GENERAL RADIO COMPANY 1608-A User manual

OPERATING INSTRUCTIONS
TYPE 1608-A
IMPEDANCE BRIDGE
;1.
GENERAL RADIO COMPANY
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OPERATING INSTRUCTIONS
TYPE 1608-A
IMPEDANCE
Form 1608·0100·A
February, 1962
BRIDGE
Copyright 1962 by General Radio Company
West
Concord, Massachusetts, USA
G ENE R A L R A 0 I 0
COMPANY
WEST CONCORD, MASSACHUSETTS, USA

TABLE
OF CONTENTS
Section 1. INTRODUCTION
1.1 Purpose. .....
1.2 Description. ...
1.3 Symbols, Abbreviations, and Definitions
1.4 Series and Parallel Parameters .
1.5 Accuracy of Measurements . .
Section 2. OPERATING PROCEDURE .
2.1
Installation • . . . . • . . .
2.2 Interpretation of "X" in Read-out
2.3 DC Resistance Measurements.. ....
2.4 AC Measurements using Internal Generator.
2.5 AC Measurements with External Generator.
1
· 1
1
1
4
• • • 4
9
• 9
• • • 9
· 9
.12
· .19
Section 3. SPECIAL MEASUREMENTS • . . . . . . . • 22
3.1 Application of DC Bias to Unknown. . . . . . . 22
3.2
Measurements on Shielded Three-Terminal Components • . .26
3.3 Remote Measurements . . . . . . . . . .26
3.4 Use of Type 1650-P1 Test Jig • • . . . . . . . . •. ..27
3.5 Measurements on Grounded Components • . . • . . . • • .27
3.6 Limit Testing . . . . . . . . . . . • . . • • • .. . 27
3.7 Measuring Resonant Frequency and Resonant Impedance of
Tuned Circuits • . . • . . • . . . . . 27
Section 4. PRINCIPLES OF OPERATION
4.1
Bridge Circuits • . . . . •
4.2 Bridge Sources and Detectors •.
4.3 Bridge Switching. .......
4.4 Centade Operation . • • • . • •
4.5 Phase-Compensation Techniques.
Section 5. SERVICE AND MAINTENANCE
5.1 General. . . • • .
5.2 Calibration Checks. ...
5.3 Adjustments. • . . • •. • •
5.4 Replacing Indicator Lamps •
5.5 Trouble-Shooting Suggestions • .
5.6 Tables of Test Voltages
.28
· .28
· . .28
.29
.29
• • • . 30
.31
.31
.31
.32
. . . • . 33
. .
.. ...33
· .34

SPECIFICA liONS
RANGES
Capacitance: 0.05 pf to 1100 ILf in seven ranges,
series
or parallel.
Inductance: 0.05 /Lh to 1100 h in seven ranges,
series
or parallel.
Resistance: 0.05 mfl to 1.1 Mfl ac or de.
Conductance: 0.05 nU to 1.1 Uac or de
(20 kMfl
to 0.9 fl).
D of Series C: 0.0005 to 1.
D of Parallel C: 0.02 to 2.
Q of Series L: 0.5 to 50.
Q of Parallel L: 1 to 2000.
Q of Seri.es R: 0.0005 to 1.2 inductive.
Q of Parallel G: 0.0005 to 1.2 capacitive.
ACCURACY
C, G, R, L
At 1kc: ±0.1 % ±0.005% of full scale except
on lowest
Rand Lranges and highest C and G
ranges where it is ±0.2 % ±0.005 %of full scale.
Additional % error terms for high frequency
and large phase angle:
C and L
[ ±0.001 (1 ~cy ±0.1D 1 {c ±0.5D
2
]%
of measured
quantity.
Rand G
[ ±0.002C ~cY±O.OOOOOIC~cY±O.lQ] %
of measured
quantity.
Residual Terminal Impedance: R ~ 1mfl, L ~
0.15 /Lh, C ~ 0.25 pf.
Dc Resistance and Conductance: Same as for
l-kc measurements, except that accuracy is
limited
by sensitivity at the range extremes.
Balances
to 0.1% are possible from Ifl to IMfl
with the internal supply and detector.
D' ( or ~) of C or L:
±0.0005 ±5% at 1kc or lower.
±0.0005 1 ~c ±5% above 1 kC.\
f
Q of R or G: ±0.0005 1kc ±2%.
GENERATOR AND DETECTOR
Internal Oscillator: 1kc ± 1% normally supplied.
Plug-in modules for
other frequencies available
on request. Level control provided.
Internal Ac Detector: Can be used either flat or
selective at frequency of plug-in module
(normally 1kc). Second-harmonic rejection
approximately 25 db; sensitivity control pro-
vided.
Internal Dc Supplies: 3.5 v, 35 v, 350 v; adjust-
able, and power limited to less than 73' watt.
Internal Dc Detector: Null indicator, 1/La/mm.
External Oscillator and Detector: TYPE 121O·C
Unit RC Oscillator and TYPE 1232-A Tuned
Amplifier and Null Detector are recommended.
Dc Bias: Provision is made for biasing capacitors
to 600 v with external supplies, and for biasing
current in inductors.
GENERAL
Accessories Supplied: TYPE CAP-22 3-Wire
Power Cord; spare fuses and indicator lamps.
Accessories Available: TYPE 1650-Pl Test Jig;
external generator and detector, if used, as
listed above.
Power Input: 105 to 125 (or 210 to 250) volts,
50-60 cps, 10
watts.
Mounting: Either relay-rack or bench, as listed
below.
Dimensions: Rack model, panel, 19 by 12~
inches (485 by 315 mm); bench model, width 19,
height 1272, depth 11 72 inches (485 by 320
by 295 mm), over-all.
Net Weight: 36% pounds (17 kg).
General Radio Experimenter reference: Vol. 36No. 3, March 1962

