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

GENERAL RADIO COMPANY
•
D-tOO
00.01
0"0
Q-O.l
WITH ORTHONULL
01
001
Figure 9. Accuracy vs D or Q.
-FALSE NULL·
CAUSED BY
Rg'g~U~ON \
"'-..,...\
°2);----;-----;------!-------:':----!:---'
z
I
>-
~ 25
>-
w
'"
o
>-
",20
>-
z
w
::<
>-
~ 15
o
..
u.
o10
Q:
w
'"
::<
:::>
z
...J
..
b
>-
/
/
V
%
.
10
Q
Figure 8. Number of Balances vs Q.
tually impossible to achieve 1% balances. The ac-
curacy that can be expected with careful adjustment
is plotted against Q in Figure 9. In the face of the
fact that for low Q values
dl zl =2 dL
/ZT Q --r=--
the eventual lack of accuracy is justified. For ex-
ample, if Q= 0.03, a 5% change in inductance is a
change of only 45 parts per million in impedance.
As far as the user is concerned, the balanc-
ing procedure with Orthonull is essentially the same
as without it. However, several suggestions for its
use are given in paragraph 5.5.
6
x
Figure 7. Loci of "Sliding Null" Balance.
The Orthonull mechanism is shown in Figure
21. The clutch material is between the pulley at-
tached to the DQ shaft and the free pulley driven by
the wire belt. The clutch is disengaged by the lever
on the panel so that normal operation is ·possible
for high Q(low D) components.
The advantage of Orthonull is illustrated in
Figure 8, which is a plot of the numbers of adjust-
ments necessary for a balance. Not only does the
Orthonull reduce the number of balances, but it per-
mits 1% measurements that would otherwise be im-
possible below a Q of 1/3, due to the finite resolu-
tion of the DQ rheostat. This finite resolution causes
the meter indication to vary in jumps when Ortho-
null is used at Q's below 1/3. However, by choos-
ing the best null, 1% accuracy is possible with Q's
of less than 0.2. As Qis further reduced, it is even-
The ratio RuIRt must be constant for varia-
tion in Rn for any initial settings of Rn and Rt,
since Rr may be moved independently of Ru. This
requires rheostats with exponential characteristics
(and logarithmic dials). The DQ rheostat is a 54-
db exponential potentiometer with the correct initial
resistance (R3) added when the Ls and Cp bridges
are used. The CRL rheostat is exponential in the
dial range from 1 to 11, and linear pelow 1. Thus,
for correct Orthonull action, the CRL dial must be
in the range above 1.
change. But when Rt is adjusted, Ru must not move
to vary only the real part. The solution is a simple
friction clutch to permit nonreciprocal action. Both
the inherent difference in friction of the two rheo-
stats and the pulley ratio favor torque transmission
in the desired direction.

TYPE 1650-A IMPEDANCE BRIDGE
Section 3
INST ALLA TIO·N
3.1 OPENING AND TILTING THE CABINET. The
directions for opening the Type 1650-A Impedance
Bridge are given on the handle support of the instru-
ment. Once open, the instrument may be tilted to
any convenient angle as shown in Figure 1. The an-
g1e should be chosen to give the most comfortable
access to the knobs and the best view of the meter
and dials.
The instrument may be locked fully open by
the same slide pins that are used to lock the instru-
ment closed. Thus, the instrument CaR be carried
in the open position with the cover firmly in place.
When the instrument is Opel1, the cover forms
a convenient storage place for the instruction man-
ual and for any other test data that should be kept
with the instrument.
3.2 POWER SUPPLY. The instrument is powered
by four D cells, which slide into the instrument
through the cap at the top. These batteries, sup-
plied with the instrument, should be installed with
the positive terminals (center buttons) facing down.
The instrument is ready to operate as soon as
it is in position and turned on.
Section 4
OPERATING PROCEDURE
4.1 RESISTANCE MEASUREMENTS USING6-VOLT
SUPPLY.
4.1.1 PROCEDURE.
a. Check the NULL meter mechanical zero
with the function switch in the OFF position, and.
if necessary, center the pointer with the mechani-
cal zero adjustment on the meter.
b. Turn the SENSITIVITY control almost fully
counterclockwise.
c. Set the CRL SELECTOR to R.
d. Connect the resistor to be measured to the
UNKNOWN terminals.
e. Turn the function switch to INT 6V.
NOTE
As
the function switchis rotated from
OFF to INT 6 V, it passes through an
undetented position where the circuit
is operative but the meter is shunted
to reduce sensitivity. A preliminary
balance may be made with the switch
in this position instead of with the
SENSITIVITY control turned down.
