Keithley 2441, 244 Service manual
INSTRUCTION MANUAL
Model 244
High Voltage Supply
(and Model 2441 Overload Protection Option)
@COPYRIGHT 1976, KEITHLEY INSTRUMENTS, INC.
FOURTH PRINTING, DEC. 1977, CLEVELAND, OHIO, U.S.A.
MODEL 244
CONTENTS
CONTENTS
SWtiO”
SPECIFIC.4TIONS
....................................
1. GENERAL DESCRIPTION.
2.
OPERATION.
....................................
3. CIRCUIT DESCRIPTION.
4. ACCESSORIES
5. REPLACEABLE PARTS.
6. CALIBRATION
SCHEMATICS
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ILLUSTRATIONS
Page
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8
13
19
25
Figure NO.
1
2 FrOnL Panel Controls.
Title
Model 244 High Volt+ Supply
..........................
3 Rear Panel Controls ...........................
4 current Limiting. ............................
5 Simplified Circuit Diagram.
6
7
8 Top Cover Assembly.
9
10
11
Overload Protection Cmmectio,, Diagram.
Overload Protection Circuit Diagram
...........................
Bottom cover Assembly
..........................
Circuit for Laad BDX LB-1
Circuit for Divider ""-1.
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Page
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3
3
5
6
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11
15
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1176
SI?ECIFICATIONS
MODEL 244 HIGH VOLTAGE SUPPLY
SPECIFICATIONS
OUTPUT :
Voltage:
-200 to -2200 volts in ZO-volt steps
current: 10 milliamperes maximum
Polarity: Negative with respect Lo chassis
ACCWACY: il% of dial setting
RESOLUTION: A O-25 volt "Trim" porentiameter permits interpolation be-
tween steps with a resolution of better than 100 millivalts.
STABILITY: ~0.005% per hour after a two-hour warm-up; +o.Ol% the first
hour or in subsequent S-hour periods after a one-hour warm-up.
LINE KECULATION: +O.OOl% for a 10% change in line voltage.
LOh" REGULATION: ,O.OOl% for a 5-milliampere load change.
RIPPLE AN" NOISE: Less than 0.5 milli"olt rms above 5 Hz.
OVERLOAD: Electronic current limiting with automatic recovery.
METER:
Provides check on OUtpUt voltage.
CONNECTOKS: Output (on rear) MHV series (UC-931/U)
POWER :
105-125 or 210.250 volts (switch-selected); 50-60 Hz; 90 watts.
OIMENSlONS: b-114" high x S-718" wide x l&7/8" deep (158 x 225 x 378 mm)
WEIGHT: net weight, 13 pounds (6,O kg).
ACCESSORIES FURNISMED: Mating Connector (MHV series, UC-932A/U)
iv
1176
MODEL 244 HIGH VOLTAGE SUPPLY
GENERAL DESCRIPTlON
SECTION I.
l-l.
GENERAL.
high-voltage supply that provides accurate, stable
outpote from -200 to -2200 volts d-c at up to 10 ,,$.
"l~Xi"l"Ul.
1-2. FEATURES.
a. In-line Calibrated Dials.- Two dials set the
output voltage in 200 and ZO-volt steps. Trim Control
permits interpolation between ZO-volt setting, with
100 millivolt resolution.
b. Overload Protection.- Repeated or continuous
overloads will not damage the instr,m,ent.
circuit limits the oucput current to less than 13
milliamperes with automatic recovery when overload is
removed.
c. Stability.- Solid-state design, stable range
The Model 244 is a negative-polarity
Protection
GENERAL DESCRIPTION
resistors, and selected zener diode provide voltage
stability of +0.005% for B-hour periods after onehour warm-up.
d. Model 2441 Overload Protection Option.- A,,
optional protection circuit is available (on special
order) which can be used to limit the current of the
Model 244 when monitored by e Keithley picoammeter
such es the Model 414A.
1-3. APPLICATIONS.
a. The Model 244 has bee,, designed primarily for
negative-polarity high voltage biasing for photomultiplier applications.
b. The stability, regulation and low noise also
make it suitable for use with photocells, ion chambers
and resietiviey measurements.
0870
1
GENERAL DESCRIPTION
MODEL 244 HIGH VOLTAGE SUPPLY
TABLE 1-l.
Front Panel Controls.
