Fluke 7380 User Manual

7380

Ultra Low Temp Bath

User’s Guide

January 2013
© 2013 Fluke Corporation. All rights reserved. Specifications are subject to change without notice.
All product names are trademarks of their respective companies.

Table of Contents

1 Before You Start . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 Symbols Used . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 Safety Information . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2.1 Warnings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2.2 Cautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.3 Authorized Service Centers. . . . . . . . . . . . . . . . . . . . . . 5

2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3 Specifications and Environmental Conditions . . . . . . . . . 11

3.1 Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.2 Environmental Conditions. . . . . . . . . . . . . . . . . . . . . . 11

3.3 Warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4 Quick Start . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.1 Unpacking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.2 Set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.3 Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.4 Setting the Temperature . . . . . . . . . . . . . . . . . . . . . . . 14

5 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

5.1 Bath Environment . . . . . . . . . . . . . . . . . . . . . . . . . . 17

5.2 “Dry-out” Period . . . . . . . . . . . . . . . . . . . . . . . . . . 17

5.3 Bath Preparation and Filling . . . . . . . . . . . . . . . . . . . . 17

5.3.1 Filling With Fluid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

5.4 Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

6 Bath Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

6.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

6.2 Comparison Calibration . . . . . . . . . . . . . . . . . . . . . . . 19

6.3 Calibration of Multiple Probes . . . . . . . . . . . . . . . . . . . 20

7 Parts and Controls . . . . . . . . . . . . . . . . . . . . . . . . 21

7.1 Front Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

7.2 Bath Tank and Lid . . . . . . . . . . . . . . . . . . . . . . . . . . 22

7.3 Back Panel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

i

8 General Operation . . . . . . . . . . . . . . . . . . . . . . . . 25

8.1 Heat Transfer Fluid . . . . . . . . . . . . . . . . . . . . . . . . . 25

8.1.1 Temperature Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

8.1.2 Viscosity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

8.1.3 Specific Heat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

8.1.4 Thermal Conductivity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

8.1.5 Thermal Expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

8.1.6 Electrical Resistivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

8.1.7 Fluid Lifetime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

8.1.8 Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

8.1.9 Cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

8.1.10 Commonly Used Fluids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

8.1.10.1 Water (Distilled) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

8.1.10.2 Ethanol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

8.1.10.3 Mineral Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

8.1.10.4 Silicone Oil (Dow Corning 200.10, 200.20) . . . . . . . . . . . . . . . . . . . . . . 28

8.1.10.5 Halocarbon 0.8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

8.1.11 Fluid Characteristics Charts. . . . . . . . . . . . . . . . . . . . . . . . . . . 28

8.1.11.1 Limitations and Disclaimer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

8.1.11.2 About the Graph . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29

8.2 Stirring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

8.3 Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

8.4 Heater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

8.5 Refrigeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

8.5.1 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

8.5.2 Important Refrigerant Information . . . . . . . . . . . . . . . . . . . . . . . 32

8.6 Temperature Controller . . . . . . . . . . . . . . . . . . . . . . . 33

9 Controller Operation . . . . . . . . . . . . . . . . . . . . . . . 35

9.1 Bath Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . 35

9.2 Temperature Set-point . . . . . . . . . . . . . . . . . . . . . . . . 35

9.2.1 Programmable Set-points . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

9.2.2 Set-point Value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

9.2.3 Temperature Scale Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

9.3 Scan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

9.3.1 Scan Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

9.3.2 Scan Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

9.4 Secondary Menu. . . . . . . . . . . . . . . . . . . . . . . . . . . 39

9.5 Heater Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

9.6 Proportional Band . . . . . . . . . . . . . . . . . . . . . . . . . . 39

9.7 Cutout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

9.8 Controller Configuration . . . . . . . . . . . . . . . . . . . . . . 41

9.9 Operating Parameters . . . . . . . . . . . . . . . . . . . . . . . . 42

9.9.1 High Limit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

9.9.2 Low Limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

ii

9.9.3 Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

9.10 Serial Interface Parameters . . . . . . . . . . . . . . . . . . . . . 43

9.10.1 Baud Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

9.10.2 Sample Period. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

9.10.3 Duplex Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

9.10.4 Linefeed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

9.11 Calibration Parameters . . . . . . . . . . . . . . . . . . . . . . . 45

9.11.1 Hard Cutout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

9.11.2 R0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

9.11.3 ALPHA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

9.11.4 DELTA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

9.11.5 BETA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

10 Digital Communication Interface . . . . . . . . . . . . . . . . 47

10.1 Serial Communications . . . . . . . . . . . . . . . . . . . . . . . 47

10.1.1 Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

10.1.2 Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

10.1.2.1 BAUD Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

10.1.2.2 Sample Period. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

10.1.2.3 Duplex Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

10.1.2.4 Linefeed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

10.1.3 Serial Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

10.2 Interface Commands . . . . . . . . . . . . . . . . . . . . . . . . 49

11 Calibration Procedure . . . . . . . . . . . . . . . . . . . . . . 53

11.1 Calibration Procedure . . . . . . . . . . . . . . . . . . . . . . . . 53

11.1.1 Calibration Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

11.1.2 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

12 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

13 Troubleshooting. . . . . . . . . . . . . . . . . . . . . . . . . . 57

13.1 Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

13.2 CE Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

13.2.1 EMC Directive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

13.2.2 Low Voltage Directive (Safety) . . . . . . . . . . . . . . . . . . . . . . . . . 58

iii

iv

Figures

Figure 1 Front Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 2 Back Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Figure 3 Chart of Various Bath Fluids . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 4 Controller Operation Flowchart . . . . . . . . . . . . . . . . . . . . . 36

Figure 5 Serial Cable Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

v

Tables

Table 1 International Electrical Symbols . . . . . . . . . . . . . . . . . . . . . 1

Table 2 Table of Various Bath Fluids . . . . . . . . . . . . . . . . . . . . . . . 31

Table 3 Controller Communications Commands . . . . . . . . . . . . . . . . . 50

Table 3 Controller Communications Commands continued . . . . . . . . . . . 51

1 Before You Start

1.1 Symbols Used

Table 1 lists the International Electrical Symbols. Some or all of these symbols
may be used on the instrument or in this manual.

