Fluke 2638A Use and care manual

August 2014
© 2014 Fluke Corporation. All rights reserved. Specifications are subject to change without notice.
All product names are trademarks of their respective companies.
2638A
HYDRA Series III Data Acquisition Unit
Calibration Manual

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

i
Table of Contents
Title Page
Introduction............................................................................................ 1
Contact Fluke ........................................................................................ 1
Safety Information ................................................................................. 2
General Specifications .......................................................................... 5
Measurement Specifications ................................................................. 6
DC Voltage ........................................................................................ 6
DC Voltage Input Characteristics .................................................. 6
DC Voltage Accuracy .................................................................... 7
DC Voltage Additional Errors......................................................... 7
AC Voltage ........................................................................................ 7
AC Voltage Input Characteristics................................................... 8
AC Voltage Accuracy..................................................................... 8
Additional Low Frequency Errors ...................................................... 8
DC Current ........................................................................................ 8
DC Current Input Characteristics................................................... 9
DC Current Accuracy..................................................................... 9
DC Current Additional Errors......................................................... 9
AC Current......................................................................................... 9
AC Current Input Characteristics................................................... 9
AC Current Accuracy..................................................................... 10
Additional Low Frequency Errors ...................................................... 10
Frequency.......................................................................................... 10
Resistance......................................................................................... 10
Resistance Input Characteristics ................................................... 11
Resistance Accuracy ..................................................................... 11
Resistance Additional Errors ......................................................... 11
RTD ................................................................................................... 11
RTD Temperature Accuracy.......................................................... 12
RTD Measurement Characteristics ............................................... 12
Thermistor ......................................................................................... 12
Thermistor Temperature Accuracy ................................................ 12
Thermistor Measurement Characteristics...................................... 13
Thermocouple.................................................................................... 13
Thermocouple Temperature Accuracy .......................................... 13
Thermocouple Measurement Characteristics................................ 14
Digital I/O........................................................................................... 14

2638A
Calibration Manual
ii
Totalizer............................................................................................. 14
Trigger ............................................................................................... 15
Alarm Output ..................................................................................... 15
2638A-100 Universal Input Module ....................................................... 15
General Maintenance ............................................................................ 16
If the Product Does Not Turn On ....................................................... 16
Clean the Product.............................................................................. 16
Replace the Line Power Fuse ........................................................... 16
Battery Replacement ......................................................................... 17
Memory and Factory Reset ............................................................... 18
Required Equipment.............................................................................. 19
Test Considerations .............................................................................. 21
Performance Tests ................................................................................ 21
Front Panel Test ................................................................................ 22
DC Volts Verification.......................................................................... 22
Volts AC and Frequency Verification................................................. 24
4-Wire Ohms Verification................................................................... 26
PRT Verification Steps ...................................................................... 27
Configure Resistance Display ........................................................... 27
Thermistor Verification Steps ............................................................ 28
Configure Resistance Display ........................................................... 28
DC Current Verification...................................................................... 29
AC Current Verification Steps............................................................ 31
2638A-100 Module Verification ......................................................... 32
Calibration Adjustment .......................................................................... 33
Unlock the Product ............................................................................ 33
Unlock the Product with a Remote Interface ..................................... 33
Reset the Admin Password ............................................................... 34
Disassembly ...................................................................................... 35
Change the Calibration Date Remotely ............................................. 37
“Mainframe” Adjustment Process ...................................................... 37
Remote Commands for Calibration ....................................................... 43
Remote Programming Examples....................................................... 44
Start a Full Calibration ....................................................................... 44
Calibrate 1 V DC Range only ............................................................ 45
Write Calibration Date to a Module.................................................... 45
Command References....................................................................... 46
User-Replaceable Parts and Accessories............................................. 51

iii
List of Tables
Table Title Page
1. Symbols..................................................................................................... 2
2. Fuses......................................................................................................... 16
3. Memory Clear Functions ........................................................................... 18
4. Required Test Equipment.......................................................................... 19
5. DC Volts Verification Steps ....................................................................... 23
6. AC Volts Verification Steps ....................................................................... 25
7. AC Volts Frequency Verification Steps ..................................................... 25
8. 4-Wire Ohms Verification Steps ................................................................ 26
9. PRT Verification Steps .............................................................................. 27
10. Thermistor Verification Steps .................................................................... 28
11. DC Current Verification Steps ................................................................... 30
12. AC Current Verification Steps ................................................................... 32
13. Adjustment Steps ...................................................................................... 37
14. List of Commands ..................................................................................... 43
15. Full Calibration Example ........................................................................... 44
16. 1 V DC Calibration Example...................................................................... 45
17. Write Calibration Date to a Module Example ............................................ 45
18. User-Replaceable Parts and Accessories................................................. 51