COntrOl
OWER Switch (S102)
Controls the a-c line power to all circuits.
Functional Description
OWER ON indicator (mlol) Pilot light glows orange when Power Switch is ON.
UTPUT Switch (5101)
oltwe Dials (s103, s104)
rim Control (R146)
Controls the a-c power to the high voltage section. 2-2g
sets oueput voltage from -200 to -2ml volts.
Permits interpolation between steps with O-25 volts maximum trim.
VBRLOAD Indicator Pilot light glows when output current exceeds 11 I&. approximately.
,eter (MlOl)
Indicates the magnitude of selected voltage.
Paragraph
2-2e
z-2f
2-b
2-a
2-3~
2-3a
Control
OUTPUT Receptacle
117V/234V
Switch (5103)
(5101)
Fuse (FlOl)
Overload Input (Cover)
2
Rear Panel
TABLE 1-2.
Connections.
Functional Description
VOl tage o"tp"t
Sets instrument far either 117 or 234 " a-c power.
117" operation: 3/4A, slow-blow.
234
Operatim: 3/&I, slow-blow.
Cover plate for optional Model 2441 installation.
Paragraph
2-la
Z-lb
2-k
2-k
0770
0”tpllt
Selector
Switch
(SlO3)
output
Selector
switch
(X04)
(MlOl)
FIGURE 2. Front Panel Controls.
Switch indicator Indicator
(SlOl) (DS102)
(OSlOl)
Switch
(5102)
0770
117/234V
Switch
(5103)
F"LTC5
(FlOl)
z.rnrmm I) "_^_ n--.7 "~~~-.-_,~
(COWS)
Overload
Input
Receptacle
OUTPUT
(J")l)
3
OPERATION
MODEL 244 HIGH VOLTAGE SUPPLY
SECTION 2.
2-1. CONNECTIONS.
a. Output Receptacle.- A rear panel mounted MHV
teflon-insulated receptacle provides connection to
the load circuit. The outer shell of the receptacle
is connected to chassis.
b. Coaxial Cables.- Use coaxial cables which are
rated for greater than 2200 volts for safe operation.
Coaxial cables provide best noise immunity for critical meaeurements.
C. Earth Ground.- For maximum operator safety use
the 3-wire power cord with third wire solidly connected to earth ground.
PRELIMINARY PROCEDURES.
2-2.
a. The instrument is shipped in operating condition
+ith all components installed for immediate use.
Set the 117-234 volt switch for operating line
b.
voltage.
C. Check the fuse for proper type and rating.
d. Provide adequate ventilation for the instrument.
Air flow should be maintained along the top and bottom
surfaces.
OPERATION
OPERATING CHECK-OUT.
2-3.
a. Meter Indication.- When the OUTPUT Switch is ON
the meter should indicate the dialed voltage.
b. Output Voltage.- Connect an accurate voltmeter
such as Keithley Model 153 to the output to verify
the power supply voltage accuracy. The Trim Control
should be set to CAL position.
output for dial settings of 200,,,500, and 1000 volts.
Accuracy should be 21% of dial setting.
c. Current Limit.- (Refer also to paragraph 2-5
for a more complete discussion of the overload current
operation.)
1. Connect an accurate ammeter such as a Keithley Model 153 in series with an adjustable resistance decade box.
Model 244 at -200 volts with the OUTPUT Switch
"OFF".
decade box set at 20 kilahms. The ammeter should
indicate 10 mA when the OUTPUT Switch is placed
nON"
Decrease the resistance load until the OVERLOAD Indicator is lighted.
between 11 mA and 12 n!A.
Apply the -200 volt output to the resistance
.
The OVERLOAD Indicator should not be lighted.
Set the dialed voltage on the
The annneter should indicate
measure the Model 244
NOTE
If air flow is constricted the internal
temperature will rise above normal design
limits causing degradation of critical
components.
e. Set the front panel controls as follows:
POWER Switch
Voltage Dials
OUTPUT Switch
f. Connect the line cord and set the POWER
Switch to ON. (The POWER indicator should
be lighted.)
NOTE
The meter should indicate 0 KILOVOLTS.
g. After a preliminary one minute warmup period,
p&ace the OUTPUT Switch to ON position. Allow another
warmup period (30 minutes) for the high voltage sec-
tion to stabilize.
imately one minor division or 200 volts.