II
9 12 10
13
3
15
4
6
Figure 1-1. The Type 1608-A Impedance Bridge
(for legend see page 2).
7 8
16 17
18

INTRODUCTION
SECTION 1
INTRODUCTION
1. 1 PURPOSE.
The Type 1608-A Impedance Bridge (Figure 1-1)
is a self-contained impedan.ce-measuring system, which
includes six bridges for the measure'Tlent of capaci-
tance, conductance, resistance, and inductance, as well
as the generators and dete·ctors necessary for de and
l-kc ac measurements.
1.2 DESCRIPTION.
1.2.1 GENERAL. The SIX bridges contained in the
Type 1608-A are shown schematically in Figure 1-2.
Provision is made for ac and de measurements, both
with internal and external generator and detector. The
generator and detector connections for the four "on"
positions of the function switch (INT AC, INT DC, EXT
AC, EXT DC) are shown schematically in Figure 1-3.
Cs
(
LOW 0\
o TO I)
SERIES CAPACITANCE
RN
Cx'R;C
r
Ox' IIIC
xRx'OICrRr
Cp
(
HIGH 0\
.02-2 )
PARALLEL CAPACITANCE
C
x
1.2.2 CONTROLS AND CONNECTORS. Table 1-1 lists
the controls and connectors on the front and rear panels
of the Type 1608-A Impedance Bridge.
1.3 SYMBOLS, ABBREVIATIONS, AND DEFINITIONS.
Table 1-2 lists symbols and abbreviations used in
this manual, together with their definitions.
Figure 1-2. The six bridges.
of the Type 16GB-A.
G
p
(CAP
Q)
0-1.2
PARALLEL CONOI/CTANCE
C
x
RS
(
INO Q\
0-1.2)
SERIES RESISTANCE
Lx
Rx' RNRA
Rr
Qx" 41L
x
:' 41C
rHr
Rx
Ls
G
LOW Q\
0.5 -50/
SERIES INOI/CTANCE
Lx
Lx 'R
N1cr
Ox ,IiIL
x
.. tIICrR
r
Rx
Lp
(
HIGHQ'\
1- 00.../
PARALLEL INOI/CTANCE
Lx
1

~ __ T-'-Y_PE_16_0_8-_A_I_M_P_E_D_A_N_C_E_B_R_I_D_G_E _
TABLE 1-1
TABLE OF CONTROLS AND CONNECTORS
CONTROLS
Fig.
1- 1 Ref
Name
Type
Function
1
Function 5-pos rotary switch
Turn instrument on or off,
selects internal or external
ac or de operation.
2
BRIDGE SELECTOR 6-pos rotary switch
Selects appropriate bridge
circuit for measurement of
Cs' Cp,Gp,Rs' L s' and Lp.
3
FULL SCALE RANGE 7-pos rotary switch
Selects measurement range,
indicates full-scale value
of CGRL indicator.
4 CGRL
coaxial rotary controls
Main balance control. Small
knob controls two right-hand
digits of indicator, large knob
controls three left-hand digits.
5DQ
Continuous rotary control
DQ balance control, used for
C
and L measurements
6 12-pos rotary switch Q balance controls, used in G
7Q
11-pos rotary sWItch and R measurements.
8
Continuous rotary control
9GEN
LEV Continuous rotary control Controls output level of internal
generator,ac and dc.
10 DET SENS
Continuous rotary control Controls sensitivity of internal
detector,ac and dc.
CONNECTORS
Fig 1-1 Ref
Name
Type Function
11 EXT GEN
Jack-top binding-post Connection to external gen-
pair
erator, ac and dc.
12
DET OUT
Jack-top binding-post
Output connection from in-
pair
ternal detector. ac only.
13 UNKNOWN
Jack-top binding-post Connection to unknown
pair component.
14
EXTDQ
Jack-top binding-post
Connection to external re-
pair sistance or capacitance to
extend DQ ranges.
15 BIAS Jack-top binding-post Connection to external
pair bias supply.
16
Power
Three-terminal recessed Power input connector
male connector
17 3RD WIRE GROUND Jack-top binding-post
Connection to ground wire
pair of three-wire power line.
18
EXT METER CON-
Three jack-top binding
Connection to external dc null
NECTIONS posts indicator.
J
2

INTRODUCTION
IN OFF POSITION
POWER OFF
EXT GEN DISCONNECTED
METER SHUNTED
OFF
IN BETWEEN OFF
AND INT DC POSITIONS
DC BRIDGE OPERATIVE
BUT METER SHUNTED
TO REDUCE SENSITIVITY
1
R;
1
c;;-
1
~-
R
~_1_
Rs
conductance <..I\M-) G
series conductance Gs
impedance, Z ~ R +jX
reactance, the imaginary part of an impedance
admittance, y ~ G+ jB
the imaginary parr of an admittance
para lIe I re sistance Rp
resistance <..I\M-) R ~ ~
1
series resistance Rs --
Gs
TABLE 1-2
EXT AC
INT AC
SYMBOLS AND ABBREVIATIONS
~
osc
cap.acitance .<-1 r- )
ex:;: l~J
osc
LEVEL
C
Cs
senes capacitance
Cp
parallel capacitance
L inductance
<-'lmQ\-)
Ls
series inductance
Lp
parallel inductance
BIAS
BIAS
z
X
Y
B
Q
G
Gp parallel conductance Gp
Rs
R
Gs
cuL
for inductors or inductive resistors Q ~ __ s_
R~
INT DC
EXT GEN
EXT DC
Figure 1-3. Generator and detector
connections.
LOWEST TWO R RANGES HIGHEST 5R RANGES
HIGHEST THREE GRANGES LOWEST 4 GRANGES
GEN
LEV
for capacitors D
R
power factor -VR2 + X2
frequency
angular frequency ~ 21Tf
ohm, a unit of resistance, reactance or impedance
kilohm 1 kD ~ 1000 D
megohm 1 MD ~ 1,000,000 ~D
milliohm 1mD ~ 0.001 D
for capacitive resistors Q ~ cuCpRp
d' . . f R G 1
ISSlpatlOn actor ~X ~ 13 ~ Q
1
cuCp Rp
D
kD
MD
mD
D
PF
mho, a unit of conductance, susceptance or admittance
m0 millimho 1m0 ~ .0010
f-LO micromho 1 f-LO 1 x 10-
60
n 0 nanomho 1 nO 1 x 10-
90
f-Lf microfarad, a unit of capacitance
nf nanofarad 1 nf ~ 0.001 f-L f ~ 1 mf-L f
pf picofarad 1 pf ~ 1x10 -6 f-L f ~ 1 f-Lf-L f
h
henry, a unit of inductance
mh millihenry 1mh ~ 0.001 h
f-Lh microhenry 1 f-L h ~ 1 x 10 -6 h
f
3

