432A carries out the computation
by forming the indicated sum and difference, perform-
ing the multiplication and displaying the result on a
meter.
4-13. The meter logic circuits change the two dc
voltages to two pulse signals which contain all the RF
power information. One of the signals will be a square
wave whose amplitude is proportional to V
RF. The other signal will have a pulse width pro-
V
portional to V
4-14. The V
-
COMP
= VRF .
COMP-VRF signal is obtained by taking
COMP -
the dc voltage outputs from the Al assembly and applying them to a chopper circuit. This chopper cir-
cuit is driven by a 5-kHz multivibrator. The output
of the chopper is a square wave signal whose amplitude is proportional to V
COMP - VRF. The output of
the chopper is coupled to the range amplifier and then
to the calibration factor amplifier. The amplification
that the signal receives in these two amplifiers depends upon the setting of the RANGE switch and the
CALIBRATION FACTOR switch.
The output of the
calibration factor amplifier is V. This current is fed
to the electronic switch. A square wave current with
amplitude proportional to (V
COMP - VRF).
Model 432A
4-15. The V
COMP + VRF signal is obtained by taking
the two dc voltages from Al assembly through a summing circuit and feeding this voltage to a voltage-totime converter.
The voltage-to-time converter is
driven by a 5-kHz multivibrator. The output of the
voltage-to-time converter is a signal whose pulse
width is proportional to the sum of V
COMP + VRF.
This signal controls the electronic switch. From the
COMP - VRF and V COMP + VRF inputs, the elec-
V
tronic switch provides a 5-kHz pulse train whose amp-
litude is proportional to V
width is proportional to V
COMP-VRF and whose pulse
COMP + VRF. The pulse
width is always 90 msec or less.
4-16. The bias circuit switch and filter provides a
zero current reference for the meter circuit. This is
accomplished by controlling the dc bias to the first
stage of the calibration factor amplifier. This circuit,
in effect, restores the dc component to the square wave
which has been amplified by ac coupled amplifiers.
4-17. The meter is 0-1 mA, full-scale meter that
has a capacitor across its terminals. The capacitor
integrates the output pulses from the current switch
so the current into the meter is proportional to the
time average of the input pulses. That is, the input
current to the meter is proportional to the product of
4-18. The output from the meter is further filtered so
the voltage at the rear panel RECORDER output is
suitable for use with either a digital voltmeter or X-Y
recorder. The RECORDER output voltage is returned
to the compensation bridge through the automatic zero
circuit when the FINE ZERO switch is depressed.
The automatic zero circuit holds a correction voltage
at the input of the compensation bridge amplifier, so
when the RF is zero, the meter indication will also
be zero.
4-2
Model 432A
4-3
Principles of Operation
Section IV
Figure 4-2.
4-4
Section IV
Principles of Operation
Figure 4-3.
Model 432A
Model 432A
4-5
Figure 4-3.
Principles of Operation
Section
IV
4-6
Section IV
Principles of Operation
Figure 4-4.
Model 432A
Model 432A
4-7
Principles of Operation
Section IV
Figure 4-4.
4-8
Section IV
Principles of Operation
Figure 4-5.
Model 432A
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