Keithley 603 Service manual
INSTRUCTION MANUAL
MODEL 603
ELECTROMETER AMPLIFIER
WARRANTY
We warrant each of our products to be free
from defects in material and workmanship. Our
obligation under this warranty is to repair or
replace any instrument or part thereof (except
tubes and batteries) which, within a year after
shipment, proves defective upon examination.
We will pay domestic surface freight costs.
To exercise this warranty, call your local
field representative or the factory, DDD 216.
795.2666. You will be given assistance and
shipping instructions.
REPAIRS AND RECALIBRATION
Keithley Instruments maintains a complete re-
pair service and standards laboratory in Cleve-
land, and has an authorized field repair
facility in Los Angeles.
To insure prompt repair or recalibration serv-
ice, please contact your local field representa-
tkve or the plant directly before returning the
instrument.
Estimates for repairs, normal recalibration?.,
and calibrations traceable to the National Bureau
of Standards are available upon request.
MODEL 603 ELECTROMETER AMPLIFIER
CON’I’ENTS
CONTENTS
SECTION
INTRODUCTION . , . . . . .
SPECIFICATIONS . . . . . . . . . . . . .
OPERATION . . . . , . . . . . . . . .
A.) Operating Controls
B.) Input Output Connections
C.) Preliminary Set Up
D.) Use of Model 603 as a Differential
Amplifier
E.) General Precautions
CIRCUIT DESCRIPTION . . . . . . . . . . . .
A.) Detailed Description of Amplifier
power Supply Voltages
B.)
C.) Operation of Power Supply
MAINTENANCE AND TROUBLE SHOOTING . . . . .
A.) Maintenance
B.) Trouble Shooting
REPLACEABLE PARTS LIST . . . . . . . . . . .
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II
. III
IV
V
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VOLTAGE RESISTANCE DIAGRAM . . . . . . . . .
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SCHEZ4ATIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1165R
i
SECTION I INTRODUCTION
--
The model 603 Electrometer Amplifier is a high gain amplifier
and voltmeter for the frequency range of dc to 50 kilocycles.
Its outstandinp characteristics are an input impedance of
greater than lOl& h
current of less than 5 x lo-lh
o ms shunted by 10 micromicrofarads, a grid
amperes, a maximum full scale
sensitivity of 2.5 millivolts, differential input, low drift
and a remote probe containinp the first stage electrometer
tubes.
as far as 21r feet from the main amplifier.
The remote probe allows the input grids to be located
By employing this
feature the input capacitance may be kept to a minimum so that
it is possible to achieve fast voltaee and current measurements
in high impedance circuits., Current measurements, either differential or single-ended are made by inserting high megohm
resistors in the place provided in the remote probe.
The outnut capability of the Model 603 is 10 volts sinale
ended or 20 volts pushnull at a maximum current of 10 milliamperes.
The output is therefore suitable for driving milliamnere recorders as well as nen amplifiers and oscilloscopes.
I-l
MODEL 603 ELECTROMETER AMPLIFIER
SECTION II SPECIFICATIONS
AS A VOLTMETER:
SPECIFICATIONS
RANGE:
Differential input from .0025 volt full scale to 1 volt in nine lx, 2.5x and 5x
ranges.
ACCURACY:
ZERO DRIFT:
INPUT IMPEDANCE:
*2% of full scale on all ranges exclusive of drift.
Less than 2 millivolts per hour after l-hour warm-up.
Greater than 1014 ohms shunted by 10 picofarads each input to ground.
AS Aiv METER (WITH MODEL 6033 SHUNT RESISTORS):
GRID CURRENT:
TYPICAL RISE TIMES:
2.5 x LO-12
2.5 x LO-l2
2.5 x LO-10
2.5 x LO-10
2.5 x 10-g
2.5 x 10-s
Less than 5 x lo-l4 ampere.
10% to 90% for selected current ranges.
Voltage
Range >
millivolts
2.5
25.0
2.5
25.0
2.5
25.0
Shunt
Resistance,
ohms
109
10 10
107
108
105
10’5
Rise Time with
No External
Capacitance,
milliseconds
60
500
0.6
6.0
0.03
0.05
Rise time with
20 pf
Across Input,
milliseconds
125
1000
1.0
12.0
0.04
0.1
AS AN AMPLIFIER:
GAIN:
With single-ended input and output, 4000, 2000, 1000, 400, 200, 100, 40, 20, and
10 for meter ranges of .0025 to 1 volt full scale.