~ __ TY_P_E_l_60_8_-A_1 M_P_E_D_A_N_C_E_B_R_I_D_G_E _
Cs= (I +D2)Cp;
1
Cp= 1 +D2 Cs
D2
11
Rs
=--R
= 1 +Q2 Rp(1
+Q2)G
p
1+D2 p
Rp1+D2
(I+Q2)R
s
=--R
D2 s
1Cp
QG
p
Gp=(1 +Q2) Rs'
=--
ev
lC
s
LSRpC
pRp
LpGpRSGp
RS
evC p
Q=-=
Gp
1+ Q2
1
jwLpR
p
Rp+jevLp
Resistance and Inductance
z
1.4 SERIES AND PARALLEL PARAMETERS.
An impedance that is neither a pure reactance nor
a pure resistance can be represented at any specific fre-
quency by either a series or a parallel combination of re-
sistance and reactance. The values of resistance and re-
actance used in the equivalent circuit depend on whether
a series or parallel representation is used. The equiv-
alent circuits are shown in Figure 1-4. A nomograph for
series-parallel conversion is given in Figure 1-7. The
relationships between the various circuit elements are as
follows:
1Lp; Lp=1+Q2 L = (1 +D2)L
1+D2 Q2 s s
Figure 1-4. Equivalent circuits lor
complex impedance.
1.5 ACCURACY OF MEASUREMENTS.
1.5.1 CGRL ACCURACY AT 1KC. The basic bridge
accuracy is 0.1%. This is a function of the accuracy of
the adjustment and stability of the bridge arms. The in-
strument is initially calibrated to an accuracy of ±0.05%
or better and should hold the 0.1% accuracy for well
beyond the two-year warranty period. A simple calibra-
tion check procedure is given in Section 5.2.
The lowest-resistance (I-ohm) resistance ratio
arm is the most difficult ratio arm to set aCfurately, is
the most affected by switch and lead resistance, and
has slightly poorer stability than the other arms. There-
fore, the accuracy specification for the lowest imped-
ance range for each bridge is 0.2%.
The fixed error of ±0.005% of full scale or one-
half a digit on the counter read-out allows for backlash
in the adj ustment and for the limitations of linearity and
resolution of the vernier rheostat. This fixed error gives
an over-all accuracy at 1 kc (on all but the lowest range)
1+D2
1
ev
CpRp
Resistance and Capacitance
• 1
Z=R +-.-
SJ evC
s
4

INTRODUCTION
of 0.105% at full scale and 0.15% at one-tenth of full
scale. Therefore, the final balance should be made with
as many digits on the counter as possible.
1.5.2 TEMPERATURE COEFFICIENT. The over-all
temperature coefficient of the instrument is less than
30 ppm/°c. This means that there may be a 0.03%
change in reading for a temperature change of lQoe
(50 OF). This change is usually negligible compared with
the change in the unknown component for a similar tem-
perature change. For the most accurate measurements,
the bridge 'and components to be measured should be
stabilized at a temperature near 23 °e (73 of).
1.5.3 ADDITIONAL ERRORS FOR HIGH DCAPACI-
TORS/ LOW Q INDUCTORS/ AND HIGH Q RESISTORS.
The DQ dial adjustments used for phase balance on the
e and L bridges are wire-wound rheostats. When lossy
(high D or low Q) components are measured, the limited
resolution of these adjustments prohibits balance of the
e or L adjustment to its full resolution. A term of
0.5%D2 is added to the specifications to allow for this
effect, but somewhat better accuracy is possible with
extreme care. Precision components generally have a
low enough D or a high enough Q to make this term neg-
ligible (see Figure 1-5).
kc
Figure 1-6; Resistance and conduct-
ance errors vs frequency.
FREQUENCY
J
ff
~'I /
JV
1;/
VI/
I
j;
/
TOTAL ERROR a·'
~
-'
~
r
IbOOI(~r
~OTAL ERloR Q·O
~
VI
.1
0
1
1%/
V/
1
12
-1
/
0002(~)
1/
1/
I
Ike
10ke
100
o
0.0100
10
The Q adjustment for the Rs and Gp bridges con-
sists of two decades of mica capacitors and a variable
capacitor with infinite resolution. Losses in the mica
capacitors appear as an R or G error when Q is rela-
tively large, and the added error term of O.l%Q is there-
fore necessa~y (see Figure 1-6).
100
1.5.4 FREQUENCY ERRORS. The main cause of addi-
tional error on the e and L bridges at higher frequencies
is the inductance of the pridge wiring in series with the
standard capacitor, effectively increasing its value .
This error is proportional to f2, and is accounted for in
the added error term 0.001% (fl1 kc)2. This term, which
amounts to a0.1% error at 10 kc and a0.4% error at 20
kc, is large enough to account for other smaller sources
of error (see Figure 1-5).
F
or high D (low Q) measurements at high frequen-
cies, there is an added error term due to the inductance
of the DQ rheostats. This term is O.lD (f/1 kc). (See
Figure 2-7.) The series rheostat (e
s
and Lp bridges)
is phase-compensated to a large degree, but neverthe-
100ke 10ke
FREOUENCY
Ike
Figure 1-5. Capacitance and induct-
ance errors vs frequency.
/ VJ
/
VA
W
TOTAL ERROR 0·1 "-..
~
V/(/II
I
~
///
(j
l.---
V
~ ~
'0
-
0'0.2 ./
~
/I
.1
TOTAL ERROR 0.6/
I
1{~0IC~.)2
I
I
o
0.0
100
10
5

