Fluke 525A User manual

®
525A
Temperature/Pressure Calibrator
Service Manual
PN 1644492
March 2002
© 2002 Fluke Corporation.All rights reserved. Printed in USA
All product names are trademarks of their respective companies.

LIMITED WARRANTY AND LIMITATION OF LIABILITY
Each Fluke product is warranted to be free from defects in material and workmanship under
normal use and service. The warranty period is one year and begins on the date of shipment.
Parts, product repairs, and services are warranted for 90 days. This warranty extends only to the
original buyer or end-user customer of a Fluke authorized reseller, and does not apply to fuses,
disposable batteries, or to any product which, in Fluke’s opinion, has been misused, altered,
neglected, contaminated, or damaged by accident or abnormal conditions of operation or
handling. Fluke warrants that software will operate substantially in accordance with its functional
specifications for 90 days and that it has been properly recorded on non-defective media. Fluke
does not warrant that software will be error free or operate without interruption.
Fluke authorized resellers shall extend this warranty on new and unused products to end-user
customers only but have no authority to extend a greater or different warranty on behalf of Fluke.
Warranty support is available only if product is purchased through a Fluke authorized sales outlet
or Buyer has paid the applicable international price. Fluke reserves the right to invoice Buyer for
importation costs of repair/replacement parts when product purchased in one country is submitted
for repair in another country.
Fluke’s warranty obligation is limited, at Fluke’s option, to refund of the purchase price, free of
charge repair, or replacement of a defective product which is returned to a Fluke authorized
service center within the warranty period.
To obtain warranty service, contact your nearest Fluke authorized service center to obtain return
authorization information, then send the product to that service center, with a description of the
difficulty, postage and insurance prepaid (FOB Destination). Fluke assumes no risk for damage in
transit. Following warranty repair, the product will be returned to Buyer, transportation prepaid
(FOB Destination). If Fluke determines that failure was caused by neglect, misuse, contamination,
alteration, accident, or abnormal condition of operation or handling, including overvoltage failures
caused by use outside the product’s specified rating, or normal wear and tear of mechanical
components, Fluke will provide an estimate of repair costs and obtain authorization before
commencing the work. Following repair, the product will be returned to the Buyer transportation
prepaid and the Buyer will be billed for the repair and return transportation charges (FOB
Shipping Point).
THIS WARRANTY IS BUYER'S SOLE AND EXCLUSIVE REMEDY AND IS IN LIEU OF ALL
OTHER WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY
IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
FLUKE SHALL NOT BE LIABLE FOR ANY SPECIAL, INDIRECT, INCIDENTAL, OR
CONSEQUENTIAL DAMAGES OR LOSSES, INCLUDING LOSS OF DATA, ARISING FROM
ANY CAUSE OR THEORY.
Since some countries or states do not allow limitation of the term of an implied warranty, or
exclusion or limitation of incidental or consequential damages, the limitations and exclusions of
this warranty may not apply to every buyer. If any provision of this Warranty is held invalid or
unenforceable by a court or other decision-maker of competent jurisdiction, such holding will not
affect the validity or enforceability of any other provision.
Fluke Corporation
P.O. Box 9090
Everett, WA 98206-9090
U.S.A.
Fluke Europe B.V.
P.O. Box 1186
5602 BD Eindhoven
The Netherlands
11/99
To registeryourproduct online,visit register.fluke.com