DC MEASUREMENTS
f. Set the CRL MULTIPLIER switch and the
CRL dial for a zero (center) meter reading, while
adjusting the SENSITIVITY control to increase sen-
sitivity. A meter deflection to the right indicates
that the unknown is larger than the multiplier and
dial setting. For greatest accuracy the final balance
should be between 1 and 11 on the CRL dial (pos-
sible above 100 milliohms).
g. The value of the unknown resistance is' the
product of the CRL dial indication and the factor in-
dicated on the CRL MULTIPLIER switch.
4.1.2 SENSITIVITY. With the internal 6-volt sup-
ply, one-percent balances may be easily made up to
10 kilohms and with care up to 100 kilohms. Above
100
kilohms a higher external voltage should be
used (refer to paragraph 4.2).
A
100-ohm resistor in series with the internal
6-volt supply limits the current in the unknown to
60 rna. The unknown is in series with the CRL
rlreostat, so that the unknown current is greatest
when the C-ItL dial is at zero.
The maximum power that can be applied to
the bridge by the internal supply is 0.09 watt; thus
there is no danger of injuring components rated at
. 1/10 watt or more.
L
7
)

GENERAL RADIO COMPANY
At range extremes it is often desirable to
make I-kc ac measurements to increase sensitivity.
Formost resistors, the difference between the meas-
ured I-ke and de values is negligible.
4.1.3 ACCURACY OF DC RESISTANCE MEAS-
UREMENTS.
The accuracy of dc resistance tneas-
urements is ±I % if the CRL dial reading is between
1and 11 as long as there is enough sensitivity. Be-
low 100 milliohms, balance must be made with the
CRL dial set below 1, and the bridge accuracy is
±I milliohm if the 1-milliohm zero resistance of
the bridge is subtracted from the reading.
For low - resistance measurements, short,
heavy leads should be used as connections to the
unknown. The zero resistance of the leads should
be measured with the free ends connected together,
and subtracted from the bridge reading with the
unknown in pJace. The user should be particularly
careful when using banana - pin connections. For
best connection to the bridge, screw the binding post
hard enough to notch the wire inserted in the hole.
4.2 RESISTANCE MEASUREMENTSUSING EXTER-
NAL DC SUPPLIES.
4.2.1 PROCEDURE.
The procedure for dc resist-
ance measurements using an external supply is the
same as that described in paragraph 4.1.1 except
that:
a. The external supply should be connected a-
cross the EXT GEN terminals.
b. Set the function switch to the DC EXT posi-
tion.
WARNING
When
using external dc supplies be
careful that there is no danger to the
TABLE I
MAXIMUM DC BRIDGE VOLTAGE
AND CURRENT
operator. It is advisable to limit
high -voltage supplies to a current of
5rna
or less by placing resistance in
series. Care should also be taken to
avoid damage to the bridge and to the
unknown component.
4.2.2 VOLTAGE AND CURRENT LIMITS. Bridge
voltages must be limited to protect the bridge and
the unknown component from damage. It is also ad·
visable to limit the current to 5rna or less to pro-
tect the operator from injury. The maximum volt-
age limit and standard EIA test voltages are de-
scribed below.
Unless the utmost in sensitivity or a standard
test voltage is desired, a supply of about 100 volts
(e.g. a 90-volt battery), with about 25 ldlohms in
series, is recommended. The available power from
such a supply is 0.1 watt, which is low enough dis-
sipation for almost all resistors, and the maximum
current is 4 rna. Such a supply permits measure-
ments up to 1 megohm with 1% accuracy. For re-
sistances over 1 megohm a higher voltage is de-
sirable for good sensitivity, but it should be noted
that the maximum EIA test voltage is 100volts, and
that various types of resistors have different volt-
age ratings.
The maximum voltage and current that may
be applied to the bridge for each range are given in
Table 1. Careful observation of both of these lim-
its will prevent damage to the bridge.
Because the full voltage may be applied to the
unknown, it is advisable to limit the available power
to a value less than the power rating of the unknown
component.
Various EIA standards for testing different
types of resistors are summarized in Tables 2 and
TABLE 2
EIA STANDARD
TEST VOLTAGES
(RS 172 -FIXED COMPOSmON RESISTORS)
•
•••
Range Range EMax
I· Max
Full Scale
Multiplier
1 n
lOOrnn 71 v100 rna
lOn
1 n 71 v100 rna
100 n10 n
71 v 71 rna
1
kn
100 n 71 v 22 rna
10
kn
1 kn
71 v14.1 rna
100
kn
10 kn 223 v14.1 rna
1
Mn
100 kn 500 v14.1 rna
10
Mn
1 Mn 500 v14.1 rna
•It
is preferable to limit current to avoid
shock
hazard or to reduce voltage to 10 v.