~ _...:..T...:Y_P:......:E.::.....1....:.6...:...:08:.....:.-A...:........:..' MP _E _D_A_N_C_E_B_R_'_D_G_E _
less adds inductance in series with the standard capaci-
tor. The inductance of the parallel rheostat (C
s
and Lp
bridges) is placed in parallel with the standard capaci-
tor, and at high enough D values effectively reduces the
capacitance of this bridge arm. The error on the Cp and
Ls bridges is somewhat less, and these bridges have
more useful D and Q ranges at high frequencies (see
Figure 2-7).
A
fr~quency-dependent error term is necessary for
the resistance and conductance bridges because of a
network built inco the standard resistance arm to com-
pensate for stray capacitance (refer to paragraph 4.5).
The effective resistance of this arm has one term pro-
portional to f2 and one proportional to f4, requiring the
added error terms ±0.002 (f/l kc)2 and ±O.OOOOO 1
(fll kc)4. The first term is more important up to 45 kc,
and adds an extra 0.2% error at 10 kc and 0.8% error at
20 kc (see Figure 1-6).
1.5.5 RESIDUAL TERMINAL IMPEDANCE. The ac-
curacy specifications are valid only if the effect of the
residual te,minal impedance of the UNKNOWN connec-
tion is considered. The residual resistance and capaci-
tance can be easily measured and subtracted from the
final measured value. At high frequencies somewhat
more complicated corrections are necessary, particu-
larly at the range extremes, and correction formulae are
given in Table 2-5.
1.5.6 DAND QACCURACY. The 5-percenc term in the
o and Q accuracy specifications for C and L measure-
ments depends upon the tracking accuracy of the DQ
6
rheostats with the dial calibration. The fixed term,
±0.0005, depends upon the phase angle of each arm of
the bridge, and many compensating components are re-
quired to achieve this accuracy (refer to paragraph 4.5).
This specification of ±O.OOO') holds for measurements
made down to 1/20 of -the full-scale CGRL counter read-
ing. Below this reading, the phase angle of the vernier
CGRL adjustment (R4), even though compensated for,
can add additional DQ error. This could amount to an
error of 0.001 at 1/100 of full scale and 0.005 at 1/1000
of full scale. The detector sensitivity is also aHmiting
factor here. Lower CGRL ranges should be used to
achieve better D and Q accuracy.
At high frequencies the DQ error increases be-
cause the phase angles of the bridge arms increase with
f. Therefore, this fixed error term is 0.0005 1 ~c above
1 kc. At frequencies below 1 kc, the D accuracy cannot
be improved because it is limited by the Dof the stand-
ard capacitor.
The percent term in the Q accuracy for Rs and Gp
bridges is ±2%, which is limited by the accuracy of the
capacitance decades used for Q adjustment. The fixed
term is ±0.0005 at 1 kc, just as in the Land C bridges,
since the same phase angle considerations apply. How-
ever, for the Rs and Gp bridges, this term is ±0.0005
rk at higher and at lower frequencies. This gives ex-
i.remely good Q accuracy at low frequencies, but does
not help in the measurement of the time constant (Q/ c..:)
of resistors, which is independent of frequency (except
at very high frequencies).

INTRODUCTION

~ _T_Y_P_E_l_60_8_-A_1 M_P_E_D_A_N_C _E_B_R_I_D_G_E _
0.01
2
0.02
3
4
0.0001
0.03
5
0.04
6
0.0002
7
0.05
8
0.06
9
10
0.0005
0.07
0.08
0.09
0.001
0.1
20
0.002
0.2
30
0.00
0
0.01
0.3
0.4
60
Q02
70
Q5
80
0.6
90
100
0.05
0.7
0.8
0.9
0.1 I
200
0.2
300
0.5
400
500
600
700
800
900
61000
7
8
9
-10
Q
XL
LS
(ANY FREQ) (I kc ONLY)
• m.o.
nh
..
.0.
ph
..
k.o.
mh
2
m.o. 1---------------------------;.
.0. 1----------------------------1 ..
k.o. 1---------------------------; ..
10
9
8
7
6
5
200
300
400
1000
900
800
700
600
500
Figure 1-8. Nomograpb for conversion of
Rs to Ls and vice versa.
8

