Keithley 415 Manual de usuario

Instruction Manual

Model 415

Micro-Microammeter

Keithley Instruments, Inc.

Instrument Division

Cleveland, Ohio, U.S.A.

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.

To exercise this warranty, contact your Keithley

field engineering representative. You will be

given assistance and shipping instructions.

REPAIRS AND RECALIBRATION

Keithley Instruments and its internat.ional dis-

tributors maintain complete repair facilities.

To insure prompt repair or recalibration service,

please contact your Keithley field representative

before returning the instrument.

Estimates for repairs, normal recalibrations, and

calibrations traceable to the National Bureau of

Standards are available upon request.

INSTRUCTION MANUAL

MODEL 415

MICRO-MICROAMMETER

CONTENTS

INTRODUCTION

SPWZIFICATIONS

REXlgeS

Accuracy

Zero Drift

Grid Current

output

Rise

Time

Current Suppress~ion

Zero Check

Tube Complement

Power

Accessories Supplied

Accessories Available

Dimensions

OPERATION

Operating Controls

Inout and Outpyt Connections

PrelimJ.nary Set Up

Makinp Measurements

Speed o.f Response

CIRCUIT DESCRIPTION

Circuit Block Diagram

Speed of Response

Detailed Circuj.t Description

MAINTENANCEAND CALIBRATION

General

Calibration

Trouble Shooting Procedure

Voltare Resistance Diagram

Circuit Schematic

Replaceable Parts List

SECTION

415

ICE= mm, nio. cLEvEm, OHIO

SkCTION I - INTRODUCTION

The Model h15 Micro-microammeter incorporates advanced

high-speed circuitry developed by Keithley Instruments for rocket

and satellite experimentation -- where measurements of Lyman-

Alpha night slow, cosmic radiation, and upper air density re-

quire fast response,

The I~15 also provides zero suppression up to 100 full scales,

permitting full scale display of one per rant variatiors of a

signal, or suppression of a steady background signal.

Excelling other Keithley LOO Series Micro-microammeters in

speed of response, the Model hl5 is ideal for current measure-

ments in ion chambers, ionization pages, and photo-multipliers.

Other applications include uses with flame and Beta-ray

ionization detectors and in gas ChromatoKranhy, mass spectrometry.

Speed of respp? se of less than 600 milliseconds to 90% of

final value at lo- ampere is possible where external circui~t

capacity is less than 50 picofarads (uuf). Critical damping of

the circuit, with any input capacity, is maintained on all ranges

through one infrequent adjustment. There is no possibili.ty of

oscillation or poor transient response on any ranpe.

Accuracy is 22% of full scale o 10m3 -8 ampere

ranses; -+3$ of full scale on 3 x 10

-9

througQ210

throuph 10 ampere

ranples.

Other features i lude capability of detecting current of

approximately 1 x 10-YE ampere; zero stability of better than

2% per day and a one volt output at one milliampere; a 1%

mirror scale pane:1 meter.

415 I -1

SECTION II - SPECIFICATIONS

RANGES: lo-=, 3 x 10-12, lo-, 3 x lo-=, etc. to 10e3 ampere

full scale.

ACCURACY: Z 2% of full scale 10e3 ttiu lOWE ampere ranges;+ 3% of

full scale 3 x 10-9 thru lo-l2 ampere ranges.

Z!SO DRIFT: After 30-minute warmup, less than 2% of full scale per

2L hours on all ranges.

GRID CT:r'WNT: Less than 5 x 10-lL ampere.

~!ITPIIT: One volt for ful! scalp

3~i.

up to 5 ma. Noise less than

20 m'llivolts.

RISE TIME: Typical value &ven in seconds to 90% of final value.