Symbol Description

AC (Alternating Current)

AC-DC

Battery

CE Complies with European Union Directives

DC

Double Insulated

Electric Shock

Fuse

PE Ground

Hot Surface (Burn Hazard)

Read the User’s Manual (Important Information)

Off

On

1

1 Before You Start

Symbols Used

Tabl e 1 International Electrical Symbols

Symbol Description

Canadian Standards Association

OVERVOLTAGE (Installation) CATEGORY II, Pollution Degree 2 per IEC1010-1 re

­fers to the level of Impulse Withstand Voltage protection provided. Equipment of
OVERVOLTAGE CATEGORY II is energy-consuming equipment to be supplied from
the fixed installation. Examples include household, office, and laboratory appliances.

C-TIC Australian EMC Mark

The European Waste Electrical and Electronic Equipment (WEEE) Directive
(2002/96/EC) mark.

1.2 Safety Information

Use this instrument only as specified in this manual. Otherwise, the protection
provided by the instrument may be impaired.

The following definitions apply to the terms “Warning” and “Caution”.

• “Warning” identifies conditions and actions that may pose hazards to the
user.

• “Caution” identifies conditions and actions that may damage the instru­ment being used.

1.2.1

Warnings

To avoid personal injury, follow these guidelines.

GENERAL

•

DO NOT use the instrument for any application other than calibration
work. The instrument was designed for temperature calibration. Any other
use of the unit may cause unknown hazards to the user.

•

DO NOT use the unit in environments other than those listed in the user’s
guide.

•

DO NOT overfill the bath. Overflowing extremely cold or hot fluid may
be harmful to the operator. See Section 5.3, Bath Preparation and Filling,
for specific instructions.

•

Follow all safety guidelines listed in the user’s manual.

•

Calibration Equipment should only be used by Trained Personnel.

•

If this equipment is used in a manner not specified by the manufacturer,
the protection provided by the equipment may be impaired.

•

Before initial use, or after transport, or after storage in humid or semi-hu

­mid environments, or anytime the instrument has not been energized for
more than 10 days, the instrument needs to be energized for a "dry-out"

7380 Ultra Low Temp Bath

User’s Guide

2

period of 2 hours before it can be assumed to meet all of the safety re

­quirements of the IEC 1010-1. If the product is wet or has been in a wet
environment, take necessary measures to remove moisture prior to apply

-

ing power such as storage in a low humidity temperature chamber operat

-

ing at 50 degree centigrade for 4 hours or more.

•

DO NOT operate high temperature baths (500°C) near flammable materi

-

als. Extreme temperatures could ignite the flammable material.

•

Overhead clearance is required. Do not place the instrument under a cabi

­net or other structure. Always leave enough clearance to allow for safe
and easy insertion and removal of probes.

•

The instrument is intended for indoor use only.

BURN HAZARD

•

Extremely cold temperatures may be present in this equipment. Freezer
burns and frostbite may result if personnel fail to observe safety precau

-

tions.

• High temperatures may be present in this equipment. Fires and severe
burns may result if personnel fail to observe safety precautions.

ELECTRICAL HAZARD

• These guidelines must be followed to ensure that the safety mechanisms
in this instrument will operate properly. This instrument must be plugged
into a 115 VAC, 60Hz (230 VAC, 50Hz optional), AC only electric outlet.
The power cord of the instrument is equipped with a three-pronged
grounding plug for your protection against electrical shock hazards. It
must be plugged directly into a properly grounded three-prong receptacle.
The receptacle must be installed in accordance with local codes and ordi­nances. Consult a qualified electrician. DO NOT use an extension cord or
adapter plug.

•

DO use a ground fault interrupt device. This unit contains a liquid. A
ground fault device is advised in case liquid is present in the electrical
system and could cause an electrical shock.

•

Always replace the power cord with an approved cord of the correct rat

­ing and type. If you have questions, contact a Hart Scientific Authorized
Service Center (see Section 1.3).

•

High voltage is used in the operation of this equipment. Severe injury or
death may result if personnel fail to observe the safety precautions. Before
working inside the equipment, turn off the power and disconnect the
power cord.

BATH FLUIDS

•

Fluids used in this unit may produce noxious or toxic fumes under certain
circumstances. Consult the fluid manufacturer’s MSDS (Material Safety
Data Sheet). Proper ventilation and safety precautions must be observed.

3

1 Before You Start

Safety Information

•

The unit is equipped with a soft cutout (user settable firmware) and a hard
cutout (set at the factory). Check the flash point, boiling point, or other
fluid characteristic applicable to the circumstances of the unit operation.
Ensure that the soft cutout is adjusted to the fluid characteristics of the ap

-

plication.

1.2.2

Cautions

•

THE DRAIN VALVE MUST BE CLOSED ON THE BACK OF THE
BATH BEFORE ATTEMPTING TO FILL THE TANK WITH
FLUID.

•

Always operate this instrument at room temperature between 41°F and
104°F (5°C to 40°C). Allow sufficient air circulation by leaving at least 6
inches (15 cm) of clearance around the instrument.

•

DO NOT overfill the bath. Overflowing liquid may damage the electrical
system. Be sure to allow for thermal expansion of the fluid as the bath
temperature increases. See Section 5.3, Bath Preparation and Filling, for
specific instructions.

• No matter what fluid is used, DO NOT exceed the recommended fluid

viscosity.

• Read Section 6, Bath Use, before placing the unit into service.

• DO NOT change the values of the bath calibration constants from the fac-

tory set values. The correct setting of these parameters is important to the
safety and proper operation of the unit.

• The refrigeration may be damaged or the lifetime shortened if the
set-point temperature is set above 60°C for more than one hour with the
refrigeration manually on. Ensure that the refrigeration is off when the
unit is used above 60°C.

•

The Factory Reset Sequence should be performed only by authorized
personnel if no other action is successful in correcting a malfunction. You
must have a copy of the most recent Report of Test to restore the test pa

-

rameters.