SECTION 2
OPERATING
2.1 INSTALLATION.
2.1.1
POWER CONNECTIONS. Connect the bridge to a
suitable power source as indicated on the plate above
the power receptacle on the rear of the instrument (115
or 230v, 50-60 cps). A three-wire power cord is sup-
plied.
2.1.2 GROUNDING. The bridge should generally be op-
erated with the bridge chassis grounded except in spe-
cific cases where the unknown component or a de bias
supply should be grounded (refer to paragraphs 3.1. 5 and
3.5). The ground connection is made through the three-
wire power cord to the 3RD WIRE GROUND terminal on
the rear of the instrument. This terminal should be con-
nected to the adjacent CHASSIS terminal unless the
bridge must be ungrounded. If the three-wire power cord
is not used, this connection should be made externally.
2.1.3 MOUNTING. The instrument is available as either
the Type 1608-AM, for bench mounting, or Type 1608-AR,
for relay-rack mounting. The bench-mounting model is
equipped with aluminum end frames, while the Type
160B-AR includes mounting brackets for relay-rack in-
stallation. I~structions for assembly accompany these
brackets, which may be ordered separately (Type ZSU-6-7)
to convert from bench to rack use.
Type ZSU-6-7 mounting brackets are of a unique
General Radio design which permits the instrument to be
pulled out on slides for service. Eith"er chassis or cabinet
can be removed from the rack independently of the other.
2.2 INTERPRETATION OF ·X· IN READ-OUT.
The main CGRL indication consists of up to five
digits displayed in an in-line read-out. Th~ three left-
hand digits are controlled by the larger of the two con-
centric CGRL controls; the two right-hand digits are
controlled by the smaller (vernier) control. To provide
an overlapping transition from full-scale vernier reading
(99) to the next higher coarse step, the vernier read:out
extends beyond 99, up to 106. To avoid the ambiguity of
two digits on the same counter, an X is used in place of
the number 10. To interpret a reading containing an X,
simply substitute 0for the X and add 1 to the digit im-
mediately to the left of the X. For example, 102X3 :::
10303; 99X2 :::10002.
The letter X is also used on two of the three Q
OPERATING PROCEDURE
dials used with the Rs and Gp bridges. Here again, sub-
stitute 0 in place of the X and add 1 to the digit to the
left of the X. For example, .IX4 :::.204; .2XX:::.310.
Users may find it helpful to record measurement
data exactly as it appears on the bridge read-out, in-
cluding any X's that appear. In that way, any possible
error in the interpretation of the X can be rechecked.
2.3 DC RESISTANCE MEASUREMENTS.
2.3.1 PROCEDURE.
a. With the function switch (1, Figure 1-1) off,
check the NULL meter mechanical zero position, and,
if necessary, center the pointer with the screw-driver
adjustment on the meter.
b. Turn the DET SENS control almost fully
counterclockwise.
c. Set the BRIDGE SELECTOR switch to Rsfor
resistance measurements from 0 to 1.1 MD and Gpfor re-
sistance measurements above 1 MD and for conductance
measurements from 0 to 1.1 mho.
d.
Connect the resistor to be measured to the UN-
KNOWN terminals.
e. Turn the function switch to !NT DC.
NOTE
As the function switch is rotated from OFF to
INT DC, it passes through an undetented posi-
tion where the circuit is operative but the
meter sensitivity is greatly reduced. A pre- "
liminary balance may be made with the switch
in this position instead of with the DET SENS
control turned down.
f. Adjust the FULL SCALE RANGE switch and
the concentric CGRL balancing controls for a zero
(center) reading, and adjust the DET SENS and GEN
LEV controls for increased sensitivity as necessary.
A meter deflection to the right indicates that the un-
known is larger than the indicated CGRL dial setting.
For greatest accuracy the" reading should have at least
four digits showing. If not, turn to the next lower range.
g. The value of the UNKNOWN is read directly on
the counter with the decimal point correctly located and
the unit illuminated above. The meaning of an X indica-
tor is explained in paragraph 2.2.
9

~ __ T_YP_E_l_6_08_-A_1 M_P_E _D_A_N_C_E_B_R_I_D_G_E _
I
I
I
I
I
~;k
~
TO 1M 100v
It'
II
~~
~
IV
flOk
TO lOOk 30 v
r
ty
I"'"""'"
eikTOIOklOv
'I
I
I
I
~
Vd100.0.
TO Ik.o. 2.5 TO 3v
I I I
11
~~
-
........ ~ 0. O·~ :,j....-
t--
I
\00
IV
~\0l;).\0~ I
I~
/V b 1.0. TO 10.0.
{;V
~
~
--
~
IV
I
~~
~ 0.1 TO 1.0.
I , Ii /V-
11
I
I
II
0I2345678 10
10
O.
100
0.0
1000
For low-resistance measurements, short, heavy
leads should be used as connections to the unknown
component. Measure the zero resistance of the lead!';
and terminals by connecting the free ends together, and
subtract this amount from the bridge reading with the un-
known in place. For best connection to the bridge,
screw the binding post hard enough to notch the wire
inserted in the hole.
2.3.3 INTERNAL VOLTAGE APPLI ED TO THE UN-
KNOWN. There are three internal dc supplies, each hav-
ing a limiting resistor to limit the available power to
1/2 watt or less to avoid damage to the bridge compon-
en~s or to the unknown. They are all controlled by the
GEN LEV panel control. The lowest voltage supply, ap-
proximating 3.5 volts open circuit, is appli~d "horizon-
tally" to the bridge (see Figure 1-3) and the 35-volt and
350-volt supplies are applied "vertically". The FULL
SCALE RANGE switch selects the optimum supply for
each range as given in Table 2-1.
Because of the limiting resistor, the maximum
voltage applied to the unknown is usually of much less
than the open-circuit value. Figure 2-1 shows the ac-
tual voltage applied to any unknown resistor when meas-
ured on the R bridge (with a Il5-volt line voltage).
EIA specifications for testing different types of
resistors are summarized in Tables 2-2 and 2-3. Figure
2-1 shows thar these standard voltages can be supplied
from the internal power supplies over most of the resis-
tance range. For low-resistance measurements the GEN
LEV control can be set for the desired test voltage by
use of a high-impedance dc voltmeter connected directly
LO the UNKNOWN terminals. For high-i:esistance meas-
urements, where the voltage is applied vertically, the
ratio between the voltage across the unknown and that
across the whoT~ bridge is fixed over each range at null
and therefore the voltmeter can be placed across the
bridge input (LOW UNKNOWN terminals to chassis) and
the GEN LEV control set to give the "bridge voltage"
given in Tables 2-2 and 2-3.
2.3.2 ACCURACY. The accuracy of dc resistance and
conductance measurements is ±0.1%, ±0.005% of full
scale (which is ±1/2 of the last digit) on all but the
lowest R and highest G ranges as long as there is suf-
ficient sensitivity. On the lowest R and highest Grange
the accuracy is limited by the sensitivity to ± 1/2%
±1 mD.
2.3.4 EXTERNAL DC DETECTOR. The internal dc
supplies and the internal detector permit measurements
from 1ohm to 1megohm to 0.1 % when the GEN LEV and
DET SENS controls are at maximum. If accurate meas-
urements beyond this range are desired or if it is neces-
sary to make measurements at lower voltages, an exter-
Figure 2.1. Dc voltage applied to unknown
resistor (115-v line).
10

