ESI 250DE User manual

BRIDGES
AND
@
e|sii,
—
Electro Scientific industries
13900 N.W, SCIENCE PARK DRIVE + PORTLAND, OREGON 97229 APRIL 1967
REPLACES JUNE 1966
MODEL
250DE
ithactim Monual
UNIVERSAL
IMPEDANCE BRIDGE
AC | INT ‘DC EXT
1 o GEN GEN | IkHs
\
BAT
TEST)
GEN DET
IMPEDANCE BRIDGE 250DE
wow FO SC ems oe '
AMD O@lcan vasa
SERIAL NUMBER:
PART NUMBER: 13202
Ohoaye ght 1966 1967 Electra Se eatte Inducer pe

The following table lists the most recent revision of each page at the
present printing:
PAGES DATE
Title 4/67
A 4/67
i and ii 6/66
1-1 6/66
1-2 4/67
1-3 6/66
2-1 thru 2-3 6/66
3-1 thru 3-5 6/66
4-] thru 4-5 6/66
4-6 4/67
4-7 thru 4-10 6/66
5-1 thru 5-12 6/66
6-1 thru 6=7 6/66
7-0 thru 7-2 4/67
A
eisii
250DE
4/67

Vv,
IV,
TABLE OF CONTENTS
. INTRODUCTION
1.1 DESCRIPTION
1.2 SPECIFICATIONS
OPERATION
2.1 CONTROLS
2.2 CONNECTIONS
2.3 BASIC OPERATION
RESISTANCE MEASUREMENT
3.1 DC RESISTANCE MEASUREMENT
3.2 AC RESISTANCE MEASUREMENT
3.3 NOTES ON RESISTANCE MEASUREMENT
3.3.1 Low Resistance
3.3.2 High Resistance
>
PACITANCE MEASUREMENT
NORMAL CAPACITANCE MEASUREMENT
CAPACITANCE MEASUREMENT WITH EXTENDED D RANGE
CAPACITANCE MEASUREMENT USING DC BIAS
4.3.1 DC Bias Supply
4.3.2 Operating Procedure
VOLTAGE ACROSS UNKNOWN CAPACITOR
NOTES ON CAPACITANCE MEASUREMENT
4.5.1 Series and Parallel Capacitance
4.5.2 Low Capacitance Measurements
4.5.3 High Capacitance Measurements
INDUCTION MEASUREMENT
5.1 NORMAL INDUCTANCE MEASUREMENTS
5.2 INDUCTANCE MEASUREMENT WITH EXTENDED Q RANGE
5.2.1 Preliminary Procedure
5.2.2 Parallel Inductance
5.2.3 Series Inductance
5.3. INDUCTANCE MEASUREMENT USING DC
5.3.1 DC Supply
5.3.2 Operating Procedure
VOLTAGE AND CURRENT IN UNKNOWN INDUCTOR
5.4.1 Voltage
5.4.2 Current
5.5
Cc
4
A
4
WOnNn-
ha
ie
5.4
OTES ON INDUCTANCE MEASUREMENT
5.1 Series and Parallel Inductance
§.5,.2 Low-Jnductance Measurements
5.5.3 High-Inductance Measurements
5.5
USEFUL MEASUREMENT TECHNIQUES
6.1 EXTERNAL DETECTOR
6.2 EXTERNAL DC GENERATOR
6.3 EXTERNAL AC GENERATOR

6.4 OPERATION AT FREQUENCIES OTHER THAN ONE KILOHERTZ
6.4.1 D and Q Corrections
6.4.2 Accuracy
6.5 SLIDING BALANCE
6.6 EXTEND LEADS WITH AC MEASUREMENTS
VII. REPLACEMENT PARTS
The following are registered trademarks of Electro Scientific Industries, Inc.:
ESI® Electro Scientific Industries, Inc.
ESIAC® Algebraic Computer
ESIPOT® Potentiometer
DEKABOX® Decade Resistors and Capacitors
DEKABRIDGE® Bridge Circuit
DEKADIAL® Decade Dials
DEKAMATIC® Automatic Unit
DEKAPOT® Decade Potentiometers
DEKASTAT® Decade Rheostat
DEKAPACITOR® Decade Capacitor
DEKAVIDER® Decade Voltage Divider
KELVIN KLIPS® Four-terminaf Clips
KELVIN KLAMPS® Four-terminal Clamps
PORTAMETRIC® Portable Measuring Instrument
PYB® Potentiometric Voltmeter Bridge
Application for registration has been filed for the following:
DEKATRAN Decade Transformer
ii
elsii 250DE 6/66

