Fluke 2180A User Manual

4 (1)

For the benefit and convenience of its customers, Fluke Corporation (Fluke) has reproduced this copy of a manual which is no longer in production. This manual has not been edited or updated since the revision date shown on the lower left hand corner of the first page. Fluke will not be liable for any claims, losses or damages of any kind

incurred by any user arising from use of this manual.

2180A

Digital Thernnometer

Instruction Manual

P/N 489211

June 1978

REV. 2, 9/88

®1988, John Fluke Mfg. Co., Inc., all rights reserved. Litho in U.S.A.

WARRANTY

Notwithstanding any provision of any agreement the following warranty is exclusive:

The JOHN FLUKE MFG. GO., INC., warrants each instrument it manufactures to be free from defects in material and workmanship under normal use and service for the period of 1 -year from date of purchase. This warranty extends only to the original purchaser. This warranty shall not apply to fuses, disposable batteries (rechargeable type batteries are warranted for 90-days), or any product or parts which have been subject to misuse, neglect, accident, or abnormal conditions of operations.

In the event of failure of a product covered bythis warranty, John Fluke Mfg. Co., Inc., will repair and calibrate an instrument returned to an authorized Service Facility within 1 year of the original purchase; provided the warrantor’s examination discloses to its satisfaction that the product was defective. The warrantor may, at its option, replace the product in lieu of repair. With regard to any instrument returned within 1 year of the original purchase, said repairs or replacement will be made without charge. If the failure has been caused by misuse, neglect, accident, or abnormal conditions of operations, repairs will be billed at a nominal cost. In such case, an estimate will be submitted before work is started, if requested.

THE FOREGOING WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS, OR ADEQUACY FOR ANY PARTICULAR PURPOSE OR USE. JOHN FLUKE MFG. CO., INC., SHALL NOT BE LIABLE FOR ANY SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, WHETHER IN CONTRACT,

TORT, OR OTHERWISE.

If any failure occurs, the following steps should be taken:

1.Notify the JOHN FLUKE MFG. CO., INC., or nearest Service facility, giving full details of the difficulty, and include the model number, type number, and serial number. On receipt of this information, service data, or shipping instructions will be forwarded to you.

2.On receipt of the shipping instructions, forward the instrument, transportation prepaid. Repairs will be made at the Service Facility and the instrument returned, transportation prepaid.

SHIPPING TO MANUFACTURER FOR REPAIR OR ADJUSTMENT

All shipments of JOHN FLUKE MFG. CO., INC., instruments should be made via United Parcel Service or “Best Way”* prepaid. The instrument should be shipped in the original packing carton; or if it is not available, use any suitable container that is rigid and of adequate size. If a substitute container is used, the instrument should be wrapped in paper and surrounded with at least four inches of excelsior or similar shock-absorbing material.

CLAIM FOR DAMAGE IN SHIPMENT TO ORIGINAL PURCHASER

The Instrument should be thoroughly inspected immediately upon original delivery to purchaser. All material in the container should be checked against the enclosed packing list. The manufacturer will not be responsible for shortages against the packing sheet unless notified immediately. If the instrument is damaged in any way, a claim should be filed with the carrier immediately. (To obtain a quotation to repair shipment damage, contact the nearest Fluke Technical Center.) Final claim and negotiations with the carrier must be completed by the customer.

The JOHN FLUKE MFG. CO., INC, will be happy to answer all applications or use questions, which will enhance your use of this Instrument. Please address your requests or correspondence to: JOHN FLUKE MFG. CO., INC., P.O. BOX C9090, EVERETT, WASHINGTON 98206, ATTN: Sales Dept. For European Customers: Fluke (Holland) B.V., P.O. Box 2269,5600 CG, Eindhoven, The Netherlands.

♦For European customers. Air Freight prepaid.

John Fluke Mfg. Co., Inc., P.O. Box C9090, Everett, Washington 98206

Rev. 7/88

2180A

Table of Contents

SECTION

 

 

TITLE

PAGE

1

INTRODUCTION AND SPECIFICATIONS ..............................................................

1-1

 

M.

 

INTRODUCTION ............................................................................................................

1-1

 

1-3.

 

DESCRIPTION ................................................................................................................

1-1

 

1-

10.

SPECIFICATIONS ...........................................................................................................

l-I

2

OPERATING INSTRUCTIONS ................................................................................

2-1

 

2-

1.

INTRODUCTION ............................................................................................................

2-1

 

2-3.

 

SHIPPING INFORMATION .........................................................................................

2-1

 

2-6.

 

INPUT POWER ...............................................................................................................

2-1

 

2-10.

INSTALLATION .............................................................................................................

2-1

 

2-14.

OPERATING FEATURES .............................................................................................

2-2

 

2-16.

OPERATING NOTES......................................................................................................

2-4

 

2-18.

Option Information ......................................................................................................

2-4

 

2-20.

Fuse Replacement ........................................................................................................

2-4

 

2-22.

RTD Installation...........................................................................................................

2-4

 

2-24.

OPERATING DIRECTIONS..........................................................................................

2-5

 

2-

26.

Additional Features.......................................................................................................

2-5

3

THEORY OF OPERATION ......................................................................................

3-1

 

3-

1.

INTRODUCTION ............................................................................................................

3-1

 

3-4.

 

FUNCTIONAL DESCRIPTION.....................................................................................

3-1

 

3-9.

 

CIRCUIT ANALYSIS......................................................................................................

3-2

 

3-11.

Digital Section...............................................................................................................

3-2

 

3-

16.

Analog Section .............................................................................................................

3-2

4

MAINTENANCE .......................................................................................................

4-1

 

4-

1.

INTRODUCTION ...........................................................................................................

4-1

 

4-3.

 

SERVICE INFORMATION ...........................................................................................

4-1

 

4-6.

 

GENERAL MAINTENANCE ........................................................................................

4-1

 

4-7.

 

Instrument Disassembly and Reassembly .................................................................

4-1

 

4-9.

 

Input Power ...................................................................................................................

4-2

 

4-11.

Cleaning .........................................................................................................................

4-2

 

4-13.

Fuse Replacement .........................................................................................................

4-2

 

4-15.

Service Tools .................................................................................................................

4-2

 

4-17.

Static Discharge Precautions........................................................................................

4-2

 

4-19.

PERFORMANCE TEST .................................................................................................

4-3

 

4-23.

CALIBRATION ...............................................................................................................