•

DO NOT operate this instrument in an excessively wet, oily, dusty, or
dirty environment.

•

The unit is a precision instrument. Although it has been designed for opti

­mum durability and trouble free operation, it must be handled with care.
Position the unit before the tank is filled with fluid. Use the handles pro

-

vided to move the unit. Due to the weight of the compressor, it may re

­quire two people to safely move the bath. If two people are used, place
one person in the front and one person in the back of the unit, carefully
slide hands under the unit and lift in unison. The area containing the com

-

pressor will be heavier than the rest of the unit. Do not move a unit filled

with fluid.

•

Most probes have handle temperature limits. Be sure that the probe handle
temperature limit is not exceeded in the air above the instrument.

7380 Ultra Low Temp Bath

User’s Guide

4

•

The instrument and any thermometer probes used with it are sensitive in

­struments that can be easily damaged. Always handle these devices with
care. Do not allow them to be dropped, struck, stressed, or overheated.

COLD BATHS

•

Refrigerated baths require that the condensing coil be cleaned periodi

-

cally. Accumulation of dust and dirt on the condenser will result in pre

-

mature failure of the compressor.

•

Bath or compressor lifetime may be affected by:

♦

Cycling the heat source through extreme temperature ranges (the full
temperature limit of the heat source). Cycling the instrument can cause
excessive stress on the compressors. Compressor manufacturers rec

-

ommend, for longest lifetime, that the instrument be set at one temper

-

ature and left on at that temperature.

♦

Turning the instrument on and off frequently adds wear and tear to the
compressor.

• This bath has been equipped with a brownout and over voltage protection
device as a safety feature to protect the system components.

• Mode of Operation: This bath needs to be plugged into the line voltage
for at least 2 minutes before operation. This is only necessary for the first
time that the bath is energized or when it is moved from one location to
another. Turning the bath ON or OFF does not trigger the delay.

• If a High/Low voltage condition exists for longer than 5 seconds, the bath
de-energizes. The display flashes “LoLinE” while the contdition exists.

• Re-energization is automatic upon correction of the fault condition and af­ter a delay cycle of about 2 minutes. If a fault condition exists upon appli­cation of power, the bath will not energize.

•

Under and Over Voltage Protection at 115 VAC

♦

Voltage Cutout: ±12.5% (101 - 129 VAC)

♦

Voltage Cut In: ±7.5% (106 - 124 VAC)

•

Under and Over Voltage Protection at 230 VAC

♦

Voltage Cutout: ±12.5% (203 - 257 VAC)

♦

Voltage Cut In: ±7.5% (213 - 247 VAC)

1.3 Authorized Service Centers

Please contact one of the following authorized Service Centers to coordinate
service on your Hart product:

Fluke Corporation, Hart Scientific Division

799 E. Utah Valley Drive

5

1 Before You Start

Authorized Service Centers

American Fork, UT 84003-9775

USA

Phone: [phone]

Telefax: +1.801.763.1010

E-mail: [e-mail]

Fluke Nederland B.V.

Customer Support Services

Science Park Eindhoven 5108

5692 EC Son

NETHERLANDS

Phone: [phone]

Telefax: [phone]

E-mail: [e-mail]

Fluke Int'l Corporation

Service Center - Instrimpex

Room 2301 Sciteck Tower

22 Jianguomenwai Dajie

Chao Yang District

Beijing 100004, PRC

CHINA

Phone: [phone]

Telefax: [phone]

E-mail: [e-mail]

Fluke South East Asia Pte Ltd.

Fluke ASEAN Regional Office

Service Center

60 Alexandra Terrace #03-16

The Comtech (Lobby D)

118502

SINGAPORE

Phone: [phone]

7380 Ultra Low Temp Bath

User’s Guide

6

Telefax: [phone]

E-mail: [e-mail]

When contacting these Service Centers for support, please have the following

information available:

•

Model Number

•

Serial Number

•

Voltage

•

Complete description of the problem

7

1 Before You Start

Authorized Service Centers

2 Introduction

The Hart Scientific 7380 is an ultra low temp bath useful in temperature cali

­bration and other applications requiring stable temperatures. An innovative
state of the art solid-state temperature controller has been incorporated which
maintains the bath temperature with extreme stability. The temperature control

-

ler uses a micro-controller to execute the many operating functions.

The user interface is provided by the 8-digit LED display and four
key-switches. Digital remote communication is available with an RS-232
interface.

The 7380 bath was designed to be compact and low cost without compromising
performance. The 7380 bath operates over a wide temperature range from
–80°C to 100°C.

9

2 Introduction

3 Specifications and Environmental

Conditions

3.1 Specifications

Range

–80°C to 100°C
(–112°F to 212°F)

Ambient Operating Range

15°C to 25°C
(59°F to 77°F)

Stability (2 sigma)

±0.006°C at –80°C (ethanol)
±0.010°C at 0°C (ethanol)
±0.010°C at 100°C (oil 5012)

Uniformity

±0.008°C at –80°C (ethanol)
±0.012°C at 0°C (ethanol)
±0.012°C at 100°C (oil 5012)

Heating Time

†

25 minutes from 25°C to 100°C (oil 5010)

Cooling Time

130 minutes from 25°C to –80°C (ethanol)

Stabilization Time

15–20 minutes

Display Resolution

0.01°

Set-Point Accuracy

±0.5°C

Set-Point Repeatability

±0.01°C

Access Opening

3.25" x 4.5" (83 x 114 mm)

Immersion Depth

7" (180 mm) max

Volu me

1 gallon (4 liters)

Refrigeration Cascade

Two ¼ HP compressors

Heater Power

500 W

Automation Package

Interface

-it

software and RS-232 included

Power

†

115 V ac (±10%), 60 Hz, 15 A or 230 V ac (±10%), 50 Hz, 8 A,
1700 VA

Size

12" W x 30" H x 24" D
(305 x 762 x 610 mm)

Weight

115 lb. (52 kg)

Safety

OVERVOLTAGE (Installation) CATEGORY II, Pollution Degree 2 per
IEC1010-1

†

Rated at listed 115 V (or optional 230 V)

3.2 Environmental Conditions

Although the instrument has been designed for optimum durability and trou

­ble-free operation, it must be handled with care. The instrument should not be
operated in an excessively dusty or dirty environment. Maintenance and clean

-

ing recommendations can be found in the Maintenance Section of this manual.