SECTION I
INTRODUCTION
1.1 DESCRIPTION
The esi® Model 250DE Impedance Bridge is an instrument that measures resistance, inductance,
capacitance, and the dissipation factor (D) and the storage factor (Q) of inductorsand capacitors.
The instrument is battery operated and completely portable. An internal generator supplies ac
and dc, and an internal solid-state ac-de detector indicates bridge balance.
Figure 1-1 is a simplified schematic diagram of the instrument in each of the four modes of
operation: resistance, capacitance, and series and parallel inductance.
R
UNK'
RESISTOR
UNKNOWN
CAPACITOR
Viv
SERIES
%
§
oO
3
2
pom
3?
oo
RESISTOR
LR DEKASTAT®
DECACE BHEQSIAT
L-R-C DEKASTAT®
DECADE SHEGSTAT
ond bia ete othis eee —
STANDARD
CAPACITOR va
G RHEOSTAT
o—_tiah
Figure 1-1. Simplified Schematic Diagrams
b-R-C DEKASTAT®
DECADE Ret OStAT
U-R-C OEKASTAT®
DECADE
AHEOSTAT
Q
RHEOSTAT
©

1.2 SPECIFICATIONS
Detector: A solid-state ac-dc-amplifier null detector
AC Characteristics:
Input Impedance: Approximately 1MQ
Sensitivity: Continuously variable, 10 V minimum detectable signal
Frequency: 1kHz (kilocycle)
DC Characteristics:
Input Resistance: Approximately 1MQ
Sensitivity: Continuously variable to 1 millivolt full scale, 20 microvolts
minimum detectable signal.
Generator: A solid state ac generator with transformer output and diode rectifiers
rdc.
AC Characteristics:
Open-Circuit Voltage: 2V rms
Short-Circuit Current: 70 mA
DC Characteristics:
Open-Circuit Voltage: 3V
Short-Circuit Current: 40 mA
Supply Power: Four 1.5-volt size D cells
Battery Life: Approximately 500 hours
FUNCTION RANGES ACCURACY
MAGNITUDE D0 ORQ RANGES MAGNITUDE oona
Resistance G@t2 Main eight ‘RUSE
tangea, 0 1 mO per eight
dal division on ranges 01% + 1 dial division
lowest R range
Inductance 0-1200 H tn seven Q=—0to105 014
(Series) ranges O1uH per per dial division
dial division on
@
03% +1
ox
{ division | 0.040 (1 + Q*)
Highest
+4
1/Q
+
0020
dial
eX
lowest L range Other 03% + 1 deal division | 0.005 (t + Q2)
five + 05% * 1/0 +0020
93% +1 set division | 0 040 (1 + QO)
Lowest | "4 '40% x 1/0 0020
Inductance -1200 H in seven Q = 10 to 1000, Highest 03% +1d eet giviaton 0640 (1 + D%
(Parallei) ranges O1uH per scale reads @ dial 9 + 40% x + 0020
dial diviston on 1g hinear in 1/Q
towest L range Other 03% + 1 dial division | 0005 (1 | 0D}
five + 05% x 1/0 + 0020
0.3% + 1 dial division | 0040 (1 + D3}
Lowest + 40% x 1/0 + 0020
Capacitance 0-1200.F inseven O-= 610105 in two Highest 02% + 1dial division | 0040 (1 + DB?)
(Serves) canges O1pF per ranges, 0 004 per a + 40% x0 +0 02D
dial divigion on dial division on
towes! C range lowest D range Other 02% + 1 dial division |0005(1 | D?}
five +05% xD + 0020
02% + 1 dial division | 0040 (1 + Dy
howest |“ "+ 40% x 6 + 902D
els|i 250DE 4/67

R
ACCURACY
CANO
C
ACCURACY
mh ft at n* NH Pa)
UNKNOWN RESISTANCE UNKNOWN CAPACITANCE OR INDUC TANCE
The specified accuracy for measurements of resistors, Low-loss inductors and capacitors.
ol
The specified accuracy for
measurements of D and Q,
9.01
ooo
D
(OR
Q}
ACCURACY
IN
0
{OR
Q)
UNITS
°
o 106
0 {OR Q} Q CIAL READING
The accuracy of inductance and capacitance
measurements is influenced by the D and Q
value. This curve shows the accuracy to be
expected at various D and Q values.
2
L
AND
C
ACCURACY
Figure 1-2.

