Keithley 414 Service manual

INSTRUCTION MANUAL

MODEL 414A

PICOAMMETER

0

COPYRIGHT PRINTED MAR.

1976,

1978,

KEITHLEY INSTRUMENTS, INC.

CLEVELAND, OHIO, U.S.A.

CONTENTS

MODEL

414A

1.

2.

3.

4.

5.

6.

7.

1

4

6

7

9

14

17

ii

0575

MODEL 414A

Fig.

No.

I

LLU

ST

RAT

I0

N

S

Title Page

ILLUSTRATIONS

3

5

6

10

12

13

21

0974

iii

S

PEC

IF

ICAT

ION

S

P

E C I

F

ICAT

MODEL

10

N

S

414A

RANGE:

ACCURACY:

ZERO DRIFT:

INPUT VOLTAGE DROP:

EFFECTIVE INPUT RESISTANCE:

RISE TIME, MAXIMUM:

MAXIMUM INPUT OVERLOAD:

CONNECTORS:

RECORDER OUTPUT:

POWER:

DIMENSIONS, WEIGHT:

ACCESSORIES SUPPLIED:

10-lo ampere full scale to

lx

and

3x

ranges, positive or negative currents.

&2%

*4%

of full scale on 3 x

0.05%

per "C on any range after a 10-minute warm-up and

with source voltages greater than meter deflection on any range when properly zeroed. ampere range, increasing to less than

ampere range.

Range,

ampere

Transient:

(or other

Continuous:

creasing to

Amphenol 8OPC2F.

Output:

deflection. Output polarity is opposite input polarity.

Noise:

414s:

414A: Less than

105-125 or 210-250 volts (switch selected),

5

watts.

net weight,

nectors.

of full scale on

Less than 0.5% of full scale per week plus

10.10

10.9

10.8

10-7

10

-6

10.5

and

1000

volts for

10

mA

600

12

volts on the ampere range.

Input: Teflon-insulated UHF type. Output:

il

volt or 1 milliampere for full-scale meter Less than

8

pounds.

10-9

Less than 1 millivolt for full-scale

Seconds, from

above

limited) High Voltage Supply. volts on 10-10 to

0.3%

1%

of full scale peak-to-peak.

5%w

lo2

ampere in seventeen

lo-*

to ampere ranges;

to 10-10 ampere ranges.

1

volt.

Less than

With

less

up

to 3 seconds using a Keithley

10-6

of full scale peak-to-peak.

high

x

Mating input and output con-

0.1

ohm on

lo7

ohms on

10%

to

90%.

up

to

500

0.75

0.15

0.13

0.09

0.05

wide

Input

0.001

pF

x

Across

than

ampere ranges, de-

8%"

50-60

10"

deep:

10-lo

Hz,

iv

0974

MODEL

414A

GENERAL DESCRIPTION

SECTION

1-1.

GENERAL.

a. The Keithley Model 414A is a completely solid-

state picoammeter which measures currents over

LO-’

from of full scale on the to of full scale on the

b. The Picoammeter employs matched tors in the input followed by a differential amplifier stage, a transistor driver and a transistor output stage. Negative feedback is used for stability and accuracy.

1-2.

b. A unique circuit provides complete overload protection for Model 414A without compromising the outstanding features of the

meter .will withstand transient overloads up to volts without damage, and overload recovery is almost

instantaneous.

to ampere full scale. Accuracy is

3

x

lo-’

FEATURES.

MOS

am ere ranges and

to

lo-‘’

FET input. The Picoam-

1.

ampere ranges.

MOS

GENERAL DESCRIPTION

17

ranges

*2%

FET transis-

1000

*4%

a. The time and temperature stability of the 414A Picoammeter is unmatched by any other inexpensive picoammeter. The Model 414A will operate for days without requiring rezeroing. Zero drift with time is less than

0.5%

of full scale per week. Temperature drift is equally small less than

c. Fast warm-up is an inherent characteristic of the Picoammeter. its most sensitive range. For maximum stability, however, about

d. One volt or tion on all ranges is provided to drive chart recorders. The

1

milliampere recorder output will drive the Keith-

370

ley ers are used, the output voltage can be conveniently divided by a shunt resistor and adjusted with the rear panel Calibration potentiometer.

-

0.5%

Recorder directly. When potentiometric record-

a change

of full scale on the most sensitive range.

It can be used almost immediately on

10

minutes warm-up time should be allowed.

1

of

10°C

affects the reading

milliampere at full-scale deflec-

for

full scale

0671

1

GENERAL DESCRIPTION

TABLE

1-1

Front Panel Controls

Control Functional Description Paragraph

MODEL

414.4

RANGE Switch Selects full-scale current range instrument is to measure.

