HP 400D, 4001, 400H, H02-400D Organizational, Ds, Gs, And Depot Maintenance Manual
TM 11-6625-1514-15
DEPARTMENT OF THE ARMY TECHNICAL MANUAL
ORGANIZATIONAL, DS, GS,
AND DEPOT MAINTENANCE MANUAL
HEWLETT-PACKARD
VOLTMETER
400D, 400H, 4001
This copy is a reprint which includes current
pages from Changes 1.
VACUUM TUBE
MODELS
AND H02-400D
HEADQUARTERS, DEPARTMENT OF THE ARMY
MAY 1967
WARNING
DANGEROUS VOLTAGES
EXIST IN THIS EQUIPMENT
Be careful when working on the power supplies and
their circuits, or on the 230 or 115-volt ac line
connections.
DO NOT TAKE CHANCES
TM 11-5625-1514-15
C1
C
HANGE
HEADQUARTERS
DEPARTMENT OF THE ARMY
No. 1
Washington DC, 28 September 1982
Organizational, Direct Support, General Support and
Depot Maintenance Manual
HEWLETT–PACKARD VACUUM TUBE VOLTMETER MODELS
400D, 400H, 400L, and H02-400D
(NSN 6625-00-643-1670)
TM 11-6625-1514-15, 23 May 1967, is changed as follows:
1. Title of manual is changed as shown above.
2. New or changed material is indicated by a vertical bar in the margin.
3. Added or revised illustrations are indicated by a vertical bar next to the figure caption.
4. Remove old pages and insert new pages as indicated below:
Remove pages
None. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
i and 1-0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i, ii and 1-0
1-0.1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-0.1
10-5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-5
5. File this change sheet in front of the publication for reference purposes.
. Warning page a/(b blank)
Insert pages
By Order of the Secretary of the Army:
Official:
ROBERT M. JOYCE
Major General, United States Army
The Adjutant General
Distribution:
To redistributed in accordance with special list.
E. C. MEYER
General, United States Army
Chief of Staff
TM 11-6625-1514-15
SAFETY STEPS
IS THE VICTIM
TO FOLLOW IF
OF ELECTRICAL
SOMEONE
SHOCK
DO NOT TRY TO PULL OR GRAB THE INDIVIDUAL
IF POSSIBLE , TURN OFF THE ELECTRICAL POWER
IF YOU CANNOT TURN OFF THE ELECTRICAL
POWER, PULL, PUSH, OR LIFT THE PERSON TO
SAFETY USING A WOODEN POLE OR A ROPE OR
SOME OTHER INSULATING MATERIAL
SEND FOR HELP AS SOON AS POSSIBLE
AFTER THE INJURED PERSON IS FREE OF
CONTACT WITH THE SOURCE OF ELECTRICAL
SHOCK, MOVE THE PERSON A SHORT DISTANCE
AWAY AND IMMEDIATELY START ARTIFICIAL
RESUSCITATION
Change 1 a/(b blank)
This manual contains copyright material reproduced by permission of the Hewlett-Packard Company.
TM 11-6625-1514-15
Technical Manual
HEADQUARTERS
DEPARTMENT OF THE ARMY
No. 11-6625-1514-15
Washington, DC, 23 May 1967
ORGANIZATIONAL, DIRECT SUPPORT, GENERAL SUPPORT AND
DEPOT MAINTENANCE MANUAL
HEWLETT-PACKARD VACUUM TUBE VOLTMETER MODELS
400D, 400H, 400L, AND H02-400D
(NSN 6625-00-643-1670)
Paragraph
Section
Section
Section
Section
Section
I.
GENERAL DESCRIPTION
Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Index of Technical Publications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Maintenance Forms, Records, and Reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reporting Errors and Recommending Improvements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reporting Equipment Improvement Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Administrative Storage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Destruction of Army Electronics Materiel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
II.
INSTALLATION
Unpacking and Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Line Voltage Requirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power Line Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operation Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
III.
OPERATING INSTRUCTIONS
Instrument Turn-On . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
General Operating Information.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Level Measurements and Ground Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Measurement of Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Measurement of Decibels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Impedance Correction Graph . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Use of Voltmeter Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IV.