SECTION il
OPERATION
The controls and connections necessary to operate the Model 250DE Impedance Bridge are shown
in Figure 2-1,
oo oO
1 GEN 2 1 MAS 2
AC DET
IAC EXT] INT
GEN | thHs
GEN ORT DET Gain
IMPEDANCE BRIDGE 250DE
creo siti a6 6 ero
POCIyaAmMO GriGon
Figure 2-1. Mode! 250DE Panel View
2.1 CONTROLS
FUNCTION switch selects the type of bridge circuit that will measure resistance, capacitance,
or inductance.
RANGE switch selects the multiplier for each function.
L-R-C decade dials are a DEKASTAT® Decade Resistor that is the main balancing element of the
bridge, The setting of the dials after the bridge is balanced indicates the value of the inductance,
resistance, or capacitance,
D-Q dial is used to balance the phase of the capacitance or inductance bridge, The setting of
the dial ye the bridge is balanced indicates the value of dissipation factor (D) or storage
factor (Q),

GEN-DET switch selects bridge generator and detector connections, ac or dc, intemal orexternal
generator, The switch also connects the internal batteries to the battery test circuit,
DET GAIN control adjusts the sensitivity of the ac-dc detector and turns on power to the generator.
2.2 CONNECTIONS
R, L, and C terminals 1, 2, and 3 are used to connect unknown resistors, inductors, and
capacitors to the bridge. Resistors and inductors are connected between terminals 1 and 2,
capacitors between terminals 2 and 3,
EXT BIAS terminals are normally connected with a shorting lug. They allow insertion of a de
voltage or current to bias capacitors or inductors.
EXT GEN terminals provide a connecfion to the bridge for an external generator. When the
GEN-DET switch is in the EXT AC GEN position, the terminals connect to an isolation transformer
so that a grounded external generator can be used. When the GEN-DET switch is in the EXT DC
GEN position, the terminals connect directly to the bridge.
EXT D-Q terminals are normally connected with a shorting lug. They allow an external rheostat
to extend the range of the D-Q dial,
EXT DET connector is a BNC coaxial socket that allows an external detector to be used with the
instrument. It is connected to the bridge at all times,
2.3 BASIC OPERATION
Simple operating instructions are inside the instrument lid, Figure 2-2 is a reproduction of these
instructions.
2-2
elslii 250DE 4/44
_

