Keithley 414 Manual de usuario

INSTRUCTION MANUAL

MODEL 414, 414C

MICRO-MICROAMMETER

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, transistors, fuses, and batteries, which,

within a year after shipment to the orig-

inal buyer, proves defective on examination.

DAMAGE IN SHIPMENT

Be sure to include the instrument model num-

ber and serial number in all communications,

if the instrument is damaged when received,

or fails to operate properly, a claim should be

filed with the carrier. Upon receipt of the claim

agent’s report, we will inform you regarding

repair or replacement.

REPAIRS

When returning an instrument for repair or

recalibration, it should be securely packed

against shipping damage and sent to the fac-

tory, freight prepaid. A brief letter describing

the difficulty should accompany the instrument.

CONTENTS

INTRODUCTION

SPECIFICATIONS

Ranges

Accuracy

Input Drop

Grid Current

Zero Drift

Response Speed

Zero Check

Tube Complement

Power Requirements

Accessories Supplied

output

Noise

Connectors

Accessories Available

Cabinet

OPERATION

Operating Controls

Operation

CIRCUIT DESCRIPTION

Basic Theory

Circuit Description

MAINTEUANCE

Factory Adjustments

Trouble Shooting

Voltage Resistance Diagram

Circuit Schematic Diagram Model klh

Circuit Schematic Diagram Model LlhC

Replaceable Parts List

414

KEITHLEY INSTRUMENTS

SECTION

III

CLEVELAND, OR10

SECTION I - INTRCDDCTION

Model klk

----

The Keithley Model lilh Micro-microammeter is a line operated

vacuum tube electrometer for measuring currents in the range

of 2 micro-microamperes to 10 milliamperes. Features include

a response speed of greater than 0.5 seconds on all ranges,

an input drop of less than 5 millivolts at full scale, a

zero drift of less than 2% per day on any range, good accu-

racy and calibration stability, negligible noise, and

simplicity of operation. For recording, an output signal

of five volts at 1 milliampere is available.

This model is identical to the klh except that a meter-relay

replaces the panel meter. An adjustable conta& pointer is

built into the meter-relay, When the indicating pointer

rises to the value set with the adjustable contact, the

contacts lock and actuate an internal relay. The relay's

SPDT s-ampere contacts are brought out through an AN con-

nector at the back of the chassis.

A manual reset button is supplied on the front panel. Reset

connections are also brought out through the AN connector for

rem&e resetting of the locked-up meter-relay.

414

I-l

SECTION II - SPECIFICATIONS

Ranges:

Accuracy:

Input Drop:

Grid Current!

Zero Drift:

Response

Speed:

Zero Check:

Tube

Complement:

Power

Requirements:

Accessories

Supplied:

output:

Noise :

Connectors:

Accessories

Available:

Cabinet:

17 ranges in overlapping 1 and

sequence, from 10

milliamperes to 0.1 milli-microamperes full scale.

Within 3% of full scale on all ranges from 10 milli-

amperes to 10 milli-microamperes, and within k% of

full scale from

milli-microamperes to 0.1 milli-

microamperes.

Less than five millivolts for full scale on any

range.

Negligible.

Less than 2% in any eight hour period after a five

minute warm-up if the source voltage is not less

than one volt.

Greater than 0.2 second for

67%

of full scale on

any range with up to 5000 micro-microfarads of

input capacity.

Zero check switch allows zeroing of the instrument

without disturbing the test circuit.

1 5886, 1 613~8, 1

6CM6,

1 082.

100-130 or 200 to 260 volts SO-60 cps, 33 watts.

Mating connectors, two wire adapter for power cord.

Five volts at up to one milliampere is developed for

full scale deflection.

Noise at output and on indicating meter is less than

1% of full scale peak to peak on any range if the

source voltage

not less than one volt.

Input: teflon insulated UHF (Amphenol 83-798)

Output: binding posts on front panel, Amphenol SOPC2F

at rear.

Model 6031 end frames for bench mounting.

Dimensions 19" x

5i”

high by 10" deep. Net weight

16 pounds.