OPERATING PROCEDURE
TABLE 2-1
DC SOURCE AND DETECTOR CONNECTIONS
FULL SCALE RANGE 1100
mD I 11 D1110 D1100 Dill kD 110 kD 11100 kD
Rs
VERTICAL METER
MVS
HVS
Bridge HORIZONTAL LVS METER
"
Gp
FULL SCALE RANGE 1100 nU I
11 j.LU 1110 j.LU 1100 j.LU III mU 110 mU 11100 mU
Bridge
VERTICAL
HVS METER
HORIZONTAL METER
MVS
LVS
HVS HIGH-VOLTAGE
SUPPLY
MVS MEDIUM-VOLTAGE SUPPLY
LVS LOW-VOLTAGE SUPPLY
350v open-circuit
35 v open-circuit
3.5 v open-circuit
TABLE 2-2
EIA STANDARD TEST VOLTAGES
Fixed Composition Resi stors (RS172)
RESISTANCE BRIDGE RANGE EIA
TEST VOLTAGE BRIDGE VOLTAGE*
2.7-9.9 DRs
llD
0.5 - 1v
**
10 -99 D Rs
1l0D
0.5 - 1v
**
100 -999 D Rs
1l00D
2.5 - 3 v
19.2-23v
1000 -9999 D Rs
II kD 8 - 10 v13.4 -16.7 v
1O-99kD Rs
1l0kD
24 - 30 v
25.6-32v
100kD-1MD
Rs
1100kD
80-100v
81 -101 v
1MD-up
Gp
1nU
80 - 100v
81 -101 v
TABLE 2-3
EIA STANDARD TEST VOL T AGES
Fixed Film Resistors (RS-A6)
Low-Power Wire-Wound
Resistors (REC-117 up to 9999 D)
RESISTANCE BRIDGE RANGE EIA
MAX VOLTAGE MAX BRIDGE VOLTS*
less tha'n 10 DRs
11D
0.3v
**
10 -99 D Rs
1l0D
Iv
**
100 -999 DRs1100 D
3v
23v
1000 -9999 D Rs
llkD 10v
16.7v
10 - 99kD Rs
1l0k D
30v 32v
100kD -1MD Rs
1l00kD
100v
101 v
1MD -up
Gpo
1nU 100v
100v
* This is the voltage from the LOW UNKNOWN terminal to chassis. In the EXT DC position, this is
also the voltage at the EXT GEN terminals.
** This voltage varies with the resistance of the unknown (see paragraph 4.3).
11

~ --,.-_TY_P_E_1_60_8_-A_1 M_P_E_D_A_N_C_E_B_R_I_D_G_E _
(a.)
EXT METER
TO
BRIDGE
c
(b)
Figure 2-2. External meter connections.
EXT METER
nal detector with increased sensitivity can be used. The
external detector can be connected in series with the
internal meter, in parallel with the meter, or in place of
the meter by appropriate connection to the EXT METER
CONNECTIONS on the rear of the instrument as shown
in Figure 2-2.
2.3.5 EXTERNAL DC SUPPLY. If higher voltage is
required on the unknown resistor, an external supply
may be used. The EXT GEN terminals are connected
directly across the vertical bridge diagonal in the EXT
DC position of the function switch and the detector is
across the horizontal diagonal on the top four ranges.
Be careful not to exceed the maximum voltage or current
given in Table 2-4 in order to avoid damage to the bridge
components.
If a higher voltage is desired on a low-valued un-
known
resistor (the lower three resistance ranges), set
the function switch to EXT GEN but apply the voltage
between the BIAS terminals and the EXT DQ terminals
(R bridge only).
When an external supply or detector is used, the
measurement procedure is the same as that with the in-
ternal supply and detector except that the GEN LEV
control does not control the level of an external sup-
ply and the DET SENS control does not control the sen-
sitivity of an external detector.
2.4 AC MEASUREMENTS USING INTERNAL GENERA-
TOR.
2.4.1 1-KC CAPACITANCE MEASUREMENT.
2.4.1.1 Procedure.
a. Set the GEN LEV control fully clockwise.
b. Set the BRIDGE SELECTOR to:
Cs- if the series capacitance is desired and D is less
than 1.
Cp - if the parallel capacitance is desired and D is be-
tween 0.02 and 2.
(Note: Cs=Cp within 0.1% if D< 0.03.)
Gp- if D is greater than 2 (measure as· a conductance,
C=QGe.).
pCt;
TABLE 2-4
MAXIMUM EXTERNAL DC BRIDGE VOLTAGE AND CURRENT
BRIDGE RANGE E MAX I MAX
TERMINALS
Rs
1100mD
1.4v 7l0ma BIAS
Rs
lID
4.5v 223ma BIAS
Rs
110D
14.2v 7lma
BIAS
Rs
1100D
22v
17.2ma
EXT GEN
Rs
llkD
7lv
17.2 rna
EXT GEN
Rs
110kD
223v
17.2ma
EXT GEN
.R
s
1100kD
400v
17.2ma
EXT GEN
Gp
1000nU 400v
. 17.2ma
EXT GEN
12