-~-NX een oh
i a
OC
RESISTANCE
MEASUREMENTS
Torn
O£T
GAIN
control
to
2
Set
FUNCTION
switch
90
Ral
of
Bx
tO.
Set
L-R-C
decade
dials
be
3.000.
Conne<i
the
uninewn
roaistor
to
R-k
terminols
t
ond
2
Set
GEN-O8T
ewitch
te
INT
OC
Adjwst
RANGE
switch
fer
mininum
datecter
deflection
Adjver
u
fd
decode
diets
ter
et
turning
DET
GAIN
conrad
|.
The
measvred
resistence
is
the
seamen
of
the
‘ba
-C
decade
dial
setting
times
the
RANGE
ond
FUNCTION
awiith
settings
CAPACITANCE
MEASUREMENTS
Turn
DET
GAIN
contre!
to
|
Set
FUNCTION
switch
ts
C,
0x0.)
of
Ox
O.00
SERIES
Set
L-R-C
decode
diats
te
3.000 ond
D-Q
dial
te
O
Connect
the
unknown
capaciter
te
C
herminats
2
and
3
Set
GEN-DET
awitch
to
INT
|
hits,
.
Adjest
RANGE
SWITCH
for
minke
dafecter
deflection
Adjwat
1-R-€
decade
dialt
ord
D-Q
dial
alternately
for
minimum
moter
deilecthen,
tuning
OT
GAIN
contre)
clockwise
te
Increase
sensitivity
an
nacessory
Tha
measured
capacitance
jn
the
product
of
the
L-R-C
darede
dial
setting
The
measured
distipation
facter
1D}
ip
the
product
of
the
D-Q
setting
times
Phe
FUNCTION
SWITCH
setting
INDUCTANCE
MEASUREMENTS
Tem
O€T
GAIN
central
te
}
Set
FUNCTION
switch
te
L
PARALLEL
HO
is
grecter
then
30,
te
L
SERIES
of
©
ie
tose
then
10.
Ser
L-8-€
decade
dinkt
te
3.000
und
0-Q
dial
te
maximum
Connec!
the
unknown
inducter
te
8-L
terminets
|
and
2
Set
GEN-OET
switch
te
INT
1
hid.
Adpest
RANGE
twitch
Fer
minimern
detector
detiecion
Adjvit
L-R-C
decade
diels
ond
D-0
die)
oltemetely
far
minl-
mum
meter
deflection,
twrnng
DET
GAIN
contral
clechwite
te
merease
sensitivity
oe:
necessary
The
moweurad
Inductance
la
the
product
wf
the
L-9-C
decode
dial
setting
Himes
the
RANGE
ewitch
setting
The
messured
steroge
focter
{Q)
ja
read
directiy
from
the
0-G
dial,
Inner
sale
fer
parallel
end
evter
wale
fer
sarias
in-
ductence
A
RUMSTON
L.R-¢
xO
oettiferee’
ah
OECADE
RHEOSTAI
fo
STANDARD
RESISTOR
STANDARO
CAPACHOR
9
%
t-@-¢
Nie
DECADE
GHEOSTAT
Figure
BATTERY
REPLACEMENT
Check
the
battery
befure
each
day's
seperation
Turn
DET
GAIN
central
te
?
and
set
GEN-DET
switch
be
BAT
TEST
ff
the
meter
deliects
beyend
the
BAT
OK
merk,
the
bottery
1s
goed.
Tha
bettery
consists
of
four
|
S-velt
D
cella
Ta
change
battery,
remeve
cover
from
battery
cempartment
using
a
serowdriver
Replece
celle
os
shown
In
Hlytteotion
L
a
UNKNOWN
INDUCTOR
PARALLEL
wa
STANDARD
Carhacitoe
Q
RHEOSTAT
tas
15
9200
2-2.
Operating
Instructions
oie?
L-A-€
pexastat®
©
*
OECADE
RHEOSTAT
we
CAPACITOR
a
ee
©
RMeOstAt
of
104
»
5@20

SECTION Ill
RESISTANCE MEASUREMENT
Resistance is usually measured with direct current for maximum accuracy, The Model! 250DE
Impedance Bridge can be used to measure resistance with alternating current, but external
reactance compensation is usually required,
UNKNOWN RESISTOR
R iia ESISTOR
i G2 o 4 9
9
STANDARD
oS > RESISTOR
L-R-C DEKASTAT®
DECADE RHECSTAT
Cibo
ir | TYPMPEDAMCE peiogt 259k
mete
Figure 3-1, DC Resistance Measurement
3.1 DOC RESISTANCE MEASUREMENT
1. Turn DET GAIN contro} to 2. This turns on all power to the instrument.
2. Set GEN-DET switch to INT DC, If an external detector or generator is
required, see paragraph 6.1 or 6.2,
3. Set FUNCTION switch to R X 1 Use the R X 10 position for resistors between
orR x 10, 1.2 and 12 megohms,
4, Set L-R-C decade dials to 3,000, This makes it easier to find the correct range,
5. Connect the unknown resistor to Make good contact with the terminals,
R-L terminals 1 and 2,
6. Adjust RANGE switch forminimum This sets the range so that the value can be
detector deflection, found with maximum resolution on the
L-R-C dials.

Adjust L-R-C decade dials for null.
Read the measured resistance as
the product of L-R-C dial setting
times RANGE and FUNCTION
switch settings.
Disconnect the unknown resistor
and turn DET GAIN control to
PWR OFF before !eaving the
instrument,
elsli
Each time the detector indication approaches
zero, turn the DET GAIN control clockwise
to increase sensitivity,
If L-R-C dial reading is less than 1,200,
turn RANGE switch one step counterclock-
wise and repeat step 7 in order to take full
advantage of the resolution.
3-2
250DE 6/66