Resistance Range Bridge Mult Range EIA
Test
Bridge·
Voltage Range
Voltage
2.7 -99 n1 n
0.5 - 1 v
••
10 n 0.5 - 1 v 50 -
71 v···
100 -999 n
lOon
2.5 - 3 v 27.5 - 33 v
1000 -9999 n1
kn
8
-lOv
16
-20v
10 -99
kn 10 kn 24 -30 v26.4 -
33 v
100
kn up 100
kn 80 -100 v80 -100 v
1
Mn
80 -100 v80 -100 v
at EXT GEN terminals
•• cannot get reqUired bridge voltage
limited to 71 vby bridge
8

TYPE 1650-A IMPEDANCE BRIDGE
3. A suggested setup for tests at these voltages is
shown in Figure 10. The voltmeter here indicates
the bridge voltage, and should be set as listed in
Tables 2 and 3. An alternate scheme is to put the
voltmeter directly across the unknown resistor, as-
suming that the input resistance of the voltmeter is
large enough to cause no error.
CURRENT-LIMITING
RESISTOR '
BRIDGE
V
VOLTAGE
Figure 10.
Circuit for Tests
at EIA Voltages.
Section
OPERATING PROCEDURE
TABLE 3
EIA STANDARD
TEST VOLTAGES
(RS 196
FIXED FILM RESISTORS
REC 117 LOW-POWER WIRE-WOUND RESISTORS)
Resistance
Bridge Mult EIA Max Max Bridg
Range Range
Test Voltage
Voltage*
less than 10 0 1 0 0.3 v
**
10 -99 010 0 1 v
**
lQO -999 0
1000 3v
33 v
1000 -9999 0 1 kO
lOv
20v
10 -99 kO
10 kO 30 v33 v
100 kO up 100 kO 100 v101 v
1
MO
100 v100 v
REC 117
applie sonly up to 9999 D.
* At EXT GEN terminals.
** Maximum allowable bridge voltage will not give
maximum test voltage.
5
l-KC MEASUREMENTS
5.1 CAPACITANCE MEASUREMENT.
5.1.1 PROCEDURE.
a. Set OSC LEVEL control fullyon (clockwise).
b. Set DETECTOR switch to 1 kc.
c. Set CRL Selector to
Cs- if series capacitance is desired and
D is less than 1.
Cp-
if parallel capacitance is desired and
D is between 0.1 and SO.
(Note: Cs=Cp within 1% if D( 0.1.)
d. Set the function switch to INT 1KC.
e. Connect the unknown capacitor to the UN-
KNOWN terminals.
f. If the proper range setting of the CRL MUL-
TIpLIER is not known, set the CRL dial at about
midscale, adjust the SENSITIVITY control adjusted
to give an upscale meter reading, and set the CRL
MUL TIPLIER switch for a minimum deflection.
9
g. Adjust the CRLand DQ controls for the best
minimum meter reading. The SENSITIVITY control
may have to be adjusted to give greater sensitivity
as balance is approached.
h. The capacitance of the unknown equals the
product of the CRL dial reading and the CRL MUL-
TIpLIER switch setting. The Dof the known is that
indicated on the appropriate scale on the DQ dial.
If the Dof the unknown is near or greater than
1, the Orthonullbalancing mechanism is useful. Re-
fer to paragraph 5.5.
Refer to paragraphs 7.4 and 7.6 for measure-
ments on shielded and grounded capacitors.
5.1.2 ACCURACY. The accuracy of the C reading
is ±1 % if the balance is made between 1 and 11 on
the CRL dial. Below 1on the dial the accuracy is
±1/2 division. Thus the over-all accuracy possible
is ±1% or ±1 Il~, whichever is greater, since 11l~
is 1/2 a dial division on the lowest range. The D
accuracy is±5% or ±0.001, whichever is greater.
The residual ("zero") capacitance of the bridge
terminals is approximately 1/2 Illlf, which is less
.J

GENERAL RADIO COMPANY
than the accuracy of the bridge, and therefore, neg-
ligible. If external leads are used to connect the
unknown, this zero capacitance is increased and
should be subtracted from the bridge reading.
The residual resistance of the bridge is 1 mil-
liohm, which theoretically causes a D error of 0.006
when Cx=1000 flf.
In practice, capacitors of this
size have such large D values that such an error is
negligible. However, if leads are used to connect
large capacitors this D error may become impor-
tant and a correction should be made. The D error
is +wRoCx (where Ro is the lead resistance), and
this amount should be subtracted from the D read-
ing.