4-4

 

4-25.

Equipment Preparation ...............................................................................................

4-4

 

4-27.

Reference Adjust ...........................................................................................................

4-4

 

4-29.

Reference Adjust (+V) ..................................................................................................

4-4

 

4-31.

Zero Adjust ....................................................................................................................

4-4

(Continued on Page ii)

i

2180A

TABLE OF CONTENTS, continued

SECTION

TITLE

PAGE

6

7

7A

8

4-33. Resolution Adjustments ...................................................................................................

4-6

4-35. RTD Input Module Adjustment.......................................................................................

4-6

4-37. Lag Bath Construction .....................................................................................................

4-6

4-39. SELECTED COMPONENT REPLACEMENT.............................................................

4-7

4-

41. TROUBLESHOOTING.....................................................................................................

4-7

LIST OF REPLACEABLE PARTS ............................................................................

5-1

 

TABLE OF CONTENTS ................................................................................................

5-1

5-

1. INTRODUCTION .............................................................................................................

5-2

5-4.

HOW TO OBTAIN PARTS..............................................................................................

5-2

OPTION AND ACCESSORY INFORMATION ..........................................................

6-1

 

TABLE OF CONTENTS ................................................................................................

6-1

GENERAL INFORMATION ..................................................................................

7-1

MANUAL STATUS INFORMATION ..........................................................................

7A-1

SCHEMATIC DIAGRAMS .........................................................................................

8-1

 

TABLE OF CONTENTS ................................................................................................

8-1

2180A

List of Tables

TABLE

TITLE

PAGE

1-1.

 

2180A Options and Accessories .........................................................................................................

1-2

1-2.

 

RTD Total Instrument Accuracy Specifications .............................................................................

1-2

1-3.

 

IPTS 68 Coefficients* .........................................................................................................................

1-4

1-

4.

General Specifications ........................................................................................................................

1-4

2-

1.

Controls, Indicators and Connectors ................................................................................................

2-3

2-2.

 

RTD Input Module Switch (SI)Settings ..........................................................................................

2-5

2-

3.

RTD Input Module Switch Functions .............................................................................................

2-6

3-

1.

Mnemonics ...........................................................................................................................................

3-2

4-

1.

Line Voltage Selection.............................................................. ................................... .......................

4-2

4-2.

 

Recommended Test Equipment .........................................................................................................

4-4

4-3.

 

2180A Performance Tests ...................................................................................................................

4-5

4-4.

 

2180A Troubleshooting .......................................................................................................................

4-8

4-5.

 

Test Point Identification .....................................................................................................................

4-11/4-12

 

 

* For 2180A curve fit Linearizations

 

iii/iv

2180A

THIS PAGE INTENTIONALLY LEFT BLANK

2180A

List of Illustrations

FIGURE

TITLE

PAGE

Frontispiece Model 2180A Digital Thermometer ......................................................................................................

vi

2-1.

 

Controls, Indicators and Connectors .................................................................................................

2-2

2-2.

 

RTD Connections .................................................................................................................................

2-5

2-

3.

RTD Input Module Access ..................................................................................................................

2-6

3-

1.

2180A Simplified Block Diagram .......................................................................................................

3-1

3-2

 

Simplified Schematic Diagram - Digital ............................................................................................

3-3

3-

3

Simplified Schematic Diagram - Analog ...........................................................................................

3-4

4-

1.

Line Voltage Selection .........................................................................................................................

4-2

4-2.

 

Performance Test Connections ...........................................................................................................

4-3

4-3.

 

Calibration Connections .....................................................................................................................

4-5

4-4.

 

Test Points and Measurement Cycle Waveforms .............................................................................

4-9

2160A

Model 2180A Digital Thermometer

2180A

Table 1-2. RTD Total Instrument Accuracy Specifications (cont)

R

R

TEMPERATURE RANGE

 

MAXIMUM

EERROR*

 

T

E

APPLICABLE PORTION OF

+/-DEGREES C

-^/-DEGREES F

D

S

 

 

AT

 

 

AT

 

 

 

 

0

 

 

90

1

90

 

1

T

L

 

 

CAL

DAYS

YR.

CAL

DAYS

 

YR.

Y

U

oc

OF

 

200

150

 

680

 

590

P

L

 

 

 

to

to

 

to

 

to

E

T

 

 

 

300

350

 

860

 

950

 

1

 

 

 

 

 

 

 

 

 

 

0

 

 

 

 

 

 

 

 

 

 

N

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

100

.01°

-200 to 0

-327.9 to 32

.009

.055

.078

.015

.100

 

.142

ohm

 

0 to 204

32 to 399.2

.009

.098

.139

.015

.177

 

.252

 

 

 

 

 

 

 

 

 

 

 

390

.1°

-200 to 0

-327.9 to 32

.08

.10

.11

.13

.16

 

.19

Pt

 

0 to 750

32 to 1382.2

.08

.23

.32

.13

.41

 

.57

 

 

 

 

 

 

 

 

 

 

 

100

.01°

-200 to 0

-327.9 to 32

.040

.086

.109

.071

.156

 

.198

ohm

 

0 to 204

32 to 399.2

.040

.13

.171

.071

.234

 

.309

 

 

 

 

 

 

 

 

 

 

 

3916

.1°

-200 to 0

-327.9 to 32

.11

.12

.14

.17

.21

 

.24

R

 

0 to 750

32 to 1382.2

.10

.26

.34

.17

.46

 

.62

 

 

 

 

 

 

 

 

 

 

 

100

.01°

-200 to 0

-327.9 to 32

.008

.055

.078

.014

.099

 

.141

ohm

 

0 to 204

32 to 399.2

.009

.098

.139

.014

.177

 

.252

 

 

 

 

 

 

 

 

 

 

 

392

.10

-200 to 0

-327.9 to 32

.08

.01

.11

.12

.16

 

.19

R

 

0 to 750

32 to 1382.2

.08

.23

.32

.12

.41

 

.57

 

 

 

 

 

 

 

 

 

 

 

100

.010

-60 to 0

-76 to 32

.129

.157

.172

.230

.282

 

.308

ohm

 

Oto 93

32 to 199.4

.129

.176

.199

.231

.317

 

.359

 

 

 

 

 

 

 

 

 

 

 

617

.10

-60 to 0

-76 to 32

.19

.20

.21

.33

.35

 

.36

Ni

 

0 to 177

32 to 350.6

.19

.22

.25

.33

.39

 

.44

 

 

 

 

 

 

 

 

 

 

 

10

.010

N/A

 

 

 

 

 

 

 

 

ohm

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CU

.10

-75 to 0

-103 to 32

.16

.18

.19

.27

.31

 

.34

 

 

-75 to 150

-103 to 302

.16

.20

.23

.27

.35

 

.41

 

 

 

 

 

 

 

 

 

 

 

ohms

 

Oto 196.99

.005

.042

.059

ALL UNITS IN OHMS

 

 

 

0 to 999.99

.05

.22

.31

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Maximum error depends on the temperature measured and the resolution used. Of the four temperature ranges presentd for each RTD, the first two represent .01° resolution. The above maximum error numbers represent instrument errors only, and do not include the RTD probe.