2638A
Calibration Manual
iv

v
List of Figures
Figure Title Page
1. Fuse Replacement .................................................................................... 17
2. DC Voltage Test Connections ................................................................... 22
3. AC Volts Verification Connections............................................................. 24
4. 4-Wire Ohms Test Equipment Setup......................................................... 26
5. PRT Verification Connection ..................................................................... 27
6. Thermistor Test Equipment Setup............................................................. 28
7. mA DC Current Equipment Setup ............................................................. 29
8. mA AC Current Equipment Setup ............................................................. 31
9. Password Reset Jumper ........................................................................... 34
10. Disassembly .............................................................................................. 36
11. Replaceable Parts ..................................................................................... 52

2638A
Calibration Manual
vi

1
Introduction
The Fluke 2638A HYDRA Series III Data Acquisition Unit (the Product or
Instrument) is a 67 analog channel bench-top data logger that measures and
records dc volts, ac volts, dc current, ac current, resistance, frequency, and
temperature. See the Specifications section for information on the types and
ranges of the measurement inputs the Product can accept.
Contact Fluke
To contact Fluke, call one of the following telephone numbers:
•Technical Support USA: 1-800-44-FLUKE (1-800-443-5853)
•Calibration/Repair 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, visit Fluke's website at www.fluke.com.
To register your product, visit http://register.fluke.com.
To view, print, or download the latest manual supplement, visit
http://us.fluke.com/usen/support/manuals.

2638A
Calibration Manual
2
Safety Information
A Warning identifies conditions and procedures that are dangerous to the user.
A Caution identifies conditions and procedures that can cause damage to the
Product or the equipment under test.
See Table 1 for a list of symbols used in this manual and on the Product.
Table 1. Symbols
Symbol Description Symbol Description
Risk of Danger. Important
information. See Manual. DC (Direct Current)
Hazardous voltage. Risk of
electric shock. AC or DC (Alternating or Direct Current)
Earth ground Digital signal

or

AC or DC (Alternating or Direct
Current) Double insulated
Recycle Power ON / OFF
Conforms to relevant South
Korean EMC Standards. Conforms to European Union directives.
CAT II Measurement Category II is applicable to test and measuring circuits connected directly to
utilization points (socket outlets and similar points) of the low-voltage MAINS installation.
CAT III Measurement Category III is applicable to test and measuring circuits connected to the
distribution part of the building’s low-voltage MAINS installation.
CAT IV Measurement Category IV is applicable to test and measuring circuits connected at the
source of the building’s low-voltage MAINS installation.

This product complies with the WEEE Directive (2002/96/EC) marking requirements. The
affixed label indicates that you must not discard this electrical/electronic product in domestic
household waste. Product Category: With reference to the equipment types in the WEEE
Directive Annex I, this product is classed as category 9 "Monitoring and Control
Instrumentation" product. Do not dispose of this product as unsorted municipal waste. Go to
Fluke’s website for recycling information.

HYDRA Series III Data Acquisition Unit
Safety Information
3
Warning
To prevent possible electrical shock, fire, or personal injury:
•Read all safety information before you use the Product.
•Carefully read all instructions.
•Use the Product only as specified, or the protection supplied
by the Product can be compromised.
•Examine the case before you use the Product. Look for cracks
or missing plastic. Carefully look at the insulation around the
terminals.
•Do not use the Product if it operates incorrectly.
•Do not use the Product if it is damaged.
•Disable the Product if it is damaged.
•Use only the mains power cord and connector approved for
the voltage and plug configuration in your country and rated
for the Product.
•Replace the mains power cord if the insulation is damaged or
if the insulation shows signs of wear.
•Make sure the ground conductor in the mains power cord is
connected to a protective earth ground. Disruption of the
protective earth could put voltage on the chassis that could
cause death.
•Do not put the Product where access to the mains power cord
is blocked.
•Use only correct measurement category (CAT), voltage, and
amperage rated probes, test leads, and adapters for the
measurement.
•Use only cables with correct voltage ratings.
•Do not use test leads if they are damaged. Examine the test
leads for damaged insulation and measure a known voltage.
•Do not exceed the Measurement Category (CAT) rating of the
lowest rated individual component of a Product, probe, or
accessory.
•Keep fingers behind the finger guards on the probes.
•Do not apply more than the rated voltage, between the
terminals or between each terminal and earth ground.
•Do not touch voltages >30 V ac rms, 42 V ac peak, or 60 V dc.
•Limit operation to the specified measurement category,
voltage, or amperage ratings.
•Measure a known voltage first to make sure that the Product
operates correctly.