i
Table of Contents
Title Page
Introduction ....................................................................................................... 1
Contacting Fluke ............................................................................................... 1
Safety Information............................................................................................. 1
Calibrator Specifications ................................................................................... 3
General Specifications .................................................................................. 3
DC Voltage Specifications, Output............................................................... 4
DC Current Specifications, Output ............................................................... 4
Resistance Specifications, Output................................................................. 5
Resistance Specifications, Input.................................................................... 5
Thermocouple Specification, Output and Input............................................ 6
TC mV Specifications, Input and Output...................................................... 7
RTD and Thermistor Specification, Output.................................................. 8
RTD and Thermistor Specification, Input..................................................... 9
Pressure Measurement .................................................................................. 11
Theory of Operation .......................................................................................... 11
Micro-Controller Section .............................................................................. 11
Analog Section.............................................................................................. 12
Basic Maintenance............................................................................................. 12
Cleaning the Calibrator ................................................................................. 12
Replacing a Line Fuse................................................................................... 12
To Check or Replace a Fuse.......................................................................... 13
Changing Line Voltage ................................................................................. 13
Modular-Level Maintenance ............................................................................. 14
Disassembly .................................................................................................. 15
Reassembly ................................................................................................... 15
Output Block Subassembly Connections.................................................. 17
Keypad to Main PCB................................................................................ 19
Display Assembly to Main PCB............................................................... 19
Opto RS232 to Main PCA ........................................................................ 20
Reinstalling the Circuit Boards................................................................. 21
Connecting the Power Module ................................................................. 21
Final Assembly and Inspection..................................................................... 22
Performance Tests............................................................................................. 23
Required Equipment List .............................................................................. 23
Testing DC Voltage....................................................................................... 24

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Service Manual
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Testing DC Current....................................................................................... 25
Testing Thermocouple Output ...................................................................... 26
Testing CJC (Cold Junction Compensation)............................................. 27
CJC (Cold Junction Compensation) Calibration....................................... 27
Testing Thermocouple Input......................................................................... 28
Testing Ohms Output.................................................................................... 29
Testing Ohms Input....................................................................................... 30
Testing Pressure Modules ............................................................................. 32
Calibration Adjustment ..................................................................................... 32
Initiating Communication ............................................................................. 32
Starting Adjustment Mode............................................................................ 32
Adjustment Sequence.................................................................................... 33
14: Calibrate DAC, Digital to Analog Converter Adjustment.................. 34
1: 100 mV Source to 4: 100 V Source, Adjusting DC Source.................. 34
5: 100 mA Source, Adjusting DC Current Source.................................... 35
6: Hi Ohms Source, Adjusting High Resistance Source........................... 37
7: Low Ohms, Adjusting Low Ohms Source............................................ 38
8: Hi Ohms, Adjusting High Resistance Measure.................................... 38
9: Low Ohms, Adjusting Low Resistance Measure.................................. 40
10: SPRT 25, Adjusting SPRT Low Resistance Measure ........................ 41
11: TC SOURCE, Adjusting TC mVolt Source ....................................... 43
12: TC Read, Adjusting TC mVolt Measure............................................ 43
Customer Replaceable Parts.............................................................................. 45

iii
List of Tables
Table Title Page
1. Symbols Used on the Calibrator............................................................................ 2
2. Replacement Fuses ................................................................................................ 13
3. Front Panel Wire Color Assignments.................................................................... 16
4. Rear Panel Wire Color Assignments ..................................................................... 16
5. Output Block to Main PCA Connections............................................................... 17
6. TC PCA to Main PCA Connections ...................................................................... 18
7. Opto RS232 to Main PCA Connections ................................................................ 20
8. Power Module to Main PCA Connections............................................................. 21
9. Power Connections ................................................................................................ 22
10. Required Equipment .............................................................................................. 23
11. Testing DC Voltage ............................................................................................... 24
13. TC Temperatures ................................................................................................... 26
14. Ohms Output Ranges............................................................................................. 29
15. Ohms Ratio Table.................................................................................................. 31
16. Calibration Dependencies...................................................................................... 33
17. List of Equipment for Voltage Calibration Adjustments....................................... 34
18. List of Equipment for Current Calibration Adjustments ....................................... 35
19. List of Equipment for High Ohms Measure Calibration Adjustments .................. 38
20. List of Equipment for High Ohms Measure Calibration Adjustments .................. 40
21. List of Equipment for Low Ohms Measure Calibration Adjustments................... 41
22. List of Test Equipment for Adjusting TC Source.................................................. 43
23. List of Test Equipment for Adjusting TC Read..................................................... 43
24. List of Test Equipment for Adjusting TC CJC...................................................... 45
25. Replacement Parts.................................................................................................. 47
26. Accessories ............................................................................................................ 48