1-3

Fluke 2180A User Manual

2180A

 

 

Table 1-3. IPTS 68 Coefficients*

 

 

 

 

 

RTD TYPE

 

RTD LINEARIZATION COEFFICIENTS

 

 

 

 

 

100 OHM

 

DIN 43760 TABLE

 

385 Pt

 

 

 

100 OHM

 

ALPHA = 0.0038994

 

390 Pt

 

DELTA = 1.494

 

 

 

A4 = -.0.265668^°''

 

 

 

C4 = -0.205984^°''

 

100 OHM

 

ALPHA = 0.003916

 

3916 Pt

 

DELTA = 1.505

 

 

 

A4 = -.099668^°'

 

 

 

C4 =-0.192912^°''

 

100 OHM

 

ALPHA = 0.00617

 

NI

 

 

 

10 OHM

 

RO = 9.042 OHM

 

eu

 

R25 = 10.005 OHM

 

 

 

ALPHA = .004260

 

 

 

 

 

 

*SEE NBS MONOGRAPH 126

 

 

 

 

 

 

Table 1-4. General Specifications

DIMENSIONS

 

 

RELATIVE HUMIDITY

10.49 cm H X 20.45 cm W x 32.64 cm D <80%, non-condensing, 0 to 50°C (4.13 in H X 8.05 in W X 12.85 in D)

WEIGHT

SHOCK AND VIBRATION

2.1 kg (4 lbs. 9 oz.)

Meets Ml L-T-28800 specifications

OPERATING POWER

INPUT CONNECTION

12V dc or 100, 120, 220, 240V ac ±10%, selectable

4-wire to screw terminal block

50 to 400 Hz; 8W typical, 14W max.

 

 

 

WARM-UP to RATED ACCURACY

INPUT IMPEDANCE

5 minutes

1000 Mohms at DC

STORAGE TEMPERATURE

STABILITY

-40°C to -H75°C

±175 ppm in 90 days, ±200 ppm p:r \ :

(Y2009 and Option 21X0A-004:0 to 40° C)

 

ii

!

|.

1-4

2180A

Table 1-4. General Specifications (cont)

OPERATING TEMPERATURE

TEMPERATURE COEFFICIENT

0 to 50°C

±15 ppm/°C from 25°C

(Y2009: Oto 40°C)

 

 

 

ACCURACY vs WIRE LENGTH

RTD EXCITATION CURRENT

No lead resistance error 4-wire RTD's if R2

Nominal 0.5 mA.

adjustment on the RTD Input Module Is

 

used. Otherwise, 0.04°C/i2 resistance of any

 

one input lead if R2 is not adjusted.

COMMON MODE VOLTAGE

 

 

 

DISPLAY

350V dc, 250V ac rms max.

F or C, switch-selectable, 7-segment LEDs 1.1 cm

 

 

high

NORMAL MODE REJECTION

 

 

RESOLUTION

>90 dB at DC, 50, 60, and 400 Hz ±0.1%.

0.01 below 204 C for platinum RTD's, automatically

 

 

shifting to 0.1° above 204°C (93°C for nickel RTD's).

RESPONSE TIME

If readings are decreasing, shift Is at 77°C for platinum,

1 second typical.

66°C for nickel.

 

 

 

MEASUREMENT METHOD

ZERO DRIFT

Dual slope integration, under microcomputer control.

Automatic zero correction.

100 ms integration period, three readings per second.

 

A/D Resolution is 100,000 counts at full-scale.

RTD TYPES

 

 

100S2 385 Pt (DIN), 390 Pt, 3916 Pt, 392 Pt,

LINEARIZATION TECHNIQUES

100S2NÌ (DIN), lOnCU.

 

Computer algorithm, 4th order curve fit.

 

 

 

COMMON MODE REJECTION

VOLTAGE RANGE (CALIBRATION ONLY)

No annunciator or decimal point.

>160 dB at DC, 50, 60, and 400 Hz ±0.1% with 100i2

99999 MV full scale (switch S2 in AUTO), resolution 1 ¡A/

unbalance at inputs.

999990 MV full scale (switch S2 in .1), resolution 10 MV

 

 

SAFETY

 

Protection Class 1

 

Relates solely to insulation or grounding properties

 

defined in lEC 348.

 

 

 

1-5/1-6

2180A

THIS PAGE INTENTIONALLY LEFT BLANK

:Si^TRODUCTION

1-2. The Model 2180A Digital Thermometer is a portable, five digit RTD thermometer. Temperature measurements are possible, depending on RTD type employed, over a range of-219° C to +664° C (-394° F to +1435°F) with 0.1° or .01° resolution. The instrument features:

1. Front Panel switch selection of Fahrenheit or Celsius readings.

2.Switch selectable RTD inputs.

3.Switch selectable input line voltage.

4.Dual slope measurement techniques.

5.Digital linearization of the RTD inputs.

1-3. DESCRIPTION

1-4. The instrument display features seven, highintensity, seven segment LEDs, and leading zero suppression. Six of the LEDs are used to display numeric data, with a minus sign for negative temperature readings. The remaining LED displays the selected temperature scale character (°F or °C).

1-5. A four connection, screw-type terminal block is provided on the removable Input PCB for RTD connections. Input switch settings on this module will determine the microcomputer program necessary to linearize the desired RTD’s input. A precision, four-wire resistance measurement of the RTD is routed through this module to the thermometer’s input circuitry.

2180A

Section 1

Introduction & Specifications

1-6. Selection of the temperature scale for display is made with a front panel pushbutton. The scale selected, Celsius or Fahrenheit, is displayed as the last character in the temperature reading (°C or ° F). A scale change can be made at any time, and has no effect on calibration of the instrument.