CIRCUIT DESCRIPTION
Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Input Voltage Divider and Step Attenuator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Broadband Voltmeter Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Indicating Meter Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
V.
MAINTENANCE
Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Precautions . . . . . . . . . . . . . . . . . . . . . . . .
Test Equipment Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Meter Zero Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cabinet Removal . . . . . . . . . . . .
Tube Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Replacement of Special Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Trouble Shooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Testing the Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Testing Voltmeter Performance
Calibration and Frequency Response Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
1-A.1
1-A.2
1-A.3
1-A.4
1-A.5
1-A.6
1-A.7
1-1
1-4
2-1
2-3
2-5
2-8
2-10
3-1
3-3
3-12
3-14
3-17
3-20
3-22
4-1
4-3
4-7
4-10
4-14
5-1
5-3
5-5
5-7
5-9
5-10
5-13
5-17
5-20
5-22
5-24
Page
1-0.1
1-0.1
1-0.1
1-0.1
1-0.1
1-0.1
1-0.1
1-1
1-1
2-1
2-1
2-1
2-1
2-1
3-1
3-1
3-2
3-2
3-3
3-3
3-4
4-1
4-1
4-1
4-1
4-2
5-1
5-1
5-1
5-1
5-2
5-2
5-2
5-3
5-3
5-5
5-8
Change 1 i
TM 11-6625-1514-15
Section
Section
Section
Section
Section
ILLUSTRATED PARTS BREAKDOWN
VI.
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
GROUP ASSEMBLY PARTS BREAKDOWN
VII.
Vacuum Tube Voltmeter 400D/H/L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Main Chassis Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Range Switch Assembly 400D-19A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Printed Circuit Board Assembly 400D-75G . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Printed Circuit Board Assembly 400D-75F . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Printed Circuit Board Assembly 400D-65C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VIII.
NUMERICAL INDEXES
Part No. Numerical Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hewlett-Packard Stock No. Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
REFERENCE DESIGNATION INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IX.
AUXILIARY EQUIPMENT
X.
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Line Matching Transformer Model 11004A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bridging Transformer Model 11005A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Final Performance Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Paragraph
6-1
7-1
7-2
7-3
7-4
7-5
7-6
10-1
10-3
10-7
10-8
Page
6-1
7-1
7-3
7-8
7-9
7-10
7-12
8-1
8-2
9-1
10-1
10-1
10-5
10-5
ii
Change 1
1-0
Change 1
TM 11-6625-1514-15
Figure 1-1.
SECTION I
GENERAL DESCRIPTION
TM 11-6625-1514-15
1-A.1. Scope
This manual includes installation and operation instructions and covers operator’s, organizational,
direct support (DS), general support (GS), and depot
maintenance. It describes Hewlett-Packard (Federal
Supply Code 28480) Vacuum Tube Voltmeter Models
400D and H02-400D, serial numbers 310-45571 and
higher; and Models 400H and 400L, serial numbers
313-22177 and higher. A basic issue items list for this
equipment is not included in this manual.
1-A.2. Index of Technical
Publications
Refer to the latest issue of DA Pam 310-4 to determine whether there are new editions, changes or additional publications pertaining to the equipment.
1-A.3. Maintenance Forms, Records,
and Reports
a. Reports of Maintenance and Unsatisfactory
Equipment.
cedures used for equipment maintenance will be
those prescribed by TM 38-750, The Army
Maintenance Management System (Army). Air Force
personnel will use AFR 66-1 for maintenance reporting and TO-00-35D54 for unsatisfactory equipment
reporting.
b. Report of Packaging and Handling Deficien-
cies. Fill out and forward SF 364 (Report of
Discrepancy (ROD)) as prescribed in AR 735-11-2/
DLAR 4140.55/NAVMATINST 4355.73/AFR 40054/MCO 4430.3E.
c. Discrepancy in Shipment Report (DISREP)
(SF 361).
ment Report (DISREP) (SF 361) as prescribed in AR
55-38/NAVSUPINST 4610.33B/AFR 75-18/MCO
P4610.19C/DLAR 4500.15.