2638A
Calibration Manual
4
•Consider all accessible channels to be hazardous live and an
electric shock hazard if any channel is connected to a
hazardous voltage source.
•Do not remove, touch, or change the internal wiring of
hazardous inputs until the input source is turned off.
•Remove inputs from hazardous voltage sources before an
input module is opened.
•Use the correct terminals, function, and range for
measurements.
•Use this Product indoors only.
•Do not use the Product around explosive gas, vapor, or in
damp or wet environments.

HYDRA Series III Data Acquisition Unit
General Specifications
5
General Specifications
Mains Voltage
100 V Setting ...................................................... 90 V to 110 V
120 V Setting ...................................................... 108 V to 132 V
220 V Setting ...................................................... 198 V to 242 V
240 V Setting ...................................................... 216 V to 264 V
Frequency.............................................................. 47 Hz to 440 Hz
Power Consumption ............................................. 36 VA peak (24 W average)
Environment Temperature
Operating ............................................................ 0 °C to 50 °C
Full accuracy....................................................... 18 °C to 28 °C
Storage ............................................................... -20 °C to 70 °C
Warm-up ............................................................. 1 hour to full accuracy specifications
Relative Humidity (non-condensing)
Operating ............................................................ 0 °C to 28 °C <90 %
28 °C to 40 °C <75 %
40 °C to 50 °C <45 %
Storage ............................................................... -20 °C to 70 °C <95 %
Altitude
Operating ............................................................ 2,000 m
Storage ............................................................... 12,000 m
Vibration and Shock ............................................. Complies with MIL-PRF-28800F Class 3
Channel Capacity
Total analog channels ........................................ 67
Voltage/resistance channels............................... 61
Current channels ................................................ 7
Digital I/O ............................................................ 8 bits
Totalizer .............................................................. 1
Alarm outputs...................................................... 6
Trigger input........................................................ 1
Safety Protection
Mains Input ......................................................... IEC 61010-1, Overvoltage Category II, Pollution Degree 2
Front Panel ......................................................... 300 V CAT II
Rear Panel.......................................................... 150 V CAT II, 250 V rms with maximum transient voltage of 1000 V
peak. These terminals are not intended for connection to mains
voltage above 150 V without external transient suppression. The
maximum input that can be applied between rear-module terminals or
between any rear-module terminal and earth ground is 250 V dc or ac
rms.
Electromagnetic Environment ............................. IEC 61326-1: Basic (Controlled EM for full specification)
Radio Frequency Emissions................................ IEC CISPR 11: Group 1, Class A. (Group 1 has intentionally generated
and/or uses conductively coupled radio-frequency energy which is
necessary for the internal functioning of the equipment itself. Class A
equipment is suitable for use in non-domestic locations and/or directly
connected to a low-voltage power supply network.)
Electromagnetic Compatibility ............................ Applies to use in Korea only. Class A Equipment (Industrial
Broadcasting & Communication Equipment) [1]
[1] This product meets requirements for industrial (Class A)
electromagnetic wave equipment and the seller or user should take
notice of it. This equipment is intended for use in business
environments and is not to be used in homes.
Math Channels
Number of channels............................................ 20
Operations .......................................................... sum, difference, multiply, divide, polynomial, power, square root,
reciprocal, exponential, logarithm, absolute value, average, maximum,
minimum
Triggers.................................................................. interval, external (trigger input), alarm, remote (bus), manual
Battery life ............................................................. 5 years

