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7911A
Constant
Temperature
Ice Bath
User’s Manual
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7911A
Constant Temperature Ice Bath
User’s Manual
PN 4329129
October 2013
© 2013 Fluke Corporation. All rights reserved. Specifications are subject to change without
notice. All product names are trademarks of their respective companies.
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TABLE OF CONTENTS
INTRODUCTION.......................................................................................................................................................... 5
D
ESCRIPTION................................................................................................................................................................ 5
ECHANICAL AND ELECTRICAL SPECIFICATIONS.......................................................................................................... 6
M
Construction ........................................................................................................................................................... 6
Dimensions ............................................................................................................................................................. 6
Weight..................................................................................................................................................................... 6
Performance ........................................................................................................................................................... 6
INSTALLATION INSTRUCTIONS ............................................................................................................................ 7
NTRODUCTION............................................................................................................................................................. 7
I
HIPPING INFORMATION ...............................................................................................................................................7
S
NSPECTION .................................................................................................................................................................. 7
I
SAFETY PRECAUTIONS FOR DEWARS............................................................................................................... 8
Glass Dewars.......................................................................................................................................................... 8
Stainless Steel Dewars............................................................................................................................................ 8
OPERATING INSTRUCTIONS................................................................................................................................... 9
REPARATION OF ICE.................................................................................................................................................... 9
P
REPARATION OF ICE BATH .......................................................................................................................................... 9
P
HECKOUT/TEST.......................................................................................................................................................... 9
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MAINTENANCE......................................................................................................................................................... 10
G
ENERAL.................................................................................................................................................................... 10
LEANING................................................................................................................................................................... 10
C
DISASSEMBLY AND REASSEMBLY OF MODEL 7911A................................................................................... 11
G
ENERAL.................................................................................................................................................................... 11
ISASSEMBLY............................................................................................................................................................. 11
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EASSEMBLY.............................................................................................................................................................. 11
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PARTS BREAKDOWN............................................................................................................................................... 12
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ENERAL.................................................................................................................................................................... 12
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INTRODUCTION
This instruction manual describes the characteristics of the Hart Rosemount
Design Model 7911A Constant Temperature Ice Bath as shown in Figure 1.
A functional description and specifications of the 7911A are included in this
handbook, as well as instructions for installation, safety precautions,
operation, maintenance and disassembly and reassembly. A dimensional
drawing (Figure 2) accompany the text to better define the Model 7911A
features and operation.
Also contained in this handbook is a parts breakdown, by part number and
description of repairable or replaceable items in the 7911A
Description
The Model 7911A is a constant temperature ice bath which is used for the
calibration of thermocouples, resistance sensors, liquid-in-glass
thermometers, and other related devices. Other applications include
production sorting of thermistors, and environmental testing of electronic
components or assemblies.
Because of the reproducibility and convenience with which an ice bath can
be prepared, the ice point is a principal reference temperature for most kinds
of temperature sensors. The ice point is the temperature at which pure ice
and air-saturated water are in equilibrium at normal atmospheric pressure,
0±.002° C. A large environmental zone is established in the bath that
maintains long term stability at 0° C.
The Model 7911A is a stirred ice bath which promotes air saturation and has excellent temperature uniformity. The
complete system consists of a dewar, flow chute, stirrer and stirrer motor. A vacuum-insulated dewar provides a large
calibration zone and long bath life. Properly prepared, the bath will maintain 0° C within 0.002° C.
Model 7911A Constant Termperature Ice Bath User’s Manual 5
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Mechanical and Electrical Specifications
Construction
Baths may be specified with a glass dewar (Model 7911A1) or stainless steel dewar (Model 7911A2). The flow chute
assembly for both models is nickel-plated stainless steel. The calibration medium is distilled or demineralized water
and flaked ice made from distilled or demineralized water.
Dimensions
See Figure 2. For best performance results, the
calibration zone, shown in the drawing, is 2-1/2 inches
(6.4 cm) in diameter and 8 inches (20 cm) deep. The
stainless steel dewar (Model 7911A2) capacity is
approximately 5.0 liters (1.4 gallons) and the glass
dewar (Model 7911A1) capacity is approximately 4.5
liters (1.2 gallons).
Weight
Model 7911A1 - 11 pounds.
Model 7911A2 - 13-1/2 pounds.
Electrical Power
The stirrer motor is designed to operate on 115 volts
AC, 60 Hz. The motor will operate on 50 Hz; however,
it will then operate hotter and slower but this will not
affect performance. A detachable 6.5 foot (2.0 m)
three-wire cord with an OFF-ON switch is furnished.
