Keithley 630 User manual

INSTRUCTION MANUAL
MODEL 630
POTENTIOMETRIC ELECTROMETER

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 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 Cleveland factory,
DDD 216-248-0400. You will be given assist-
ance 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 and in all countries outside the
United States having Keithley field repre-
sentatives.
To insure prompt repair or recalibration serv-
ice, please contact your local field representa-
tive or the plant directly before returning the
instrument.
Estimates for repairs, normal recalibrations,
and calibrations traceable to the National Bu-
reau of Standards are available upon request.

MODEL 630 POTENTIOMETRIC ELECTROMETER CONTENTS
TABLE OF CONTENTS
section
Page
1.
2.
3.
,4.
GENERALDESCRIPTION . . . . . .
1-L. Description . . . . . .
1-2. Operating Modes . . . .
1-3. Applications. . . . . .
l-4. Specifications. . . . .
1-5. Accessories . . . . . .
1-6. Equipment Shipped . . .
OPERATION . . . . . . . . . . .
2-l.
2-2.
2-3.
2-4.
2-5.
2-6.
2-7.
2-8.
2-9.
Front Panel Controls
and Terminals . . . .
Rear Controls and
Terminals . . . . . . .
Preliminary Procedures. .
Operating Procedures. . ,
Recorder Output . . . . ,
Effective Input Resis-
tance . . . . . . . . .
Null Sensitivity and
Source Resistance . . .
AC Effects on Measurement
Current Measurements. . .
CIRCUIT DESCRIPTION . . . . . .
3-1. General . . . . . . . .
3-2.
Reference Voltage Supply.
3-3.
Kelvin-Varley Divider . .
3-4.
Null Detector . .
3-5.
Oscillator. . . . .
3-6.
Guarding . . . . .
SERVICING . . , . . .
4-l. General . . . . . .
4-2.
Servicing Schedule.
4-3.
Parts Replacement .
4-4.
Troubleshooting . .
4-5.
Adjusting Grid Bias
Cathode Follower.
. . . . .
14
. . . . .
15
. . . . . 16
. . . . . 17
. . . . . 17
. . . . . 17
. . . . . 17
. . . . . 17
of
. . . . .
19
4-b. Zener Diode Replacement . . . 20
4-7.
Meter Adjustment . . . . . . 20
4-a. Adjusting Quadrature Control. 20
. . 1
. . 1
. . 1
. . 2
. . 2
. . 3
. . 3
. . 5
. . 5 6.
ACCESSORIES . . . . . . . . . , . 35
. . 5
. . 6
. . 6
. . 9
6-1.
Model 6301 Guarded Probe. . 35
6-2.
Rack Mounting . . . . . . . 35
6-3. Placing in Rack . . . . , . 36
6-4. Model 6013 pH Electrode
Adapter . , . . . . . . . 37
. . 9
. . 11
. . 11
. . 11
. . 13
. . 13
. . 13
. . 14
7.
REPLACEABLE PARTS , . . . . . , . 39
7-l. Replaceable Parts List. . . 39
7-2.
How to Order Parts. . . . . 39
Model 630 Replaceable
Parts List. . . . . . . . 40
Model 6302 Replaceable
Parts List. . . . . . . 48
Model 630 Schematic Diagram
1826lE . . . . . . . . . 51
Green Repair and
Calibration Form . . . . . 53
Section Page
5.
CALIBRATION . . . . . . . ., . . 21
5-l. General . . . . . . . . . . 21
5-2. Calibration Schedule. . . . 22
5-3. Kelvin-Varley Divider . . .
Verification. . , . . . . 22
5-4. Input Divider Calibration . 23
5-S. Range Calibration , . . . . 23
5-6. Reference Voltage Supply
Stability Test , . . . . 26
5-7. Oscillator Adjustment . . . 27
*Change Notice . . . . . . . . . . . Last
Page
*Yellow Change Notice sheet is included
only for instrument modifications affect-
ing the Instruction Manual.
0 168il