11

3 Specifications and Environmental Conditions

Specifications

4 Quick Start

CAUTION: READ SECTION 6 TITLED BATH USE before placing the

bath in service. Incorrect handling can damage the bath and void the war

-

ranty.

This chapter gives a brief summary of the steps required to set up and operate
the bath. This should be used as a general overview and reference and not as a
substitute for the remainder of the manual. Please read Section 5 through 8
carefully before operating the bath.

4.1 Unpacking

Unpack the bath carefully and inspect it for any damage that may have oc

-

curred during shipment. If there is shipping damage, notify the carrier immedi

-

ately. Verify that all components are present:

• 7380 Bath

• RS-232 Cable

• Access Hole Cover

• Power Cord

• Manual

• Report of Test

If you are missing any item, please call a Hart Authorized Service Center (see
Section 1.3).

4.2 Set-up

CAUTION: The drain valve on the back of the bath must be closed before

attempting to fill the tank with fluid.

WARNING: The instrument is equipped with a soft cutout (user settable

firmware) and a hard cutout (set at the factory). Check the flash point,
boiling point, or other fluid characteristic applicable to the circumstances
of the unit operation. Ensure that the soft cutout is adjusted to the fluid
characteristics of the application. As a guideline, the soft cutout should be
set 10°C to 15°C below the flash point of the bath fluid. See Section 8.1,
Heat Transfer Fluid, for specific information on bath fluids and Section

9.7, Cutout.

Set up of the bath requires careful unpacking and placement of the bath, filling
the bath with fluid, and connecting power. Consult Section 5 for detailed in

-

13

4 Quick Start

Unpacking

structions for proper installation of the bath. Be sure to place the bath in a safe,
clean and level location. Fill the bath tank with an appropriate liquid. For oper

-

ation at moderate bath temperatures, clean distilled water works well. For lower
temperatures, ethanol (denatured) works well but is NOT USABLE AT
HIGHER TEMPERATURES due to flammability.

Carefully pour the fluid into the bath tank through the large rectangular access
hole above the tank avoiding spilling any fluid. The fluid must not exceed a
height of 1/2 inch below the top of the tank or be less than 2 inches (50 mm)
below the top.

4.3 Power

Plug the bath power cord into a mains outlet of the proper voltage, frequency,
and current capability. See Section 3.1, Specifications, for power details. Refer
to and read the CAUTION at the front of this manual concerning brownout and
over voltage protection.

Turn the bath on using the front panel “POWER” switch. The bath begins to
heat or cool to reach the previously programmed temperature set-point. The
front panel LED display indicates the actual bath temperature. Set the cooling
switch to “OFF” for temperatures above approximately 50°C. Set the switch to
“ON” for lower temperatures. When the cooling switch has been turned on, the
first stage compressor powers up. The second stage comes on automatically
when proper conditions are met. This takes 2 to 4 minutes. The bath does not
begin to cool until the second stage starts.

4.4 Setting the Temperature

In the following discussion and throughout this manual a solid box around the
word SET, UP, DOWN or EXIT indicates the panel button to press while the
dotted box indicates the display reading on the front panel. Explanation of the
button function or display reading is written at the right.

To view or set the bath temperature set-point proceed as follows. The front
panel LED display normally shows the actual bath temperature.

24.68 C Bath temperature display

When “SET” is pressed the display shows the set-point memory that is cur

-

rently being used and its value. Eight set-point memories are available.

S

Access set-point selection

1. 25.0 Set-point 1, 25.0°C currently used

Press “SET” to select this memory and access the set-point value.

7380 Ultra Low Temp Bath

User’s Guide

14

S

Access set-point value

C 25.00 Current value of set-point 1, 25.00°C

Press “UP” or “DOWN” to change the set-point value.

U

Increment display

C 30.00 New set-point value

Press SET to accept the new value. The bath begins heating or cooling to the
new set-point.

S

Store new set-point

Press “EXIT” and the bath temperature is displayed again.

E

Return to the temperature display

24.73 C Bath temperature display

The bath heats or cools until it reaches the new set-point temperature. Turn off
the cooling to reach and control at higher temperatures.

When setting the set-point temperature be careful not to exceed the temperature
limit of the bath fluid.

To obtain optimum control stability adjust the proportional band as discussed in
Section 9.6.

15

4 Quick Start

Setting the Temperature

5 Installation

CAUTION: READ SECTION 6 TITLED BATH USE before placing the

bath in service. Incorrect handling can damage the bath and void the war

-

ranty.

5.1 Bath Environment

The Model 7380 Bath is a precision instrument which should be located in an
appropriate environment. The location should be free of drafts, extreme temper

­atures and temperature changes, dirt, etc. The surface where the bath is placed
must be level. Allow at least six inches of clearance around the bath for air cir

-

culation. The top surface of the bath may become hot at high temperatures. Be

-

ware of the danger of accidental fluid spills.

A fume hood should be used to remove any vapors given off by hot bath fluid.

5.2 “Dry-out” Period

If this equipment is used in a manner not specified by the manufacturer, the
protection provided by the equipment may be impaired.

Before initial use, or after transport, or after storage in humid or semi-humid
environments, or anytime the bath has not been energized for more than 10
days, the instrument needs to be energized for a "dry-out" period of 2 hours be­fore it can be assumed to meet all of the safety requirements of the IEC 1010-1.
If the product is wet or has been in a wet environment, take necessary measures
to remove moisture prior to applying power such as storage in a low humidity
temperature chamber operating at 50 degree centigrade for 4 hour or more.

5.3 Bath Preparation and Filling

CAUTION: Before filling the tank with fluid, the drain valve at the back

of the bath must be closed.