525A
Service Manual
iv

v
List of Figures
Figure Title Page
1. Accessing the Fuse................................................................................................. 14
2. Wiring Connections............................................................................................... 17
3. Solder Connections for the TC PCA...................................................................... 18
4. Keypad PCA Connections..................................................................................... 19
5. Connections for the Opto RS232 PCA .................................................................. 20
6. Power Module Connections................................................................................... 22
7. Measuring DC Current........................................................................................... 25
8. Testing TC Output................................................................................................. 26
9. Connections for CJC Calibration........................................................................... 27
10. Connections for Measuring TC Input .................................................................... 28
11. Connection for Measuring Resistance Output....................................................... 29
12. 1281 Connection Diagram..................................................................................... 30
13. Connection for Measuring Ohms........................................................................... 31
14. Exploded View of the 525A .................................................................................. 46

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Service Manual
vi

1
525A
Introduction
This manual provides user-service information for the 525A Temperature/Pressure
Calibrator (hereafter referred to as "the Calibrator"). Details regarding verification of the
Calibrator’s functionality and calibration, basic maintenance, contacting Fluke service
centers, and important safety information are also contained within this manual.
Contacting Fluke
To contact Fluke, order accessories, or locate the nearest Fluke Service Center or
distributor, call:
•USA: 1-888-99-FLUKE (1-888-993-5853)
•Canada: 1-800-36-FLUKE (1-800-363-5853)
•Europe: [phone]
•Japan: [phone]
•Singapore: [phone]
•Anywhere in the world: [phone]
Or, visitFluke’sWeb siteatwww.fluke.com.
Safety Information
The Calibrator complies with EN 61010, ANSI/ISA-S82.01-1994, and CAN/CSA-C22.2
No. 1010.1-92. Use the Calibrator only as specified in this manual, otherwise the
protection provided by the Calibrator may be impaired.
CAT II equipment is designed to protect against transients from energy-consuming
equipment supplied from a fixed installation, such as televisions, personal computers,
portable tools, and other household appliances.
A “WWarning” statement identifies hazardous conditions and actions that could cause
bodily harm or death.
A “WCaution” statement identifies conditions and actions that could damage the
Calibrator or the equipment under test.
International symbols used on the Calibrator and in this manual are explained in Table 1.

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Service Manual
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WWarning
To avoid possible electric shock or personal injury, follow these guidelines:
•Use the Calibrator only as specified in this manual or the protection provided by the
Calibrator might be impaired.
•Inspect the Calibrator before use. Do not use the Calibrator if it appears damaged.
Look for cracks or missing plastic. Pay particular attention to the insulation around
the connectors.
•Have the Calibrator serviced only by qualified service personnel.
•Do not apply more than the rated voltage between the terminals, as marked on the
Calibrator, or between any terminal and earth ground.
•Always use the power cord and connector appropriate for the voltage and outlet of
the country or location in which you are working.
•Never operate the Calibrator with the cover removed or the case open.
•Never remove the cover or open the case of the Calibrator without first removing the
power source.
•Use caution when working with voltages above 30 V ac rms, 42 V ac peak, or
60 V dc. These voltages pose a shock hazard.
•Use only the replacement fuse(s) specified in this manual.
•Use the proper terminals, function, and range for your measurements.
•Do not operate the Calibrator around explosive gas, vapor, or dust.
•When servicing the Calibrator, use only specified replacement parts.
Table 1. Symbols Used on the Calibrator
AC (Alternating Current) Earth ground
DC (Direct Current) ΩResistance
Pressure Conforms to European Union directives
Chassis protective ground Canadian Standards Association,
NRTL
Important Information. Refer to the
manual. International ON/OFF symbol.
Caution, risk of electric shock