MODEL 630 POTENTIOMETRIC ELECTROMETER GENERALDESCRIPTION
SECTION 1. GENERAL DESCRIPTION
l-l. DESCRIPTION
a. The Keithley Model 630 Potentiometric Electrometer is a convenient, self-contained
potentiometer, It measures from 300 millivolts to 500 volts dc with 0.01% limit of error
from source resistances as high as lOlo ohms, and below 300 millivolts within 30 microvolts.
The upit need not be constantly calibrated or manually restandardized for a full year;
the limit of error is specified for one year.
in ut resistance of 1013 ohms,
F"'
Using the guarded, vibrating-reed null detector, the Model 630 has a minimum (slewing)
on the l-millivolt to l-volt ranges, increasing to over
10 5 ohms at 1% off null and to infinite resistance at null. With this extremely high in-
put resistance , .the Model 630 draws an absolute minimum of current to avoid loading and
polarizing the source.
c. Features for convenient use include: 5 in-line readout dials with automatically
lighted decimal points; one-volt, one-milliampere output for full-scale deflection on all
ranges except the l-millivolt; input polarity switch; floating operation up to 500 volts
off chassis ground; better than 60 db line-frequency rejection on the l-millivolt range.
Also, full guarding minimizes leakage problems.
l-2. OPERATING MODES. The Model 630 can be used as a five-dial potentiometer or as a
vibrating-reed electrometer. As a potentiometer, it can measure from 300 millivolts to
500 volts full scale with *O.Ol% limit of error and from 1 millivolt full scale to 300
millivolts within 30 microvolts. As a vibrating-reed electrometer, the Model 630 can
measure from 1 millivolt full scale to 500 volts within 23% full scale.
FIGURE 1. Keithley Instruments Model 630 Potentiometric Electrometer.
1265R 1

GENERAL DESCRIPTION MODEL 630 PO'TENTIOMETRIC ELECTROMETER
l-3. APPLICATIONS.
a. Due to its very high input resistance, the Model 630 is very useful in making accur-
ate dc measurements from high resistance sources frequently encountered in electrochemical
and physical-chemical research. It is especially useful for measuring potentials from
piezo-electric crystals, electro-chemical cells, grids and plates of tubes, biological
cells and pH electrodes. The Model 630 is also ideally suited for making Hall-effect and
fuel-cell studies, silicon resistivity and capacitor charge measurements, and for mrasur-
ing gate potentials of field effect transistors.
b. The null-detector output permits use with potentiometric recorders and digital volt-
meters equipped with automatic print-out. The Model 630 is
useful in quality control, pro-
duct development, inspection and production.
l-4. SPECIFICATIONS.
AS A POTENTIOMETRIC ELECTROMETER:
LIMIT OF ERROR: ?O.Ol% of reading or 30 microvolts, whichever is greater, after 30-min-
ute warm-up. Accuracy is exclusive of null-detector drift.
LONG-TERM STABILITY: Will operate within stated limit of error for one year.
TEMPERATURECOEFFICIENT: Does not exceed 0.001% per OC.
REPEATABILITY: Within 0.0025% or 30 microvolts, whichever is greater.
MAXIMUMNULL SENSITIVITY: 1 millivolt full scale with 30-microvolt resolution.
INPUT RESISTANCE: Infinite at null, from 0 to 500 volts. 10 15 ohms at.l% off null frop
0 to 500 volts with DETECTORINPUT Switch in OPEN position.
FLOATING OPERATION: 500 volts maximum off chassis ground.
INPUT ISOLATION: Circuit ground to chassis ground: 108 ohms shunted by 0.05 microfarad.
AS A VIBRATING REED ELECTROMETER:
VOLTAGE RANGES: O-5 volt full scale to 500 volts in four decade ranges.
NULL RANGES: 1 millivolt full scale to 100 volts in six decade ranges.
INPUT RESISTANCE: 1013 ohms or 1010 ohms selectable by switch, L-millivolt to l-volt
ranges; 1010 ohms, 5 to 500-volt ranges.
ELECTROMETERACCURACY: f3% of full scale on all ranges, exclusive or noise and drift.
ZERO DRIFT: Less than 2 millivolts per 24 hours after Z-hour warm-up. Long term drift is
non-cumulative.
RISE TIME (10% to 90%): Less than 2.5 seconds on any range with 1010 ohm source resistance.
LINE-FREQUENCY REJECTION: Greater than 60 db on the l-millivolt range, decreasing to 35
db on the 500-volt range.
2 1067R