2638A
Calibration Manual
6
Memory
Scan data RAM................................................... 75,000 readings with timestamp
Data/Setup flash memory ................................... 20 MB
Non-volatile memory life ..................................... 5 years
USB Host Port
Standard ............................................................. 2.0, full speed
Connector type ................................................... Type A
Function .............................................................. Memory
File system.......................................................... FAT32
Memory capacity................................................. 32 GB
USB Device Port
Connector type ................................................... Type B
Class................................................................... Instrument
Function .............................................................. Control and data transfer
Command protocol ............................................. SCPI
LAN
Function .............................................................. Control and data transfer
Network protocols............................................... Ethernet 10/100, TCP/IP
Command protocol ............................................. SCPI
Dimensions
Height ................................................................. 150 mm
Width................................................................... 245 mm
Depth .................................................................. 385 mm
Weight................................................................. 6 kg (typical configuration)
Shipping Weight.................................................. 9.5 kg (typical configuration)
Conformity............................................................. CE, CSA, IEC 61010 3rd ed.
Measurement Specifications
Accuracy specifications generally are valid for 6 ½ digit resolution mode (unless otherwise noted) for front panel input
(Channel 001), after a minimum of 1-hour warm-up, and within an environment temperature range of 18 °C to 28 °C.
24-hour specifications are relative to calibration standards and assume a controlled electromagnetic environment per EN
61326. The confidence level for accuracy specifications is 99 % within 1 year of calibration (unless otherwise noted).
Scan rate (typical, depending on function and range)
Fast..................................................................... 46 channels per second max (0.02 seconds per channel)
Medium ............................................................... 10 channels per second (0.1 seconds per channel)
Slow .................................................................... 2 channels per second (0.5 seconds per channel)
Display Resolution................................................ 4 ½ to 6 ½ digits, depending on Sample Rate or NPLC
DC Voltage
Maximum Input...................................................... 300 V on any range
Common Mode Rejection..................................... 140 dB at 50 Hz or 60 Hz (1 kΩunbalance for NPLC of 1 or greater,
±500 V peak maximum in the low lead)
Normal Mode Rejection ........................................ 55 dB for NPLC of 1 or greater and power-line frequency ±0.1 %,
±20 % of range peak maximum
Measurement Method ........................................... Multi-ramp A/D
A/D Linearity.......................................................... 2 ppm of measurement + 1 ppm off range
Input Bias Current................................................. <30 pA at 25 °C
DC Voltage Input Characteristics
Range Resolution
Resolution
Input Impedance
Fast
4½ Digits
Medium
5 ½ Digits
Slow
6 ½ Digits
100 mV 100.0000 mV 10 μV 1 μV 0.1 μV 10 MΩor >10 GΩ[1]
1 V 1.000000 V 100 μV 10 μV 1 μV 10 MΩor >10 GΩ[1]
10 V 10.00000 V 1 mV 100 μV 10 μV 10 MΩor >10 GΩ[1]
100 V 100.0000 V 10 mV 1 mV 100 μV 10 MΩ±1 %
300 V 300.000 V 100 mV 10 mV 1 mV 10 MΩ±1 %
Note:
Input beyond ±12 V is clamped. The clamp current is up to 3 mA. 10 MΩis default input impedance.

HYDRA Series III Data Acquisition Unit
Measurement Specifications
7
DC Voltage Accuracy
Accuracy is given as ± (% measurement + % of range).
Range 24 Hour
(23 ±1 °C)
90 Days
(23 ±5 °C)
1 Year
(23 ±5 °C)
T.C./ °C
Outside
18 °C to 28 °C
100 mV 0.0025 % + 0.003 % 0.0025 % + 0.0035 % 0.0037 % + 0.0035 % 0.0005 % + 0.0005 %
1 V 0.0018 % + 0.0006 % 0.0018 % + 0.0007 % 0.0025 % + 0.0007 % 0.0005 % + 0.0001 %
10 V 0.0013 % + 0.0004 % 0.0018 % + 0.0005 % 0.0024 % + 0.0005 % 0.0005 % + 0.0001 %
100 V 0.0018 % + 0.0006 % 0.0027 % + 0.0006 % 0.0038 % + 0.0006 % 0.0005 % + 0.0001 %
300 V 0.0018 % + 0.002 % 0.0031 % + 0.002 % 0.0041 % + 0.002 % 0.0005 % + 0.0003 %
Notes:
•For conducted disturbances on mains input >1 V from 10 MHz to 20 MHz, add 0.02 % of range. For disturbances
>3 V, accuracy is unspecified.
•For radiated disturbances >1V/m from 450 MHz to 550 MHz, add 0.02 % of range. For disturbances > 3 V/m,
accuracy is unspecified.
DC Voltage Additional Errors
Digits NPLC Ch. x01 – x20 Additional NPLC Noise
Error
6 ½ 200 add 2 μV -
6 ½ 100 add 2 μV -
6 ½ 10 (Slow) add 2 μV -
5 ½ 1 (Medium) add 2 μV add 0.0008 % of range
4 ½ 0.2 (Fast) - add 0.002 % of range + 12 μV
4 ½ 0.02 - add 0.014 % of range + 17 μV
AC Voltage
AC voltage specifications are for ac sine wave signals >5 % of range. For inputs from 1 % to 5 % of range and <50 kHz,
add an additional error of 0.1 % of range. For 50 kHz to 100 kHz, add 0.13 % of range.
Maximum Input...................................................... 300 V rms or 425 V peak or 3 × 107volts-Hertz product (whichever is
less) for any range.
Measurement Method ........................................... AC-coupled true-rms. Measures the ac component of input with up to
300 V dc bias on any range.
AC Filter Bandwidth:
Slow .................................................................... 20 Hz
Fast..................................................................... 200 Hz
Maximum Crest Factor ......................................... 5:1 at full scale
Additional Crest Factor Errors ............................ Crest factor 1-2, 0.05 % of full scale
Crest factor 2-3, 0.2 % of full scale
Crest factor 3-4, 0.4 % of full scale
Crest factor 4-5, 0.5 % of full scale