525A
Calibrator Specifications
3
Calibrator Specifications
General Specifications
Warm up time Twice the time since last warmed up, to a maximum of 30 minutes
Settling time Less than 5 seconds for all functions and ranges except as noted
Standard interface RS-232
Optional interface IEEE-488 (GPIB)
Temperature performance Operating 0 °C to 50 °C
Calibration (tcal) 18 °C to 28 °C
Storage -20 °C to 70 °C
Electromagnetic compatibility CE: Conforms to EN61326
Temperature coefficient Temperature coefficient for temperatures outside tcal ±5 °C is
10 % of the 90 day specification (or 1 year if applicable) per °C
Relative humidity Operating < 80 % to 30 °C, < 70 % to 40 °C, < 40 % to 50 °C
Storage < 95 % noncondensing
Altitude Operating 3,050 m (10,000 ft) maximum
Nonoperating 12,200 m (40,000 ft) maximum
Safety EN 61010 Second, ANSI/ISA-S82.01-1994,
CAN/CSA-C22.2 No. 1010.1-92, NRTL
Analog low isolation 20 V
Line power Line Voltage (selectable) 100 V/120 V or 220 V/240 V
Line Frequency 47 to 63 Hz
Line Voltage Variation ±10 % about line voltage setting
Power consumption 15 VA maximum
Dimensions Height 13.3 cm (5.25 in) plus 1.5 cm (0.6 in) four feet on bottom
Width ¾ standard rack width
Depth 47.3 cm (18.6 in) overall
Weight (without options) 4 kg (9 lb)

525A
Service Manual
4
DC Voltage Specifications, Output
Absolute Uncertainty,
tcal ±5 °C
±(ppm of output +µV) Stability
Ranges190 days 1 year 24 hours, ±1 °C
±(ppm of output +µV) Resolution Maximum
Burden2
0 to 100.000 mV 25 3 30 3 5 +2 1 µV 10 mA
0 to 1.00000 V 25 20 30 20 4 +20 10 µV 10 mA
0 to 10.0000 V 25 200 30 200 4 +200 100 µV 10 mA
0 to 100.000 V 25 2 mV 30 2 mV 5 +1 mV 1 mV 1 mA
1. All outputs are positive only.
2. Remote sensing is not provided. Output resistance is < 1Ω.
Noise
Ranges Bandwidth 0.1 to 10 Hz
(ppm of output +µV p-p) Bandwidth10 Hz to 10 kHz (µV rms)
0 to 100.000 mV 1 µV6µV
0 to 1.00000 V 10 µV 60 µV
0 to 10.0000 V 100 µV 600 µV
0 to 100.000 V 10 ppm+1 mV 20 mV
DC Current Specifications, Output
Absolute Uncertainty,
tcal ±5 °C ±(ppm of output +µA)
Ranges190 days 1 year Resolution
Maximum
Compliance
Voltage
Maximum
Inductive
Load
0 to 100.000 mA 85 2 100 2 1 µA 10 V 100 µH
1. All outputs are positive only.
Noise
Ranges Bandwidth
0.1 to 10 Hz p-p Bandwidth 10 Hz to 10 kHz rms
0 to 100.000 mA 2000 nA 20 µA

525A
Calibrator Specifications
5
Resistance Specifications, Output
Absolute Uncertainty,
tcal ±5 °C,
±(ppm of output ±Ω)
Ranges190 days 1 year Resolution Allowable Current2
5 to 400.00 Ω0.025 0.03 0.01 Ω1 to 10 mA
5 to 4.0000 kΩ0.25 0.3 0.1 Ω250 µA to 1 mA
1. Continuously variable from 0 to 4 kΩ.
2. For currents lower than shown, the floor adder increases by Floor(new) = Floor(old) x Imin/Iactual.
For example, a 500 µA stimulus measuring 100 Ωhas a floor uncertainty of 0.025 Ωx 1 mA/500 µA =
0.05 Ω.
Resistance Specifications, Input
Absolute Uncertainty,
tcal ±5 °C, ±(ppm of output ±Ω)
Ranges 90 days 1 year Resolution Stimulus Current
0 to 400.00 Ω35 0.003 40 0.003 0.001 Ω1 mA
401 to 4001.00 Ω35 0.03 40 0.03 0.01 Ω0.1 mA