3.2 AC RESISTANCE MEASUREMENT
For greatest accuracy, resistors should be measured with dc, The accuracy of ac resistance
measurements made with the Model 250DE Impedance Bridge is 0.3% for resistors of low reactance
with resistance between 1 ohm and 1 kilohm.
The capacitor and potentiometer shown connected in Figure 3-2 compensate for series inductance
or parallel capacitance. It is impossible to separate the correction for the unknown resistance
from the correction for the rest of the bridge circuit,
{oO 59
L-R DEKASTAT®
OFCADE QHEQSTAT
5002
I
LOW.-LOSS
CAPACITOR
LINEAR
POTENTIOMETER
UNKNOWN
RESISTOR
IOOOpF
uy IMPTDASCE BOIRGE | 156K
Figure 3-2. AC Resistance Measurement
1. Turn DET GAIN control to 1.
2. Set FUNCTION switch to R X 1
or R x 10,
Set L-R-C decade dials to 3,000,
4. Connect the unknown resistor to
R=L terminals 1 and 2,
Set GEN-DET switch to INT IkHz.
This turns on all power fo the instrument.
Use the R X 10 position for resistors between
1,2 and 12 megohms.,
This makes it easier to find the correct range,
Make good contact with the terminals.
If an external ac detector or generator is
required, see paragraph 6.1 or 6.3.

10;
Ws
Adjust RANGE switch for minimum
detector deflection.
Try to balance bridge by adjusting
L-R-C dials.
If a null cannot be reached,
connect potentiometer and
capacitor to the terminals as
shown in Figure 3-2.
Balance the bridge by adjusting
L-R-C decade dials and external
potentiometer alternately.
Read measured resistance as the
product of L=-R-C dials times
RANGE and FUNCTION switch
settings.
Disconnect the unknown resistor
and turn DET GAIN control to
PWR OFF before leaving the
instrument.
elsii
3-4
Turn DET GAIN control clockwise to increase
sensitivity if necessary. If no range gives
noticeably fess deflection than any othery,
try measuring resistance on de for a first
approximation of the range.
The null indication on the meter may not be
very sharp, which indicates that there is an
uncompensated phase shift.
Be sure to use a low-loss capacitor; air and
polyethylene dielectrics are sufficient.
A higher value capacitor may be necessary
to compensate for phase shift when measuring
resistors that have large reactive components.
The measured resistance is correct for an
equivalent circuit consisting of a resistor
and a capacitor in parallel or a resistor and
and inductor in series,
250DE 6/66

3.3 NOTES ON RESISTANCE MEASUREMENT
3.3.1 Low Resistance
On the low resistance ranges, the lead resistance becomes significant. A procedure to
correct for the lead resistance by finding its value and subtracting it from the measured
resistance is:
1.
2.
3.
4,
Short the test leads together at the point at which they are to be connected
to the unknown resistor,
Measure the resistance of the leads. There is no loss of accuracy if the
resistance of the leads is measured on the same range that the unknown
resistor will be measured on,
Connect the leads to the unknown resistor and measure the resistance,
Subtract the lead resistance (step 2) from the measured resistance (step 3).
3532 High Resistance
On the high resistance ranges, take care to avoid leakage across a resistor under test,
Insulation with a resistance of 109 ohms, which is adequate for most purposes, will cause
a measurement error of 1% if it shunts a 10-megohm resistor.

SECTION IV
CAPACITANCE MEASUREMENT
The Mode! 250DE Impedance Bridge measures capacitance in terms of a two-element equivalent
circuit consisting of a capacitor in series with a resistor. The internal ac generator and detector
of the Model 250DE bridge are tuned to 1 kilohertz (kilocycle), Other frequencies can be used
but an external generator and detector are required. (See paragraph 6.4).
UNKNOWN CAPACITOR
Cc UN' CAPACITOR
SERIES qi bw
2.
¢
CaF
ores
L-R-C DEKASTAT®
DECADE AMEOSTAT
m iyytmrteae Cl beGE tSt0E
Figure 4-1, Capacitance Measurement
4,1 NORMAL CAPACITANCE MEASUREMENT
1, Turn DET GAIN control to 1, This turns on all power to the instrument,
2. Set FUNCTION switch to C, This is the preferred D range for a prelim-
D x 0.1 SERIES. inary balance
3. Set L-R-C decade dials to 3,000 These settings make it easier to find the
and D-Q dial to 0. correct C range,
4. Connect the unknown capacitor Make good contact with the terminals.
to C terminals 2 and 3.
5. Set GEN-DET switch to INT If an external ac detector or generator is
1 kHz. required, see paragraph 6,1 or 6,3,

