Instruction Manual Model 640 Electrometer Keithley Instruments, Inc. Cleveland, Ohio, U.S.A. MODEL 640 ELECIROMETER CONTENTS 1. GENERAL OESCRIPTION------------------------------------------------- 1 2. OPERATION----------------------------------------------------------- 5 3. CIRC”IT DESCRIPTION------------------------------------------------- 14 4. *CCESSORIES--------------------------------------------------------- 1, 5. SER”ICING----------------------------------------------------------- 20 6. CALIBRATION--------------------------------------------------------- 30 7. REPLACE&&E PARTS--------------------------------------------------- 35 SCHEMATICS---------------------------------------------------------- 51 0472B MODEL 640 ELECTRO”ETER SPECIFICATIONS AS A MICROVOLTMETER: ACCURACY: Integrating capacitance ia 20 picofarads +0.25%. RANGE: 30 microvolts full scale to 30 volts in thir- METER NOISE: Less than 3 x Lo-16 coulomb rms (1.5 x teen lx and 3x ranges. lo-L5 coulomb p-p) on lowest recommended range. ACCURACY: il% of full scale on 30-volt to 300-micro- Less than 24 alpha pulses per hour a8 observed on volt ranges, decreasing to 25% on 30-microvalt range. 30-mFllivolt range. ZERO DRIFT: seas than 35 6” in the first hour and in each succeeding 24-hour period after l-hour warm-up. AS AN AMPLIFIER: Less than 35 wVv/‘C. METER NOISE: Less than 0.4 microvolt rm‘m8(2 microvolts RECORDER0"TPLPl': +l vole at up to 1 ma for full- p-p) with 1 megohm or less input resistance on most scale input. output polarity is opposite input sensitive range. DOlaritY. INPUl’ IMPEDANCE: Greeter than 1016 ohms shunted by Gain: 6.033 to 3.3 x 104. less than 2 picofarads. Input reaistsnce may also Frequency Response (Within 3db): dc to 0.07 cps at be selected in four steps from 106 to 1012 ohms. e 9 ain of 3.3 x 104, rising to 35 cps at a gain of RISE TINS (IO%-90%, with up to 100 megohms source re- 10 or below. sistance and no external capecitance): Less than 10 NOiS*: Below 1 cps: same 88 meter noise for spec- milliseconds on 1-mv and higher ranges, increasing ified function. Above 1 cps: less than 2% of full to 6 seconds on the 30-p’! range. output p-p on the 30-v to lo-mv ranges, increasing to 10% on the 1-w and lower ranges. AS AN AMmiTER: UNITY GAIN ODTPW: At dc, output ia equal to input within .Ol% or 10 p’f, excLuaiva of zero drift, for RANGE: 10-15 ampere fuL1 scale to 3 x 10-5 ampere in output C”rre*ts of LOO * or less. twenty-two lx and 3x ranges using built-in high- megoh,,, resistors and range switch. ACCLmcY: 23% of full scale on 3 x 10-5 to 10-11 am- pere ranges using the smallest recommended multi- ZERO cHEcx: Remote “zero” solenoid shorts input to plier setting; 24% of full scale on 3 x 10-12 to low through L kilohm in volt8 position, to feedback 10-15 ampere ranges. Instrurwnt can be calibrated in current or integrate position. to 22% accuracy below IO-9 ampere with external ISOLATION: Circuit ground to chassis ground: Greater voltage supply and built-in calibrating circuits. than LOgG shunted by 0.05 j.,f. Circuit ground may METER NOISE: mess ,rhan 2 x 10-l’ ampere rms (lo-16 be floated up to +LOOV with respect to main case. -15 ampere range when overdamped Head case is circuit nround. On battery o,,eration, :;;“li-:&,::,‘:. (5 x lo-16 ampere p-p) when instrument nay be cc.m;Letely isolated f;om’power critically damped. Less than 24 alpha pulses per Line and ground. hour as observed on the 30-millivolt range. POIARITY: Meter switch selects Left-zero (wsieive DAMPING: Variable from critical damping to overdamp- OK W3.StiVa) or center-zero sce3les. Mete; switch ing with 20 picofarads shunting the high-megohm ra- does not reverse polarity of output. sister. CONNECTORS: Input: Special type, metes with many CURRENT STABILITY: Setter than 5 x 10-L’ ampere/day commercially available ion chambers and other ac- after stabilization. Long-term drift is non-cumu- cessories (adapter to “SF included). Low: Binding lative. pst. Recorder output: Amphenol SO-PCZP. “nity- MAX. EXTERNAL CAPACITANCE (Feedback c”rrent ranges): Gain Output and Case Ground: Binding posts. 500 pf. PCUER: RISE TIME: Seconds, from 10% to 90%. Line operation: 105-125 or 210-250 volts (switch selected), 50 or 60 cps, 20 watts. Critically Overdamped; Battery Operation: Rechargeable nickel-cadmium 6- Recommended Resistor Damped; up to volt battery pack, S hours full charge to complete Full-Scale Value, no external maximum discharge. For maximum battery life, battery oper- Ranges ohms cepeeitenC* capecitance ation recomuanded for no more than 6 consecutive hours before recharge. 