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Service Manual
6
Thermocouple Specification, Output and Input
Absolute Uncertainty,
tcal ±5 °C, ±(°C)1
Range (°C) Output/Input
TC Type Minimum Maximum 90 days 1 year
B 600 °C
800 °C
1000 °C
1550 °C
800 °C
1000 °C
1550 °C
1820 °C
0.42 °C
0.39 °C
0.40 °C
0.44 °C
0.46 °C
0.39 °C
0.40 °C
0.45 °C
C0°C
150 °C
650 °C
1000 °C
1800 °C
150 °C
650 °C
1000 °C
1800 °C
2316 °C
0.25 °C
0.21 °C
0.23 °C
0.38 °C
0.63 °C
0.30 °C
0.26 °C
0.31 °C
0.50 °C
0.84 °C
E -250 °C
-100 °C
-25 °C
350 °C
650 °C
-100 °C
-25 °C
350 °C
650 °C
1000 °C
0.38 °C
0.16 °C
0.14 °C
0.14 °C
0.16 °C
0.50 °C
0.18 °C
0.15 °C
0.16 °C
0.21 °C
J -210 °C
-100 °C
-30 °C
150 °C
760 °C
-100 °C
-30 °C
150 °C
760 °C
1200 °C
0.20 °C
0.18 °C
0.14 °C
0.14 °C
0.18 °C
0.27 °C
0.20 °C
0.16 °C
0.17 °C
0.23 °C
K -200 °C
-100 °C
-25 °C
120 °C
1000 °C
-100 °C
-25 °C
120 °C
1000 °C
1372 °C
0.25 °C
0.19 °C
0.14 °C
0.19 °C
0.30 °C
0.33 °C
0.22 °C
0.16 °C
0.26 °C
0.40 °C
L -200 °C
-100 °C
800 °C
-100 °C
800 °C
900 °C
0.37 °C
0.26 °C
0.17 °C
0.37 °C
0.26 °C
0.17 °C
N -200 °C
-100 °C
-25 °C
120 °C
410 °C
-100 °C
-25 °C
120 °C
410 °C
1300 °C
0.33 °C
0.20 °C
0.16 °C
0.14 °C
0.21 °C
0.40 °C
0.24 °C
0.19 °C
0.18 °C
0.27 °C
1. Does not include thermocouple wire error.

525A
Calibrator Specifications
7
Thermocouple Specification, Output and Input (continued)
Absolute Uncertainty,
tcal ±5 °C, ±(°C)1
Range (°C) Output/Input
TC Type Minimum Maximum 90 days 1 year
R0°C
250 °C
400 °C
1000 °C
250 °C
400 °C
1000 °C
1750 °C
0.58 °C
0.34 °C
0.31 °C
0.30 °C
0.58 °C
0.35 °C
0.33 °C
0.40 °C
S0°C
250 °C
1000 °C
1400 °C
250 °C
1000 °C
1400 °C
1750 °C
0.56 °C
0.36 °C
0.30 °C
0.35 °C
0.56 °C
0.36 °C
0.37 °C
0.46 °C
T -250 °C
-150 °C
0 °C
120 °C
-150 °C
0 °C
120 °C
400 °C
0.51 °C
0.18 °C
0.13 °C
0.12 °C
0.63 °C
0.24 °C
0.16 °C
0.14 °C
U -200 °C
0 °C0 °C 600 °C0.56 °C 0.27 °C0.56 °C 0.27 °C
mV -10 to 75.000 mV
1. Does not include thermocouple wire error.
TC mV Specifications, Input and Output
Absolute Uncertainty,
tcal +/-5 °C
+/-( ppm of output + µV)
Range
(mV) 90 Days 1 Year
Stability
24 Hours +/-1°C
+/- ( ppm of output + µV) Resolution Maximum Burden
-10 to
75.000 25 + 3µV 30 + 3µV5+2µV1µV 10 Ohms