Department of the Army forms and pro-
Fill out and forward Discrepancy in Ship-
1-A.4. Reporting Errors and Recom-
mending Improvements
You can help improve this manual. If you find any
mistakes or if you know of a way to improve the procedures, please let us know. Mail your letter or DA
Form 2028 (Recommended Changes to Publications
and Blank Forms) direct to Commander, US Army
Communications-Electronics Command and Fort
Monmouth, ATTN: DRSEL-ME-MQ, Fort Monmouth, NJ 07703. A reply will be furnished direct to
you.
1-A.5. Report Equipment Improve-
ment Recommendations (EIR)
If your vacuum tube voltmeter needs improvement,
let us know. Send us an EIR. You, the user, are the
only one who can tell us what you don’t like about
your equipment. Let us know why you don’t like the
design. Tell us why a procedure is hard to perform.
Put it on an SF 368 (Quality Deficiency Report).
Mail it to Commander, US Army CommunicationsElectronics Command and Fort Monmouth, ATTN:
DRSEL-ME-MQ, Fort Monmouth, NJ 07703. We’ll
send you a reply.
1-A.6. Administrative Storage
Administrative storage of equipment issued to and
used by Army activities will have preventive
maintenance performed before storing. When
removing
storage, the PMCS should be performed to assure
operational readiness.
1-A.7. Destruction of Army Elec-
Destruction of Army electronics materiel to prevent
enemy use shall be in accordance with TM 750244-2.
the equipment from administrative
tronics Materiel
Change 1
1-0.1
TM 11-6625-1514-15
Paragraphs 1-1 to 1-5
Section I
1-1. INTRODUCTION.
1-2. This manual contains operating and servicing
instructions, and a parts breakdown, for the Models
400D, 400H, and 400L Vacuum Tube Voltmeters manufactured by the Hewlett- Packard Company. The Model
400D Voltmeter is similar to a military counterpart,
Electronic Voltmeter ME-30A/U, in appearance and
operation, but contains modified electrical circuits
to obtain improved performance. Applicable Federal
Stock Numbers for the voltmeters are as follows:
Model 400D: 6625-643-1670
Model 400H: 6625-557-8261
Model 400L: 6625-729-8360
1-3. The Models 400D, 400H, and 400L Voltmeters
are the same except for the differences listed in Figure 1-2.
a. Voltage Range: 400D/H - 0.1 millivolt to 300
volts; 400L - 0.3 millivolt to 300 volts, in 12 ranges
providing full-scale readings of the following voltages:
0.001
0.003 0.300 30.00
0.010
0.030 3.000
b. Decibel Range: -72 to +52 db, in 12 ranges.
c. Frequency Range: 10 cps to 4 mc.
d. Input Impedance: 10 megohms shunted by 15 pf
(15 µµf) on ranges 1.0 volt to 300 volts; 25 pf on ranges
0.001 volt to 0.3 volt.
e. Stability: Line voltage variations of ±10% do not
reduce the specified accuracy, and line voltage transients
are not reflected in the meter reading. Electron tube
deterioration to 75% of normal transconductance affects
accuracy less than 0.5% from 20 cps to 1 mc.
f. Amplifier: OUTPUT terminals are provided so
that the voltmeter can be used to amplify small signals
or to enable monitoring of waveforms under test with
an oscilloscope. Output voltage is approximately 0.15
volt rms on all ranges with full-scale meter deflection.
Amplifier frequency response is same as the voltmeter.
Internal impedance is approximately 50 ohms over
entire frequency range.
(See figure l-l. )
0.100
1.000
10.00
100.00
300.00
a. The front panel meters are different in each
model, as described in paragraph 1-6.
b. The accuracy specifications are different for
each model, as described in figure 1-2.
1-4. DESCRIPTION.
1-5. The Hewlett-Packard Models 400D, 400H, and
400L Vacuum Tube Voltmeters are general purpose,
portable electronic a-c voltmeters of high sensitivity
and stability. They are suited to both laboratory and.
field use. Models 400 D/H measure a-c voltages from
0.001 to 300 volts and Model 400L from .003 to 300
volts rms full scale, with a frequency bandwidth covering 10 cps to 4 megacycles. The voltmeters are compact, accurate, and rugged and have fast meter response, high input impedance, stable calibration accuracy, and freedom from the effects of normal line
—
voltage variations.
long instrument life with a minimum of servicing.
g. Accuracy: Model 400D -
± 2% of full scale, 20 cps to 1 mc;
± 3% of full scale, 20 cps to 2 mc;
± 5% of full scale, 10 cps to 4 mc.