2638A
Calibration Manual
8
AC Voltage Input Characteristics
Range Resolution
Resolution
Input Impedance
4 ½
Digits
5 ½
Digits
6 ½
Digits
100 mV 100.0000 mV 10 μV 1 μV 0.1 μV
1 MΩ±2 % shunted by 150 pF
1 V 1.000000 V 100 μV 10 μV 1 μV
10 V 10.00000 V 1 mV 100 µV 10 μV
100 V 100.0000 V 10 mV 1 mV 100 μV
300 V 300.000 V 100 mV 10 mV 1 mV
AC Voltage Accuracy
Accuracy is given as ± (% measurement + % of range).
Range Frequency 24 Hour
(23 ±1 °C)
90 Days
(23 ±5 °C)
1 Year
(23 ±5 °C)
T.C./ °C
Outside
18 °C to 28 °C
100 mV
20 Hz to 20 kHz 0.1 % + 0.05 % 0.11 % + 0.05 % 0.11 % + 0.05 % 0.01 % + 0.005 %
20 kHz to 50 kHz 0.2 % + 0.05 % 0.22 % + 0.05 % 0.22 % + 0.05 % 0.01 % + 0.005 %
50 kHz to 100 kHz 0.55 % + 0.08 % 0.6 % + 0.08 % 0.6 % + 0.08 % 0.05 % + 0.01 %
1 V
20 Hz to 20 kHz 0.1 % + 0.05 % 0.11 % + 0.05 % 0.11 % + 0.05 % 0.01 % + 0.005 %
20 kHz to 50 kHz 0.2 % + 0.05 % 0.22 % + 0.05 % 0.22 % + 0.05 % 0.01 % + 0.005 %
50 kHz to 100 kHz 0.55 % + 0.08 % 0.6 % + 0.08 % 0.6 % + 0.08 % 0.05 % + 0.01 %
10 V
20 Hz to 20 kHz 0.1 % + 0.05 % 0.11 % + 0.05 % 0.11 % + 0.05 % 0.01 % + 0.005 %
20 kHz to 50 kHz 0.2 % + 0.05 % 0.22 % + 0.05 % 0.22 % + 0.05 % 0.01 % + 0.005 %
50 kHz to 100 kHz 0.55 % + 0.08 % 0.6 % + 0.08 % 0.6 % + 0.08 % 0.05 % + 0.01 %
100 V
20 Hz to 20 kHz 0.1 % + 0.05 % 0.11 % + 0.05 % 0.11 % + 0.05 % 0.01 % + 0.005 %
20 kHz to 50 kHz 0.2 % + 0.05 % 0.22 % + 0.05 % 0.22 % + 0.05 % 0.01 % + 0.005 %
50 kHz to 100 kHz 0.55 % + 0.08 % 0.6 % + 0.08 % 0.6 % + 0.08 % 0.05 % + 0.01 %
300 V
20 Hz to 20 kHz 0.1 % + 0.05 % 0.11 % + 0.05 % 0.11 % + 0.05 % 0.01 % + 0.005 %
20 kHz to 50 kHz 0.2 % + 0.05 % 0.22 % + 0.05 % 0.22 % + 0.05 % 0.01 % + 0.005 %
50 kHz to 100 kHz 0.55 % + 0.27 % 0.6 % + 0.27 % 0.6 % + 0.27 % 0.05 % + 0.03 %
Note:
For conducted disturbances on mains input >1 V from 10 MHz to 40 MHz, add 0.02 % of range. For disturbances >3 V,
accuracy is unspecified.
Additional Low Frequency Errors
Error is stated as % of reading.
Frequency
A
C Filte
r
20 Hz 200 Hz
20 Hz to 40 Hz 0 % −
40 Hz to 100 Hz 0 % 0.55 %
100 Hz to 200 Hz 0 % 0.2 %
200 Hz to 1 kHz 0 % 0.02 %
>1 kHz 0 % 0 %
DC Current
Input Protection .................................................... 0.15 A / 600 V Resettable PTC