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Service Manual
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RTD and Thermistor Specification, Output
Range (°C) Absolute Uncertainty tcal ±5 °C, ±(°C)1
RTD Type Minimum Maximum 90 days 1 year
Pt 385, 100 Ω-200 °C
-80 °C
0 °C
100 °C
300 °C
400 °C
630 °C
-80 °C
0 °C
100 °C
300 °C
400 °C
630 °C
800 °C
0.06 °C
0.08 °C
0.08 °C
0.07 °C
0.07 °C
0.08 °C
0.08 °C
0.07 °C
0.10 °C
0.10 °C
0.09 °C
0.09 °C
0.09 °C
0.10 °C
Pt 3926, 100 Ω-200 °C
-80 °C
0 °C
100 °C
300 °C
400 °C
-80 °C
0 °C
100 °C
300 °C
400 °C
630 °C
0.06 °C
0.06 °C
0.06 °C
0.07 °C
0.07 °C
0.08 °C
0.07 °C
0.07 °C
0.08 °C
0.08 °C
0.09 °C
0.09 °C
Pt 3916, 100 Ω-200 °C
-190 °C
-80 °C
0 °C
100 °C
260 °C
300 °C
400 °C
600 °C
-190 °C
-80 °C
0 °C
100 °C
260 °C
300 °C
400 °C
600 °C
630 °C
0.06 °C
0.06 °C
0.06 °C
0.06 °C
0.07 °C
0.07 °C
0.07 °C
0.08 °C
0.08 °C
0.07 °C
0.08 °C
0.08 °C
0.08 °C
0.08 °C
0.08 °C
0.09 °C
0.09 °C
0.09 °C
Pt 385, 200 Ω-200 °C
-80 °C
0 °C
100 °C
260 °C
300 °C
400 °C
600 °C
-80 °C
0 °C
100 °C
260 °C
300 °C
400 °C
600 °C
630 °C
0.31 °C
0.32 °C
0.33 °C
0.33 °C
0.36 °C
0.36 °C
0.42 °C
0.42 °C
0.38 °C
0.38 °C
0.39 °C
0.39 °C
0.43 °C
0.43 °C
0.50 °C
0.50 °C
Pt 385, 500 Ω-200 °C
-80 °C
0 °C
100 °C
260 °C
300 °C
400 °C
600 °C
-80 °C
0 °C
100 °C
260 °C
300 °C
400 °C
600 °C
630 °C
0.13 °C
0.13 °C
0.13 °C
0.14 °C
0.14 °C
0.15 °C
0.16 °C
0.16 °C
0.15 °C
0.15 °C
0.16 °C
0.17 °C
0.17 °C
0.18 °C
0.19 °C
0.19 °C
1. 2-wire output