1-7. Options and accessories available for the 2180A are listed in Table 1-1. More information concerning these items is given in Section 6 of this manual. Option and Accessory Information.

1-8. The measurement range of the 2180A Digital Thermometer is determined by the type of RTD used as the input device. RTD Types and total instrument accuracy specifications are listed in Table 1-2. Linearization of the RTD input is accomplished through toggling of the input switch segments on the RTD Input Module. Switch positions, numbers and applications are printed on the removable module beside the switch.

1-9. Four input line voltages are available for switch selection. Selection may be made for 100,120,220, or 240 volts ±10% as required to meet local conditions. Fre­ quency may vary between 50 and 440 Hertz for all voltage selections. Refer to Section 4 of this manual when changing the selected input line voltage. Refer to Section 2, “Input Power” for 12 volt dc operation.

1-10. SPECIFICATIONS

1-11. Specifications for the 2180A Digital Thermometer are given in Table 1-4. These specifications assume that microcomputer type #2 has been installed in your instru­ ment and at power-up the display reads “8002.2”

1-1

2180A

 

Table 1-1. 2180A Options and Accessories

 

 

ACCESSORY

DESCRIPTION

 

 

Y2000

Multipoint Selector, RTD

Y2009

Battery Pack, 12V Rechargeable

Y2010

Rack Panel PTI, single, A size (for Y2000)

Y2014

Rack Panel PTI, single, C size (for 2180A and Y2002)

Y2015

Rack Panel PTI, double, C size (for 2180A and Y2002)

Y2016

7-inch Rack Adapter PTI, single, D size

Y2017

7-inch Rack Adapter PTI, double, D size

Y2020

Panel Mount PTI-DIN, C size (for 2180A and Y2002)

Y2021

145 mm Panel Mount PTI, D size

Y2022

Divider, Thermometer Calibrator

Y2024

Power Cord, 3-way

Y2026B

Cable, Output Unit, RS-232-C

Y2031

Input Module (for 2180A)

Y2035

Thermal Paper (box of 10)

Y2037

Pt 390 RTD Probe

Y2039

Pt 392 Probe

 

 

Table 1-2. RTD Total Instrument Accuracy Specifications

R

R

TEMPERATURE RANGE

 

MAXIMUM ERROR*

 

 

T

E

APPLICABLE PORTION OF

+/-DEGREES C

+/-DEGREES F

D

S

 

 

AT

90

1

AT

 

90

1

 

0

 

 

 

T

L

 

 

CAL

DAYS

YR.

CAL

 

DAYS

YR.

Y

U

oc

OF

 

200

150

 

 

680

590

P

L

 

 

 

to

to

 

 

to

to

E

T

 

 

 

300

350

 

 

860

950

 

1

 

 

 

 

 

 

 

 

 

 

1

 

 

 

 

 

 

 

 

 

 

0

 

 

 

 

 

 

 

 

 

 

N

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

100

,0lo

-190 to 0

-309.9 to 32

.043

.089

.112

.076

 

.161

.203

ohm

 

0 to 204

32 to 399.2

.043

.132

.173

.076

 

.239

.314

 

 

 

 

 

 

 

 

 

 

 

385

.10

-190 too

-309.9 to 32

.11

.12

.14

.18

 

.21

.24

R

 

0 to 750

32 to 1382.0

.11

.26

.37

.18

 

.46

.62

 

 

 

 

 

 

 

 

 

 

 

1-2

Knowing that there is a problem. Learning the guidelines for handling them. Using the procedures, and packaging and bench techniques that are recommended.

Some semiconductors and custom IC’s can be damaged by electrostatic discharge during handling. This notice explains how you can minimize the chances of destroying such devices by:

1.

2.

3.

The Static Sensitive (S.S.) devices are identified in the Fluke technical manual parts list with the symbol

“ ( X ) ”

The following practices should be followed to minimize damage to S.S. devices.

 

3DISCHARGE. PERSONAL STATIC BEFORE

 

HANDLING DEVICES. USE A HIGH RESIS­

1. MINIMIZE HANDLING

TANCE GROUNDING WRIST STRAP.

KEEP PARTS IN ORIGINAL CONTAINERS

4. HANDLE S.S. DEVICES BY THE BODY

UNTIL READY FOR USE.

Page 1 of 2

5.USE STATIC SHIELDING CONTAINERS FOR HANDLING AND TRANSPORT

6.DO NOT SLIDE S.S. DEVICES OVER ANY SURFACE

7.AVOID PLASTIC, VINYL AND STYROFOAM« IN WORK AREA

PORTIONS REPRINTED

WITH PERMISSION FROM TEKTRONIX, INC.

AND GENERAL DYNAMICS, POMONA DIV.

® Dow Chemical

Page 2 of 2

a o

iiiiiiHumir-wiiuuiiiiLimi

8. WHEN REMOVING PLUG-IN ASSEMBLIES, HANDLE ONLY BY NON-CONDUCTIVE EDGES AND NEVER TOUCH OPEN EDGE CONNECTOR EXCEPT AT STATIC-FREE WORK STATION. PLACING SHORTING STRIPS ON EDGE CONNECTOR HELPS TO PROTECT INSTALLED SS DEVICES.

9.HANDLE S.S. DEVICES ONLY AT A STATIC-FREE WORK STATION

10.ONLY ANTI-STATIC TYPE SOLDERSUCKERS SHOULD BE USED.

11.ONLY GROUNDED TIP SOLDERING IRONS SHOULD BE USED.

A complete line of static shielding bags and acces­ sories is available from Fluke Parts Department, Telephone 800-526-4731 or write to:

JOHN FLUKE MFG. CO., INC. PARTS DEPT. M/S 86

9028 EVERGREEN WAY EVERETT, WA 98204

J0089D-07U8604/SE EN Litho in U.SA

Rev. 1 MAR 86

2180A

Section 2

Operating Instructions

2-1. INTRODUCTION

2-2. This section of the manual contains information regarding installation and operation of the 2180A Digital Thermometer. It is recommended that the contents of this section be read and understood before any attempt is made to operate the instrument. Should any difficulties arise dur­ ing operation, please contact your nearest Fluke Technical Service Center, or John Fluke Mfg. Co., Inc. P.O. Box C9090, Everett, WA 98206, Tel(206) 356-5400. A list of Technical Service Centers is located in Section 7 of this manual.

