Keithley 485 Manuale utente

MODEL 485

AUTORANGING PICOAMMETER

QUICK REFERENCE GUIDE

INTRODUCTION

This reference and programming guide contains condensed specifica-

tions and information which describes the various features of the

Model 485. Each feature is described in three segments of informa-

tion. The first segment describes the features. The second segment

gives an exact procedure on how to use the feature. The third seg-

ment gives application examples. These segments are brief, but the

information presented in this format is designed for a quick reference

of the Model 485 features and functions. Refer to the Model 485 In-

struction Manual for complete information and essentialsafety infor-

mation.

With the Model 4853 IEEE-488 interface installed, the Model 485 can

be controlled over the IEEE-488 bus. This booklet also contains infor-

mation concerning Model 485 bus operation. Several example pro-

grams using some commonly used controllersare outlined to get the

Model 485/4853 “up and running”.

CONTENTS

CONDENSED SPECIFICATIONS .......................... 2

MODEL485 FEATURES ................................... 5

IEEE-488 PROGRAMMING.. ............................. 13

PROGRAMS ............................................ 18

IBM-PCorXTPersonalComputer.. ....................... 19

(Keithley Model 8573 Interface)

APPLE II (Apple Interface) ............................... 21

HP-85 ................................................. 22

HP-9825A.. ........................................... 23

HP-9816 ............................................... 24

HP-9845B.. ........................................... 25

TEK4052 .............................................. 26

DECLSIll.. ......................... ___. .......... _.- 27

PETlCBM2001 ........................................ 29

EH7000 Computer ..................................... 30

01984. Keithley Instruments, Inc.

Cleveland, Ohio, U.S.A.

Document Number: 485903-OlA

CONDENSED SPECIFICATIONS

Range

2nA

20 nA

2OilnA

Resolution

O.lpA

1 PA

10 pA

100 nA

1llA

10 nA

100 nA

Accuracy (1 year) Maximum

18O-2WC Continuous

*(%rdg + countsIt InputS

0.4 + 4 35OVdc

0.4 -t 1 35OVdc

0.2 + 1 35OVdc

0.15 + 1 35OVdc

0.1 +1 5OVdc

0.1 +1 5OVdc 1

W&h no limitiw resistance: 1OOOVdc with external lOOk series resistance.

INPUT VOLTAGE BURDEN: Lessthan 2OOhV.

RANGING: Manual or autoranging.

AUTORANGING TIME: 2COmsper range.

SElTLING TIME AT DISPLAY: Lessthan lsec to within 1cuunt after

ranging.

CONVERSION PERIOD: 300ms.

TEMPERATURE COEFFICIENT: -z f0.1 x applicable accuracy

specificationper T.

MAXIMUM COMMON MODE VOLTAGE: BOVrms, DC to 60Hz

sinewave.

ANALOG OUTPUT:

Output Voltage: +lV, = -10000 counts. (Except +lOOmV =

-1OoM) wunts on 2nA range.)

Output Resistance: 1OOOQ.

RELATIVE: Pushbutton allows zeroing of on range readings. Allows

readings to be made with respect to baseline value. Front panel

annunciatorindicatesREL mode.

DATA STORE and MINIMAX: 100 readingstoragecapacity. Records

date at one of seven selectable rates from Brdgs/s to lrdg/hr and

manual triggering. Also detects and stores maximum and minimum

readingscontinuouslywhile in the data store mode.

LOG: Displaysthe logarithm(base10)of the inputcurrentreferencedto

1A.

SAFETY SYMBOLS AND TERMS

The ayrnboj

Q I on the instrument denotes that user shouldrefer to

the operating section in the Model 455 InstructionManual.

The WARNING usedinthisguideexplainsdangers that could resultin

personalinjuryor death.

SAFETY PRECAUTIONS

1. Before operation, ground the instrument through a properly earth

grounded power receptacle.

2. Before servicing,disconnectthe instrumentfrom the power line, all

other equipmentand consultthe Model 455 InstructionManual.

3. Do not touch the inputterminalwhile the instrumentisturned on or

connacted to any other tast equipment. Commonmodevoltagemay

be prasent.

DISPLAY ANNUNCIATORS

the fol\owing annunciators are displayA on the LCD Kiquid Crystal

Display1

AUTO-Indicates that the h+nfel485 is in the autorange mode.

REL--lnticates that the relativemodeisselecttxl. The readingisr&t&

to some previousreading.

LOG-Log mode readingisdirectlyin log (base 101.

SO-Indicates that the data store and minimax hold function is run-

ning. Displayedraadjng ispresent input.

RCL-Indicates that the displayedreadingis recalleddata.

BAT-Indicates that the battery requires recharghg (operates only if

the battery pack option Model 1758, is instaliedl.

ZERO CHECK-Indicates that the Model 485 is in the zero check

mode. Input impedancechangeswhen inthe zero check mode.

nA, & or mA-Nanoamps, microamps or milliampsselected. Read

measurementdirectlyfrom the display. (e.g. 1.2345fll

RMT--(Remote) Model 485 is beingcontrolledover the IEEE-488 bus

(Model 4853 installed).

