GR 1650-A User manual

GENERAL RADIO COMPAN'Y
OPERATING INSTRUCTIQ S
TYPE 1650-A
IMPEDANCE BRIDGE
3005-C
.....

..
Q'PERATING INSTRUCTIONS
TYPE 1650-A
IMPEDANCE BRIDGE
Form 300S-C
April, 1960
G E N 'E R A L R A D I 0 COM PAN Y
WEST CONCORD, MASSACHUSETTS, USA

TABLE OF CONTENTS
Section 1. INTRODUCTION.
1.1
Description.
1.2 Symbols, Abbreviations, and Definitions
1.3 Series and Parallel Components •
Section 2. PRINCIPLES OF OPERATION
2.1
General •
2.2 Bridge
Switching. •
2.3 Compensation Techniques
2.4 Bridge Sources and Detectors.
2.5 Orthonull .
Section 3. INSTALLATION.
3.1 Opening and Tilting the Cabinet
3.2 Power Supply . •
Section 4. DC MEASUREMENTS •
4.1
Resistance Measurements Using 6-Volt Supply.
4.2 Resistance Measurements Using External DC Supplies •
Section 5. OPERATING PROCEDURE 1KC MEASUREMENTS
5.1
Capacitance Measurement. •
5.2
Inductance Measurements •
5.3
AC Resistance Measurement •
5.4 Notes on AC Measurements •
5.5 Operating Procedure with Orthonull.
Section 6. OPERATING PROCEDURE WITH EXTERNAL AC GENERATOR
6.1
Procedure .
6.2 Connection of External Generator •
6.3
Maximum AC Voltage •
6.4 Allowable D
and Q Ranges vs Frequency
6.5 Corrections for Residual and Lead Impedances.
6.6 Extending the D and Q Ranges at Low Frequencies. •
Section 7. SPECIAL MEASUREMENTS •
7.1
Application of DC Bias to Capacitors
7.2 Application of Direct Current in Inductors
7.3 DC Bias .for AC Resistance Measurements
7.4 Measurement of AC Resistance with Reactance.
7.5 Resonant Frequency of Tuned Circuits.
7.6 Measurements on Shielded Three-Terminal Components.
7.7 Remote Measurements. • •
7.8
Measurement of Grounded Components.
7.9 Use of the Type 1650-P1 Test Jig.
7.10
Limit Testing.
Section 8. SERVICE AND MAINTENANCE •
8.1
General •
8.2 Battery Replacement. • •
8.3 Adjustments
8.4 Trouble-Shooting Suggestions.
PARTS LIST.
SCHEMATIC DIAGRAM •
1
1
2
2
3
4
4
5
5
7
7\
7
7
7
8
9
9
10
11
11
12
13
13
13
14
14
14
15
16
16
17
18
18
19
19
19
19
20
20
21
21
21
21
21
24
25

SPECIFICA liONS
Ranges:-
Resi stance: 1mD - 10 MD, 8 ranges ac or dc.
Capacitance: 1 f..Lf..Lf -1000 f..Lf, 7 ranges se-
ries on parallel.
Inductance: 1 f..Lh -1000 h, 7 ranges series
on parallel.
D(of series C): 0.001 - 1 at 1 kc.
D(of parallel C): 0.1 -50 at 1 kc.
(C
s=Cp
within 1% if D< 0.1.)
Q(of series L): 0.02 -10 at 1 kc.
Q{of parallel L}: 1 - 1000 at 1 kc.
(L
s=Lp
within 1% if Q> 10.)
Accuracy:
Resistance: ±1% ±1 mD (residual R~l mD).
(external dc supply required for 1% accuracy a-
bove 100 k.0.)
Capacitance: ±1% ±1 f..Lf..Lf (residual C ~ 0.5
f..Lf..L
f
).
Inductance: ±1% ±1 f..Lh (residual L< 0.2 f..Lh).
it ±5%; ±0.001 at 1 kc or lower.
lIQ: ±5%; ±0.001 at 1 kc or lower.
Frequency Range (1 kc supplied internally): for
1% accuracy for Land C, 20 cps to 20 kc; for R,
U.S.
Patent No. 2,872,639.
20 cps to 5 kc. (D and Q ranges are functions
of frequency.)
Internal Oscillatar Frequency (external ac and
dc sources can also be used): 1 kc ±2%.
Internal Detector: Response, flat or selective at
1 kc; sensitivity control provided.
Internal DC Supply: 6 v, 60 rna max.
Power Supply: 4 D cells, supplied. Current drain
for ac measurements, 10 rna.
DC
Polari zation: 600 vmay be applied (from ex-
ternal source) to series capacitance measure-
ments.
Accessories Supplied: One Type 274-MB Double
Plug.
Other Accessories Available: Type 1650-P1 Test
Jig.
Other Accessories Required: None. Earphones
may be used for high precision at extremes of
bridge ranges.
Mounting: Aluminum cabinet, with captive cover.
Dimensions: Height 12-3/4 in., width 12-1/2 in.,
depth 7-3/4 in., including handle.
Weight: 17 lb.
General Radio Experimenter reference: Volume 33, No.3, March 1959;
"Orthonull", Volume 33, No.4, April 1959.
SPECIAL REQUEST TO THE USER OF TillS INSTRUMENT
We believe that the most effective way to make our products more
useful is to learn from the experience and opinions of those who use them.
For this reason we have included a questionnaire at the rear of this
manual. Your answers to the questions contained, based on your experi-
ence in using this instrument, will be of great value to General Radio
engineers and other personnel concerned with new products. Such com-
ments will have a strong influence on the direction of future development
work. The resulting better products will benefit our customers as well
as ourselves.
The questionnaire sheet is its own postage-paid envelope. Simply
cut it out, fold as directed, staple, and mail.
Any information you supply will not go outside our company without
your specific advance authorization. May we have your opinions?