HYDRA Series III Data Acquisition Unit
Measurement Specifications
9
DC Current Input Characteristics
Range Resolution
Resolution Reference
Resistance
(Ohms)
Burden
Voltage
Fast
4½
Digits
Medium
5 ½
Digits
Slow
6 ½
Digits
100 μA 100.0000 µA 10 nA 1 nA 0.1 nA 1k Ω<1 mV
1 mA 1.000000 mA 100 nA 10 nA 1 nA 1k Ω<1 mV
10 mA 10.00000 mA 1 μA 100 nA 10 nA 10 Ω<1 mV
100 mA 100.0000 mA 10 μA 1 μA 100 nA 10 Ω<1 mV
DC Current Accuracy
Accuracy is given as ± (% measurement + % of range).
Range 24 Hour
(23 ±1 °C)
90 Days
(23 ±5 °C)
1 Year
(23 ±5 °C)
T.C./ °C
Outside
18 °C to 28 °C
100 μA 0.005 % + 0.003 % 0.015 % + 0.0035 % 0.015 % + 0.0035 % 0.002 % + 0.001 %
1 mA 0.005 % + 0.001 % 0.015 % + 0.0011 % 0.015 % + 0.0011 % 0.002 % + 0.001 %
10 mA 0.005 % + 0.003 % 0.015 % + 0.0035 % 0.015 % + 0.0035 % 0.002 % + 0.001 %
100 mA 0.005 % + 0.001 % 0.015 % + 0.0035 % 0.015 % + 0.0035 % 0.002 % + 0.001 %
DC Current Additional Errors
Digits NPLC
Additional NPLC Noise Error
for 10 mA, 100 mA
Additional NPLC Noise
Error for 100 µA, 1 mA
6 ½ 200 - -
6 ½ 100 - -
6 ½ 10 (Slow) - -
5 ½ 1 (Medium) 0.0008 % of range 0.0008 % of range
4 ½ 0.2 (Fast) 0.002 % of range + 1.2 µA 0.002 % of range + 12 nA
4 ½ 0.02 0.014 % of range + 1.7 µA 0.014 % of range + 17 nA
AC Current
Input Protection .................................................... 0.15 A / 600 V resettable PTC
Measurement Method ........................................... AC-coupled true-rms, dc-coupled to the shunt (no blocking capacitor).
AC Filter Bandwidth:
Slow .................................................................... 20 Hz
Fast..................................................................... 200 Hz
Maximum Crest Factor ......................................... 5:1 at full scale
Additional Crest Factor Errors ............................ Crest factor 1-2, 0.05 % of full scale
Crest factor 2-3, 0.2 % of full scale
Crest factor 3-4, 0.4 % of full scale
Crest factor 4-5, 0.5 % of full scale
AC Current Input Characteristics
Range Resolution
Resolution
Reference
Resistance
Burden
Voltage
4 ½
Digits
5 ½
Digits
6 ½
Digits
100 μA 100.0000 µA 10 nA 1 nA 0.1 nA 1 kΩ<10 mV (RMS)
1 mA 1.000000 mA 100 nA 10 nA 1 nA 1 kΩ<10 mV (RMS)
10 mA 10.00000 mA 1 μA 100 nA 10 nA 10 Ω<20 mV (RMS)
100 mA 100.0000 mA 10 μA 1 μA 100 nA 10 Ω<50 mV (RMS)