Range Gin-50 uuf

amps f.s. seconds Cin=150 uuf

seconds Cin=1500 uuf

seconds

10-12

3 x 10-12

10-11

3&o-ll

3 x 10-10

10-9

3 x 10'9

and above

CURRENTSUPPRFSSION:

.600 .800 2.5

.200 .300 1.0

,060 .080 .250

.020 ,030 .lOO

.006 ,010 .030

,002 .003 .OlO

.OOl .OOl .003

.OOl .OOl .OOl

Up to 100 full scales; maximum buckout 10-5

ampere. One setting of bucking current serves

five adjacent ranges within above limits. FINE

adjustment allows precise control up to 100 times

suppression.

ZEROCHECK: Allows zeroing without disturbing the circuit.

TUBE COMPLEMENT: 2-5886, 2-6CB6, l-6Ch6, l-12BLA; 2-12AX7, l-OG3.

POAER: loo-130 v, 60 cps, 50 watts; 50 cps and 230 v units on

special order.

ACCESSORIESSUPPLIED1 Mating connectors for input, output; six

foot power cord.

ACCESSORIESAVAILABLE: Mating 6032 End Frames, mounting hardware,

rubber feet. Model L102 Input Assembly,

2-5886 electrometer tubes in a plug-in

can (replacement spare).

CABINET: 19" x 59 high x 10" deep. Net wei&ht 21 lbs.

415 II - 1

SECTION III - OPERATION

A. OPERATINGCONTROLS

The controls are discussed in order from left to right on the

front panel.

(1)

(2)

(3)

(Ii)

(5)

(6)

ZEROCHECK: Depressins this control effectively re-

moves all current from the amplifier input and allows

the meter to be set to zero with the ZEROADJUST con-

trol. After the button is depressed it may be locked

in position by turning the button one quarter turn as

indicated by the panel marking.

AMPERESFULL SCALE: The full scale meter sensitivity

is selected by this control. The use of zero suppres-

sion does not change the sensitivity.

CURRENTSUPPRESSI

(a) MULTIPLIER and AMPEHES: The combination of these

two dials set the amount of zero suppression. On

the OFF position of the AMPERESdial, the suppres-

sion circuit is disconnected.

(b) FINE8 The FINE control extrapolates between posi-

tions of the MULTIPLIER switch. For example when

the MULTIPLIER control is on aero, the FINE con-

trol has a ranpe of 0 to 1. If the control is on

1, the range of the FINE control is

from

1 to 2 and

so forth.

METER: The METERswitch allows the choice of plus or

minus current polarity; using the meter for indica-

tion; or switching it off. In the METEROFF position,

the switch still permits choice of plus or minus cur-

rent polarity.

ON: This switch turns on power. The instrument is

ready to operate in about 60 seconds.

ZEROADJlJSTz This control is used with the ZEROCHECK

button depressed to adjust the micro-microammeter zero.

B. INPUT AND OUTPUTCONNECTIONS

(1) Input Connections: The input connections and the

current generator being measured must be carefully

shielded since power line frequencies are well within

the pass band of the amplifier on most ranges. Also,

unless the electrostatic shielding is thorough, any

alteration in electrostatic field in the neighborhood

will cause marked output disturbances. The insulation

415 III - 1

used in brinping the signal into the amplifier must

be either polyethylene, polystryene, teflan or similar

hish resistance, low-loss material. Any Coaxial cables

used must be of the low-noise type. This type of cable

employs a graphite coating between the dielectric and

the surrounding shield braid. Satisfactory types are

made

by Amphenol, Microdot and Simplex. The use of

low-noise cable is mandatory due to the wide frequen-

cy response of the instrument. The Model hl5 is,

therefore, markedly more sensitive to external dis-

turbances than other Keithley Electrometers. Any

chance in the capacitance of the measuring circuit

to ground will, cause extraneous disturbances. It is,

therefore, recommended that the measuring set-up be

made as rigid as possible and any connecting cables

be tied down to prevent their movement. If continuous

vibration is present, itmay appear on the output as

a sinusoidal sJFna1 and some precautions may be nec-

essary to isolate the instrument and connectinS cable

from this vibration.