The residual inductance causes negligible er-
ror at 1 kc even if Cx=1000 flf. However, c.onnect-
ing leads could have enough inductance to cause a
C
error when large capacitors are measured. The
error is +wLoCx(when Lo is the lead inductance)
and this amount should be subtracted from the C
reading.
>The capacitance aGcuracy is reduced on the
Cp bridge when D becomes larger than..lO. However,
even witli the Orthollull balancing mechanism, bal-
ance to 1% precision is impossible, so that this er-
ror is negligi,ble. Refer to paragraph 2.1, and Fig-
ure 9.
Errors for capacitance measurements at other
frequencies are discussed in paragraphs 6.5 and 6.6.
Table 5 (page 15) lists the corrections for residual
and lead impedances.
5.2 INDUCTANCE MEASUREMENTS.
5.2.1 PROCEDURE.
a. Set the OSC LEVEL fully on (clockwise).
Note: for some iron-cored inductors the inductance
measured will depend upon the excitation level (refer
to paragraph 5.4.4).
b. Set the DETECTOR switch to 1Kc.
c. Set the CRL SELECTOR to
Ls- if series inductance is desired and Q
is between 0.02 and 10.
Lp-
if parallel inductance is desired and
Q is greater than 1.
If Q is not known, use Lp.' If unable to bal-
ance, switch to Ls• ,
(Note: Ls=Lp
within 1% if Q> 10)
d. Set the function switch to INT 1KC.
e. Connect the inductor to be measured to the
UNKNOWN terminals.
10
f. If the proper range setting of the CRL MUL-
TIPLIERis not known, set the CRL dial set at about
midscale, set the SENSITIVITY control to give an
upscale meter reading, and adjust the CRL MUL-
TIPLIER switch for a minimum deflection.
g. Adjust the CRL control and the DQ control
for the best minimum meter reading. The SENSI
TIVITY
control may have to be adjusted to give
greater sensitivity as balance is approached.
h. The inductance of the unknown inductor equals
the product of the CRL dial reading and the CRL
MUL
TIPLIER setting. The Qof the unknown is that
indicated on the appropriate scale on the DQ dial.
If the Qof the unknown is near or less than 1,
the Orthonull balancing mechanism is useful. Re-
fer to paragraph 5.5.
5.2.2 ACCURACY. The accuracy of the L reading
is ±1 % if the balance is made between 1 and 11 on
the CRL dial. Below 1on the dial the accuracy is
±1/2 division. Thus the over-all accuracy is ±1%
or ±1 flh, whichever is greater, since 1 flh is 1/2
dial division on the lowest range. The Q accuracy
is given in terms of D= 1/Q and is ±5% or ±0.D01,
whichever is greater.
The residual (zero) inductance is less than
0.2 flh, whichis less than the accuracy of the bridge
and therefore negligible. If external leads are used
to connect to the unknown, this zero inductance is
increased and should be subtracted from the bridge
reading.
The residual resistance of the bridge is 1 mil-
liohm, which causes a small D (1/Q) error. This
error is less than 0.001 if Lx is more than 160 flh.
If long leads are used to connect to the unknown, this
error may become appreciable and require a cor-
R
rection. The D error is + _0_ (the Q error is
RwLx
Q2
w;:'x ) where Ro is the total lead resistance.
The residual zero capacitance of 0.5 flfli theo-
retically causes an error for inductors above 250
henries. However, this small capacitance is al-
most always negligible compared with the capaci-
tance of the winding of such a large inductor. If the
inductoris shielded, a three-terminal measurement
will reduce the effect of stray capacitance to the
shield (refer to paragraph 7.6). In order to reduce
the effect of the winding capacitance it is necessary
to reduce the measurement frequency. The induc~
ance error due to a shunt capacitance Co is w2Co L:l{ ,
and this amount should be subtracted from the bridge
reading. (Refer to Table 5.)
The inductance accuracy is reduced slightly
if Q is less than 0.1. However, even with Orthonull
______________ ~ J

TYPE 16S0-A IMPEDANCE BRIDGE
balance to 1%, precision is impossible, so that this
error is negligible. Refer to paragraph 2.5 and
Figure 9.
Errors for inductance measurements at other
frequencies are discussed in paragraphs 6.5 and 6.6.
prevent a satisfactory balance, an external capac-
itor may be used to make a reactance balance (re-
fer to paragraph 7.4).
5.4 NOTES ON AC MEASUREMENTS.
Cb
100% = - 0.1 J1.f x100%
Since Ct is large it takes 1000 Wf to produce a 1%
error (when D is small).