414

II - 1

SECTION III - OPERATION

A. OPERATINGCONTROLS

1. Zero Check: This is a push-button located at the extreme left

of the panel. Its function is to allow the zero of

the instrument to be checked while the current source

is attached. To uss, depress and set the zero with

ZEROCONTROL. It is a feature of the instrument that

the external circuit is not disturbed during the test.

2. Range Switchr The RANGESWITCHis the dial next to and to the right

of the ZEROCHECKbutton. The range in use is always

at the top of the dial for convenient operation.

3. Power, Meter

Reverse Switch: The knob to the right of the RANGESWITCHis the

Ir. Zero I

B. OPERATION8

Precautions:

Operation:

power and meter polarity switch. This control per-

mits positive or negative meter readings. The out-

put voltage at the recorder terminals is not re-

versed by this switch.

This knob, next to the meter, is used in conjunction

with the ZEROCHECKswitch as described above to set

the instrument zero.

If the instrument is to be used at its extreme sen-

sitivity it is necessary to shield all input leads.

The lead-in cable should be polyethylene or teflon

insulated coaxial cable; and a low noise, graphits-

coated, dielectric cable such as Amphenol 21-537 is

recommended. At low sensitivities some of these

precautions may be disregarded.

(a) Connect to a power line of proper voltage. The

instrument is shipped for 117 volt SO-60 cps opera-

tion. For 230 volt operation see oircuit diagram

at the rear of the manual.

(b) Turn the RANGESWITCHto 10 milliamperes.

is ready to operate.

(d) Depress ZEROCHECKbutton and set meter to zero.

CAUTION1 Do not use control to set meter to any

other point than zero.

(e) Instrument is now ready to operate. Attach

current source and turn RANGESWITCHto proper

range.

III - 1

Special Instructions for Contact Meter Models:

(a) The operation of the instrument is identical to the non-

contact meter models with the exception that, on ttrn-on,

the meter pointer will strike the meter contact and lock.

Therefore, after the instrument is on for about one minute

press RESET button to release pointer and zero the meter.

At this point proceed as in Sections 1 and 2.

(b) Special Output Connection: The output connector at the

rear of the contact models is an AN connector which contains

the output terminals, the control relay contacts and the re-

setting circuit. It is necessary that ccntacts A and B in the

resetting circuit be shorted if the panel reset button is to

be operative. If remote resetting is desired terminals A and

B may be connected through a remote normally closed switch.

The wiring of thi~e connector is shown in detail in DR12&9C

AT THE REAR of the manual.

volts AC or 2L volts DC.

IL. Recording:

The Model hlh is provided with binding posts at the front of

the instrument and a connector at the rear for connection to

a recorder. A mating plug is provided for the rear connector.

The wiring of the connector is shown in the schematics at the

rear of the manual and is different for the hlh and the UC.

The output is five volts and 1 milliampere for full scale

meter deflection. The terminals may be connected directly

to high impedance recording devices. A series resistor is

necessary when driving a milliampere recorder or a mirror

galvanometer. The exact value of resistance varies from

recorder to reccrder. For a one milliampere recorder, ap-

proximately 3.S kilohms is required. The exact sensitivity

may be set by means of a potentiometer in series with the

output if desired.

5. Speed of Response:

The speed of response of the instrument is specified as not slower

than 0.2 seconds for 67% of full scale with 5000 micro-microfarads

of input capacity. Capacities greater than 5000 micro-microfarads

may cause instability on some ranges. However, the above speci-

fications allows up to 500 feet of 10 mmf per foot coaxial cable.

III - 2

414

SECTION IV - CIRCUIT DESCRIP'TION

i in --

FIG. I

A. BASIC 'THEORY:

Figure 1 shows the basic circtiit. The input current 1 flows into

the input termj.nal. If we neglect Cl and C2 for the moment, the

current i flows throuph R the feedback resistor. Since A is an

amplifie? of gain k and the feedback is negative.

ein = co/k (1)

and since all the current must flow through R,

-e, + e, /k

--.-_,-~_ ~_--

(2)

now

if &, the loop gain is large, the current flowing through

the input is e,/R and may be read from a properly calibrated

meter at the output. ei,, is the input drop of the ammeter.