Model 400H -
± 1% of full scale, 50 cps to 500 kc;
± 2% of full scale, 20 cps to
± 3% of full scale, 20 cps to
+ 5% of full scale, 10 cps to
Model 400L -
±2% of reading or ±1% of full scale,
whichever is more accurate,
50 cps to 500 kc.
±3% of reading or ±2% of full scale,
whichever is more accurate,
20 cps to 1 mc.
±4% of reading or ±3% of full scale,
whichever is more accurate,
20 cps to 2 mc.
±5% of reading 10 cps to 4 mc.
h. Power Requirement:
1000 cps, approximately 100 watts.
i. Size: 11-3/4 in. high, 7-1/2 in. wide, 12 in. deep.
j. Weight: 18 lbs; shipping weight approximately
23 lbs.
The voltmeters are designed for
1 mc;
2 mc;
4 mc.
115/230 volts ±10%, 50 to
00102-3
Figure 1-2. Table of Specifications
1-1
TM 11-6625-1514-15
Section I
Paragraphs 1-6 to 1-10
1-6. Each model voltmeter has three calibrated scales
on the panel meter.
two linear VOLTS scales, 0 to 1 and 0 to 3, and one
DECIBELS scale,
the Models 400H and 400L are larger and include a
mirror to eliminate parallax in viewing and to facilitate
use of the higher scale calibration accuracy of these
models. The Model 400L VOLTS scales are logarithmic
in calibration, from 0.3 to 1 and 0.8 to 3; and the
DECIBELS scale is linear. In all models, the VOLTS
scales are calibrated to indicate the root-mean-square
(rms) value of an applied sine wave. Actual meter
deflection is proportional to the average value of the
applied signal, thereby minimizing additional meter
deflection due to noise and harmonic distortion.
1-7. A voltmeter output signal is provided at the front
panel OUTPUT terminals.
to the meter reading and has a waveshape similar to the
applied signal.
rms for a full-scale meter reading, regardless of the
input signal level. The internal impedance at the
OUTPUT terminal is 50 ohms over the full frequency
range.
adversely affect the accuracy of the voltmeter. This
output is valuable for increasing the sensitivity of
bridges, etc., where distortion added to the waveform
is not a factor.
1-8. The voltmeter chassis is constructed of aluminum
alloy throughout. The panel is finished in non-reflecting,
light-grey baked enamel; the cabinet is finished in
dark-blue, baked wrinkle paint. The cabinet is equipped
with rubber feet and a leather carrying handle. Control
markings on the front panel are engraved and black
filled. INPUT and OUTPUT terminals are special
binding posts which accept either bare wire or banana
plugs; the 3/4-inch spacing between binding posts accepts
standard dual-banana plugs. The “ground” side of the
INPUT and OUTPUT terminals is connected to the
instrument chassis which is in turn connected to the
power line ground through the third (round) prong of
the plug on the power cable.
High-impedance loads (above 100K) will not
The Models 400D and 400H have
-12 to +2 db. The meters used in
This output is proportional
This signal level is about 0.15 volts
1-9. The voltmeter is equipped with a non-detachable
power cord. Test leads, which may be plain wire leads
or coaxial cable, and test probes must be supplied by
the user.
1-10. Instruments designated Models 400DR, 400HR,
and 400LR are rack mount configurations of the 400D,
400H, and 400L, respectively. They are identical to
their cabinet model counterparts in every other re-
spect. They are designed to be mounted in a standard 19 inch wide x 7 inch high relay rack space. Refer to Appendix C for Replacement Parts information.
1-2
2-1. UNPACKING AND INSPECTION.
TM 11-6625-1514-15
Section II
Paragraphs 2-1 to 2-11
SECTION II
INSTALLATION
2-2. There are no special precautions for unpacking
the voltmeter. Save the shipping carton and packing
materials for possible storage or reshipment. When
unpacking, inspect instrument and packing materials
for signs of damage in shipment. Make an operation
check as directed in paragraph 2-10 to determine if
performance is satisfactory. If there is any indication
of damage or deficiency, refer to
paragraph 1-A.3.