Figure 1.
Type 1650-A Impedance Bridge.

TYPE 1650-A
IMPEDANCE BRID'GE
Section 1
INTRODUCTION
1.1 DESCRIP'IlON.
1.1.1 GENERAL. The Type 1650-A Impedance
Bridge (Figure 1) is a self-contained impedance-
measuring system, which includes five bridges for
the measurement of capacitance, resistance, and in-
ductance' as well as the generators and detectors
necessary for dc and 1-kc ac measurements. Fea-
tures of this bridge include one-percent C, R, and
L accuracy over all ranges, high 0 and Qaccuracy,
a mechanism to facilitate low Q measurement, vis-
ual ac and dc null indications, complete portability,
and a convenient tilting mechanism and carrying
case.
1.1.2 CONTROLS. The Table of Contro!sgiven be-
low lists the controls located on the front panel of
the Type 165O-A Impedance Bridge.
1.1.3 CONNECTORS. The Table of Connectors
given below lists the connectors located on the front
panel of the Type 1650-A Impedance Bridge.
TABLE OF CONTROLS
Name No.
Type
Function
CRL MULTIPLIER Sl
8 -po~ition selector switch Selects impedance range.
CRL SELECTOR S2
5-position selector switch Selects bridge circuit. •
FUNCTION Switch S3
5-position selector switch Turns bridge on to type of
operation required.
CRL Dial Rl Continuous rotary control Adjusts for bridge balance.
DQ Dial
R2 Continuous rotary control Adjusts for bridge balance.
ORTHONULL Lever Mechanical lever Engages Orthonull mechanism.
DETECTOR Switch S4
Toggle switch Controls detector response.
OSC LEVEL R18
Thumbset rotary control
Controls ac oscillator level.
SENSITIVITY R15 Continuous
rotary control Controls ac and dc detector
R16
sensitivity.
TABLE OF CONNECTORS
Name
No.
Type
Function
UNKNOWN
]7, J8 Jack -top binding -post pair
Com.ects unknown impedance
EXT GEN
Jl, J2
Jack -top binding -post pair
Connects ac or dc external
source
BIAS
J3, J4 Jack
-top binding-post pair
Connects dc bias
DET OUTPUT J5, J6
Jack-top binding-post pair
Connects external amplifier
or phones