2638A
Calibration Manual
10
AC Current Accuracy
Accuracy is given as ± (% measurement + % of range). Basic accuracy specification is for a sinusoidal signal with
amplitude greater than 5 % of range. For input signals between 1 % to 5 % of range, add 0.1 % of range.
Range Frequency 24 Hour
(23 ±1 °C)
90 Days
(23 ±5 °C)
1 Year
(23 ±5 °C)
T.C./ °C Outside
18 °C to 28 °C
100 μA 20 Hz to 2 kHz 0.2 % + 0.06 % 0.25 % + 0.06 % 0.3 % + 0.06 % 0.015 % + 0.005 %
1 mA 20 Hz to 2 kHz 0.2 % + 0.06 % 0.25 % + 0.06 % 0.3 % + 0.06 % 0.015 % + 0.005 %
10 mA 20 Hz to 2 kHz 0.2 % + 0.06 % 0.25 % + 0.06 % 0.3 % + 0.06 % 0.015 % + 0.005 %
100 mA 20 Hz to 2 kHz 0.2 % + 0.06 % 0.25 % + 0.06 % 0.3 % + 0.06 % 0.015 % + 0.005 %
Additional Low Frequency Errors
Error is stated as % of reading.
Frequency
A
C Filte
r
20 Hz 200 Hz
20 Hz to 40 Hz 0 % −
40 Hz to 100 Hz 0 % 0.55 %
100 Hz to 200 Hz 0 % 0.2 %
200 Hz to 1 kHz 0 % 0.02 %
>1 kHz 0 % 0 %
Frequency
Gate Times............................................................. 100 milliseconds to 1 second.
Measurement Method ........................................... Flexible counting technique. AC-coupled input using the ac voltage
measurement function.
Settling Considerations........................................ When measuring frequency after a dc offset voltage change, errors
may occur. For the most accurate measurement, wait up to 1 second
for the input blocking capacitor to settle.
Measurement Considerations.............................. To minimize measurement errors, shield inputs from external noise
when measuring low-voltage, low-frequency signals.
Frequency Accuracy
Accuracy is given as ± % of measurement.
Range Frequency
24 Hour
(23 ±1 °C)
90 Days
(23 ±5 °C)
1 Year
(23 ±5 °C)
T.C./ °C
Outside 18
°C to 28 °C
100 mV to
300 V [1] [2]
20 Hz to 40 Hz 0.03 % 0.03 % 0.03 % 0.001 %
40 Hz to 1 MHz 0.006 % 0.01 % 0.01 % 0.001 %
[1] Input >100 mV. For 10 mV to 100 mV, multiply percent measurement error by 10.
[2] Limited to 3 x 107volt-Hertz
Resistance
Measurement Method ........................................... Current source referenced to LO input.
Max. Lead Resistance (4-wire ohms) .................. 10 Ωper lead for 100 Ω, 1 kΩranges. 1 kΩper lead on all other
ranges.
Input Protection .................................................... 300 V on all ranges.

HYDRA Series III Data Acquisition Unit
Measurement Specifications
11
Resistance Input Characteristics
Range Resolution
Resolution
Source Current
Fast
4½ Digits
Medium
5 ½ Digits
Slow
6 ½ Digits
100 Ω100.0000 Ω10 mΩ1 mΩ0.1 mΩ1 mA / 4 V
1 kΩ1.000000 kΩ100 mΩ10 mΩ1 mΩ1 mA / 4 V
10 kΩ10.00000 kΩ1 Ω100 mΩ10 mΩ100 µA / 6 V
100 kΩ100.0000 kΩ10 Ω1 Ω100 mΩ100 µA / 12 V
1 MΩ1.000000 MΩ100 Ω10 Ω1 Ω10 µA / 12 V
10 MΩ10.00000 MΩ1 kΩ100 Ω10 Ω1 µA / 12 V
100 MΩ100.0000 MΩ10 kΩ1 kΩ100 Ω0.1 µA / 12 V
Resistance Accuracy
Accuracy is given as ± (% measurement + % of range). Basic accuracy specification is for 4-wire resistance. For 2-wire
resistance add 0.02 Ωinternal resistance if using Channel 1 or 1.5 Ωif using channels x01 through x20, and add external
lead wire resistance.
Range 24 Hour
(23 ±1 °C)
90 Days
(23 ±5 °C)
1 Year
(23 ±5 °C)
T.C./ °C
Outside 18 °C
to 28 °C
100 Ω0.003 % + 0.003 % 0.008 % + 0.004 % 0.01 % + 0.004 % 0.0006 % + 0.0005 %
1 kΩ0.002 % + 0.0005 % 0.008 % + 0.001 % 0.01 % + 0.001 % 0.0006 % + 0.0001 %
10 kΩ0.002 % + 0.0005 % 0.008 % + 0.001 % 0.01 % + 0.001 % 0.0006 % + 0.0001 %
100 kΩ0.002 % + 0.0005 % 0.008 % + 0.001 % 0.01 % + 0.001 % 0.0006 % + 0.0001 %
1 MΩ0.002 % + 0.001 % 0.008 % + 0.001 % 0.01 % + 0.001 % 0.001 % + 0.0002 %
10 MΩ0.015 % + 0.001 % 0.02 % + 0.001 % 0.04 % + 0.001 % 0.003 % + 0.0004 %
100 MΩ0.3 % + 0.01 % 0.8 % + 0.01 % 0.8 % + 0.01 % 0.05 % + 0.002 %
Note:
For conducted disturbances on mains input >1 V from 10 MHz to 40 MHz, add 0.6 % of range. For disturbances >3 V,
accuracy is unspecified.
Resistance Additional Errors
Digits NPLC Additional NPLC Noise Error
6 ½ 200 0 % of range
6 ½ 100 0 % of range
6 ½ 10 (Slow) 0 % of range
5 ½ 1 (Medium) 0.0008 % of range
4 ½ 0.2 (Fast)(only for 2-wire) 0.002 % of range + 12 mΩ
4 ½ 0.02 (only for 2-wire) 0.01 % of range + 17 mΩ
RTD
Temperature Range .............................................. -200 °C to 1200 °C (depending on the sensor)
Resistance Range ................................................. 0 Ωto 4 kΩ
Maximum Lead Resistance (4-wire Ω)................ 2.5 % of range per lead for 400 Ωand 4 kΩranges
Sample Rate
Slow .................................................................... 10 PLC
Medium ............................................................... 2 PLC
Fast..................................................................... 1 PLC