10,
Us
Adjust RANGE switch forminimum
detector deflection.
Adjust L-R-C decade dials and
D-Q dial alternately for minimum
meter deflection.
If D-Q dial setting is less than 1,
set FUNCTION switch to D x 0,01,
Read measured capacitance as the
product of L-R-C dial setting times
RANGE switch setting.
Read the measured dissipation factor
(D) as the product of D-Q dial
setting times FUNCTION switch
setting.
Disconnect the unknown capacitor
and turn DET GAIN control to
PWR OFF before leaving the
instrument,
4-2
Turn DET GAIN control clockwise to increase
the sensitivity if necessary .
As the null is approached, turn the DET
GAIN control clockwise to increase
sensitivity.
If there is some difficulty in balancing the
bridge, especially if the D is greater than 1,
it may be due to a sliding balance. See
paragraph 6.5.
If L-R-C dial reading is less than 1.200,
turn RANGE SWITCH one step clockwise
and repeat steps 7 and 8 in order to take full
advantage of the bridge resolution.
If the frequency is other than 1 kilohertz
(kilocycle) see paragraph 6.4,
els|i 250DE 6/66

4.2 CAPACITANCE MEASUREMENT WITH EXTENDED D RANGE
The D and @ ranges of the bridge can be extended by use of an external rheostat connected to
terminals provided. Figure 4-2 shows the ranges for which this technique is advisable.
STORAGE FACTOR (Q)
i00.)=— «1000 10,000 0.0l 0.1 1
{OkHz
>
W
Z kHz
Lu
=>
o 0.1 kHz
os
LL
0.01 kHz
100 1d I
0.01 0.001 0,000!
DISSIPATION FACTOR {D)
Figure 4-2. Dand Q Range
1. Remove shorting lug from between
EXT D-Q binding posts.
2, Connect an external rheostat
between EXT D-Q binding posts.
3. Balance the bridge using external
rheostat and D-Q dial.
4, Calculate D
D= f, 0.628 8 + Dasa)
The lug may be pivoted to one side,
See Figure 4-3,
The measured capacitance is the product of
the L-R-C dial setting times the setting of
the RANGE switch,
D is the dissipation factor
FL is the frequency in kilohertz (kilocycles}
Ry is the resistance of the external D
rheostat in kilohms,
D is the D-Q dial reading.
dial
fi. = 1 if the internal generator and detector
are used,

EXTERNAL RHEOSTAT
ey
UNKNOWN CAPACITOR
SERIES re
j oO ‘oO UNKNOWN
cl A Cc CAPACITOR
RANGE
RESISTOR
se
CAPACITOR
DETECTOR
D RHEOSTAT
Lyé]
L-R- ofKasTAT®
DECADE RHEOSTAT
[ T)IMPEGANCE BRIDGE = ESDOE
Figure 4-3, External D Rheostat
4-4
esli 250DE 6/66

4,3 CAPACITANCE MEASUREMENT USING DC BIAS
Some capacitors need a polarizing voltage. Electrolytic and tantalum capacitors, for example,
may give erroneous readings unless they are biased to prevent polarity reversal during test. Many
electrolytic and tantalum capacitors can be damaged by the reverse half=cycle of an alternating
current, although not generally by a low voltage level such as used in the Model 250DE
Impedance Bridge.
4.3.1 DC Bias Supply
The de bias should be supplied from o power-limited source in order to prevent damage to
the bridge in case the unknown capacitor terminals are shorted, The de supply circuit is
shown in Figure 4~4,
SUPPLY LIMITING VOLTAGE
VOLTAGE RESISTOR | CONTROL
E Ry Rp
(VOLTS} {OHMS} {OHMS)
] 0,27 2
O O 1.5 0.56 5
BYPASS CAPACITOR 2 V.0 10
boy 3 2.7 25
1€ 4 4:7 40
1SuF 4.5 5.6 50
VOLTAGE CONTROL & 10 100
Rp 9 22 250
12 39 400
LIMIT RESISTOR 15 56 500
Rh 22.5 150 1.5k
p——4 [1 24 150 1.5k
BATTERY E . han 28 220 2.5k
VP- 30 270 2.5k
45 560 3.0k
67.5 1.2k 10k
90 2.2k 20k
103.5 2.7k 30k
120 3.9k 50k
225 13k 100k
300 27k 250k
Figure 4-4. DC Bias Supply Circuit
The power in the circuit shown is limited to 1 watt by resistor R,- Values shown are for commonly
available voltages. The limiting resistors can have tolerances of 20% and should be rated at 5
watts or more. If the proper value of resistance is not available, use a larger value rather than
smaller. The voltage control potentiometer may differ from the listed value by a factor of 2. It
should be rated ot | waft or more.