DET
The effects of stray capacitances to the panel
(ground) are usually negligible in the capacitance
bridges (see Figure 11). Capacitance from the LOW
terminal to ground (Ca) shunts the detector and
causes no error. Capacitance from the other ter-
minal to ground (C~ shunts the standard capacitor
(Ct) and produces an error of
Figure I!.
Capacitance to Ground
for Capacitance Measurerr;ent.
Figure 12.
Capacitance to Ground
for Inductance MeasureIT'ent.
5.4.1 CAPACITANCE TO GROUND. TheType 1650-A
Bridge generally measures "ungrounded" compo-
nents, since neither UNKNOWN terminal is connected
directly to the panel. The panel should be connected
to a good ground, especially if high -impedance com-
ponents are to be measured. If the panel is not
grounded, stray capacitances from the UNKNOWN
terminals and panel to ground can produce au ef-
fective capacitance across the UNKNOWN terminals.
With the panelgrounded,capacitances from the UN-
KNOWN terminals to ground have a much less se-
rious effect. (For measurements of grounded com-
ponents refer to paragraph 7.6.)
In the inductance bridge (see Figure 12) Ca
is across the detector and has no effect, but Cb shunts
the CRL rheostat. Capacitance across this rheostat
5.3.2 ACCURACY OF AC RESISTANCE MEAS-
UREMENTS. The accuracy of the R reading is ±1%
if the balance is made between 1 and 11 on the CRL
dial. Below 1on the dial the accuracy is ±1/2 a di-
vision. Thus the over - all accuracy is ±1% or ±1
milliohm, whichever is greater, as long as the 1-
milliohm residual resistance is subtracted from the
R reading.
The residual resistance of 1 milliohm is that
of the binding posts themselves. For low-resistance
measurements, short, heavy leads should be used
as connections to the unknown. The zero resistance
of the leads should be measured with the free ends
connected together, and subtracted from the bridge
reading with the unknown in place. The user should
be particularly careful when using banana -pin con-
nections. For best connection to the bridge, screw
the binding post hard enough to notch the wire in-
serted in the hole.
h. The resistance of the unknown equals the
produce of the CRL dial reading and CRL MULTI-
pLIER switch setting.
f. If the proper range setting of the CRL MUL-
TIpLIER is not known, set the CRL dial at about
midscale, set the SENSITIVITY control to give an
upscale meter reading, and set the CRL MUL TI-
PLIER switch for a minimum deflection.
g. Adjust the CRL control for the best rmm-
mum meter reading. The SENSITIVITY control may
require adjustment to give greater sensitivity as
balance is approached.
5.3 AC RESISTANCE MEASUREMENT.
5.3.1 PROCEDURE.
a. Set the OSC LEVEL control fully on (clock-
wise).
e. Connect the unknown resistor.
c. Set the CRL SELECTOR to R.
b. Set the DETECTOR switch to 1 kc.
d. Set the function switch to INT 1KC.
Since there is no internal Q adjustment on the
R bridge, reactance affects only the ability to get a
good sharp null. If the reactance is large enough to
11

GENERAL RADIO COMPANY
causes aD (1/Q) error of -wRnCb' The L error is
usually negligible except when Qx is very low
Thus, for inductance measurements, it is desirable
to connect the terminal with the most capacitance
to ground to the UNKNOWN terminal marked LOW.
5.4.2 VOLTAGE ON THE UNKNOWN. The voltage
applied to the bridge is approximately I volt, with
a source impedance of about 150 ohms. The actual
voltage on the unknown may be calculated with the
aid of the circuit diagram of Figure 3 and Table 4,
or may. be measured with a high-impedance volt-
meter.
TABLE 4
RATIO
ARM VALUES AND VOLTAGE RATINGS
CRL MULTIPLIER
RaRa Max
Rb Rb
Max
Setting
Value
Voltage
Value
Voltage
100 IJlJf - mn - IJh
1 n 0.71 v10
kn
71 v
1mlJf - n - mh
IOn 2.2 v10
kn
71 v
10 mlJf - n - mh 100 n7.1 v10 kn 71 v
100 mlJf - n -
mh 1 kn
22
v10 kn 71 v
1 IJf : kn - h 10
kn 71 v10 kn 71 v
10 IJf - kn - h 100 kn 71 v10 kn 7lv
100 IJf - kn - h 1 Mn
500 v
10 kG 7lv
1 Mn
1 Mn
500 v 1
kn 22 v
5.4.3 SENSITIVITY. The generator -bridge-detector
system is sensitive enough to permit 1% balances
with the meter used as a detector. If higher sensi-
tivity is required for precise measurements of D
or 0 at the range extremes, headphones or an ex-
terna} amplifier may be connected to the DET OUT-
PUT terminals.