2-3. LINE VOLTAGE REQUIREMENT.
2-4. The voltmeter is wired at the factory for use on
115-volt a-c power. This voltage may vary ±10% without
adverse effect upon voltmeter performance. The voltmeter can be wired for use on 230-volt a-c power by
reconnecting the dual primary windings on the power
transformer as shown in the schematic diagram in
Section V. When using 230-volt power, change from
a 1-amp to a 1/2-amp slow-blow fuse. If necessary,
provide an adapter for attaching the standard 115-volt
plug on the voltmeter to the 230-volt outlet.
2-5. POWER LINE CONNECTION.
2-6. The three-conductor power cable on the voltmeter
is terminated in a polarized three-prong male connector.
The third contact is an offset round pin added to a standard two-blade connector, which grounds the instrument
chassis when used with the appropriate receptacle.
To connect this plug in a standard two-contact receptacle,
use an adapter. The chassis ground connection is
brought out of the adapter in a green pigtail lead for
connection to a suitable ground.
The lower INPUT and OUTPUT signal terminals
on the panel of the voltmeter are connected
directly to the chassis of the voltmeter. Any
voltage applied to the lower terminal will be
shorted directly to ground. If the ground connection in the power cord is disconnected by
use of an adapter, the entire voltmeter cabinet
will carry whatever potential is applied to the
lower terminal and may be a hazard to the
operator.
2-8. INSTALLATION.
2-9. The voltmeter is a portable instrument requiring
no permanent installation. The voltmeter is for benchtop operation, standing on its rubber feet with its front
panel near the vertical plane. A bail is provided for
raising the front of the cabinet to obtain a better viewing
angle.
2-10. OPERATION CHECK.
2-11. The voltmeter is ready for use as received from
the factory. The simple check described below can be
made by incoming inspectors to determine if electrical
damage was incurred in shipment. If more complete
proof of instrument performance is required, the over-all
performance check described in paragraph 5-22 must be
used. Make a simple performance check as follows:
a. Connect voltmeter to the power line through a
variable transformer. Set transformer for 115 volts,
turn on and allow a five-minute warmup.
2-7. The power plug normally supplied with the volt-
meter is made of molded rubber and is an integral
part of the power cable. On certain military contracts,
a modification of the Model 400D, termed the H02-400D,
is equipped with a removable plug having the same pin
configuration but constructed of corrosion-resistant
material. In all other respects the H02-400D is the
same as the Model 400D and carries the same Federal
Stock Number.
00102-2
b. Measure any sine wave voltage, excepting the power
line,
from 0.01 to 300 volts whose exact voltage is known.
Note that the lower INPUT terminal is connected to the
power line ground.
c. While making the above measurement, adjust the
line voltage from 103 to 127 volts. The reading on the
meter must not change by more than the width of the
pointer.
2-1
TM 11-6625-1514-15
Section III
3-0
Figure 3-1. Voltmeter Front Panel, Showing Controls and Connectors
00102-2
SECTION III
OPERATING INSTRUCTIONS
TM 11-6625-1514-15
Section III
Paragraphs 3-1 to 3-9
3-1. INSTRUMENT TURN-ON.
3-2. The voltmeter is ready for use as received from
the factory and will give specified performance after a
few minutes warmup. See Section II for information
regarding connection to the power source and to the
voltage to be measured. Controls are shown in figure 3-1.
3-3. GENERAL OPERATING INFORMATION.
3-4. METER ZERO CHARACTERISTIC. When the
Model 400D and 400H Voltmeters are turned off, the
meter pointer should rest exactly on the zero calibration
mark on the meter scale. If it does not, zero-set the
meter as instructed in paragraph 5-7. The meter
supplied in the Model 400L Voltmeter is not provided
with a mechanical meter zero adjustment. When the
voltmeter is turned on with the INPUT terminals
shorted, the meter pointer may deflect upscale slightly;
this deflection does not affect the accuracy of a reading.