Q2 LpLp
1+Q2 1+D2
1+Q2 Ls
(l +D2) Ls
Q2
lcs
Ls
Rp
l'
cp
Rp
Lp
R
s
Resistance and Inductance
Q __ 1_ = wL
s
=~
D Rs wL
p
Figure 2. Equivalent Circuits for Complex Impedance.
are:
bination is used. The equivalent circuits are shown
in Figure 2.
The relationships between the circuit elements
1
(l +Q2) Rs
Rs1+Q2 Rp;Rp
wL
s
Rs
=--.
Rp= QWL
p
Q,
Resistance and Capacitance
RD1
02R +--
I jCcC
pp .
CcC
JP
ZRs
+~
-
JW s11+02
R +--
P 'CcC
J P
11
0
=-
wRsC
s=
QWRpCp
Cs
(l +D2) Cp;CpCs
+02
021+D2
Rs1+D2 Rp; RpD2 Rs
D1
Rs
=--'
Rp
wC
s,
CcCpD
2
1
=Q
1
1
=~
=c1p
parallel inductance
resistance ~), the real part of an impedance
series resistance
series capacitance
parallel capacitance
inductance (~)
series inductance
parallel resistance
reactance, the imaginary part of an impedance
impedance
quality factor =+
wL
s
for inductors
~
d· . . fR
IsslpatiOn actor = X-
for capacitors wcsR
s=
wCpI),
R R
power factor =-c -;:=:;:==::;-
Izl \lR2 +X2
GENERAL RADIO COMPANY
Lp
R
Rs
Rp
X
z
Q
1.2 SYMBOLS, ABBREVIATIONS, AND DEFINITIONS.
The following symbols, abbreviations, and defini-
tions are used on the panel of the Type 1650-A and
this instruction manual:
C capacitance' (-n---)
f frequency
w angular frequency 2m
Q ohm, a unit of resistance, reactance, or
impedance
kQ kilohm 1kQ =1000 ohms
M multiplying factor applied to 0 and Q at
frequencies other than 1 kc
MQ megohm 1MQ =1 x 10
6
ohms
mQ milliohm 1 mQ =0.001 ohm
flf microfarad, a unit of capacitance
mfli millimicrofarad 1mfli =0.001 fli
flfli
micromicrofarad 1flfli =1 x 10-
6fli
h henry, a unit of inductance
mh millihenry 1 mh = o.(Xn h
flh microhenry 1 flh =1 x 10-
6h
1.3 SERIES AND PARALLEL COMPONENTS. An
impedance that is neither a pure reactance or a
pure resistance may be represented at any specific
frequency by either a series or a parallel combina-
tion of resistance and reactance. The values of re-
sistance and reactance used in the equivalent cir-
cuit depend on whether a series or a parallel com-
Cs
Cp -
L
Ls
o
PF

TYPE 16S0-A IMPEDANCE BRIDGE
Section 2
PRINCIPLES OF OPERATION
2.1 GENERAL. Figure 3 shows the five bridge cir-
cuits used in the Type 1650-A Impedance Bridge, as
well as the balance equations. Hays and Maxwell
inductance bridges and series and parallel capaci-
tance comparison bridges are used to provide wide
coverage over the D and Q ranges, as shown in Fig-
ure 4. Full use of these wide ranges at low Q and
high D values is achieved by means of an Orthonull
balancing mechanism (refer to paragraph 2.5). Both
ac and dc measurements may be made with the
bridge, which has no internal phase balance.
The variable bridge components are General
Radio precision wire-wound rheostats. The CRL
rheostat uses a mechanical justifying mechanism
for high accuracy, and the DQ rheostat has a 54-db
logarithmic range. The standard capacitor is a
General Radio Type 505 s~lvered-mica capacitor,
Cs
(LOW
0)
o TO I
SERIES CAPACITANCE
C=RNC
XRAr
Ox =fIIR
xCx=
fIIRrC
r
Cp
(
HIGH 0)
01 TO 50
PARALLEL CAPACITANCE
Cx
RN
Cx=RACT
I I
Ox =fIIRx C~ =fIIRrCr
R
(A.C.)
O.C.
REStSTANCE
LS
(
LOW 0 )
.02 TO I
SERIES INOUCTANCE
Lx
Lp
(
HIGH 0)
0./- 00
PARALLEL INOUCTANCE
Lx=R
N1Cr
0= i =_,-
fIILx fIIRrC
r
Figure 3. Bridge Circuits Used in Impedance Bridge.
3

GEN~AL RADIO COMPANY
EXT GEN
~
INT AC
EXT DC·
BIAS
OFF
IN OFF POSITION
BATTERY DISCONNECTED
EXT GEN DISCONNECTED
METER SHUNTED
OSC
LEVEL
LJ
INT DC
EXT AC
BIAS
E1
GEN
~ 150,Q
D=I
Q=I
Cp
LS
(MAXWELL)
Lp
(HAY)
Q=IO
Figure 4. DQ Coverage Chart.
and the resistors are General Radio wire-wound
cards except for the I-megohm ratio arm, which
uses a 1/4% precision film resistor.
2.2 BRIDGE SWITCHING. The CRL MULTIPLIER
switch (SI) selects the bridge range by switching in
various ratio -arm resistors. Clockwise rotation of
this two -rotor .switch increases the multiplier value
for the R, L, and C bridges. Both ends of the range
resistor are switched out so that the unused resis-
tors may be grounded to reduce capacitance across
this arm. Double, solid silver contacts insure low
switch resistance and long switch life.
Figure 5. Source and Detector Diagrams.
several compensating schemes are used. The com-
ponents used for this purpose are listed below, with
brief description of their functions.
SENS
SENS
C2 and LI: These components are used to make
the standard resistance arm (Rb, Figure 3) appear
resistive over awide frequency range. This arm is
shunted with considerable stray capacitance, which,
without
compensation, would cause a poor ac null
2.3 COMPENSATION TECHNIQUES. To achieve
the required D-Q accuracy over such wide ranges,
The CRL SELECTOR switch (S2) switches the
bridge circuits. The actions of this switch are such
that it (1) selects the correct rotors of SI and grounds
one of the unused rotors, (2) selects the correct
standat'd arm, and (3) reverses the bottom two arms
of the bridge to form the Land R or C bridges.
The function switch (see Figure 5) sets up the
correct internal source and detector circuits for
the desired operation. When this switch is in either
of the two EXT positions, the EXT GEN terminals,
used for externally applied ac or dc, are connected
in as the bridge source.