2-3. SHIPPING INFORMATION

2-4. The 2180A is packaged and shipped in a foampacked container. Upon receipt of the instrument, a thorough inspection should be made to reveal any possible, shipping damage. Special instructions for inspection and claims are included on the shipping carton.

2-5. If reshipment of the instrument is necessary, the original container should be used. If the original container is not available, a new one can be obtained from the John Fluke Mfg. Co., Inc. Please reference the instrument model number when requesting a new shipping container.

2-6. INPUT POWER

2-7. The 2180A will operate at any of four switch selected input line voltages, all of which operate at frequencies from 50 to 440 Hertz. Before connecting the 2180A to the local ac line, verify that the present setting of the instrument matches the local line voltage. A decal on the instrument rear panel defines the original setting

required for operation. Refer to Section 4 of this manual for instructions on verifying or changing the input line voltage switch settings.

2-8. The rear panel ac input connector is a three-prong, U-ground connector which permits the instrument to be connected, via the power cord, to the applicable line voltage. The offset prong on this connector is attached to the 2180A power supply, and should be connected through the power cord to a high quality earth ground.

2-9. The 2180A will also operate on 12V dc power. A rear panel terminal block, with screw tightened connections, (TBl), allows for ease of attachment. Actual input voltage may vary from 11 to 15V dc; most 12V dc power supplies capable of supplying lA (e.g., a car battery) can be utilized.

2-10. INSTALLATION

2-11. The 2180A is contained in a special molded plastic instrument case. Other associated accessories used with the 2180A will be packaged in similar PTI (Portable Test Instrument) cases varying only in size. The cases are, in all other respects, compatible and can be stacked vertically and latched together to form miniature portable test systems. Instrument stacks should be limited to a total of 40 pounds.

2-12. Use the following procedure when attaching PTI cases to each other:

1. For the top case, pull out latches found on either side of the instrument.

2.Nestle top and bottom cases together.

3.Push latches in to secure units together.

2-1

2180A

2-13. Prepare the 2180A for operation by plugging the input line power cord into the applicable power source or connecting the external input connector to an external 12V dc source.

2-14. OPERATING FEATURES

2-15. The location of the 2180A controls, indicators, and connectors is shown and described in Figure 2-1 and Table 2-1 respectively.

Figure 2-1. Controls, Indicators and Connectors

2-2

2180A

 

Table 2-1. Controls, Indicators and Connectors

REF

NAME

FUNCTION

1

Digital Display

Displays a five digit readout of the measured input temperature. Leading

 

 

zero suppression and a variable position decimal point are included. A

 

 

minus sign is displayed for negative temperature measurements. Flashes

 

 

when overranged.

2

Temperature Scale Indicator

Displays the temperature scale represented by the digital display data:

 

 

Or» Oc

 

 

C or F.

3

Power Switch

Push on/Push off.

4

SCALE

Selects the temperature scale for display: °C or °F.

5

LIMIT and FUNCTION

Part of the —006 Limits Option. When installed, the thumbwheels may

 

 

be set to a four digit LIMIT value (+ or —). The FUNCTION thumbwheel

 

 

can then be set to define the limit value and signal (LIMIT EXCEEDED)

 

 

when the displayed temperature has exceeded the limit value (>, <). Dis­

 

 

play will read the difference between the thumbwheel setting and the

 

 

actual temperature when (A) is set in FUNCTION. Set FUNCTION thumb­

 

 

wheel for storage of maximum (T ) or minimum (J_) measured since

 

 

last initializing (no limit value settings).

6

LIMIT EXCEEDED

Part of the —006 Limits Option. Indicator illuminates when the preset

 

 

limits have been exceeded.

7

CALIBRATION COVER

Sliding cover for calibration adjustments.

8

INITIALIZE MAX/MIN

Part of the —006 Limits Option. Resets the previous maximum and

 

 

minimum readings stored by the microcomputer.

9

DIGITAL OUTPUT

Connector for the ASCII coded data for the Output Unit, if 21XOA-002 is installed.

 

 

Connector for the IEEE-488 if 21X0A-004 is installed (instead of 21X0A-002).

9a

ANALOG OUTPUT

Banana jack connector for an Analog Output (1 mV per degree), if 21XOA-002 Is

 

 

installed. (Only used with 21X0A-002.)

10

RTD INPUT MODULE

Removable module houses RTD Input connections and type selection

 

 

switch.

11

F2

External 12V dc input fuse (3/4A MDL slo-blo).

12

ACCESSORY CONNECTOR

Cable connector for accessory bus connection from accessory units.

13

FI

Input line power fuse 1/8A (100 or 120 VAC) 1/16A (220 or 240 VAC).

 

 

MDL (slo-blo).

14

LIMITS

When the Limits Option is installed, it provides contact closure when

 

 

the set limit has been exceeded.

1b

±12 VDC

Input terminals for the external 12V dc power source.

16

LINE VOLTAGE

Input connector for the input line voltage.

 

CONNECTOR

 

 

 

 

2-3

2180 A

2-16. OPERATING NOTES

2-17. The following paragraphs describe various conditions that could affect operation of the thermometer. The operator should familiarize himself with these conditions prior to operating the 2180A.

2-18. Option Information

2-19. Supplementary operating instructions are necessary when operating the 2180A equipped with one of the available options. Detailed information regarding the operation of each available option is given in Section 6 of this manual, Option and Accessory Inforamtion.

2-20. Fuse Replacement

2-21. The ac line input and external dc input are individually fuse protected. Both fuses are readily accessible on the outside of the rear panel. The ac line input fuse (FI) should be replaced with a 1 /8A MDL(sloblo) fuse if either 100 or 120 volt operation has been selected. Usea 1/16A MDL(slo-blo) replacement for 220 or 240 volt operation. The external dc input (F2) requires a 3/4A MDL (slo-blo) fuse for a replacement.

CAUTION

Remove the power connector from the 2180A before changing fuses.

2-22. RTD Installation

2-23. Use the following procedure when installing an RTD and conducting temperature measurements:

1.Set POWER switch to OFF.

2.Remove the RTD Input Module from the instrument (rear panel).

3.Route the selected RTD lines through the Input Module’s rear access port, and connect them to the input terminals; depending on the type of RTD, connections may involve 2, 3, or 4 wires. Refer to Figure 2-2 as a reference when connecting RTD lines to the Input Module (TBl). Lines of the same color usually go to the same polarity connections (T-V and TS, or -V and -S). Refer to instructions included with the RTD for specific connection directions.