NOTE
When the voltmeter RANGE switch is set to the
lowest ranges and the INPUT terminals are not
terminated or shielded, noise pickup can be
enough to produce up to full-scale meter deflection. This condition is normal and is caused
by stray voltages in the vicinity of the instrument. For maximum accuracy on the .001-volt
range, the voltage under measurement should
be applied to the voltmeter through a shielded
test lead.
3-5. METER SCALES. The two voltage scales on each
of the voltmeter models are related to each other by
a factor of 1 10 (10 db). In conjunction with the calib-
rated RANGE switch steps, this provides an intermediate
range step spaced 10 db between “power of ten” ranges,
which are 20 db apart. The relationship of the DECIBELS
scale to the 0 to 1 VOLT scale is determined by making
0 db on the DECIBELS scale equal to the voltage required
to produce 1 milliwatt in 600 ohms (0.775 volts). Thus,
the DECIBELS scale reads directly in dbm (decibels
referred to one milliwatt) across a 600-ohm circuit,
and can be used to measure absolute level of sine wave
signals. It can also be used to measure relative levels
of any group of signals which have the same waveform,
across any constant circuit impedance. The RANGE
switch changes voltmeter sensitivity in 10-db steps
accurate to within ± 1/8 db. The RANGE switch position
indicates the value of a full-scale meter reading.
3-6. CONNECTIONS. Voltmeter test leads must be
provided by the user. The type of leads and probes
used will depend upon the application, as listed below:
a For connection to low-impedance signal sources,
plain wire leads often are sufficient.
00102-2
b. For high-impedance sources, or where noise pickup
is a problem, low-capacity shielded wire must be used
with a shielded, dual banana plug for connection to the
voltmeter terminals.
c. If a probe is used, it should also be shielded to
prevent pickup from the hand.
d. For signals above a few hundred kilocycles, the
capacity of the test leads must be kept to a minimum
by using very short leads, preferably unshielded. An
alligator clip should be used at the test end so that
connection can be made without adding the capacity of
the user’s hands.
3-7. MAXIMUM INPUT VOLTAGE. Do not apply more
than 600 volts de to the INPUT terminals. To do so exceeds the voltage rating of the input capacitor.
3-8. If an applied voltage momentarily exceeds the
selected full-scale voltmeter sensitivity, a few seconds
may be required for circuit recovery, but no damage
will result.
3-9. INPUT VOLTAGE WAVEFORM. The voltmeter
is calibrated to indicate the root-mean-square value
of a sine wave; however, meter pointer deflection is
proportional to the average value of whatever waveform
is applied to the input.
is not a sine wave, the reading will be in error by an
amount dependent upon the amount and phase of the
harmonics present, as shown in figure 3-2 below.
When harmonic distortion is less than about 10%, the
error which results is negligible.
INPUT VOLTAGE
CHARACTERISTICS
Fundamental = 100
Fundamental +10%
2nd harmonic
Fundamental +20%
2nd harmonic
Fundamental +50%
2nd harmonic
Fundamental +10%
3rd harmonic
Fundamental +20%
3rd harmonic
Fundamental +50%
3rd harmonic
Note: This chart is universal in application since
these errors are inherent in all average-responding type voltage-measuring instruments.
Figure 3-2. Effect of Harmonics on Voltage
Measurements
If the input signal waveform
TRUE
RMS
VALUE
100
100.5
102
112
100.5
102
112
METER
INDICATION
100
100
100-102
100-110
96-104
94-108
90-116
3-1
TM 11-6625-1514-15
Section III
Paragraphs 3-10 to 3-16
Figure 3-3. Test Setup for Avoiding Ground Loop
3-10. Since the voltmeter meter deflection is propor-
tional to the average value of the input waveform, it
is not adversely affected by moderate levels of random
noise. The effect that noise has on the accuracy of the
meter reading depends upon the waveform of the noise
and upon the signal-to-noise ratio. A square wave has
the greatest effect, a sine wave intermediate effect, and
“White” noise has the least effect on the meter reading.
3-11. If the noise signal is a 50% duty cycle square wave
and the signal-to-noise ratio is 10:1 (between peak
voltages), the error will be about 1% of the meter
reading. If the noise signal is “white” noise and the
signal-to-noise ratio 10:1, the error is negligible.