5.3.1 Filling With Fluid

The Model 7380 Bath is not provided with a heat transfer fluid. Various fluids
are available from Hart Scientific and other sources. Depending on the desired
temperature range, any of the following fluids, as well as others, may be used
in the bath:

•

Water

•

Ethanol (Ethyl Alcohol)

•

Ethylene glycol/water

17

5 Installation

Bath Environment

•

Mineral oil

•

Silicone oil

•

Halocarbon 0.8

Caution: Ensure the valve handle is in the closed position before attempt

-

ing to add fluid to the tank.

Fluids are discussed in detail in Section 8.1.

Remove any access hole cover from the bath and check the tank for foreign
matter (dirt, remnant packing material, etc.).

Fill the bath with clean unpolluted fluid. Fill the bath carefully through the
large square access hole to a level that allows for stirring and thermal expan

­sion. DO NOT turn on the bath without fluid in the tank. The fluid should never
exceed a height of 1/2 inch (12 mm) below the top of the tank or be less than 2
inches (50 mm) below the top. Carefully monitor the bath fluid level as the bath
temperature rises to prevent overflow or splashing. Cautiously, remove excess

hot fluid if necessary.

5.4 Power

With the bath power switch off, plug the bath into an AC mains outlet of the
appropriate voltage, frequency, and current capacity. See Section 3.1, Specifica­tions, for power details. Refer to and read the CAUTION at the front of this
manual concerning brownout and over voltage protection.

7380 Ultra Low Temp Bath

User’s Guide

18

6 Bath Use

CAUTION: READ this section BEFORE PLACING THE BATH IN SER

-

VICE.

The information in this section is for general information only. It is not de

­signed to be the basis for calibration laboratory procedures. Each laboratory
should write their own specific procedures.

6.1 General

Be sure to select the correct fluid for the temperature range of the calibration.
Bath fluids should be selected to operate safely with adequate thermal proper

-

ties to meet the application requirements. Also, be aware that some fluids ex

­pand and could overflow the bath if not watched. Refer to General Operation,
Section 8, for information specific to fluid selection and to the MSDS sheet
specific to the fluid selected. The temperature range of any single fluid is likely
less than that of the bath itself. This means that the type of bath fluid may have
to change to cover the full range of the bath (see Section 8.1.1). Baths are most
often set up to operate with a single fluid only over the useful range of that
fluid. Other baths can be set up with other fluids to cover other temperature
ranges required. This is generally the most productive and efficient approach.

The bath generates extreme temperatures. Precautions must be taken to prevent
personal injury or damage to objects. Probes may be extremely hot or cold
when removed from the bath. Cautiously handle probes to prevent personal in­jury. Carefully place probes on a heat/cold resistant surface or rack until they
are at room temperature. It is advisable to wipe the probe with a clean soft cloth
or paper towel before inserting it into another bath. This prevents the mixing of
fluids from one bath to another. Always be sure that the probe is completely
dry before inserting it into a hot fluid. Some of the high temperature fluids
react violently to water or other liquid mediums. Be aware that cleaning the
probe can be dangerous if the probe has not cooled to room temperature.

For optimum accuracy and stability, allow the bath adequate stabilization time
after reaching the set-point temperature.

6.2 Comparison Calibration

Comparison calibration involves testing a probe (unit under test, UUT) against
a reference probe. After inserting the probes to be calibrated into the bath, al

­low sufficient time for the probes to settle and the temperature of the bath to
stabilize.

One of the significant dividends of using a bath rather than a dry-well to cali

­brate multiple probes is that the probes do not need to be identical in construc

­tion. The fluid in the bath allows different types of probes to be calibrated at
the same time. However, stem effect from different types of probes is not to

-

19

6 Bath Use

General

tally eliminated. Even though all baths have horizontal and vertical gradients,
these gradients are minimized inside the bath work area. Nevertheless, probes
should be inserted to the same depth in the bath liquid. Be sure that all probes
are inserted deep enough to prevent stem effect. From research at Hart Scien

­tific, we suggest a general rule-of-thumb for immersion depth to reduce the
stem effect to a minimum: 20 x the diameter of the UUT + the sensor length.
Do not submerge the probe handles. If the probe handles get too warm dur

­ing calibration at high temperatures, a heat shield could be used just below the
probe handle. This heat shield could be as simple as aluminum foil slid over the
probe before inserting it in the bath or as complicated as a specially designed
reflective metal apparatus.

When calibrating over a wide temperature range, better results can generally be
achieved by starting at the highest temperature and progressing down to the
lowest temperature.

Probes can be held in place in the bath by using probe clamps or drilling holes
in the access cover. Other fixtures to hold the probes can be designed. The ob

­ject is to keep the reference probe and the probe(s) to be calibrated as closely
grouped as possible in the working area of the bath. Bath stability is maximized
when the bath working area is kept covered.

In preparing to use the bath for calibration start by:

• Placing the reference probe in the bath working area.

• Placing the probe to be calibrated, the UUT, in the bath working area as

close as feasibly possible to the reference probe.

6.3 Calibration of Multiple Probes

Fully loading the bath with probes increases the time required for the tempera

­ture to stabilize after inserting the probes. Using the reference probe as the
guide, be sure that the temperature has stabilized before starting the calibration.

7380 Ultra Low Temp Bath

User’s Guide

20

7380

HIGH PRECISION BATH –80°C to 100°C

indicator is lit the heater is on, and when it is off the heater is off and the
bath is cooling.

5) The cooling switch turns on the refrigeration for control below 50°C and

rapid cool down.

7.2 Bath Tank and Lid

The bath tank and lid assembly includes: the tank, the control probe, the stir

-

ring motor, the access hole, and the access hole cover.

•

The bath tank is constructed of stainless steel. It is very resistant to oxida

-

tion in the presence of most chemicals and over a wide range of tempera

-

tures.