The meter should indicate approx-
Off
2-o-o
Off
NOTE
Resistor load power dissipation is approx-
imately 2.2 Watts.
2. Connect an ammeter and 50 kilohm resistive
load to the output of the Model 244. Set the dialed voltage an the Model 244 at -200 volts with the
OUTPUT Switch "OFF".
"ON" position. Reduce the load to zero ohms (short
circuit) and measure the output current. The
ammeter should indicate less than 14 milliamperes
with the Model 244 OVERLOAD Indicator lighted.
SETTING OUTPUT VOLTAGE. The setting of the
2-4.
Voltage Dials and Trim Control determines the magni-
tude of the output.
a. The two Voltage Diala set the output from -200
to -2200 volts d-c in calibrated 200 and 20-volt
steps. With the Trim Control in CAL position the
output is set by the Voltage Dials within specified
kXC"K%Y.
b. The Trim Control interpolates between 20-volt
settings with 100 millivolt resolution. The Trim
Control range is 0 to 25 volts.
Place the OUTPUT Switch to
4
0770
MODEL 244 HIGH VOLTAGE SUPPLY
OPERATION
2-5. OVERLOAD PROTECTION.
a. The Model 244 has an overload current limiting
circuit which limits the output short-circuit current
to a maximum 14 milliamperes. The circuit is adjusted
so that the OVEKLOAD Indicator will be lighted when
the output current exceeds 11 milliamperes. When the
overload is removed the Model 244 will automatically
reset to normal operation and the OVERLOAD Indicator
will turn off.
b. Current Limiting Characteristic.- The Model 244
current limiting is shown graphically by the typical
V-I characteristic curves in Figure 4. The OVERLOAD
Indicator is factory-adjusted to turn on at approxi-
mately 11 milliamperes. However the output voltage
remains constant for current exceeding 11 milliamperes
as shown.
The current limiting occurs typically from
11.3 to 12.2 milliamperes depending on the dialed
voltage.
c. Model 2441 Overload Protection Option.- An
optional protection circuit is available which can
bz used to limit the current of the Model 244 when
w>nitored by a Keithley picoammeter such as the
I!zrdel 414A. Consult your Keithley representative or
t:,e Sales Service Department for further information
regarding the Model 2441 Option.
2-6.
CAPACITIVE La4ix.
a. When a capacitive load is connected to the output, Model 244 will deliver a charging current up to
14 milliamperes maximum until the dialed voltage is
developed across the load. During the charging time
the OVERLOAD Indicator will be lighted as long as the
output current exceeds 11 milliamperes. The OVERLOAD
Indicator will turn off automatically when the charging current is reduced to less than 11 milliamperes.
b.
Before reducing the dialed voltage with large
capacitive loads (exceeding 1 joule of energy), set
the OUTPUT Switch to “OFF”. Readjust the dialed
voltage and set the OUTPUT Switch to “ON”.
NOTE
A resonant condition (with increased output
noise) could result for large capacitive
loads.
If this should occur, change the
load capacitance slightly to remove the
resonant condition and reduce the output
noise.
2-7.
OUTPUT NOISE. The Model 244 output ripple and
noise is less than 0.5 millivolt rms above 5Hz with
maximum load. The output noise is typically 200 WV
rms ~with no load. Transient power line noise will
tend to increase the output noise.
2-8.
SHORT-TERM STABILITY. The Model 244 stability
is specified to be + 0.005% per hour worst-case after
0
10
12
f .
14 mA
I
a two-hour warm-up. After warm-up, the short-term
stability is typically 0.003% per hour for constant
line voltage, load, and ambient temperature.
2-9.
TEMPFJATURE
COEFFICIENT. The temperature co-
efficient is typically 30 PPM1 C (with a maximum
FIGURE 4. Current Limiting.
temperature coefficient not to exceed 60 ppml C).
1176
5
CIRCUIT DESCRIPTION
MODEI: 244 HIGH VOLTAGE SUPPLY
SECTION 3. CIRCUIT DESCRIPTION
3-1. GENERAL.
a. The Model 244 High Voltage Supply haa been
designed to provide a,, accurate voltage from -200
to -2200 volts d-c.
A
simplified circuit diagram is
shown in Figure 5.
b. The Model 244 is composed of high and low voltage supply sections and various other circuits for
control and overload protection. These circuits include the following.