TYPE 16S0-A IMPEDANCE BRIDGE
and an error. The resistances of LI and R4 add up
to the reqUired 10 kilohms.
C3: This capacitor corrects the phase angle of
the first section of the DQ potentiometer (Rt) to
compensate for the inductance of the winding. With-
out compensation, this inductance would cause an
error in Cs and Lp at high frequencies, and in Cp
and Ls when the Unknown has a very low Q or high
D.
C4: This capacitor corrects for the phase shift
caused by stray capacitance across the CRL rheo-
stat (RN). This capacitor forms a three-terminal
T network with the two parts of the rheostat to pro-
duce an effective inductance to balance out the stray
capacitance.
C5: This capacitor compensates for the stray
capacitance across the I-megohm ratio arm (R12
and R13). The three-terminal T network formed by
these components produces an effective inductance
to balance out the stray capacitance.
C6: This capacitor compensates for the induct-
ance of the I-ohm ratio arm (R5).
2.4 BRIDGE SOURCES AND DETECTORS. The dc
bridge supply is taken from the four internal D
cells, which supply about 6 volts limited by a 100-
ohm resistor to a maximum of 60 mao The dc in-
dicator on the panel has a sensitivity of' 2\la/mm
near zero, a resistance of 75 ohms, and a shaped
characteristic (Marion Type C null indicator)..
The ac source is a I-kc transistor LC oscil-
lator, which uses the primary of the bridge trans-
former as the inductor in the tuned circuit. The
output voltage is about 1 volt at the secondary of
the 4-to-I step-down transformer. This secondary
is wound with resistance wire to increase the re-
sistance to about ISO ohms, preventing external loads
from affecting the bridge frequency. The OSC LEVEL
contfol adjusts output voltage by loading the trans-
former secondary.
The ac detector is a three-transistor, vari-
able-gain amplifier, which uses a twin-T RC filter
to obtain selectivity with the DETECTOR switch in
the 1 kc position. This amplifier drives the panel
meter to provide a visual ac null indication, and the
output from the amplifier is supplied to the panel
DET OUTPUT terminals.
The ac oscillator and detector combined draw
less than 10 rna from the internal 6-volt battery.
2.5 ORTHONULL. Orthonull is a mechanical device
that improves the bridge balance convergence when
low Q inductors or high D capacitors are measured.
5
Ordinarily, balances with such components are tedi-
0us and often impossible due to the "sliding null"
resulting from the interdependence of the two ad-
justments. Rapid balances are possible with Ortho-
null, which does not affect electrical balance but
which does help avoid false nulls, improving bridge
accuracy for low Q measurements.
The bridge output voltage for the Ls(Maxwell)
bridge can be expres sed:
(1)
Denominator
We will assume that the denominator is more or
less constant in the region of the null. The numer-
ator is the difference between the unknown imped-
ance Rx+jWLx and what can be called the "bridge
impedance". The bridge output is proportional to
this difference, which is the distance between them
on the complex plane. To balance the bridge, the
"bridge impedance" is varied by adjustment of Rn
(the CRL dial) and Rt (the DQ dial) until it equals
the unknown impedance. An adjustment of Rr varies
only the real part of the bridge impedance, whereas
an adjustment of Rn varies both parts, and is there-
fore a multiplier of the bridge impedance. Thus,
adjustment of Rt moves the bridge impedance hori-
zontally on the complex plane, while adjustment of
Rn
moves it radially (see Figure 6). Each control
is adjusted for a minimum voltage.
RNVARIED
-===-------- __ R
Figure 6. Loci of Rn and Rt Adjustments on Z Plane.
When X»R (i.e. when Q is high) these two ad-
justments are almost orthogonal, and rapid con-
vergence is possible. When Q is low, however, the
adjustment becomes more parallel and convergence
is slow, causing a "sliding null", as shown in Fig-
ure 7, where Q= 1/2. With smaller Q' s, conver-
gence is even slower.
The Orthonull device makes the two adjust-
ments orthogonal by nonreciprocally ganging Rn
and Rt. From equation (1) it is apparent that if
Rn/Rt remained constant as Rn was varied, only
the imaginary part of the bridge impedance would