2638A
Calibration Manual
12
RTD Temperature Accuracy
Accuracy is for 4-wire 100 Ωnominal RTD, using the slow sample rate. With 3-wire PRT/RTD add 0.015 °C if using
Channel 1, or add 0.15 °C internal resistance mismatch to the accuracy specification if using channels x01 through x20,
and add external lead wire resistance mismatch. When using medium or fast sample rate (NPLC <10), add the number
given in the table to the accuracy specification. If the environment temperature is outside the specified range, multiply the
Temperature Coefficient number by the temperature deviation and add to the accuracy specification. Linear interpolation
may be used between points in the table. Specifications do not include sensor accuracy. The practical range of
temperature measurement depends on the sensor and characterization.
Temperature Accuracy Medium/Fast Sample
Rate (NPLC <10)
T.C./ °C Outside
18 °C to 28 °C
-200 °C 0.016 °C add 0.02 °C 0.0026 °C
0 °C 0.038 °C add 0.02 °C 0.0041 °C
300 °C 0.073 °C add 0.03 °C 0.0063 °C
600 °C 0.113 °C add 0.03 °C 0.0089 °C
Note:
For conducted disturbances on mains input >1 V from 10 MHz to 40 MHz, add 0.2 Celsius. For disturbances >3 V,
accuracy is unspecified.
RTD Measurement Characteristics
Range
Temperature Display Resolution
Source Current
Slow
Sample Rate
Medium/Fast
Sample Rate
0 Ωto 400 Ω0.001 °C 0.01 °C 1 mA
400 Ωto 4 kΩ0.001 °C 0.01 °C 0.1 mA
Thermistor
Temperature Range .............................................. -200 °C to 400 °C (depending on the sensor)
Resistance Range ................................................. 0 Ωto 1 MΩ
Sample Rate
Slow .................................................................... 10 PLC
Medium ............................................................... 2 PLC
Fast..................................................................... 1 PLC
Thermistor Temperature Accuracy
Accuracy specifications are for a 4-wire thermistor using medium or slow sample rate. With 2-wire thermistor add the
number given in the table to the accuracy specification for internal resistance. When using fast sample rate (NPLC <10),
multiply the accuracy specification by 3. If the environment temperature is outside the specified range, increase the
accuracy specification by 25 % for every 1 °C outside the specified environment temperature range. Specifications do not
include sensor accuracy. The practical range of temperature measurement depends on the sensor.
Temperature
Accuracy
2.2 kΩ
thermistor
5 kΩ
thermistor
10 kΩ
thermistor 2-wire
-40 °C 0.002 °C 0.007 °C 0.007 °C add 0.002 °C
0 °C 0.005 °C 0.004 °C 0.003 °C add 0.004 °C
25 °C 0.013 °C 0.007 °C 0.005 °C add 0.016 °C
50 °C 0.019 °C 0.01 °C 0.011 °C add 0.05 °C
100 °C 0.116 °C 0.054 °C 0.026 °C add 0.34 °C
150 °C 0.527 °C 0.239 °C 0.1 °C add 1.7 °C
Note:
For conducted disturbances on mains input >1 V from 10 MHz to 40 MHz, add 0.2 Celsius. For disturbances >3 V,
accuracy is unspecified.