NOTE

When 2- or 3~wire RTDs are used, there is

some error created due to the RTD excitation

current in the Sense (S) wire leads. To

minimize this error. The user should (when possible) use the 4-wire RTD connection as show in Figure 2-2.

2-4

4. On the Input Module, toggle the RTD SekOi Switch (S1) to obtain the desired RTD type, see TD

2-2.

NOTE

The RTD Input Module may be printed with microcomputer Type 41 selector switch set­ tings. Refer to Table 2-2 when changing RTD types.

5. Slide the Input Module, RTD lines attache back into the 2180A securely.

NOTE

Refer to Section 6 of this manual or applicable

accessory

manuals

for instructions on

the

operation

of

any

installed

options

or

connected accessories.

 

 

 

6.Set POWER switch to ON.

7.Expose the RTD to a temperature within the

RTD’s specified range (see Specifications in Section

1).

8. The RTD temperature, in the scale selected, is displayed on the front panel.

 

 

 

NOTE

 

 

 

R2

on

the

2180A

is adjusted

at

the

factory

with a

100 ohm input resistance. If the 2180A

is

used

with

a 100

ohm 385

Pt

RTD

probe

meeting DIN standard 443760, then the R2 adjustment in the following paragraph may be ignored.

9. Adjust R2 on the RTD Input Module to com­ pensate for variations in lead resistance and in RTD probe Ro values. Refer to Section 4 for RTD input module adjustment procedures. This adjustnieni must be performed when an RTD probe is initially installed and whenever the leads or the RTD are changed.

NOTE

The RTD adjustment can be used to calibrate

the 2180A and the probe near a specific

temperature. Adjust R2 for compatibility

between the 2180A and a customer supplied temperature reference.

2-24. OPERATING DIRECTIONS

2-25. Operate the 2180A Thermometer using the following procedure:

1. Verify the instrument has the correct RTD connected.

2.Connect the input line cord to the applicable power source.

3.Select the temperature scale desired for display by pressing the Front Panel SCALE switch (in for °C, and out for °F).

4.Set POWER switch to ON.

2-26. Additional Features

2-27. The following paragraphs describe how the 2180A may be used to measure voltage or resistance. In both cases, the RTD will be replaced with a length of standard electrical wire. To connect the standard wire to the RTD Input Module, use steps 1-3 of the RTD Installation procedure, ignoring all reference to the RTD.

2-28. HOW TO MEASURE VOLTAGE

2-29. The 2180A can be used to measure positive voltages only up to +100 mV or +1V maximum in two ranges, with 1 )uV or 10 /zV resolution respectively. To obtain the desired range, refer to the following steps and Figure 2-3.

2180A

4-WIRE CONNECTIONS +V +S

-V -S

3-WIRE CONNECTIONS +V

+S

-V

-s

2-WIRE CONNECTIONS +V

+S

-V -S

Figure 2-2. RTD Connections

Table 2-2. RTD Input Module Switch Settings

 

DISPLAY

 

 

RTD SELECTOR SWITCH (SI) SETTINGS

 

 

 

 

TYPE

 

 

 

 

 

 

 

 

 

 

 

READING

 

 

 

 

 

 

 

 

 

 

 

pP

AT TURN

0

1

2

3

4

5

 

6

7

8

9

 

ON

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

100*

100*

100*

100*

100*

10*

 

 

 

2

8002.2

385**

390**

3916**

392**

N1

cu

 

OHM

CAL

 

 

 

 

 

 

 

 

 

 

 

 

 

* = OHMS

** = PLATINUM

EXAMPLE: To select a switch setting of 5, position the RTD selector switch (1) as shown:

12

4

8

[zz:

1+4 + 5

2-5

2180A

 

 

Table 2-3. RTD Input Module Switch Functions

SWITCH

SWITCH

SWITCH FUNCTIONS

NO.

POSITION

 

 

 

 

 

0-5

Programs the microcomputer (juc) for each RTD probe type (See Table 2-2.)

 

 

 

SI

6,7

NOT USED

 

 

8

''RESISTANCE'', programs the ¡JLC to read ohms.

 

 

 

 

 

9

"CAL'', programs the ¡ic to read juV (bypasses the linearization program).

 

 

 

 

.1

Causes the analog to digital converter circuitry (A/D) to have JJLV input sensitivity and

 

displays temperature to 0.1° resolution only.

 

 

S2

 

 

AUTO

Causes the A/D to automatically change from .01° to 0.1° resolution for overrange or

 

 

0.1° to .01° resolution for underrange.

 

 

 

 

 

 

Scan

Not Used

S3

 

 

Man

MUST BE LEFT IN THIS POSITION DURING NORMAL OPERATION.

 

 

 

 

2-6

NOTE

The decimal point and temperature scale indicator should be ignored during the following steps, the user must be aware of the selected range.

2-30. 100 millivolt Range

1. Install lead wire to the RTD Input Module, refer to RTD Installation procedures, steps 1-3 (this section).

2.Set RTD Input Module switches, S1 to position

9and S2 to AUTO.

3.Replace RTD Input Module and turn 2180A

on.

4.The 2180A is now ready to measure positive voltages up to +100 mV.

2-31. 1 Volt Range

1. Install lead wire to the RTD Input Module, refer to RTD Installation procedures, steps 1-3 (this section).

2.Set RTD Input Module switches, S1 to position

9and S2 to .1°.

3.Replace RTD Input Module and turn 2180A

on.

4.The 2180A is now ready to measure positive voltages up to +1V.

2-32. HOW TO MEASURE RESISTANCE

2-33. The 2180A can be used to measure positive resistances up to 999.9il with 10 mil resolution (RTD

2180A

excitation M).5 mA). To set up the 2180A as a resistance measurement device, refer to the following steps and Figure 2-3.

NOTE

The temperature scale indicator (^Cj'^F) should be ignored during the following steps.

2-34. Resistance Measurements

1.Install lead wires to the RTD Input Module, refer to RTD Installation procedure, steps 1-3.

2.Set RTD Input Module switches, S1 to position

8and S2 to .1°.

3.Connect a known resistance, less than 1 kfl, to the wires connected to the RTD Input Module, and use the following steps to compensate for lead resistance.

4.Replace RTD Input Module and turn 2180A

on.