1. High voltage supply.
2. LOW voltage supply.
3. Series high voltage regulator.
4.
Error amplifier.
5. Reference supply.
6. Overload circuit.
7. Voltage Divider.
C. Over-all Operation.
The output voltage is
selected by the front panel dials which control the
voltage divider. The error amplifier senses any
difference between the voltage across the divider
string (which is connected to the output) and the
fixed reference supply.
The amplified difference
drives the series regulator circuit to correct the
output voltage.
The overload circuit senses the output load current and controls the current within
design limits.
This circuit also provides an over-
load indication.
3-2. HIGH VOLTAGE SECTION.
The high voltage is developed by a voltage doubler circuit composed of
diodes 0101, DlC2, DlC3, and 0104 and fileer capacitars Cl13 and C114.
The filtered d-c voltage (approxFmaeely 3200 volts) is applied between the - OUTPUT
and the anode of the series pass element (tube VlOl).
The high voltage section is controlled by the OUTPUT
Switch SlOl which provides
ON/OFF
control of the a-c
power to transformer TlOl.
R
H
WWER LDAD
LAMP UMP
I
FIGURE 5. Simplified Circuit Diagram.
6
0770
MODEL 244 HIGH VOLTAGE SUPPLY
CIRCUIT DESCRIPTION
SERIES HIGH VOLTAGE REGULATOR. The series regu-
3-3.
lator tube VlOl is biased by the collector voltage of
transitor QlOE to form a “cascade amplifier” with the
output load serving as the plate resistor. The Model
244 - OUTPUT is effectively the algebraic sum of the
unregulated high voltage (3200 V) and the drop across
“101 and QlOE. When the OUTPUT Switch SlOl is off
(e.g. no plate voltage is on “101) the voltage at pin
8 (Screen Voltage) of VlOl will be significantly less
than nominal + 95 volts since the tube current will
cause a voltage drop across R169.
VOLTAGE CONTROL. The output voltage is divided
3-4.
by a resistor divider composed of resistors R146
through R167 located an switches S102, 5103, and S104.
The sampling voltage is compared with the reference
supply voltage. (The reference supply is composed of
zener D119 and resistors Rl40 through R145). The
difference voltage is amplified by the error amplifier
(transistors QllO, Qlll, Q112, and Q113) which drives
cathode biasing transistor ~108. Diodes 0114 through
Dl17 and resistors R115, R117, R139, and R144 protec?
the comparator and zener reference from switching
transients when the output is changed.
Diode Dill
prevents a reverse bias on transistor QlOV beyond its
breakdown voltage.
3-5. CURRENT CONTROL,
b. Overload Indication.- The OVERLOAD Indicator
05102 is driven by transistors 4104, Q106, and Q107.
Transistor QlO5 is an emitter-follower which biases
9106 to insure that the OVERLOAD Indicator turns on
before the current limiting actually occurs.
(The
OVERLOAD Indicator is designed to turn on at approx-
imately 11 milliamperes load current.)
LOW VOLTAGE SECTION. The low voltage for the
3-6.
control circuitry is obtained from a full-wave rec-
tifier composed of diodes D109 and I1110 and filter
capacitor c115.
+ 95 v d-c. This voltage is applied to a bias
a.
screen on “101. The + 95 v is developed across R113
and D105.
+ 20 v d-c. This voleage is regulaeed by zener
b.
diode D105. A regulated current sowce (25~) supplies
a constant current far zener diodes D105 and D106.
The current source is composed of transistors QlOl,
9102, and Q103 and reference zener D107. The regulated
current is sampled at R116 and compared to zener 0107
by transistor Q102. The action of QlOl and Q102
regulates the currene through 0105, D106, and R113.
- 10 v d-c. This voltage is regulated by zener
c.
diode 0106.
a. The output current is sensed by measuring the
voleage drop across resistor R124. A current limit
amplifier consisting of Q107 controls the error amplifier through diode D112. When the current through
R124 exceeds approximately 11 milliamperes, transistor
Q107 forward biases D112 and turns off the error amplifier which reduces the Model 244 through the action
of VlOl.
NOTE
The a-c power to the high and low voltage
sections is controlled by the POWER ON
Switch ~102. The POWER ON Indicator
ix101 is driven by the low voltage d-c
SUPPlY.
0770
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