5.4.4 EFFECT OF LEVEL ON IRON-CORED IN-
DUCTOR MEASUREMENTS. Iron -cored inductors
are nonlinear devices and the value of inductance
depends on the level of the applied voltage. In order
12
to make measurements repeatable, the signal level
should be specified. The "initial permeability" in-
ductance' or inductance at zero level, is often used
as a reference (as is done on GR Type 1481 Stand-
ard Inductors). To obtain this value, plot Lvs volt-
age applied and extrapolate to zero voltage. The
OSC LEVEL control permits such measurements,
and it is often useful to make a level change in or-
der to see if the unknown inductance depends on the
signal level.
5.5 OPERATING PROCEDURE WITH ORTHONULL.
In the measurement of inductors whose Q is less
than 1 or capacitors whose D is greater than 1, bal-
ancing procedure can be simplified and false nulls
avoided by the use of Orthonull (refer to paragraph
2.5). The balancing procedure (essentially the same
as without Orthonu11 once the Orthonu11 mechanism
is engaged) is as follows:
a. Set the bridge switches as described in para-
graph 5.1.1, 5.2.1,or 6.1,depending onwhat is being
measured. Connect the unknown to the UNKNOWN
terminals, and connect the external generator (if one
is used) as described in paragraph 6.2.
b. Set the Orthonulilever to ORTIiONULL.
c. Set the CRL dial upscale (10 or 11).
d. Make the first balance with the DQ dial.
e. Adjust the CRL dial for further balance (the
DQ dial, ganged to the CRL dial by the Orthonull
mechanism, will follow). If the CRL setting is less
than 1 at balance, turn the CRL MULTIPLIER switch
to a lower range and rebalance.
f. Make further balances using first the DQ
dial, then the CRL dial, then the DQ dial, etc. until
the meter reading cannot be reduced further.
When the Q is very low, the meter deflection
will give several sharp dips as the CRL dial is ro-
tated. To find the best dip, rotate the CRL dial
slowly over a wide range without making another
DQ adjustment.
Often the Q is higher at some other frequency,
and it is desirable to change the frequency of mea-
surement. This is necessary if the inductor is above
resonance and appears capacitive.

OPERATING
WITH
EXTERNAL
~-~~------------------
TYPE 1650-A IMPEDANCE BRIDGE
Section 6
PROCEDURE
AC GENERA TOR
6.1 PROCEDURE. The procedure for making meas-
urements with an external oscillator is the same as
that with the internal l-kc oscillator except for the
following:
a. Connect the external oscillator to the instru-
ment as described in paragraph 6.2. (Note that the
esc LEVEL adjustment controls the level of exter-
nal ac applied to the EXT GEN terminals.)
b. Set the DETECTOR switch to FLAT (if fre-
quency is not 1 kc).
c. Set the function switch to AC EXT.
d. Multiply the D and Q readings by the factor
M, which is given on each scale of the DQ dial.
for low D and low Q M = f/l kc
for high D and high Q M =1 kc/f
e. The accuracy of the bridge is within 1% if
the value of D or Q lies within the limits of para-
graph 6.4, and if the effects of the bridge residual
impedance and of lead impedances are taken into
account (refer to paragraph 6.6). The accuracy is
1%up to 20 kc for the C and L bridges and up to 5
kc for the re~istance bridge.
If the presence of a nonlinear unknown causes
appreciable distortion in the detector, the best null
maynot give the correct value. Earphones are help-
flJl in distinguishing a null at the fundamental !re-
quency, or an external selective amplifier, such as
the Type 1231-B Amplifier and Null Detector with
appropriate filter, can be used.
6.2 CONNECTION OF EXTERNAL GENERATOR.
The external generator may be connected to the
bridge by anyone of several methods. The choice
depends on frequency and on the amount of overvolt-
age to be supplied.
The simplest method is to connect the gener-
atorto the EXT GEN terminals, which are connected
to the primary of the bridge transformer when the
function switch is set at AC EXT. Because the in-
ternal bridge transformer is used in this method,
one terminal of the oscillator is tied to ground, and
capacitance across the oscillator has no effect. How-
ever, the inductance of the bridge transformer pri-
mary is low (23 mh) because it is used in the inter-
nal LC oscillator, and becomes quite a load on the
external oscillator at low frequencies. A resistor
may be put in series with the oscillator to avoid
overloading and consequent distortion. (See Figure
13a and paragraph 6.3.)