METER Switch Turns instrument on; selects meter polarity; checks instrument zero.

ZERO

ADJ.

Control Zeroes meter on any range.

Pilot Light Glows to indicate instrument is on.

TABLE

1-2

Rear Panel Controls

Control Functional Description Paragraph

INPUT Receptacle Connects input to source. Receptacle

UHF

connector.

is

a Teflon-insulated

2-2

2-2,2-4

2-2

---

2-1, 2-2

OUTPUT Receptacle Connects output to monitoring device.

1

MA

-

1

V

1

MA

CAL Control Adjusts output from

117-234

I

Fuse

2

V

Switch

Selects output

Sets instrument for

3AG Slow-Blow.

of

instrument: 1 milliampere or 1 volt.

117-volt 234-volt - .062

0.95

117

to

or

-

1.05

mA.

234

volt ac power line.

.125

A;

A.

2-4

2-2, 2-5

2-2.

2-5

0671

MODEL

414A

METER MlOl

-

GENERAL

RANGE SWITCH s102

DESCRIPTION

METER

ZERO

'I-

POWER

LAMP

DS201

FIGURE

t

I

ADJ

ZERO CONTROL R123

1.

Front Panel Controls.

METER

SWITCH SlOl

\

1

SWITCH

S

103

0671

INPUT 5102

FIGURE

F~SE

IMA'CAL

F201 CONTROL

R133

-

2.

Rear Panel Controls.

OUTPUT

5103

-

117-234V SELECTOR s201

3

U'

MODEL

414A

0

PE

RAT

ION

PICOAMMETER

SECTION

2-1.

INPUT CONNECTIONS. Use the following precautions

when using the Picoammeter on the more sensitive ranges.

a. The INPUT Receptacle of the Model 414A lon-insulated the high impedance terminal, and the outer shield

case ground.

b. Carefully shield the input connection and the current source being measured, since power line frequencies are well within the pass band of the Picoammeter on all ranges. Unless shielding is thorough, pickup may cause definite meter disturbances.

c. Use high resistance, low-loss materials

as polyethylene, polystyrene or Teflon

tion. The insulation resistance of test leads and fixtures should be several orders of magnitude higher than the source resistance. Excessive leakage

accuracy. Any coaxial cable used should be a lownoise type which employs a graphite coating between the dielectric and the surrounding shield braid.

d. Any change in the capacitance of the measuring

circuit to ground

ing, especially on the more sensitive ranges. Make the

measuring setup as rigid as possible, and tie

necting cables to prevent their movement. If a contin-

uous vibration

as a sinusoidal signal and other precautions may be necessary to isolate the instrument and the connecting cable from the vibration.

UHF

connector. The center terminal

will

cause disturbances in the read-

is

present,

it

may appear at the output

NOTE

is

-

for insula-

will

a Tef-

-

such

reduce

down

2.

is

con-

OPERATION

1.

When the etc. positions, use the upper meter scale. Full scale current range ting.

2.

When the etc. positions, use the lower meter scale. scale current range is equal to the setting

2-3, MEASUREMENT CONSIDERATIONS.

a. The Picoammeter employs the fast method

rent measurement the amplifier input and output in the feedback loop.

This method largely neutralizes the effect of input

capacity and greatly increases the response speed.

Also, the input voltage drop

of one millivolt on any range.

b. Rise time varies with the current range and the

input capacity (see specifications, Table time, though, across the input; however, Picoammeter nearer the current source than to the data reading instrument, Transmitting the input signal

through long cables of capacitance noise.

c. The internal resistance should not be less than the reciprocal of the current range being used, otherwise the zero stability affected. The instrument

ever, but the stability amount given by equation

Stability = 0.5%/week x (R, + Rf)/Rs

.

RANGE

Switch is set to

is

equal to the

RANGE

Switch

-

the measuring resistor

is

not affected with up to 500 picofarads

-

with greater than

will

increase response time and meter

is

set to 3,

is

reduced to a maximum

it

is better to place the

of

the unknown source

will

still be operable, how-

be degraded by the

1.

10,

RANGE

1).

500

Equation

1,

0.1,

Switch set-

0.3,

Full

Switch

of

is

between

The rise

picofarads

will

0.03,

cur-

be

1.

Keep the shield cap on the INPUT Receptacle

when the Picoarmneter

2-2.

OPERATING PROCEDURES.

a. Check the fuse and the 117-2341 V Switch for the

proper line voltage.

b. Connect the power cord to the power source.

+

RANGE

(+).

Within seconds the meter needle should

RANGE

METER

or

Switch to the polarity of the input

-.