The input resistance Rin is given by e-in/i and is,

Since in the Model hlh, the amplifier gain k is about 1000, the

input drop, ein will be about 5 millivolts for a five volt output

and the effective innut resistance Rin will be about l/1000 of

the range resistor being used.

IV - 1

If the capacities Cl and C2 are considered, the time constant

of the circuit is given by,

T = RCl/k + RC2

Thus the input time constant is reduced by a factor equal to

the loop gain. Capacitor C2 is placed across R to damp the

response and prevent ringing.

B. CIRCIJIT DiQXRIl'TION: Refer to DR127580 at the rear of the manual:

The input circuit consists of Vl, a type

5886

electrometer tube,

followed by a 6BH8 and a 6CM6 cathode-follower. This arrange-

ment provides a loop gain of about 1000. A high decree of zero

stability is assured by regulation of the filament supply of Vl

and B+ supply by Vlr the OA2 voltage regulator. The negative

bias supnly is regulated to the necessary degree by an NE81

neon lamp. The amplifier is a simple single ended direct-

coupled amplifier. Vl and V2 are directly coupled and the

coupling between V2 and V3 is by means of a NE81 neon lamp.

RlZh, the zero control, operates by varying the screen poten-

tial of Vl.

The current sensitivity is changed by either changing the

feedback resistor (RlOO through R113) or by changing the

feedback voltage by means of resistors Rll6 and R117. From

10 milliampers to 10 millimicroamperes a feedback voltage

of five volts is used and one resistor is used per range.

From 3 millimicroamperes to 0.1 millimicroamperes one resisLor

is used per decade and the feedback voltage is either one or

three volts depending on whether a

or 10x range is being

used.

The power supply consists of a conventional rectifier-filter

circuit for the positive and negative supplies.

IV - 2

SECTION V - MAINTENANCE

Except for occasional tube replacement very little maintenance is

required for the model hlh. Components are operated well below

rating, and high quality components have been used throughout.

1. FACTORYADJlJSTMENTS

Only one factory adjustment is made. This is Rl32, the meter

calibration potentiometer. This adjustment is only necessary

if the panel meter is changed. To calibrate set the instrument

on the 1 or 10 milliampere range anti set the meter to the cor-

rect reading with a calibration current sufficient to deflect

the panel meter to at least 75% of full scale.

2. TROUBLESHOOTING

Refer to DR12758-C and the voltage-resistance diagram at therear

of the manual.

Follow this general procedure in trouble shooting if the fault

is not apparent from the tabulated list below:

1. Check the B+ and J?- potentials: The E+ poten,tial can be

measured between the rectifier string and R201 and should

be about 320 volts. The ripple should not exceed 3 volts

rms. The B- potential may be measured between the negative

rectifier string (RFh,5) and R2O5 and should be about 2irO

volts. The ripple again should not exceed 3 volts RMS. If

either potential is no't correct the trouble is probably due

to a defective rectifier or filter component although in

some cases the transformer may be defective. Refer to the

schematic diagram to locate the defective component.

2. SPECIFIC FAULTS

a. Instrument will not balance: If no defect has been

foundT%x%zpection suggested in l., check the volt-

age at pin 1 or 5 of Vlr. This should be 150 volts. If the

voltage is not 15Ov, check R2O3, 202, and 201 for continuity

and check Vh. If the voltage is correct, check the voltage

at pin 3 of Vl (The red dot is next to lead 1) the reading

should be 3.2 volts. If the voltage at this point has risen

to 150 volts, the filament of Vl is open and this tube should

be replaced. If this voltage checks correctly, the following

procedure should be started: Short circuit the input to

ground with the range switch on 1 microampere full scale.

This removes the negative feedback and allows the operating

points of the individual tubes to be checked. It will usually

be found that the amplifier will become very sensitive and

difficult to balance, however it is only necessary that the

voltage swing through the correct operating value to confirm

that the circuit is operating correctly. Then with the input

V-l

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