525A
Calibrator Specifications
9
RTD and Thermistor Specification, Output (continued)
Range (°C) Absolute Uncertainty tcal ±5 °C, ±(°C)1
RTD Type Minimum Maximum 90 days 1 year
Pt 385, 1000 Ω-200 °C
-80 °C
0 °C
100 °C
260 °C
300 °C
400 °C
600 °C
-80 °C
0 °C
100 °C
260 °C
300 °C
400 °C
600 °C
630 °C
0.06 °C
0.06 °C
0.07 °C
0.07 °C
0.07 °C
0.07 °C
0.08 °C
0.08 °C
0.07 °C
0.08 °C
0.08 °C
0.08 °C
0.09 °C
0.09 °C
0.09 °C
0.09 °C
PtNi 385, 120 Ω
(Ni 120) -80 °C 0 °C
100 °C
0 °C
100 °C
260 °C
0.04 °C
0.04 °C
0.03 °C
0.05 °C
0.04 °C
0.03 °C
Cu 427, 10 Ω2-100 °C 260 °C 0.63 °C 0.75 °C
YSI 400 15 °C 50 °C 0.005 °C 0.007 °C
1. 2-wire output
2. Based on MINCO Application Aid No. 18.
RTD and Thermistor Specification, Input
Range (°C) Absolute Uncertainty, tcal ±5 °C, ±(°C)1
RTD Type Minimum Maximum 90 days 1 year
Pt 385, 100 Ω-200 °C
-80 °C
0 °C
100 °C
300 °C
400 °C
630 °C
-80 °C
0 °C
100 °C
300 °C
400 °C
630 °C
800 °C
0.031 °C
0.018 °C
0.018 °C
0.027 °C
0.031 °C
0.042 °C
0.050 °C
0.012 °C
0.020 °C
0.020 °C
0.030 °C
0.035 °C
0.047 °C
0.057 °C
Pt 3926, 100 Ω-200 °C
-80 °C
0 °C
100 °C
300 °C
400 °C
-80 °C
0 °C
100 °C
300 °C
400 °C
630 °C
0.031 °C
0.014 °C
0.018 °C
0.026 °C
0.031 °C
0.041 °C
0.031 °C
0.015 °C
0.019 °C
0.029 °C
0.034 °C
0.046 °C
Pt 3916, 100 Ω-200 °C
-190 °C
-80 °C
0 °C
100 °C
260 °C
300 °C
400 °C
600 °C
-190 °C
-80 °C
0 °C
100 °C
260 °C
300 °C
400 °C
600 °C
630 °C
0.026 °C
0.011 °C
0.014 °C
0.018 °C
0.025 °C
0.026 °C
0.031 °C
0.040 °C
0.042 °C
0.028 °C
0.012 °C
0.015 °C
0.019 °C
0.028 °C
0.029 °C
0.034 °C
0.045 °C
0.047 °C
Pt 385, 200 Ω-200 °C
-80 °C
0 °C
100 °C
260 °C
300 °C
400 °C
600 °C
-80 °C
0 °C
100 °C
260 °C
300 °C
400 °C
600 °C
630 °C
0.071 °C
0.075 °C
0.079 °C
0.082 °C
0.090 °C
0.093 °C
0.100 °C
0.101 °C
0.072 °C
0.076 °C
0.081 °C
0.085 °C
0.093 °C
0.097 °C
0.105 °C
0.106 °C
1. 4-wire mode. Uncertainties listed do not include probe uncertainties.

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Service Manual
10
RTD and Thermistor Specification, Input (continued)
Range (°C) Absolute Uncertainty, tcal ±5 °C, ±(°C)1
RTD Type Minimum Maximum 90 days 1 year
Pt 385, 500 Ω-200 °C
-80 °C
0 °C
100 °C
260 °C
300 °C
400 °C
600 °C
-80 °C
0 °C
100 °C
260 °C
300 °C
400 °C
600 °C
630 °C
0.046 °C
0.049 °C
0.043 °C
0.030 °C
0.032 °C
0.037 °C
0.047 °C
0.048 °C
0.047 °C
0.050 °C
0.045 °C
0.033 °C
0.035 °C
0.041 °C
0.052 °C
0.076 °C
Pt 385, 1000 Ω-200 °C
-80 °C
0 °C
100 °C
260 °C
300 °C
400 °C
600 °C
-80 °C
0 °C
100 °C
260 °C
300 °C
400 °C
600 °C
630 °C
0.031 °C
0.034 °C
0.039 °C
0.025 °C
0.027 °C
0.030 °C
0.041 °C
0.042 °C
0.032 °C
0.035 °C
0.040 °C
0.028 °C
0.030 °C
0.034 °C
0.045 °C
0.047 °C
PtNi 385, 120 Ω
(Ni120) -80 °C 0 °C
100 °C
0 °C
100 °C
260 °C
0.209 °C
0.210 °C
0.211 °C
0.210 °C
0.211 °C
0.212 °C
Cu 427, 10 Ω2-100 °C 260 °C 0.300 °C 0.069 °C
YSI 400 15 °C 50 °C 0.005 °C 0.304 °C
SPRT, 25 ΩUser Defined User Defined 0.05 °C 0.06 °C
1. 4-wire mode. Uncertainties listed do not include probe uncertainties.
2. Based on MINCO Application Aid No. 18.