A
matching transformer (see Figure 13b) Will (
prOVide
more power in the bridge at low frequen-
cies. This need not be a shielded bridge trans'"
former; a filament transformer (110 to 6.3 v) is
useful at low frequencies.
CURRENT-LIMITING 23mh
RESISTOR ( 120n
EXT.~I~
OSC. ~I~BRIDGE
= ~NTERNAL BRIDGE
7TRANSFORMER
a
SHIELDED
LEAD
EXT.~
OSC'LJ ~S
c
120n.
EXT.~II~· II~BR'DGE
OSc.~ GEN. ~'
EXTERNAL: = (INTERNAL BRIDGE
MATCHING TRANSFORMER TRANSFORMER
b
13
EXT.
OSC.
Figure 13.
Methods of Applying
External AC.
TYPE 57B-A
BRI DGE -TRANSFORMER
I ,.......;.-..-:1""'---0
II B7AS
I .':::7--++-1 ---{)
L-- ___. ANY PANEL
CONNECTOR
d

GENERAL RADIO COMPANY
The external generator can also be connected
directly into the bridge circuit through the BIAS
terminals (be sure to open the jumper strap). See
Figure 13c. In this connection capacitance from
either terminal of the generator to ground should
be considered. Capacitance from the + BIAS ter-
minal to the bridge chassis causes little difficulty
in the capacitance bridge if it is less than 1000 IJlJf,
but causes a Q error in the inductance bridges (re-
fer to paragraph 5.4.1). Capacitance from the neg-
ati ve BIAS terminal to chas sis can cause a more se-
vere error especially at high frequencies on the low
impedance ranges, and should be kept to a minimum.
Use ofa shielded lead (Figure 13c) keeps this capac-
itance low.
At
times, to reduce the effects of hum between
oscillator and power line, it is best to ground the
oscillator and to leave the bridge chassis floating.
A
shielded bridge transformer, such as the
GR Type 578-A Shielded Transformer, may be used
to make connections to the BIAS terminals to reduce
capacitance difficulties. Connections are shown in
Figure 13d.
6.3 MAXIMUM AC VOLTAGE. The maximum ac
voltage that may be applied to the Type 1650-A
Bridge depends on:
a. the voltage and power ratings of each com -
ponent (including the unknown),
b.
the bridge circuit used,
c. the range used,
d. the position of the variable components,
e. the method of applying the voltage.
Exact limits for any specific measurement
may be calculated from the data in Table 4 using
the circuit diagrams of Figure 3. If such a maxi-
mum voltage is applied, care must be taken to a-
void any adjustments of the panel controls that would
result in an overload.
A much simpler approach is to limit the power
into the bridge to 1/2 watt so that no bridge compo-
nent can be damaged under any conditions. If the
power rating of the unknown is less than 1/2 watt,
the input power should be reduced accordingly.
If the external signal is applied to the EXT
GEN terminals, the maximum voltage is limited to
E
max
= (f-) volts (rms) f in cps, or
60 volts (rms) whichever is smaller
With 60 volts inputthe maximum power to the bridge
14
is 1/2 watt and the open-circuit secondary voltage
is 15 volts.
If the external signal is connected to the BIAS
terminals, the maximum voltage is 280volts (rms),
and a series resistor of ( ~2 -120) ohms (where E
is in volts) should be placed in series to limit the
power to 1/2 watt. Note that if E is 15 volts or less
no resistor is required, since the resistance of the
transformer secondary limits the power to the bridge.
6.4 ALLOWABLE DAND QRANGES VSFREQUEN-
CY. The D and Q readings and ranges are functions
of frequency. Also, in order to avoid errors in the
C and L readings, the D or Qof the unknown is fur-
ther limited. The resulting allowable D and Q ranges
are given in terms of frequency and D or Qof the
unknown at the measurement frequency in Figure 14.
The numbers on the various limits refer to
the explanations below:
1. End of DQ rheostat range.
2. First division on Low D(0.001) and High
Q(1000)
scales (no C or L Error).
3. Limited by Dof standard capacitor (no C
or L Error).
4. 20-cps limit because of meter response.
5. 20 kc, a nominal limit (range narrow a-
bove 20 kc).
6. C or L error due to capacitance across
standard Ct and Re
7. C or L error due to inductance in DQ po-
tentiometer.
8. End of the low D and high Q scales. Use
the low Q scale to - extend the low P range, and the
high-D scale to extend tbe high Q range.
9. Limit of 1% C and L accuracy, even with
Orthonull (refer to paragraph 2.5).
10. C
and L error may be 2% above this line
owing to inductance in the DQ potentiometer.