(2) Output Connections: The output of the instrument is

one volt for full scale meter deflection. up to 5 ma.

may be drawn from the output. The output is intended

primarily for driving oscilloscopes and pen recorders.

It may be divided down to drive 10 and 50 millivolt

recorders by placing: a suitable network across the

output. In general it will not satisfactorily drive

1 ma. Ester-line-Angus and Texas Instruments recorders

directly since the output voltage is too low for full

scale deflection or for providing the proper coil

dampin!?.

C. PRELIMINARY SET-UP

(1) Connect current source to input terminals per directions

in paragraph Bl above.

(2) Depress and lock ZEROCHECKbutton.

(3) Set CURRENTSUPPRESScontrols as follows:

(a) MULTIPLIER: Set to zero.

I”{ $W’BES: Set to OFF.

(Z, METEA: Turn to most counter-clockwise position.

Turn to +position.

(b) Turn on power. After about 30 seconds meter should

indicate on scale.

(5) Set meter to zero with ZEROADJUST.

III - 2

D. MAKINGMEASUREMENTS

(1)

(2)

Current Measurements 'Without Zero Suppression? With

the current source attached and the AMPEREScontrol

on OFF, turn the AMPERESFULL SCALr; switch to the

most insensitive range and open the ZEROCHECKswitch.

Increase the instrument sensitivity until the largest

possible reading is obtained before full scale is ex-

ceeded, The reading is now %he actual current beinF

generated by the attached device,

Current Measurements With Zero Suppression: Proceed

as in paragraph (1) above. Then set the CURRENTSUP-

PRESSMULTIPLIER and AMPERESdials to correspond as

closely as their restilutlon permits to the current

reading obtained in para,sraph (1). This operation

should cause the meter needle to approach zero. Now

use the FINE control as necessary to set the meter ex-

actly to zero. Then

move

AMPERESFULL SCALE switch to

the next more sensitive range and ad,just the FINE con-

trol as necessary. The input current is still the same.

Yowever , variations in current are beinp presented on

a scale three times as sensitive as before. Tf it is

desired to expand the scale further, the next more

sensitive range may be used. This nrocess

may

be re-

peated until one ner cent of the orifrinal scale is

presented as full scale. The sero suppression cir-

cuit is limited to this amount of suppression.

E. SPEEDOF RESPONSE

The specifications detail the possible speed of response with

various input capacities. It is evident from the data that

the less the input capacity, the better the speed of response.

Therefore, the Model hl5 should be located as closely as pos-

sible to the current source. The amount of capacity does not

affect the dampins. Under all conditions, tho response will

be aprroximately critically damped.

III - 3

SECTION IV - CIRCIJIT DESCRIPTION

A. CTRCIITTBLOCKDTACRAh~

I- O 0

Eln A Eo

0 v

+R- - +

X)BO

OUTPUT

FIG. 1

(1) The Electrometer: In block A Figure 1 is a high rain amp-

lifier with electrometer

tube

input. It can be assumed

with a high degree of accuracy that current neither enters

or leaves its input terminals, The amplifier is so arranged

that

the output is the negative of the input. Therefore,

sjnce a feedback connection exisj.ts between e, and the innut,

any positive voltaae appearing at the i~nout of A, ~1~11 cause

a nepatjve voltage applied through R and B. Tf, for the

moment, we omit the box labeled B from the discussion, the

voltage e, will increase until it equals iR, the drop across

the resistor. This is necessary since this feedback connec-

tion results in

circuit designed to keep the input drop to

a minimum, Therefore,

a first approximation,

i = e,/R (1)

and a properly calibrated meter at the amplifier output will

read current directly.

(2) Current Suppression: In Figure 1, when an input current is

flowing, the output voltage is iR from (1). The output assumes

this voltage in order to

balance

out the input current so that

the input terminal remains at ground. Either the output must

supply this voltage, in which case the meter indicates a read-

ing; or

voltage may be inserted in series with the feedback

415 IV - 1

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