FREQUENCY RESPONSE (Within 3 db):
on the .0025-volt range,
rising to 50 kc on the l-volt range.
From 1-kilohm SOUL-ce resistance ox less, dc to 10 kc
NOISE: Less than 25 microvolts rms referred to the input on the .0025-volt range, in-
creasing to 2 millivolts rms on the l-volt range.
COMMON MODE REJECTION: More than 1OO:l at dc.
Input grids must be within one volt of
ground for minimum grid current; can be run at maximum of i3 volts.
INPUT IMPEDANCE: Greater than 1014
OUTPUT:
f20 volts differential or i-10 volts single ended at up to 10 milliamperes for
ohms shunted by 10 picofarads each input to ground.
full-scale input.
1165R
11-l
MODEL 603 ELECTROMETER AMPLIFIER SPECIFICATIONS
GENERAL:
INPUT HEAD: Contains input section of amplifier and may be connected directly to front
panel or operated remotely through cabling at distances of up
to
24 feet from the ampli-
fier.
INPUT SWITCH:
Located on remote head and shorts each side of the input through 1 megohm
to ground.
ZERO SUPPRESSION:
POLARITY:
CONNECTORS:
POWER:
Zero-center scale.
Input: BNC type; Output; Amphenol 31-PC3F; binding posts on front panel.
105-125 or 210-250 volts, 50-60 cps., 120 watts.
DIMENSIONS, WEIGHT:
Input Head:
2-l/4 inches high x 3-l/2 inches wide x 3-l/2 inches deep.
up to one volt.
Amplifier: 5-l/4 inches high x 19 inches wide x 10-l/2 inches deep.
pounds.
4CCESSORIES SUPPLIED:
Mating input and output connectors; binding post adapter; Model
6031 Connecting Cable, 12 feet long.
Net weight, 21
II-2
1165R
OPZRATING CONTROLS
A.
The operating controls for the Model 603 are all located on the
front panel.
- OFF switch is located below and to the left of the
ON
panel meter.
COARSE BALANCE is the first of three large knobs starting
from the left of the panel. This control is a 19 posi-
tion switch.
the meter zero by approximatelv 100 millivolts.
FINE BALANCE is the knob following the coarse balance control.
the zero by approximately 10 millivolts.
MILLIVOLTS is the third knob in the row. This control
selects the full scale sensitivity or the amplifier Cain
as stated in the specifications.
OUTPUT LEVEL is a screw driver adjustment located below
the meter and to the right of the output. Its function
is to adjust the output dc, so that the output terminals
are at ground potential when the panel meter reads zero.
SECTION III - OPERATION
Their location and functions are as follows:
Moving the switch by one position changes
It is a ten-turn potentiometer and each turn shifts
B.
INPUT AND OU'PPUT CONNECTIONS
Input connections are made via either BNC input connector
in the remote probe.
If the cover is removed and the
interior exposed as shown in Figure I, it is seen that a
place is provided for two input resistors between the
input grids and
ground.
If it is desired to use the instrument only as a single ended device, the other grid
is shorted to ground by placing a length of wire between
the diode clips furnished to hold the resistor.
maining pr'd may be left open or shunted with the appropriate resiStor as desired. The cover is then replaced
and either a BNC connector is used to mate with the BNC
receptacle on the probe or the binding post adapters fur-
nished may be used.
If particularly low capacity is de-
sired, it is possible to force a pin into the central
oortion of the connector, employing the binding post for
the ground connection.
The input head is either plugged directly into the panel
of the main amplifier or plugged in at the end of a cable
not to exceed 2b feet in length. The instrument should
be turned on only if the input head is connected to the
amplifier.
The re-
0163 III - 1
Outnut connec~tions are furnished either on the panel with bind-
ing posts or at the rear of the instrument with a three pin connector. The two red binding po.+,s are connected to the balanced
output cathode followers and output is exactly 180 degrees out of
phase between the two signal outputs.
AT NO TIME SHOTTLD EITHER
OUTPUT BE GROUNDED TO THE CHASSIS.