•

The control probe provides the temperature feedback signal to the con

­troller allowing the controller to maintain a constant temperature. The
control probe is a precision platinum resistance thermometer (PRT). It is
delicate and must be handled carefully. The probe is placed in the small
hole in the top of the bath so that the probe tip is fully immersed in the
bath fluid. It is located underneath the motor cover.

• The stirring motor is mounted on the bath tank lid under the motor cover.
It drives the stirring propeller to provide mixing of the bath fluid. Proper
mixing of the fluid is important for good constant temperature stability.

• On the bath lid is a work area access hole. This is used for filling the bath
with fluids and for placement of thermometers and devices into the bath.
When possible the access hole should be covered (must be covered to
reach minimum temperatures).

• An insulated access hole cover is provided and should be used to cover
the access opening in the top of the bath. This improves bath temperature
stability, prevents excess fluid evaporation or fumes and increases safety
with hot fluid. The user may drill or cut holes in the cover to accommo

-

date the instruments to be calibrated or immersed in the bath. Spare cov

-

ers are available from Hart Scientific.

7.3 Back Panel

On the back of the bath are 1) the circuit breaker, 2) the connector for the
power cord, 3) the drain valve, 4) the RS-232 interface connector, and remov

-

able vent panel.

1) The circuit breakers are 15 amp, 250V for 115V operation and 8 amp
250V for 230V operation.

2) IEC power connector

3) A drain valve (not shown) is provided for ease of removing the fluid me

­dia from the bath. Always use a container of adequate size to hold the
FULL LOAD of fluid. Some oils are more easily drained at higher
temperatures.

7380 Ultra Low Temp Bath

User’s Guide

22

FLUKE CORPORATION

EVERETT, WA USA

www.flukecal.com

8 General Operation

8.1 Heat Transfer Fluid

Many fluids work with the 7380 bath. Choosing a fluid requires consideration
of many important characteristics of the fluid. Among these are temperature
range, viscosity, specific heat, thermal conductivity, thermal expansion, electri

­cal resistivity, fluid lifetime, safety, and cost. If the viscosity becomes too great,
the stirrer may not function.

Use the fluid chart in the manual to choose the type of fluid that is best suited
for your intended purpose.

8.1.1 Temperature Range

One of the most important characteristics to consider is the temperature range
of the fluid. Few fluids work well throughout the complete temperature range
of the bath. The temperature at which the bath is operated must always be
within the safe and useful temperature range of the fluid. Set the cutout to meet
the temperature limits of the selected fluid. The lower temperature range of the
fluid is determined by the freeze point of the fluid or the temperature at which
the viscosity becomes too great. The upper temperature is usually limited by
vaporization, flammability, or chemical breakdown of the fluid. Vaporization of
the fluid at higher temperatures may affect temperature stability because of
cool condensed fluid dripping into the bath from the lid.

8.1.2 Viscosity

Viscosity is a measure of the thickness of a fluid, how easily it can be poured
and mixed. Viscosity affects the temperature stability of the bath. With low vis

­cosity, fluid mixing is better which creates a more uniform temperature
throughout the bath. This improves the bath response time which allows it to
maintain a more constant temperature. For good control the viscosity should be
less than ten centistokes. Twenty centistokes is about the upper limit of allow

­able viscosity. Viscosities greater than this cause very poor control stability and
may also overheat or damage the stirring motor.

With oils viscosity may vary greatly with temperature. Viscosity increases as
temperature decreases. When fluid viscosity increases, stability performance of
the unit may decrease.

Ensure that stirring occurs at all temperatures.

When using fluids with higher viscosities the controller proportional band may
need to be increased to compensate for the reduced response time (see Section

9.6). Otherwise the temperature may begin to oscillate.

25

8 General Operation

Heat Transfer Fluid

8.1.3 Specific Heat

Specific heat is the measure of the heat storage ability of the fluid. Specific
heat, to a small degree, affects the control stability. It also affects the heating
and cooling rates. Generally, a lower specific heat means quicker heating and
cooling. The proportional band may require some adjustment depending on the
specific heat of the fluid.

8.1.4 Thermal Conductivity

Thermal conductivity measures how easily heat flows through the fluid. Ther

-

mal conductivity of the fluid affects the control stability, temperature unifor

­mity, and probe temperature settling time. Fluids with higher conductivity
distribute heat more quickly and evenly improving bath performance.

8.1.5 Thermal Expansion

Thermal expansion describes how the volume of the fluid changes with temper

-

ature. Thermal expansion of the fluid used must be considered since the in

­crease in fluid volume as the bath temperature changes may cause overflow.
Excessive thermal expansion may also be undesirable in applications where
constant liquid level is important. Many fluids including oils have significant
thermal expansion.

8.1.6 Electrical Resistivity

Electrical resistivity describes how well the fluid insulates against the flow of
electric current. In some applications, such as measuring the resistance of bare
temperature sensors, it may be important that little or no electrical leakage oc­cur through the fluid. In such conditions choose a fluid with very high
resistivity.

8.1.7 Fluid Lifetime

Many fluids degrade over time because of evaporation, water absorption, gel

­ling, or chemical breakdown. Often the degradation becomes significant near
the upper temperature limit of the fluid, substantially reducing the fluid’s
lifetime.

8.1.8 Safety

When choosing a fluid always consider the safety issues associated. Obviously
where there are conditions of extreme hot or cold there can be danger to people
and equipment. Fluids may also be hazardous for other reasons. Some fluids
may be considered toxic. Contact with eyes, skin, or inhalation of vapors may
cause injury. A proper fume hood must be used if hazardous or bothersome va

-

pors are produced.

7380 Ultra Low Temp Bath

User’s Guide

26

WARNING: Fluids at high temperatures may pose danger from BURNS,

FIRE, and TOXIC FUMES. Use appropriate caution and safety equip

-

ment. Read the MSDS sheets.