525A
Theory of Operation
11
Pressure Measurement
The Calibrator can accept either the Fluke 700 or 6100 series pressure modules. Pressure
modules plug directly into the front panel Lemo connector. The Calibrator firmware
automatically detects the type and value of the module you are attaching, and recognizes
the following units of measurement:
•PSI
(pounds per square inch)
•inH2O4°C
(inches of water at 4 degrees Celsius)
•inH2O20C
(inches of water at 20 degrees Celsius)
•cmH2O4°C
(centimeters of water at 4 degrees Celsius)
•cmH2O20C
(centimeters of water at 20 degrees Celsius)
•BAR
(bars)
•mBAR
(millibars)
•KPAL
(kilopascals)
•inHG 0°C
(inches of mercury at 0 degrees Celsius)
•mmHG 0°C
(millimeters of mercury at 0 degrees
Celsius)
•Kg/cm2
(kilograms per square centimeter)
Theory of Operation
The Calibrator serves as an accurate laboratory device for calibrating thermocouples,
RTDs, pressure devices, and low-level dc voltages and currents. The main PCB
assembly, and several subassemblies, work together to provide high-reliability and easy
maintenance.
Micro-Controller Section
The Atmel ATmega 103 micro-controller is the heart of the 525A. It contains all of the
program memory, nv-ram, FlashROM, static RAM, and EEProm. The micro-controller
allows a minimal amount of external glue logic. The main external digital ICs are the RS-
232 driver, relay drivers, LCD controller, and the digitally controlled analog switches.
Many of the ICs are interfaced through the micro-controller’s three-wire SPI bus
minimizing interconnecting lines. Inputs or outputs begin with instructions entered
through the keypad or through remote communications (serial or IEEE-488) into the
micro-controller. The micro-controller processes the commands and sets conditions that
are appropriate for the command.

525A
Service Manual
12
Analog Section
The Calibrator can source DC voltage to 100 V, DC current to 100 mA, resistances from 5 to
4000 Ω, and thermocouples and RTDs. The main components of the analog circuit consist of a
precision 2.5-volt temperature compensated reference, 20-bit DAC and a 24-bit ADC. Precision
metal foil resistor networks and several chopper-stabilized OP-AMPS are the most critical analog
components.
When sourcing, the micro-controller, using stored calibration constants, adjusts the D/A to
generate an output based on the function and range selected. To achieve high accuracy, a low drift
24-bit A/D converter is used as a feedback element near the output of the D/A converter. The
scaled output DAC_CK is routed to the A/D converter.
In the input mode, the A/D is used directly to measure either the T/C or the resistance (RTD)
inputs. The A/D features an internal self-calibration function that continually nulls out zero drift
due to temperature changes. A programmable gain stage in the A/D is adjusted by the micro-
controller to allow direct T/C and RTD inputs without requiring external amplification. In the
RTD mode, a constant current source is used to excite the RTD and the voltage developed across
the RTD is measured by the A/D, then the resistance can be calculated.
Basic Maintenance
WWarning
To avoid personal injury or damage to the Calibrator, use only
the specified replacement parts and do not allow water into the
case.
Cleaning the Calibrator
WCaution
To avoid damaging the case, do not use solvents or abrasive
cleaners.
Clean the Calibrator and pressure modules with a soft cloth dampened with water or mild
soap and water.
Replacing a Line Fuse
WWarning
To avoid electrical shock, disconnect line power before opening
the case or line voltage selector.
The line power fuses and line voltage selector switch are located in a compartment above
the power switch on the right rear of the Calibrator. The fuse-rating label on the rear
panel shows the correct replacement fuse for each line voltage setting.
Table 2 lists the fuse part numbers for each line voltage setting. Figure 1 shows how to
remove the fuse compartment cover.