PRELIMINARY SET-UP
C.
1.
Plug in input head either directly at the panel or at the
end of the cab1.e.
Observe the instructions about input connections in section
2.
III-B.
3.
Connect the instrument to the power line. Unless otherwise
marked the unit may be used on 117 volt 50 to 60 cps power only.
To convert to 2’20 operation refer to the schematic DR 12669-D at
the rear of this manual.
grounds the cabinet.
A three wire cord is furnished which
If a three wire receptacle is not available,
use the two pin adapter furnished and ground the third lead to an
external ground.
IL.
Set the controls as follows:
Coarse and Fine Balance: To center of their range.
Range: 1000 millivolts.
Input: Short Inputs to ground.
on instrument and wait approximately 60 seconds.
5.
a.
b.
C.
Turn
instrument should now indicate on scale.
The
Bring the meter to zero
by adjusting the Balance Controls as necessary. To increase the
sensitivity, turn the Millivolt switch to the desired range and
rebalance as necessary. It should be realized that on the more
sensitive ranpes (about 25
millivolts
and
below)
that the warm-up
drift will be apparent. It is therefore recommended that on the
most sensitive ranges about one hour warm-up be allowed before
use.
0662~
6.
Driving of Recorders: The model 603 furnishes an output of
10 volts sinple ended (one output terminal to around) or 20 volts
push-pull (across both output terminals) for full scale meter deflection at a maximum current of 10 milliamperes. This output
may be used directly with oscilloscopes and pen amplifiers.
Milliampere recorders and galvanometers must be connected to the
output in series with the appropriate resistance to limit the
output current.
Use of the Model 603 as a Differential Amnlifier:
D.
The basic circuit of the Model 603 incorporates a differential
amulifier with an in-phase rejection of 1Wk. Differently stated
this means that a signal applied to one input grid with the other
grounded will produce an output signal which is 100 times greater
than the output signal produced if the innut is applied to both
grids in parallel.
However in the Model 603 t&E is a basic
TIT - 2
restriction that the DC potential between the grids and ground
must not exceed one volt plus or minus with respect to around
if the grid current specifications are to be met.
Nevertheless, where the balanced input can be used, it will give
considerable improvement in spurious signal rejection if it can
be arranged that the desired signal appears across the input
grids while any spurious signal is picked up equally and in
phase at the two grids.
In this way the snuri~ous signal will
be discrimi.nated against and the desired sivnal will be ampli-
fled.
If the balanced input is used,
it should be remembered that each
input grid must have a DC return to ground and it is not sufficient to connect between the two input terminals. Very often the
resistance of the surroundings will provide the return path to
ground.
However if a sufficient return path does not exist it
can be provided by shunting resistors to ground in the place provided in the input head. (See section IIIB.)
If this precaution
is not observed the input will rapidly charge up due to grid current flow and the amplifier will be inoperative until a return
path is provided. The value of resistance to ground will best
be determined by considering the impedance that, in the first
place, is necessary and the permissible voltage that can be al-
lowed to build up at the grids due to grid current.
GENERAL PRECAUTIONS:
E.
1.
Input wires should be as short as possible and well shielded
in order to reduce power line pickup as well
as
the pick-up of
stray electrostatic fields. When the Model 603 is used at its
maximum input impedance, electrostatic pick-up must be carefully
eliminated. In some cases it may be necessary to shield the
entire test object.
If the high input resistance of the Model 603 is to be
2.
realized in practice,
careful attention should be paid tothe
quality of insulation used in the input circuit, Ordinary rubber
and plastic insulation should be avoided in favor of teflon or
polystyrene. Insulation for switches,
standoffs and bushings in
contact with the signal lead should be made of polystyrene, polyethylene, ceramic, teflon or other high quality insulation ma-
terial. If cables are necessary, most types of polyethylene or
teflon insulated cable will be satisfactory. However if critical
work at low levels is contemplated, a very substantial reduction
in cable noise will be obtained with a coaxial cable using a
graphite-coated dielectric. One satisfactory type is Amphenol
21-537.
Avoid leaving the input grids floating and unshielded.
3.
Large signals can be induced at the input of the amplifier.
Although no permanent damage will occur, some temporary loss
of DC stability may be experienced.
III - 3
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