3-12. LOW-LEVEL MEASUREMENTS AND GROUND
CURRENTS.
3-13. When the voltmeter is used to measure signal
levels below a few millivolts, ground currents in the
meter test leads can cause an error in meter reading.
Such currents are created when two or more ground
connections are made between the instruments of a
test setup and/or between the instruments and the power
line ground. Two ground connections complete an
electrical circuit (ground loop) for the voltages which
are generated across all instrument chassis by stray
fields, particularly the fields of transformers. These
ground currents can be minimized by disconnecting
the ground lead in the power cord from either the
voltmeter or the signal source being measured, at the
power outlet as shown in figure 3-3, and by making
sure that in the test setup no other ground loop is
formed that can cause a ground current to flow in the
voltmeter test leads. Although the resultant voltage
developed across a test lead is in the order of microvolt, it is enough to cause noticeable errors in
measurements of a few millivolts. The presence of
ground currents can sometimes be determined by
simply changing the grounds for the instruments in the
3-2
setup and watching for a change in meter reading. If
changing the ground system causes a change in meter
reading, ground currents are present.
3-14. MEASUREMENT OF VOLTAGE.
3-15. The meter has two VOLTS scales, 0 to 1 and
0 to 3. When the RANGE switch is set to .001, .01,
.1, 1, 10, or 100 VOLTS, read the 0 to 1 scale. When
the RANGE switch is set to .003, .03, .3, 3, 30, or 300
VOLTS, read the 0 to 3 scale.
The lower (black) signal INPUT and OUTPUT terminals and the instrument case are
connected to the power system ground when
the instrument is used with a standard threeterminal (grounding) receptacle. Connect
only ground-potential circuits to the black
INPUT and OUTPUT terminals.
3-16. Operate the instrument as follows:
a. Connect the voltmeter to the a-c power source.
b. Turn the Power switch ON and allow a warmup
period of approximately five minutes.
c. Disconnect any external equipment from the OUT-
PUT terminals.
d. Set the RANGE switch to the VOLTS range which
will read the voltage to be measured at mid-scale or
above. If in doubt, select a higher VOLTS range.
e. Connect the voltage to be measured to the INPUT
terminals.
00102-2
AVOID A SHORT CIRCUIT ACROSS THE POWER LINE! To measure power line voltage, first
connect only the upper (red) INPUT terminal to
each side of the power line, in turn, leaving it
connected to the side that causes meter indication. Then connect the lower (black) INPUT
terminal (grounded internally) to the other side
of the line. If this procedure is not followed,
the power line may be short-circuited through
the grounded INPUT terminal of the voltmeter.
TM 11-6625-1514-15
Section III
Paragraphs 3-17 to 3-21
f. Note the meter indication on the DECIBELS scale
(-12 to +2 db). The signal level is the algebraic sum of
the meter indication and the db value indicated by the
RANGE selector. Study the following examples:
Example 1
If the indication on the DECIBELS scale is +2 and the
RANGE switch is in the +20 DB position, the level is
+22 dbm.
Example 2
If the indication on the DECIBELS scale is +1.5 and the
RANGE switch is in the -40 DB position, the level is
-38.5 dbm.
f. Read the meter indication on the appropriate VOLTS
scale, in accordance with the full-scale value indicated
on the RANGE switch. Evaluate the reading in terms
of the full-scale value indicated on the RANGE switch.
Study the following examples:
Example 1
When the RANGE switch is in the .1 VOLTS range, read
the 0 to 1 VOLTS scaIe. If the meter indicates .64 on
that scale, the voltage being measured is:
Example 2
When the WGE switch is in the 30 VOLTS range, read
the 0 to 3 VOLTS scale. If the meter indicates 1.6 on
that scale, the voltage being measured is:
3-17. MEASUREMENT OF DECIBELS.
3-18. The DECIBELS meter scale is provided for
measuring dbm directly across 600 ohms and for
measuring db ratio for comparison purposes when
each measurement is made across the same circuit
impedance. To measure signal level directly in dbm
(0 dbm equals 1 milliwatt into 600 ohms) proceed as
follows:
a. Connect the voltmeter to the a-c power source.
b. Turn the Power switch ON and allow a warmup
period of approximately five minutes.
c. Disconnect any external equipment from the OUT-
PUT terminals.
d. Set the RANGE switch to the DB range which will
give an upscale reading of the signal to be measured.