10-15 to 3x10-11 1012 1.5 44 DIMENSIONS, WRIGHT: 10-12 to 3x10-9 1010 0.2 0.5 Power Chassis: 7” high x S-314” wide x LO” deep; 10-11 to 3x10-7 108 0.05 0.05 net weight, 14 lbs. 10-9 to 3x10-5 106 0.01 0.01 Amplifier Head: 6” high x 5” wide x 6” deep; net weight, 6 Lbs. AS A CO”LOMS”ETER/C”RRENT INTEGRATOR: ACCESSORIES SUPPLIED: Connecting Cable: 5’ long, con- nects head to main chassis. UHF Adapter: adapts RANGE (recoannended): 2 x lo-14 coulombs full scale to input to UtlF connw.tor. Shield Cap. Mating output 6 x lo-lo coulombs in ten 2x and 6x ranges. COll”*CtO=. InternaLly mounted nickel-cadmium bat- tery pack and charging circuit. LL’LR GENERAL DESCRIPTION SECTION 1. GENERAL DESCRIPTION l-l. GENERAL. The Model 640 Vibrating Capacitor 1-2. FEATURES. Electrometer is an ultra-stable, solid-state microvolt electrometer. a. Excellent Stability. A stability specified at better than 5 x lo-11 ampere/day is useful for mass a. As a Microvoltmeter. When used as a microvolt- spectrometer, resistivity, end ion chamber meesure- meter, the Model 640 has an input resistance greeter menes. than 1016 ohms with thirteen ranges from 30 micravolts full scale to 30 volts. b. Remote Inwt Head. A compact Remote Input pre- amplifier permits convenient set up of en experiment. b. As a Picoammeter. When used with the built-in, high-megohm SHUNT RESISTORS, the instrument has twenty C. High Input Impedance. Guarding plus the use of two ranges from lo-l5 ampere full scale to 3 x 10m5 sapphire insulation provides an input resistance ampere. greater then 1016 ohms shunted by less than 2 pico- farads. C. As a Coulombmeter. By switching en accurate guarded capacitor in rhe feedback loop the instrument d. Battery or Line Operation. A choice af beteery is useful as a coulombmeter or current integrating or line operation permits complete isolation (in amplifier. In the CURRENT INTEGRATE mode the instru- battery mode) from power line when required. ment has ten ranges Pram 2 x lo-14 coulomb full scale to 6 x l’~?-~~ coulomb. e. Built-In Shunt’Resistors. Four high-megahm shunt resistors ten be switch selected (Input Head) d. As an Amplifier. The analog OUTPUT permits we for shunt or feedback current measurements. of the instrument as e very stable, variable gain amplifier. 1170 GENERAL DESCRIPTION MODEL 640 ELECTROMETER TABLE l-l. Front Panel Controls. CO”trOl Functional Description Paragraph POWERSwitch (5301) Controls the power to the instrument. 2-3, a FINCTION Switch (S402) Selects the mode of operation. 2-3, b RANGE Switch (S403) Selects the meter sensitivity. 2-3, c METER Switch (S404) Selects meter polarity, center scale, and meter off. 2-3, d ZERO Controls KEDIUM (S407) Adjusts meter zero. 2-3, e FINE (R431) Adjusts meter zero (fine control). 2-3, e ZERO CHECK Switch (S401) Permits a meter zero check. 2-3, f ! TABLE 1-2. Input Head Controls and Terminals. Control Functional Description Paragraph SHUNT RESISTOR Switch (5102) Selects P shunt or feedback resistc.r frw 106 to 2-2, a 1Ol2 ohms. ZERO CHECK Switch (SlOl) Permits a meter zero check. 2-2, b FEEDBACK Terminal (5103) Useful for unity gain or guarded wsauremsnts. 2-2, d Input Receptacle (5105) Provides connection to Input High 2-2, c DAMPING Control (RlOS) Adjusts damping for CURRENT INTEGRATE function. 2-2, e I 2 1170 MODEL 640 ELECTROELETER GENERAL DESCRIPTION POWER Switch (S301) ZERO Switch (S407) FUNCTION Switch METER (5402) Switch (S404) RANGE ZERO Switch CHECK (S403) (S401) FIGURE 2. Front Panel Controls. SHUNT RESISTOR FEEDBACK (5103) Input ZERO (JlO5) CHECK (SlOl) FIGURE 3. Input Head Controls. 1170 3 GENERAL DESCRIPTION MODEL 640 ELECTROMETER TABLE l-3. Rear Panel Controls and Terminals. CO”tr01 Functional Description Paragraph REMOTE HEAD Receptacle (5405) Provides connection to Input Head. 2-4, a OUTPUT Receptacle (5404) Provides an analog output. 2-4, b GND Terminal (5406) Connection to Main Chassis ground. 2-4, c LO Terminal (3402) Provides connection to Input LO. 2-4, d FEEDBACK Terminal (5403) Useful for unity gain or guarded measurementa. 2-4, e COARSE ZERO Switch (S405) Adjusts meter zero (coarse control). 2-4, f LINE VOLTAGE Switch (S302) Sets instrument far either 117 or 234 V power. 2-4, g Line Power Fuse (f301) Protects line power circuit. 2-4, h Battery Power Fuse (F302) Protects battery power circuit. 2-4, i lV-1MA Switch (S406) Sets OUTPUT for either 1V or 1W.. 2-4, j IHA CAL Control (R423) Adjusts OIJTPLW current for .95-1.05 MA. 2-4, k FIGURE 4. Rear Panel Controls and Terminals. 4 1170 MODEL 640 ELECTROMETER GENERAL DESCRIPTION SECTION 2. OPERATION 2-1. INPUT CONSIDERATIONS. NOTE a. Input Head Connections. The input terminal and sapphire insulator should be protected from contamination so 1. Remote Cable. A shielded coaxial cable (5 that the insulation will not be degraded. feet long) is supplied to permit remote location of Clean, dry connections and cables are very the Input Head from the Main Chassis.