Fluids may be flammable and require special fire safety equipment and proce

­dures. An important characteristic of the fluid to consider is the flash point. The
flash point is the temperature where there is sufficient vapor given off that
when sufficient oxygen is present and an ignition source is applied, the vapor
ignites. This does not necessarily mean that fire is sustained at the flash point.
The flash point may be either of the open cup or closed cup type. Either condi

­tion may occur in a bath situation. The closed cup temperature is always the
lower of the two. The closed cup represents the contained vapors inside the
tank and the open cup represents the vapors escaping the tank. Oxygen and an
ignition source are less available inside the tank.

The soft cutout should be set to meet the temperature limits of the selected
fluid.

Environmentally hazardous fluids require special disposal according to applica­ble federal or local laws after use.

8.1.9 Cost

Cost of bath fluids may vary greatly, from cents per gallon for water to hun­dreds of dollars per gallon for synthetic oils. Cost may be an important consid­eration when choosing a fluid.

8.1.10 Commonly Used Fluids

Below is a description of some of the more commonly used fluids and their
characteristics.

8.1.10.1 Water (Distilled)

Water is often used because of its very low cost, availability, and excellent tem

­perature control characteristics. Water has very low viscosity and good thermal
conductivity and heat capacity which makes it among the best fluids for control
stability at low temperatures. Temperature stability is much poorer at higher
temperatures because water condenses on the lid, cools and drips into the bath.
Water is safe and relatively inert. The electrical conductivity of water may pre

­vent its use in some applications. Water has a limited temperature range, from a
few degrees above 0°C to a few degrees below 100°C. At higher temperatures
evaporation becomes significant. Water used in the bath should be distilled or
softened to prevent mineral deposits. Consider using an algaecide chemical in
the water to prevent contamination.

8.1.10.2 Ethanol

Denatured ethanol (ethyl alcohol) is often used at lower temperatures between
–80°C and 10°C. It has good viscosity over its range and is inexpensive. Toxic

-

27

8 General Operation

Heat Transfer Fluid

ity, vapors, and flammability at temperatures higher than 10°C are significant
issues that must be considered.

8.1.10.3 Mineral Oil

Mineral oil or paraffin oil is often used at moderate temperatures above the
range of water. Mineral oil is relatively inexpensive. At lower temperatures
mineral oil is quite viscous and control may be poor. At higher temperatures
vapor emission becomes significant. The vapors may be dangerous and use of a
fume hood is highly recommended. As with most oils, mineral oil expands as
temperature increases. Be careful not to fill the bath so full that it overflows
when heated. The viscosity and thermal characteristics of mineral oil is poorer
than water so temperature stability may suffer. Mineral oil has very low electri

­cal conductivity. Use caution with mineral oil since it is flammable and may
also cause serious injury if inhaled or ingested.

8.1.10.4 Silicone Oil (Dow Corning 200.10, 200.20)

Silicone oils are available which offer a much wider operating temperature
range than mineral oil. Like most oils, silicone oils have temperature control
characteristics which are somewhat poorer than water. The viscosity changes
significantly with temperature and thermal expansion also occurs. These oils
have very high electrical resistivity. Silicone oils are fairly safe and non-toxic.
Silicone oils are fairly expensive.

8.1.10.5 Halocarbon 0.8

Halocarbon 0.8 is a low temperature fluid with a wide temperature range. It
may be used as low as –90 to –100°C before viscosity becomes too great. It
may be used as high as 70°C before evaporation becomes excessive.
Halocarbon does not absorb water. This allows ice to form at temperatures be

­low 0°C. Ice crystals turn the fluid into a slush which effectively increases the
viscosity and reduces temperature stability. Pumping systems may be rendered
ineffective due to ice blockage. The ice (water) can be removed occasionally by
heating the fluid up to 100°C for brief periods of time. Use halocarbon under a
fume hood at higher temperatures to remove vapors. Toxicity is low but caution
is always recommended. Halocarbon has excellent electrical resistivity. This
fluid is fairly expensive.

8.1.11 Fluid Characteristics Charts

Table 2 and Figure 3 on pages 31 and 30 have been created to provide help in
selecting a heat exchange fluid media for your constant temperature bath.
These charts provide both a visual and numerical representation of most of the
physical qualities important in making a selection. The list is not all inclusive.
There may be other useful fluids not shown in this listing.

The charts include information on a variety of fluids which are often used as
heat transfer fluid in baths. Because of the temperature range some fluids may
not be useful with your bath.

7380 Ultra Low Temp Bath

User’s Guide

28

8.1.11.1 Limitations and Disclaimer

The information given in this manual regarding fluids is intended only to be
used as a general guide in choosing a fluid. Though every effort has been made
to provide correct information we cannot guarantee accuracy of data or assure
suitability of a fluid for a particular application. Specifications may change and
sources sometimes offer differing information. Hart Scientific cannot be liable
for any personal injury or damage to equipment, product or facilities resulting
from the use of these fluids. The user of the bath is responsible for collecting
correct information, exercising proper judgment, and insuring safe operation.
Operating near the limits of certain properties such as the flash point or viscos

-

ity can compromise safety or performance. Your company’s safety policies re

­garding flash points, toxicity, and such issues must be considered. You are
responsible for reading the MSDS (material safety data sheets) and acting
accordingly.

8.1.11.2 About the Graph

The fluid graph visually illustrates some of the important qualities of the fluids
shown.

Temperature Range: The temperature scale is shown in degrees Celsius. The
fluids’ general range of application is indicated by the shaded bands. Qualities
including pour point, freeze point, important viscosity points, flash point, boil­ing point and others may be shown.

Freezing Point: The freezing point of a fluid is an obvious limitation to stir­ring. As the freezing point is approached high viscosity may also limit
performance.

Pour Point: This represents a handling limit for the fluid.

Viscosity: Points shown are at 50 and 10 centistokes viscosity. When viscosity

is greater than 50 centistokes stirring is very poor and the fluid is unsatisfactory
for bath applications. Optimum stirring generally occurs at 10 centistokes and
below.

Fume Point: A fume hood should be used. This point is very subjective in na

­ture and is impacted by individual tolerance to different fumes and smells, how
well the bath is covered, the surface area of the fluid in the bath, the size and
ventilation of the facility where the bath is located and other conditions. We as

­sume the bath is well covered at this point. This is also subject to company
policy.