c. Set the function switch to !NT AC.
d.
Connect the unknown capacitor to the UN-
KNOWN terminals.
e. If the proper range setting of the FULL SCALE
RANGE is not known, set the concentric CGRL controls
for a reading somewhere near 5000, adjust the DET
SENS control for an upscale meter reading and set the
FULL SCALE RANGE switch for aminimum meter de-
flection.
f. Adjust the concentric CGRL controls and the
DQ control for minimum meter deflection. The DET
SENS control may have to be readjusted to give greater
sensitivity as balance is approached.
g. The capacitance of the unknown is indicated
directly on the counter readout with the correct decimal
point and unit illuminated. The D of the unknown is in-
dicated directly on the illuminated scale on the DQ dial.
The meaning of an X indicator is explained in para-
graph 2.2.
2.4.1.2 Accuracy. The accuracy of the C reading is
±O.I% 'of the reading ±0.005% of full scale (which is
± 1/2 of the last digit) on all but the highest capacitance
range, where the accuracy is ±0.2% of the reading
±0.005% of full scale. On the lowest C range it is nec-
essary to subtract the residual (" zero") capacitance of
the bridge terminals, approximately 0.25 pf, from the
r~ading to determine the correct value of the unknown
capacitor. If external leads are used to connect the un-
known,
this zero capacitance is increased and should be
subtracted from the reading. The error caused by capac-
itance
between the terminals and leads may be removed
by means of a three-terminal shielded capacitance meas-
urement (refer to paragraph 3.2).
The residual resistance and inductance of the
bridge have negligible effect on the Cor D accuracy
except for a slight D error on the highest C range (D
error = 0.006 when Cx= 1000 pf). However, if long
leads are used when measurements are made on large
capacitors, a correction for the lead resistance and in-
ductance may be necessary. The correction terms are
given in Table 2-5.
When
capacitors with high 0' s are measured, an
additional error of ±(0.5%) D2 is added to the specifica-
tion (refer to paragraph 1. 5. 3). This error is negligible
when D is less than 0.2.
2.4.2 l-KC INDUCTANCE MEASUREMENT.
2.4.2.1
Procedure.
a. Set the GEN LEV control fully clockwise.
OPERATING PROCEDURE
Note: For some iron-cored inductors the induc-
tance measured will depend upon the excitation level
(refer to paragraph 2.4.5.4).
b. Set the BRIDGE SELECTOR to:
Ls - if the series inductance is desired and Q is be-
tween 0.5 and 5"0.
Lp - if the parallel inductance is desired and Q is greater
than 1.
(Note: Ls = Lp within 1% if Q )32)
Rs- if Q is less than 0.5 (measure Rs and Q;
Ls= QRs refer to paragraph 2.4.3).
cu
c. Set the function switch to INT AC.
d.
Connect the inductor to be measured to the UN-
KNOWN terminals.
e. If the proper range setting of the FULL SCALE
RANGE is not known, set the concentric CGRL controls
for a reading somewhere near 5000, adjust the DET
SENS control for an upscale reading, and set the FULL
SCALE RANGE switch for aminimum meter deflection.
f. Adjust the concentric CGRL controls and the
OQ control for minimum meter deflection. The DET
SENS control may have to be readjusted to give greater
sensitivity as balance is approached.
g. The inductance of the unknown is indicated
directly on the counter readout with the correct decimal
point and unit illuminated. The Q of the unknown is in-
dicated directly on the illuminated scale of the OQ dial.
The meaning of an X indicator is explained in paragraph
2.2.
2.4.2.2 Accuracy. The accuracy of the L reading is
±O.I% of the reading ±0.005% of full scale (which is
± 1/2 of the last digit) on all but the lowest ranges,
where the accuracy is ±0.2% of the reading ±0.005% of
full scale. When Q is low there is an additional error
of 0.5% d2' which is negligible when Q is approximately
5 or higher.
On the lowest range, the residual inductance of
the binding posts (0.14 /-ih) must be subtracted from the
reading in order to obtain full accuracy. If external
leads are used to connect the unknown inductor to the
bridge, then the residual inductance should be measured
and subtracted from the L reading. To measure this lead
inductance, short the leads together, measure the imped-
ance on the Rs bridge, and calculate Ls= ~s. Be
careful to keep the lead configuration the same for the
residual inductance measurement and the total induc-
tance measurement, since an increase in the area be-
tween the leads would increase the residual inductance.
13