MODEL 630 POTENTIOMETRIC ELECTROMETER GENERALDESCRIPTION
GENERALCHARACTERISTICS:
LINE STABILITY: Better than 5 ppm for 10% change in line voltage.
RECORDEROUTPUT:
output: 1 volt, 1 milliampere for full-scale meter deflection on all ranges except on
l-millivolt range, where it is 10% less.
Noise: 30 microvolts peak-to-peak referred to input up to 1 cps.
Note: Recorder used must have fully isolated input, lOlo ohms minimum to ground.
POLARITY: Positive or negative, selectable by switch.
CONNECTORS: Input: Special Triaxial. output: Banana jacks.
POWER: 105-125 or 210-250 volts (switch selected); 50, 60 or 400 cps; 50 watts.
DIMENSIONS, WEIGHT: 5-l/2 inches high x 17-l/2 inches wide x 13-l/2 inches deep; net
weight, 24 pounds.
ACCESSORIES SUPPLIED: Model 6302 Input Cable consisting of a mating plug and 3-foot
triaxial cable.
l-5. ACCESSORIES.
a. Model 6301 Guarded Probe with 3-foot connecting cable allows measurements to be made
more conveniently. Using the Probe does
not affect any Model 630 specification.
b. Model 4000 Rack Mounting Kit, containing two brackets and a top cover, converts the
Model 630 to fit standard 19-inch racks. Rack mounted, the Model 630 is 5-l/4 inch&s
high x 19 inches wide x 13-l/2 inches deep. Section 6 has assembly instructions.
C. Model 6013 pH Electrode Adapter,which has a Z-foot cable and triaxial connector,
accepts Leeds & Northrop and Beckman pH electrode connectors. The Adapter allows accurate
and convenient,pH potential measurements with the Model 630.
l-6. EQUIPMENT SHIPPED. The Model 630 Potentiometric Electrometer is factory-calibrated
and is shipped with all components in place. All units are shipped for bench use. Model
4000 Kit may be ordered for rack mounting; refer to Section 6 for assembly instructions.
The shipping carton also contains the Instruction Manual and the Model 6302 Mating Connec-
tor with 3-foot triaxial cable.
016GR 3

OPERATION ?4ODEL630 POTENTIOMETRIC ELECTROMETER
-
Reference Voleage Dials
s303 5304 s305 S-306 It381
DETECTORINPUT
Swirch (5102)
Receptacle 5103 5104 Switch CO"tL-01 Switch SwFtch
.JlOl (S101) (R122) (5104) (5301)
FIGUKlc L.
I'W~~L OJU rronr: .raneL wncrols and Terminals. The designations refer to the.
Replaceable Parts List and schematic diagram.
1265
FIGURE 3. Model 630 Rear Panel Controls and Tarminzlr.
4

MODEL 630 POTENTIOMETRIC ELECTROMETER OPERATION
SECTION 2. OPERATION
2-1. FRONT PANEL CONTROLSAND TERMINALS. (See Figure 2).
a. POLARITY Switch. The POLARITY Switch turns the instrument on and sclccts
the input
polarity. The Switch reverses the polarity of the internal rc,Ccrcncc voltage supply so
both positive and negative voltages may be measured; it does not reverse the meter polar-
ity.
b. DETECTORINPUT Switch. A 3-position toggle switch allows selection of
the Model
630 input resistance and also allows checking the meter zero.
1) Setting the Switch to 1010 OIIMS sets the input resistance at 1010 ohms for all
ranges.
2)
Setting the Switch to OPh'N sets the input resistance at 1013 ohms for the l-milli-
volt through l-volt ranges. The input resistance remains
at 1010 ohms for the ranges
above 1 volt.
3) Setting the Switch to ZERO CK internally disconnects the input from the vibrating
capacitor and shunts the capacitor to the amplifier low. This allows meter zeroing on
any range without removing the input signal.
'c. NULL Switch. The NULL Switch sets the null detector sensitivity for six decade
ranges from 1.0 millivolt full scale to 100 volts. When the Switch is in the VTVM posi-
tion, the Model 630 operates as a vibrating-reed electrometer for the four ranges of the
RANGE Switch.
d. RANGE Switch. The RANGE Switch adjusts the sensitivity of the VTVM in four steps:
0.5, 5, 50 and 500 volts full scale. It also determines the voltage acrws the Kelvin-
Varley divider and the position of the decimal point light - which also serves as a pilot
light - between the five Reference Voltage Dials.
e. Reference Voltage Dials. Five in-line dials at the top of the front panel set the
reference voltage when the Model 630 is used as a potentiometer. The first four switches
have decade steps as indicated on the dial. The last dial is continuously adjustable.
f. METER ZERO Control. The METER ZERO Control adjusts the meter needle to zero. The
Control allows precise meter zeroing on all ranges when the DETECTORINPUT Switch is set
to ZERO CK. The Control has a. range of approximately 120 millivolts.
g. Input Terminals. The Model 630 uses a special triaxial receptacle for its INPUT
Receptacle. The Receptacle is similar to a bnc connector, but requires using the furnished
Model 6302 Input Cable. Using a standard bnc conmctor could damage the INPUT Receptacle.
A set of binding posts marked LO and GND is provided for grounding the LO input terminal
to the chassis when desired. The LO terminal and the shell of the triaxial INPUT Recep-
tacle are internally connected.
2-2. REAR CONTROLSAND TERMlNALS. (See Figure 3)
a. Fuse. For LOS-125 volt operation, the Model 630 uses a l-ampere 3 AG fuse. For
210-250 volt operation, the Model 630 uses a 0.5-ampere 3 AG fuse.
0166R 5