Note that in the overlap area either the Cs or
the Cp bridge may be used. Below 100 cycles is an
area not covered by either bridge, requiring an ex-
ternal adjustment (refer to paragraph 6.6).
6.5 CORRECTIONS FOR RESIDUAL AND LEAD IM-
pEDANcEs. At high frequencies, the errors result-
ing from the residual bridge impedances and from
the connecting lead impedances become more im-
portant' often requiring corrections. The formulas
forthe correction terms are given in Table 5. These
correction terms are first-order terms only.
___________ ~ __ ~_~ ~ ~.l

TYPE 1650·A IMPEDANCE BRIDGE
TABLE 5
ERRORS DUE
TO RESIDUAL AND LEAD IMPEDANCES
CORRECTION TERMS; ADD OR SUBTRACT
FROM MEASURED VALUE
AS INDICATED
Measured
Series Resistance
Series Inductance Parallel Capacitance
Quantity
Ro (l rnn + leads)
Lo(0.2 Ilh + leads)
Co (0.5 Illlf + leads)
---
CsNo
Error
-w
2
4> Cx2
-Co (1 - Dx2)
-wCxR
o2
+0 Co
(l + 0 2)
0
-w LoCxDxCx
..
Cp2
-w
2L C 2
(1 -0 2)
-Co
+2 RowDxCxo x x
:2
-w2LoCxDx(1 +Ox 2)
Co
0
-wCxR
o
(1 +Ox )
+~Dx
R
-Ro
LsNo
Error
-L
o
-w
2CL2(1 -
~
-.
o x Qx
Q2 RoLo21
+Q
xwL
--Q
+w CoLx (Qx +~)
x
Lx x
Qx
2Ro 12 2
Lp
+Qw
-L
o
(1 - Q2)
-w, CoLx
+~ (1 +Q2) Lo12
QwLx-
Lx (Q+Qi
+w CoLxQ
"-
I'\.
~
"-,
I@
f"
9
1'<'
'<:1
~-
~~
--- -
~
-~
ICD
~
CpIHIGH, DJ
"-, "\
EXT DO ~
LSILOW 0
I"
ADJUSTMENV-
"\.§YI'
,'''
NCE!SARY
"-
, -~,
ICD
YX
RANGE "0
~
OVERLA~
/
"\ ®
I@
IV "\
..-'
/CslLOW
DJ
I'"
4LplHIGH
0)
1"\ /
I
'" V
'"
,-
-
LA l®
/
I3
~
10 100, IkC IOkC IQOI(C
FREQUENCY
Figure 14. DQ Ranges vs Frequency.
(Refer to paragraph 6.4.)
0,1 10
100 0.0
1.0 to
10 0,1
1000 000
0,01 100
o Cl
low 0=(low 0 dial reading +0.628R,) x f (kO, kc)
low Q=(low Q
dial reading +0.628R) xf(kO, kc)
The low Q circuit has a fixed 32 -ohm resistor
in series with the potentiometer, but that is included
in the dial calibration.
. The low 0 and low Q scales are directly pro-
portional to frequency. Therefore, the total 0 or Q
value is the sum of the dial reading plus the wRC
product due to the external resistor. That is:
The high 0 and high Q scales are inversely
proportional to frequency, and the effects of the in-
temal and ~xterna1 resistors are therefore not ad-
ditive. The DQ rheostat should be. set to a minimum
(high Q=0 or high 0=50), and the whole adjust-
ment will be on the external resistance and will be:
(kO, kc)
(kO, kc)
f (R +0.032)
high 0=
high Q= 1f~2
1.592
6.6 EXTENDING
THE 0 AND QRANGES AT LOW
FREQUENCIES. The wide overlap of ranges (see
Figure 14) permits 0 and.Q coverage down to 100
cycles without external adjustment. Below 1 kc,
more of tlfe lo\\:, 0and high Q range may be used
than is calibrFJ,ted. In this region, the low Q scale
may be used to indicate 0 directly and the high 0
scale used to indicate Q directly with a maximum
additional error of 2%;
Below100 cycles there is a0 and Q range not
covered by the internal DQ adjustment. An external
rheostat or decade box may be used to extend the
range of any of the 0 or Q scales. (However, to a-
void error, the low 0 and high Q ranges should not
be extended beyond a value of 1 at frequency of
measurement (see Figure 14).
To connect the external resistance, remove
the bridge from its cabinet and connect the two wires
from the external resistance to the terminals marked
16 and 17, which are on the bracket directly behind
the BIAS terminals (see Figure 21). Remove the
jumper between terminals 16 and 17, and bring the
leads out through the panel hole directly below the
BIAS terminals after removing the snap button.
.... - -.- --...~
15