If in doubt, select a higher-level scale.
e. Connect the voltage to be measured to the INPUT
terminals.
00102-2
3-19. To measure db across impedances other than
600 ohms, follow the above procedure and evaluate the
results as follows:
NOTE
Since the measurement is made across other
than 600 ohms, the level obtained in step f is in
db, but not in dbm.
a. To obtain the difference in db between measurements made across equal impedances, algebraically
subtract the levels being compared.
b. To obtain the reading of a single measurement
in dbm, note the impedance across which the measurement is made and refer to the Impedance Correction
Graph, described in paragraph 3-20.
c. To obtain the difference in dbm between measure-
ments made across different impedances, convert each
measurement to dbm using the Impedance Correction
Graph described in paragraph 3-20. Then algebraically
subtract the dbm levels being compared.
3-20. IMPEDANCE CORRECTION GRAPH.
3-21. As the voltmeter DECIBELS scale is calibrated
to indicate dbm for measurements made across 600-ohm
circuits, a correction factor must be used when measurements are made across circuit impedances other
than 600. ohms, if absolute dbm levels are desired. The
correction factor is not necessary in measuring relative
db levels (not dbm) across the same impedance, but it is
required for comparison of db levels measured across
different impedances.
in figure 3-4 gives the correction factor for conversion
of the meter reading to dbm when the impedance of
the circuit under test is known. To use the graph, read
the conversion factor corresponding to the test circuit
impedance and add it to the meter reading determined
by the method of paragraph 3-17. Observe the algebraic
sign of the correction factor in making the algebraic
addition. Use the following examples:
Example 1
If the measurement is made across 90 ohms, the
indication on the DECIBELS scale is +2, and the RANGE
switch is at the +30 DB position, the level in dbm is
obtained as follows:
The Impedance Correction Graph
3-3
TM 11-6625-1514-15
Section III
Paragraphs 3-22 to 3-25
+ 2 (meter indication)
+30
(RANGE switch position)
+32 (sum)
+8
(correction factor from the Impedance
+40 dbm
Example 2
For the same conditions as given above, except that
the measurement is made across an impedance of 60,000
ohms, the level in dbm is obtained as follows:
+ 2 (meter indication)
+30
(RANGE switch position)
+32 (sum)
-20
(Correction factor from the Impedance
+12 dbm
3-22. USE OF VOLTMETER AMPLlFIER.
3-23. The amplifier in the voltmeter may be used for
amplifying weak signals. With full-scale meter deflection, the open-circuit output of the amplifier is approxi-
mately 0.15 volt rms regardless of the RANGE switch
position. The impedance looking into the OUTPUT
terminals is approximately 50 ohms. The frequency
Correction Graph)
Correction Graph)
response and calibration of the voltmeter may be
affected by the impedance of a load applied to the
OUTPUT terminals. To check the effect of the applied
load: observe the meter reading obtained with no load
connected to the OUTPUT terminals and then note any
shift of reading when the external circuit is connected
to the OUTPUT terminals. If the shift is negligible,
the measurement is not being affected appreciably by
the load. Whenever the input signal is changed, i.e., a
different frequency or band of frequencies is applied,
repeat the quick check described above.
3-24. Maximum gain from the amplifier is obtainable
only on the lowest (.001 volts) range, since output level
is the same for all bands. This is due to the 10-db
amplification loss per step inserted by the RANGE
switch as it is turned clockwise. Amplification may
also be obtained on the .003, .01, .03, and 1 volt ranges.
3-25. When the voltmeter is used as an amplifier,
select a range which gives a meter deflection near
full scale. Off-scale signals more than twice the value
of the position of the RANGE switch will cause severe
distortion.
3-4
00102-2
TM 11-6625-1514-15
Section III
Figure 3-4. Impedance Correction Graph
3-5
4-0
Section IV
TM 11-6625-1514-15
00102-2
Figure 4-1.
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