~ __ TY_P_E_l_60_8_-A-,--' M_P_E..:....O_A_N_C_E_B_R_'_O_G_E _
The residual resistance of the bridge is approxi-
mately 0.9.0. This can cause a small Q error when Lx
is small. If long leads are used, the Q error becomes
more important (see Table 2-5). The residual bridge
capacitance of 0.25 pf can cause an L error when Lx is
very large. However, this capacitance is usually neg-
ligible compared with the capacitance of a large induc-
tor. Long leads to the inductor may appreciably change
the total capacitance. The corrections for these lead
effects are given in Table 2-5.
When inductors with low Q's are measured, an ad-
ditional error term of ±0.5% ~ 2 is added to the specifi-
cations (ref er to paragraph 1.5. 3). This error is neglig-
ible when Q is greater than 5.
TABLE 2-5
CORRECTIONS FOR ERRORS CAUSED BY TERMINAL AND LEAD IMPEDANCES
(Add or subtract from the measured value as indicated.)
Measured
Series Resi stance Series Inductance Parallel Capacitance
Ro=0.9 mD t leads
Lo=0.14
J.1.h tleads
Co =0.25 pf t leads
CsNO ERROR
-u.;2LoCx2
-C
o
(1-D
x
2)
D-u.;CxRc -w
2LoCxDx+ D
Co (1 +D2)
ex
Cp
+2R
oDx
u.;C
x2
-w
2Lo
Cx
2(1 - Dx
2)
-Co
D -u.;C
xRo(1 +
D/)
-w
2LoCxDx(1 + Dx
2)
+ Co Dx
Cx
Gp+Gx
2R
o
(1 + Qx
2)+u.;2L 2G
3(1 - ~)
NO ERROR
o x u.;GxLo
Q+QxGxRo(1 -
Qx
2)
+wLoG
x(1 +
Qx
2)-
u.;C
o
Gx
2Qx
Rs
-R
oNO
ERROR
+u.;2C 2R 3(1- -~)
o x u.; CoR
x
Ro
u.;L
Q
QXR
___ 0+
u.; Co Rx(1 + Qx
2)
xRx
1
LsNO
ERROR
-L
o
-w
2CL2(1
--)
o x Qx2
Q2 Ro_ LoQ1
+Q
--
+u.;2C L(Q +-)
x u;L
L x o x x Qx
xx
2Ro1
Lp
+--
-L (1--)
-u.;2CoLx2
Qw
o Qx2
QRoLo1+u;2CoLxQx I
+ - (1 +Q2)
-
CQ
x+
Q}
wL
x
Lx
14

2.4.3 1-KC RESISTANCE AND CONDUCTANCE MEAS-
UREMENTS.
2.4.3.1 Procedure.
a. Set the GEN LEV control fully clockwise.
b. Set the BRIDGE SELECTOR to:
Rs - if series resistance is desired, and the resistance
of the unknown is between 0 and 1 MD or if the unknown
is inductive.
Gp - if parallel conductance is desired, and the conduc-
tance of the unknown is between 0 and 1mho or if the
unknown is capacitive.
(Note: Any resistor small enough to require use
of the Rs bridge because of value will be induc-
tive; likewise, any resistor large enough to re-
quire use of'the Gp bridge will be capacitive.
In the range between 1 .0 and 1 MD the phase of
the resistor will determine which bridge is re-
quired unless Q is small enough to permit use of
either bridge. Rsmay be calculated from Gp, and
vice versa, from the formula Rs= _.-L
1_
(1 +Q2) Gp
c. Set the function switch to INT At.
d. Connect the unknown resistor to the UNKNOWN
terminals.
e. If the proper range setting of the FULL SCALE
RANGE is not known, set the concentric CGRL controls
for a reading somewhere near 5000, adjust the DET
SENS control for an upscale meter reading and set the
FULL SCALE RANGE switch for aminimum meter de-
flection.
f. Adjust the concentric CGRL controls and the
three Q controls for the best minimum meter deflection.
The DET SENS control may have to be readjusted to give
greater sensitivity as balance is approached.
g. The resistance or conductance of the unknown
isindic~ted directly on the counter readou~ with the dec-
imal point and unit illuminated. The Q of the unknown
is read directly on the Q readout. and is inductive or ca-
pacitive as indicated by the lights (unless the Q balance
is less than 0, in which case the opposite is true). Note
the decimal point in the first· (coarsest) adjustm'ent,
which makes major divisions on the vernier dial steps
of 0.001. The meaning of an X indicator is explained
in paragraph 2.2.
2.4.3.2 Accuracy. The accuracy of the R or G reading
is ±0.1% of the reading ±0.005% of full scale (which is
± 1/2 of the last digit) on all but the lowest R and high-
est G ranges where the accuracy is ±0.2% of the reading
±0.005% of full scale.
On the lowest R range the residual resistance of
the bridge (approximating 0.9 mD) should be subtracted
OPERATING PROCEDURE
from the measured resistance. Use short, heavy leads
to connect the unknown resistor, measure the resis-
tance of these leads by connecting the free ends to-
gether, and subtract this value from the measured value.
Residual inductance and capacitance affect only
the Q of the resistor. Corrections for these effects are
given in Table 2-5. When resistors with high Q's are
measured, an additional error term of O.I%Q is added to
the specification (refer to paragraph 1.5. 3). This term
is practically negligible when Q is less th~n 0.2.
2.4.4 MEASUREMENTS USING INTERNAL GENERA-
TOR AT FREQUENCIES OTHER THAN 1KC. If <tn os-
cillator-detector tuning unit other than the l-kc unit
usually supplied is· used, the operating procedure is the
same as for l-kc measurements, but the accuracy speci~
fications and D and Q ranges are the same as those for
an external generator at the same frequency (refer to
Section 2.5). The plug-in unit gives the DQ multiplier
required for the various bridges so that it does not have
to be calculated (refer to paragraph 2.5.1).
2.4.5 NOTES ON AC MEASUREMENTS.
2.4.5.1 Capacitance to Ground. The Type 1608-A Im-
pedance Bridge generally measures "ungrounded" com-
ponents, since neither UNKNOWN terminal is connected
directly to the panel, which should be grounded except
for measurements on grounded components (refer to· para-
graph 3.5). Capacitance from the LOW UNKNOWN ter-
minal is placed directly across the detector (see Figure
2-3) and does not cause an error, but can, if large
enough, cause a reduction in sensitivity. Capacitance
from the other UNKNOWN terminals shunts an arm of the
bridge and therefore causes an error which can be signi-
ficant if the stray capacitance is large enough. Table
2-6 gives the error caused by a stray capacitance for
each quantity measured.
Note that for the capacitance bridges stray capa-
citance causes a small capacitance error. Since Ct is
0.15 Ilf, it takes a stray capacitance of 150 pf to cause
D
Figure 2-3. Capacitance and inductance
bridge diagrams, showing capacitances
to ground.
15