5.Adjust R2 through the rear panel of the RTD’s Input Module until the 2180A’s display reads the same value as the known resistance.

6.Remove the known resistance, the 2180A is now calibrated and ready to measure positive resistances up to 999.9il.

NOTE

For measuring resistances of less than 196Ci, switch S2 on the RTD Input Module should be set to the A UTO position.

2-7Z2-8

2180A

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2180A

Section 3

Theory of Operation

3-1. INTRODUCTION

3-2. This section of the manual contains an overall functional description and a brief circuit analysis of the 2180A Digital Thermometer. Simplified circuit diagrams are provided, as necessary, to supplement the text. Detailed schematics are given in Section 8 of this manual.

3-3. The Model 2180A is a single point RTD Digital Thermometer with 0.1° and .01° resolution for either degrees F or C. This instrument features dual slope A/D conversion, microcomputer control logic, and a 5-digit display with temperature scale indicator. Various RTD types can be used over a temperature range of -394° F to 1435°F (-219°C to 664°C). Refer to Figure 3-1 for the following functional description. Mnemonic definitions are provided in Table 3-1.

3-4. FUNCTIONAL DESCRIPTION

3-5. The Model 2180A executes a continuous series of measurement cycles. These cycles, controlled entirely by a microcomputer, include three major periods: the AutoZero, the Integrate, and the Read periods. During each period, digital controls are applied to the analog section of a dual slope converter. The converter in turn generates a compare output. The configuration of the analog section during each phase of the measurement cycle is established by the condition of microcomputer controlled FET switches.

3-6. The measurement cycle begins with the Auto-Zero period. During this period, the input to the Buffer Amplifier is connected to ground through an FET switch and the accumulated dc offset voltages present in the analog section are sampled and held by the Auto-Zero capacitor. This voltage is used later in the measurement cycle to cancel measurement errors introduced by offset voltages in the analog circuitry. The final measurement is

therefore proportional to the RTD probe output voltage and does not include offset errors.

3-7. During the Integrate period, the RTD input voltage read across the RTD, is applied to the integrator. The algebraic sum of the AZ and RTD input voltages is integrated over a 100 ms period. At the end of this period, the RTD input voltage is removed from the integrator, and the Read period is started.

3-8. A reference voltage is applied to the integrator during the Read period, causing the integrator capacitor to be discharged at a linear rate. When the integrator output reaches zero, a compare signal is generated to end the Read period. The duration of the Read period is translated by the microcomputer, to provide a digital indication of the RTD temperature.

RTD

DUAL SLOPE

ANALOG CIRCUIT

^i

ki

i UJ

 

 

cc

5

 

<

N

a.

LU

<

O

QC

 

ow

MICROCOMPUTER

CONTROL & LINEARIZATION

DATA

DISPLAY

Figure 3-1. 2180A Simplified Block Diagram

3-1

2180A

 

Table 3-1. Mnemonics

ANALOG COM

Measurement common

AZ

Auto-Zero

CM

Compare input to the microcomputer

DATA

Data on bus

DCLK

Data clock

DE+

Positive read command

DE-

Negative read command

DIGITAL COM

—15V with respect to Analog Com

D.P./NEG

Drives decimal point, depending on reading and resolution

INT 1

Causes the unknown voltage to be integrated

LINEAR

Used to command the microcomputer to display linear counts

WRT

Write

WRT ADR

Write address, signals that an address is being transmitted

X10

Selects a buffer gain of X10 (0.1° resolution)

X100

Selects a buffer gain of X100 (0.01° resolution)

A 2

Hold command

+SENSE

Voltage sense wires from RTD - no current flows In these wires

-SENSE

Voltage sense wires from RTD - no current flows in these wires

+Vm

An intermediate voltage - not used directly

-V

Current return

3-9. CIRCUIT ANALYSIS

3-10. Circuit analysis of the 2180A is discussed in two sections: digital and analog. The digital section is covered first; particular attention is paid to digital control of the analog section. The analysis of the analog section covers the analog measurement circuitry and the 2180A power supply.

3-11. Digital Section

3-12. The digital section of the 2180A consists of a single-chip microcomputer with a self-contained, programmed, read only memory (U9), a hex CMOS open drain buffer (U13), and an LED display. This section, shown in Figure 3-2, will provide the following functions:

1. Conversion of the non-linear RTD probe voltage, as measured by the analog section, into a linear digital display.

2.Control of the analog section.

3.Control of all accessories on the accessory bus.

3-13. The microcomputer (U9) contains all of the 2180 A programming, control logic, and linearizing capability. It also provides all signals necessary to update the display. Linearization of the RTD signal is accomplished by using a piece-wise, 4th order, curve-fit approximation for each

type of RTD. One of the seven operating programs is selected for the RTD type by setting S1 on the RTD Input Module. A table showing RTD switch setting numbers and corresponding RTD types is printed on the RTD Input Module PCB.

3-14. Measurement data is continuously strobed out of the microcomputer in decoded-seven-segment, bitparallel, character-serial format. This data is then sent to the LED display.

3-15. The total measurement cycle takes 300 ms. The cycle consists of the following periods:

1.Auto-Zero period (100 to 200 ms).

2.Integrate period (100 ms). A 1 ms nominal hold signal is inserted at the beginning and end of the Integrate period to accomodate settling times in the analog section.

3.Read period (variable 0 to 100 ms).

3-16. Analog Section

3-17. ANALOG MEASUREMENT CIRCUIT

3-18. The analog measurement circuitry consists of an RTD input circuit, two voltage reference circuits, a ground sense amplifier, a buffer amplifier, a dual slope

3-2

2180A

 

 

AOU/DOU

LIMITS

 

 

 

OPTION

OPTION

 

 

 

ri__rt

 

 

05

04

015 Oil

 

 

Q22 ( ^ © © © ©

AZ

 

 

 

 

 

021 ( k

 

 

INTI

 

 

 

MICRO­

 

 

 

 

COMPUTER

 

 

 

 

U9

 

Q7 k

 

 

A2

CO

 

 

 

 

 

 

 

I

 

 

 

X10

CJ 016 k

 

 

 

 

 

CO

 

 

 

 

h-

 

 

 

XI00

LU

017 ( k

 

 

 

 

 

 

 

Q10{ k

 

-<U^

DE-

 

 

 

DE+

014 (k

013 ( k

U16

Q9 k

Figure 3-2. Simplified Schematic — Digital

>

<

T ^

f^o MHz

A/D Converter (integrator, gain stage, and comparator), and a combination of FET switches. Refer to Figure 3-3 in conjunction with the following individual circuit descriptions. All FET switches will be shown in their open state; they are closed during measurement cycle commands from the 2180A’s digital section.