OPERATION MODEL 630 POTmTIOMETRIC ELECTROMETER
b. Power Cord. The Model 630 is designed for a 105-125 volt, 60-cps line source, un-
less otherwise specified on the rear panel. The 3-wire power cord with the NEMA approved
3-prong plug provides a ground connection for the cabinet. A 3:2 prong adapter is provi-
ded.
C. NULL DETECTOROUTPUT. Two terminals, marked + and -, supply a dc signal from the
null detector.
d. COARSEZERO Switch. A screwdriver adjustment is provided for bucking out the con-
tact potential of the vibrating-reed capacitor. The Switch has a i-100 millivolt span in
ten ZO-millivolt steps.
e. 117-234 Switch. The screwdriver-operated slide switch sets the Model 630 for 117
or 234volt ac power lines.
2-3. PRELIMINARY PROCEDURES.
a. Check the 117-234 Switch and the Fuse for the proper ac line voltage. Connect the
power cord.
b. Set the Model 630 front panel controls as follows:
DETECTORINPUT Switch ZERO CK
RANGESwitch 500
NULL Switch VTVM
POLARITY Switch -I.
Reference Voltage Dials ZWXJ
The decimal light between the third and fourth Dials will light. Allow the instrument
to'warm up 30 minutes to meet the specified accuracy on all ranges.
c. Set the NULL Switch to 1.0 MV. Zero the meter with the METER ZERO Control. Nor-
mally, using the COARSEZERO Control on the rear panel is not necessary. Return the
NULL Switch to VTVM.
Check meter zero periodically. Null detector drift can be up to 2 millivolts
per day, which will cause inaccuracies in continuous readings. Setting the
DETECTORINPUT Switch to ZERO CK disconnects the input signal source from the
instrument, avoiding polarization. It is not necessary to disconnect the input.
2-4. OPERATING PROCEDURES,
a. The Model 630 is used first as a voltmeter to determine the approximate value of
the unknown voltage. It is then used in the potentiometric mode to determine the voltage
to 10.01%.
6
Vibrating capacitors are extremely sensitive to shock and vibration. when
making a measurement,place the Model 630 on a vibration free, rigid structure
or on some material which will minimize vibration. Also, tightly tie down
the input cable and any attached circuitry; any cable flexure will generate
electrostatic charges which the Model 630 will detect.
L265R

MODEL 630 POTENTIOMETRIC ELECTROMETER OPERATION
FIGURE 4. Input Connections to Model 630. The two diagrams show the input circuit for
measuring at ground and for floating.
In A, the unknown voltage has one terminal at ground. The shorting Link is between
the LO and GND Posts of the Model 630.
In B, the unknown voltage has both terminals off ground potential. The floating or
off-ground potential must be less than 500 volts. Also note the shorting line is pe&
used.
b. The Model 630's high input resistance allows circuit measurements without causing
circuit loading. (See paragraph 2-6.) On the l-millivolt to L-volt null ranges, the in-
put resistance can be set to 1013 er 1010 ohms with the DETECTORINPUT Switch. Use the
OPEN (1013 ohm input) setting for high source resistances; use the LOLO OHMSsetting to
avoid pickup problems or to increase response speed.
resistance is 1010 ohms for either setting. On ranges above 1 volt, the input
NOTE
When making measurements on devices with high contact resistances (such as
silicon), completely isolate the power supply from ground to avoid measuring
the drop acress the contact resistance.
c. Voltmeter Operating Procedures.
1. Ten full-scale ranges are available for VTVM operation. When the NULL Switch is
at VTVM, the RANGE Switch determines one of four full-scale ranges. By putting the five
Reference Voltage Dials at zero, the Model 630 can then operate as a voltmeter on the
six null ranges.
2. Connect the unknown voltage to the INPUT Receptacle, using the Model 6302 Input
Cable or the Model 6301 Guarded Probe. When using the guarded probe, use a separate
lead to the LO Terminal.
3. Switch the RANGE Switch to the most sensitive range for an on-scale meter deflec-
tion.
7