Increase sensitivity with the

c. Set the

S

itch to

read zero. Zero the meter with the

After a few moments increase the current sensitivity b

advancing the ampere range. Continue zeroing with the

trol. The instrument

d. If long term measurements are to be made, allow

the instrument to warm up for at least

e. Attach the current source to the INPUT Receptacle and turn the signal, Switch until the greatest

is

not in a circuit.

Switch to ampere, the

ZERO

Switch in decade steps to the

is

now ready to use.

10

on

scale deflection is achieved.

ADJ.

Control.

ZERO

ADJ

minutes.

METER

RANGE

10-

Con-

4

where

Rf

is the feedback resistance in ohms;

Rs

is

the source resistance in ohms.

For example, if the source to be measured has a resis-

tance of

back resistor

gain of the Picoammeter stability of .5%/week the offset due to temperature

.5%/OC. This is the reason that

have the source resistance at least equal to the feed-

back resistor.

18

d. Overload Protection. complete overload protection for the Model 414A without compromising the features of the MOS Recovery

meter can withstand overloads of up to

for

volts without damage.

is

105

ohms and the current is

will

be

106

ohms. This means that the

is

106/105

will

be

.5%

will

A

unique circuit provides

is

instantaneous for most overloads.

1.

At

the ampere range and below the Picoam-

3

seconds and continuous overloads of up to

2.

Above amperes, the max. continuous overload

a function of rated power dissapation in the resistor.

lom6

=

10.

X

10 = 5%/week, and

be .05%

it

is

advantageous to

FET

1000

then the feed-

Then the zero

X

lo.=

input.

volts

600

0671

MODEL 414A OPERATION

TABLE

Allowable Overloads on Ranges Above 10-6 Ampere.

4.

Range Voltage Overload Current Overload

10-5

A

10-4 A 10-3

A

10-2 A

I

3. For maximum protection, use a Keithley Model

240A Voltage Supply, or some other

current limited supply, in combination with the

Picoammeter.

2-4. RECORDER OUTPUTS.

a. For recording with the Model 414A, use the Keithley Model 370 Recorder for ease, economy, versatility and performance. The Model 370 is a pen recorder with

10

chart speeds and put cable has a connector which mates directly with the OUTPUT Connector

interface problems often encountered between a measuring instrument and a recorder. The Picoammeter output,

when set to the

preamplifier is needed.

b.

Other recorders, oscilloscopes and similar in-

struments can be used with the Model 414A. The Pico-

ammeter has two outputs,

to amplify signals for recorders, oscilloscopes and similar instruments. These can be used on all ranges.

Max. Continuous Max. Continuous

300 V

120

v

30 V

v

12

1%

linearity. The Model 370's in-

on

the Picoammeter; this avoids

1

mA

position, will drive the 370; no

No

special wiring is required.

21

volt and

1mA

4mA

10

mA

40

mA

10

milliampere

21

milliampere,

I

J

$

1

Mode 414A

output

(5103)

FIGURE 3.

for Driving

d. 1-Milliampere Output. Connect 1-milliampere instruments to the OUTPUT Receptacle. Pin no, the high terminal. Set the

The output is approximately 1 milliampere for full-

scale meter deflection on any range. apply a known full scale signal to the Picoammeter and

adjust the

full scale. Check the recorder and meter zero and repeat adjustment if necessary. The METER Switch does

not reverse the output polarity which is always oppo-

site input polarity.

e. For servo rebalance recorders, use a divider across the Picoammeter OUTPUT Receptacle. See Figure

3. Set the OUTPUT Switch to Control to trim the output for full-scale recorder de-

flections. Operation is the same as for current outputs.

Divider Circuits Across Picoammeter Output

50

and 100-Millivolt Recorders.

1

mA

CAL Control until the recorder reads

kR

t

1

mA

mA.

Recorder

-

1

V Switch to

For exact output,

Use the.1

1

mA

is

1

mA.

CAL

c. 1-Volt Output. Connect oscilloscopes and pen

recorder amplifiers to the OUTPUT Receptacle. Pin

1

is the high terminal and pin no. 2 is ground. Set

1

mA

-

1

the

is now range. Internal resistance is approximately

Noise is less than.l% peak-to-peak of full scale. The

METER Switch does not reverse the output polarity.

Output polarity is always opposite input polarity.

V Switch

21

volt for full scale meter deflection on any

to

1

V. The Picoarmeter output

1

kilohm.

no.

2-5. 234-VOLT OPERATION. The instrument is shipped

for use with a 117-volt power source unless otherwise

ordered. To convert the Picoammeter for 234-volt

sources, use a screwdriver to change the slide switch

on

the back panel to the 234-volt position. Change the fuse from 0.125 ampere to .062 ampere. adjustment is necessary. To switch from 234 to 117-

volt operation, reverse the procedures.

No

other

0671

5