WARNING
ALWAYS CONNE CT THE POWER CORD TO A
THREE WIRE GROUNDED OUTLET TO AVOID
ELECTRICAL SHOCK HAZARD.
Performance
The bath is designed to maintain a constant temperature of 0° C. To achieve, this, it is very important that the water
and ice be distilled or demineralized, and the ice should be finely shaved or flaked. Temperature uniformity is ±0.002
C, or better, and is defined as the maximum deviation, at a given time, between the temperature at any given point
within the calibration zone and the mean temperature in the zone. Temperature stability is ±0.002° C, or better, and is
defined as the slope of a best-fit line plotted at a given point within the calibration zone.
°
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INSTALLATION INSTRUCTIONS
Introduction
Installation of the Model 7911A Ice Bath is explained in this section. These instructions should be read thoroughly
before installing and operating the bath. Should any difficulties arise, please contact Hart Scientific Customer Service
at 801-763-1600.
Shipping Information
The ice bath is packaged and shipped in a custom shipping container. Upon receipt of the instrument, a thorough
inspection should be made to determine any possible shipping damage. If damage is found, a damage claim should be
filed with the transportation agency.
Inspection
Rotate the stirring shaft by hand to make sure that the propeller does not rub on the inside of the flow chute. If the
propeller contacts the flow chute, either straighten the stirring shaft by hand or readjust the motor mounting nuts to
correct the problem.
Place the flow chute into the dewar. Connect the line cord to a grounded 115 VAC source and turn on the stirring
motor to make sure it operates satisfactorily. It is not necessary to fill the dewar with ice or water for this test.
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SAFETY PRECAUTIONS FOR DEWARS
Glass or Stainless steel dewar flasks are used in the ice bath. When used carefully, these dewars will provide years of
trouble free service.
Glass Dewars
Glass dewars are susceptible to implosion and breakage if subject to mechanical shock or temperatures sufficient to
soften the glass. The glass dewars used are made of Pyrex® glass and are protected by metal shields on the outer
diameter. The use of safety glasses is recommended when handling, washing, or filling the dewars. SAFETY
GLASSES PROVIDE ADDITIONAL PROTECTION AGAINST FLYING GLASS SHOULD AN ACCIDENT
CAUSE A DEWAR IMPLOSION.
Stainless Steel Dewars
Stainless steel dewars are more rugged than glass and can be used over a wide r temperature range. While breakage is
not a problem, an undetected loss of vacuum can cause dewar failure.
When a stainless steel dewar is placed in service for the first time, it should be visibly inspected for any large dents or
scratches which might indicate mishandling and loss of vacuum. Another simple qualitative test is to snap the side of
the dewar with a fingernail. A dewar with a good vacuum will ring like a bell, but if there is air present, only a dull
thud will result.
A more conclusive test is to fill the dewar with liquid nitrogen. Frost or condensation normally occurs where the inner
and outer sides of the dewar are joined and around penetrations of the vacuum jacket by drains. However, if
condensation or frost occurs over most of the outer surface of the dewar, a vacuum leak is indicated. Rapid boiling of
the liquid nitrogen is also a good indication of a leak.
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OPERATING INSTRUCTIONS
Preparation of Ice
The successful preparation of an ice bath depends on the purity of the water which is used. Slight amounts of
contamination will lower the freezing point, depending on the nature and amount of the contaminant. Distilled,
demineralized or deionized water is sufficient for ±0.002° C reproducibility. Ordinary tap water is not recommended
but will usually freeze within 0.05° C of the true ice point.
When water freezes naturally, the impure portion freezes last. In commercial block ice, the clear, bubble-free portion is
of the highest purity and is suitable for use in making a reproducible ice bath. Chip off the outer clear portions and
wash them with water. Discard the cloudy central part of the block. An alternate procedure is to make ice using
distilled or demineralized water.
The ice should be finely shaved or crushed into pieces smaller than about 6 mm (1/4 inch). Larger pieces or cubes may
allow temperature gradients to exist in the bath. If ice baths are used routinely, an ice-making machine which
automatically shaves the ice is more efficient and convenient. A commercial ice machine which is supplied with
distilled or deionized water, will automatically form, shave, and store many pounds of ice.
Preparation of Ice Bath
Before preparing the bath, wash the dewar thoroughly and exterior parts of the flow chute which will contact the ice
and rinse them with distilled or demineralized water. Place the flow chute into the dewar before filling the dewar with
shaved ice. DO NOT fill the flow chute with ice.
Add precooled distilled or demineralized water and more ice if necessary until the water level is about 15 mm (1/2
inch) below the dewar rim. A properly prepared bath should be completely filled with ice (all the way to the bottom).