3-19. The RTD Input circuit comprises the RTD probe, the RTD Input Module, and a low pass filter on the Input Module’s PCB. Source current flows through a series combination of the RTD probe, R2 (RTD Input Module), and R1 (Main PCB). The voltage sensed across the RTD is routed through the Input Module, and onto the Main PCB. The TSense line (always a positive voltage) is then applied to the low pass filter.

3-20. The ground sense amplifier (Q20, U7 and associated circuitry) maintains the -Sense line at measurement ground. This amplifier compensates for noise and offsets on the -V and -Sense lines.

3-21. To achieve switching between 0.01° and .1° resolution, the buffer gain is shifted by a factor of ten. For 0.01° resolution, FET switch Q17 is on, and a reference voltage of-100 mV is applied to the buffer (Q19, U5). The buffer gain is set to 100. For 0.1° resolution, FET switch Q16 is on, and a reference voltage of -1 .OOV is applied and the buffer gain is 10.

3-22. The first voltage reference consists of a resistor network supplied by an accurate 6.2V dc reference voltage. The resistive divider network is set to provide 200 mV to Q14, lOOmVtoQ15, l.OVtoQl l,and2.0VtoQlO.

3-3

CA)

IVO

00

о

>

»

CO

I

CO

CO

i’

■ö

ü

CO

о

0

1

>

3

&

When 0.01° resolution is in use, Q12 will allow reference capacitor C19 to attain a -100 mV charge. For 0.1° resolution, Q8 will allow C20 to charge to ° l.OV. Either reference capacitor will be placed at the -Sense level during Auto-Zero. Recovery deintegrate is applied to QIO and Q14.

3-23. A second voltage reference (U15-6) provides an accurate 6.2V across the series combination of R1 (Main Thermometer PCB), R2 (RTD Input PCB), and the RTD. This voltage therefore provides the source (+V) voltage for the RTD.

3-24. The Buffer, Integrator, Gain Stage, and Comparator Amplifiers combine to perform the analog functions of the Integrate, Read, and Auto-Zero periods. The Buffer is used to provide integrator inputs during all three periods. The Integrator integrates the Buffer output voltage during the Integrate and Read periods and, in combination with the Gain Stage, functions as a closedloop amplifier during the Auto-Zero period.

3-25. An Auto-Zero period is commanded during the first phase of each measurement cycle. During this time, five auto-zero switches (Q4, Q5, Q11, Q15, and Q22) are closed by the microcomputer. Three of the switches (Q11, Q15, and Q22) charge the reference capacitors to +100 mV on Cl9 and +1.0V on C20. Closing switch Q4 connects the Integrator and Gain Stage into a closed-loop configuration. This action also allows the Auto-Zero capacitor (Cl2) to charge to a value proportional to the algebraic sum of all the offset voltages in the Buffer, Integrator and Gain Stage. At the end of the Auto-Zero period, switches Q4, Q5, Q11, Q15, and Q22 are opened. The reference capacitors (Cl9 and C20) and the AutoZero capacitor retain their charges for later use in the measurement cycle.

3-26. The Integrate period (see Figure 4-4) starts on the leading edge of the integrate command from the microcomputer; switch Q21 is closed and switch Q7 is opened. The RTD input voltage is applied through switch Q21 to the Buffer input. After a 1 ms settling period, switch Q7 closes, and the Buffer output is applied to the Integrator for 100 ms. As the integrator capacitor C2 charges, the Integrator drives the comparator, through the gain stage to +5V dc which indicates that the charge on C2 is more negative than the Auto-Zero Reference Cl2. At the end of the Integrate period, the integrate capacitor is charged to a level and polarity proportional to the RTD voltage, and switches Q21 and Q7 return to the open state.

3-27. The Read period starts at the end of the Integrate period. Depending upon the input polarity sensed by the comparator during the Integrate period, one of two Read modes is enabled if a positive input is sensed, a positive

2180A

Read mode is enabled. Similarly, a negative Read mode is enabled when a negative input is sensed.

3-28. When the positive Read mode is commanded, FET switches Q13 and Q9 are closed. If 0.1° resolution is in effect, Q8 will place the positive side of reference capacitor C20 at ground. With 0.01° resolution in effect, Q12 will place the positive side of reference capacitor Cl 9 at ground. Reference capacitors C20 and Cl9 will then apply either -1 .OV or -100 mV, respectively, to the Buffer input.

3-29. When the negative Read mode is commanded, switches QIO and Q14 are closed; Q9 and Q13 are open. With .01° resolution selected, approximately +200 mV will be applied to the positive side of reference capacitor Cl9. The algebraic sum of the voltage at the Buffer input will then be +100 mV. When 0.1° resolution is selected, approximately +2.0V will be applied to the positive side of reference capacitor C20. Buffer input voltage will then be +1.0V (only during recover deintegrate).

3-30. After a 1 ms settling time, switch Q7 closes and the Buffer output voltage is applied to the Integrator input. The integrator capacitor now begins to discharge at a linear rate (determined by the reference voltage). This discharge continues until the integrator voltage reaches the comparator trip point, which is referenced to the voltage on the Auto-Zero capacitor. When this level is reached, the comparator changes state, commanding the microcomputer to terminate the Read period. To facilitate auto-zero, the microcomputer then calls a reference voltage opposite in polarity to the one previously used (DEor DE+). When the integrator reaches the trip point, the microcomputer immediately begins the Auto-Zero period.

3-31. Offset voltages present during the Integrate and Read periods are cancelled by offset voltages that were sampled and held during the Auto-Zero period.

3-32. POWER SUPPLY

3-33. The 2190A Power Supply consists of a DC to DC Converter and regulating circuitry. AC inputs are made via the input power cord, line fuse, and power transformer/rectifier. External +12V dc inputs can also be made directly to the DC to DC Converter circuitry via line TBl (see Main PCB schematic. Section 8). The function of the power supply is to provide +5V, +5V unregulated, +15V, and -15V dc operating voltages for the 2180A circuitry. The power supply can be driven from ac line or 12V dc external source. The DC to DC conversion and voltage regulation is accomplished using conventional power supply design techniques.

3-5/3-6

2180A

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