CAL-Indicates that the Model 435 isin the calibrationmode.

MODEL 485 FEATURES

RANGE t2nA to 2mAl

I z&v I 35ov 5ov 5ov 5ov

MAX MAX MAX MAX

Description

The range buttonsse&t the desiredrange of current measurementfor

the Model 485. The range may’be selected manuallyor automatically.

With manual range selection always use the range that allows the

greatest amount of resolution.

Operation

Manual

1. Determinesignalto be measured.

2. Pressappmpriate range button.

3. Apply signal.

Auto

1. Pressthe AUTO button.

2. Apply signal.

ZERO CHECK

DesctiptIon

The ZERO CHECK button is used to correct interna ofFsetsand also

protects the sensitiveinput circuitryfrom buildup during overloads. In

the zero check mode or input overload, the input impedance of the

Modal 495 is changed as outlinedin the followingtable.

INPUT RESISTANCE WITH ZERO CHECK ENABLED

Current Maximum Effective

Ranae lmut Resistance

2nA 1 1GMl

Impedance In

Zero Check/Overload

9MWX3IpF

1. Select range.

2. Depress ZEFtOCHECK. The ZERO CHECK button operatas on the

push-pushprinciple.That is, pressingin the button locksthe instru-

ment inzero check, pressingthe button againreleasesthe zero check

mode.

Typical Use

Used in zeroing the2nA range for precise measurements. Refer to

paragraph 2.72 in the Model 495 InstructionManual.

REL (Relative Function)

REL

Description

The relativefunctionservesasa meansof baselinesuppressionallowing

a storedoffset valueto be subtractedfrom subsequentreadings.When

the REL button is pressed, the instrumentstores the baselinereading

with the next conversion. All subsequent readings represent the di-

ferences between the applied signalleveland the stored baseline.The

stored baselinecan be as smallas the resolutionof the instrumentwill

allow or as large as full range.

It isimportantto note that the RELfunctionreducesthe dynamicrange

of measurementsby that level (stored baseline). For example:assume

that the RELlevelis + Id and the Model495 ismanuallyset to thew

range. The maximum positivedisplayed reading, before overranging,

would be + 0.9999& Thisisbecausethe A/D converterwould be see-

ing + 1.9999fi to + 0.9999fi (2.999&A) as compared to the normal

-1.9999fi to + 1.9999d (3.9998fi). Actually, the dynamic range is

reduced by lfi or 10,000 counts. The effects on dynamicrangecan be

reduced by selectinge higher range or usingautorange.

Operation

1. Select measurementmodeand range. Forexample:normalmeasure-

ment mode and the w range.

2. PressREL. The displayreads zero.

3. The value that appeared on the displayis now the stored offset.

Typical Use

1. Nullingout external source offset (e.g. calibratoroffset).

2. Nulling out desired levels of offset (e.g. electrode dark current of

phototube).

LOG (Log Function)

Description

The log function givesthe log (base 101of the measuredinput current

referenced to 1A. Log can be used to make any current levelthe 0.0

(zero) point for log measurements. This can be done by selecting

autorange and log. Then measuringthe desiredcurrentthat isto be the

0.0 [zero) point. The logarithm is taken on the absolute value of the

measurement so that both positive and negative currents can be

displayedas e log. Pressthe REL button and the displaywiil read 0.0

(zero). The measured current is now the 0.0 (zero) point for the log

function. The mathematical equation for the log function is shown as

follows:

Input

Display = Log -

I I

1 Amp

Operation (referenced to IA)

1. Select the auto range mode.

2 Apply the source.

3. Pressthe LOG button. The LOG annunciatoron the displayturnson.

4. Take the log readingfrom the display.

Typical Use

1. For use in measuringe wide range of current. Nuclear reactorshave

variousoutputsof currentthat could be compressed(inreadingson-

ly) by usingthe log function.

2 Measuring the current output of a phototube. REL can be used to

nu[lthe dark current of the phototube.

DATA STORE (100 Point Data Store1

Description

The 100pointdata storefunctionservesto saveupto 100pointsof data

at the rate of one of six selectable rates from every reading (3 per

second) to one reading per hour. Also, manual data entry is available

(RN. This feature is usefulin applicationswhere data is requiredto be

logged over a periodof time.

Operation

1. Connect desiredmeasurement configurationto the Model 485.

2. Select rate of storage and begin data store:

A. Pressand hold in the STO/CLR button.

6. The rates are scrolled on the display. Tithe rates are described

below).

C. Releasethe STWCLR button when the desiredrate isdisplayed.

D. The ST0 annunciator turns on indicatingthat the data is being

stored at the selected rate.

Typical Use

1. Saving data pointsof current driftof a low leakagedevicesuch as e

FEr.

2. Monitoringand saving current levelsthat fluctuate over a period of

time.

r = 0 (every reading)

r = 1 (1 reading per second)

r = 2 (1 reading per 10 seconds)

r = 3 I1 readingper minute)

r = 4 I1 reading per 10 minutes)

r = 5 (1 reading per hour)

T = S (everytime STOKLR is pressed)

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