Turn on the stirring motor. A vortex should develop around the stirring shaft which draws some air into the water in the
flow chute, assuring air-saturation. This condition can also be noticed by air bubbles rising in the calibration zone and
a gurgling noise when the motor is on. If air is not being drawn into the bath, remove some of the water with a syringe.
After allowing the bath to stabilize for about 5 minutes, the ice bath is ready to use.
Checkout/Test
When setting up the ice bath for the first time, and if highest accuracy is desirable, the bath should first be monitored
with a precision temperature sensor, or a primary standard such as a Model 162CE SPRT. This can be done by
immersing a platinum resistance temperature standard into the ice bath to a depth of from 12 to 20 cm (4.72 inches to
7.87 inches) and monitoring the output resistance of the standard with a high accuracy bridge. (Use a glass, plastic or
metal rod to make a hole in the ice to accommodate the standard.) If the ice bath has been properly prepared and the
standard has a known ice point value (R
), the resistance reading on the bridge should be within 0.002° C of the known
O
value. While it normally is not necessary to monitor the temperature of an ice bath, one may choose to do so until
confidence is gained in the purity of the ice source.
A well-prepared ice bath will normally last several hours without attention; however, the ice will eventually melt and
float to the top. This may cause a warmer area near the bottom of the bath since at 0° C, warm water is more dense than
cold water. When this happens, draw some water off the top of the bath with a syringe and add more flaked ice.
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MAINTENANCE
General
Once the stirring shaft has been centered in the flow chute so that the propellers do not touch the walls, no further
adjustments are required. The motor should be oiled at least once each year. If the motor should fail to operate, it can
be replaced by any equivalent motor which operates in the range 1000-1550 RPM
Cleaning
If clean water and clean ice are used, the Model 7911A should not require cleaning. However, if cleaning of the Ice
Bath is required, any cleaning solutio n may be used. To avoid contamination of the Ice Bath, thoroughly rinse the
dewar and all external parts that will contact the ice with distilled or demineralized water.
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DISASSEMBLY A ND REASSEMBLY OF MODEL 7911A
General
Complete disassembly is not required for repair or replacement purposes of the 7911A Constant Temperature Ice Bath.
Refer to parts list in the Parts Breakdown Section, when performing disassembly procedures. Disassemble only to the
extent necessary to effect a repair. All other malfunctions or problems require that the ice bath be sent back to the
factory. Call Hart Scientific Customer Service at 801-763-1600. The numbers in parentheses in the following
procedures are index numbers on the parts list.
WARNING
ALL PROCEDURES SHOULD BE PERFORMED
WITH THE POWER SOURCE DISCONNECTED.
Disassembly
1. Disconnect power cable assembly (1) from motor assembly (2).
2. Lift motor assembly (2), propeller assembly (3), and flow chute (6) from stainless steel (7) or glass (8) dewar.
3. Remove two self-locki ng nuts (9) and two flat washers(10) securing motor assembl y (2) to flow chute (6).
4. Lift motor assembly (2) and propeller assembly (3) from flow chute (6).
5. Unscrew set screw (4) from coupling (5) on the propeller assembly.
6. Pull propeller assembly (3) from shaft of motor assembly (2).
Reassembly
1. Insert propeller assembly (3) on shaft of motor assembly (2).
2. Tighten set screw (4) securing coupling (5) to motor assembly (2).
3. Place motor assembly (2) and propeller assembly (3) in flow chute (6).
4. Secure motor assembly (2) to flow chute (6) with two self-locking nuts (9) and two washers (10).
5. Place motor assembly (2), propeller assembly (3), and flow chute (6) in dewar.
6. Connect power cable assembly (1) to motor assembly.
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PART S BREAKDOWN
General
This section contains a parts list. Refer to the specific part number when ordering.
The quantity listed indicates the number of the particular part required for the 7911A ice bath assembly, and not
necessarily the replacement quantity. Order replacement quantities as required.
MODEL 7911A
PARTS LIST
Index Number Part Number Item Description Quantity
1 00911-0045-0001 Power Cable Assembly 1
2 00911-0046-0001 Motor Assembly 1
3 00911-0047-0001 Propeller Assembly 1
4 AN565DC8H3 Screw, Set, 8-32 x 3/16 1
5 00911-0040 Coupling 1
6 00911-0009-0001 Flow Chute 1
7 00910-0065-0001 Dewar, SST, 5.0L (7911A2) 1
8 00910-0500-0002 Dewar, Glass, 4.5L (7911A1) 1
9 MS21083C08 Nut, Self-Locking, 8-32 2
10 AN960C8 Washer, Flat, No. 8 2
11 C11885-0002 Grommet, Rubber 4
12 00910-0120-0001 Beaker, Aluminum (Optional) 1
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