Flash Point: The point at which ignition may occur. The point shown may be
either the open or closed cup flash point. Refer to the flash point discussion in
Section 8.1.8.

Boiling Point: At or near the boiling point of the fluid, the temperature stabil

­ity is difficult to maintain. Fuming or evaporation is excessive. Large amounts
of heater power may be required because of the heat of vaporization.

29

8 General Operation

Heat Transfer Fluid

Decomposition: The temperature may reach a point at which decomposition of
the fluid begins. Further increasing the temperature may accelerate decomposi

-

tion to the point of danger or impracticality.

8.2 Stirring

Stirring of the bath fluid is very important for stable temperature control. The
fluid must be mixed well for good temperature uniformity and fast controller
response. The stirrer is precisely adjusted for optimum performance.

7380 Ultra Low Temp Bath

User’s Guide

30

Figure 3 Chart of Various Bath Fluids

8.3 Power

Power to the bath is provided by an AC mains supply. See Section 3.1, Specifi

­cations, for power details. Refer to and read the CAUTION at the front of this
manual concerning brownout and over voltage protection. Power to the bath
passes through a filter to prevent switching spikes from being transmitted to
other equipment.

Turn the bath on by switching the control panel power switch to the ON posi

-

tion. The stirring motor turns on, the LED display begins to show the bath tem

­perature, and the heater turns on or off until the bath temperature reaches the
programmed set-point. When powered on the control panel display briefly
shows a four digit number. This number indicates the number of times power
has been applied to the bath. Also briefly displayed is data which indicates the

31

8 General Operation

Power

Fluid
(# = Hart Part No.)

Lower
Temperature
Limit*

Upper
Temperature
Limit*

Flash
Point

Viscosity
(centistokes)

Specific
Gravity

Specific Heat
(cal/g/°C)

Thermal
Conductivity
(cal/s/cm/°C)

Thermal
Expansion
(cm/cm/°C)

Resistivity
(10

12

Ω

-cm )

Halocarbon 0.8
#5019

–90°C (v)** 70°C (e) NONE 5.7 @ –50°C

0.8 @ 40°C

0.5 @ 70°C

1.71 @ 40°C 0.2 0.0004 0.0011

Methanol –96°C (fr) 60°C (b) 54°C 1.3 @ –35°C

0.66 @ 0°C

0.45 @ 20°C

0.810 @ 0°C

0.792 @ 20°C

0.6 0.0005 @ 20°C 0.0014 @ 25°C

Water 0°C (fr) 95°C (b) NONE 1 @ 25°C

0.4 @ 75°C

1.00 1.00 0.0014 0.0002 @ 25°C

Ethylene
Glycol—50% #5020

–35°C (fr) 110°C (b) NONE 7 @ 0°C

2 @ 50°C

0.7 @ 100°C

1.05 0.8 @ 0°C 0.001

Mineral Oil 40°C (v) 190°C (fl) 190°C 15 @ 75°C

5 @ 125°C

0.87 @ 25°C

0.84 @ 75°C

0.81 @ 125°C

0.48 @ 25°C

0.53 @ 75°C

0.57 @ 125°C

0.00025 @ 25°C 0.0007 @ 50°C 5 @ 25°C

Dow Corning 200.5
Silicone Oil

–40°C (v)** 133°C (fl, cc) 133°C 5 @ 25°C 0.92 @ 25°C 0.4 0.00028 @ 25°C 0.00105 1000 @ 25°C

10 @ 150°C

Dow Corning 200.10
#5012

–35°C (v)** 165°C (fl, cc) 165°C 10 @ 25°C

3 @ 135°C

0.934 @ 25°C 0.43 @ 40°C

0.45 @ 100°C

0.482 @ 200°C

0.00032 @ 25°C 0.00108 1000 @ 25°C
50 @ 150°C

Dow Corning 200.20
#5013

7°C (v) 230°C (fl, cc) 230°C 20 @ 25°C 0.949 @ 25°C 0.370 @ 40°C

0.393 @ 100°C

0.420 @ 200°C

0.00034 @ 25°C 0.00107 1000 @ 25°C
50 @ 150°C

Dow Corning 200.50
Silicone Oil

25°C (v) 280°C (fl, cc) 280°C 50 @ 25°C 0.96 @ 25°C 0.4 0.00037 @ 25°C 0.00104 1000 @ 25°C

50 @ 150°C

Dow Corning 550
#5016

70°C (v) 232°C (fl, cc)

300°C (fl, oc)

232°C 50 @ 70°C

10 @ 104°C

1.07 @ 25°C 0.358 @ 40°C

0.386 @ 100°C

0.433 @ 200°C

0.00035 @ 25°C 0.00075 100 @ 25°C
1 @ 150°C

Dow Corning 710
#5017

80°C (v) 302°C (fl, oc) 302°C 50 @ 80°C

7 @ 204°C

1.11 @ 25°C 0.363 @ 40°C

0.454 @ 100°C

0.505 @ 200°C

0.00035 @ 25°C 0.00077 100 @ 25°C
1 @ 150°C

Dow Corning 210-H
Silicone Oil

66°C (v) 315°C (fl, oc) 315°C 50 @ 66°C

14 @ 204°C

0.96 @ 25°C 0.34 @ 100°C 0.0003 0.00095 100 @ 25°C
1 @ 150°C

Heat Transfer Salt
#5001

145°C (fr) 530°C NONE 34 @ 150°C

6.5 @ 300°C

2.4 @ 500°C

2.0 @ 150°C

1.9 @ 300°C

1.7 @ 500°C

0.33 0.0014 0.00041

1.7

Ω

/cm

3

*Limiting Factors — b - boiling point e - high evaporation fl - flash point fr - freeze point v - viscosity — Flash point test oc = open cup cc = closed cup
**Very low water solubility, ice will form as a slush from condensation below freezing.

Tabl e 2 Table of Various Bath Fluids

controller hardware configuration. This data is used in some circumstances for
diagnostic purposes.

8.4 Heater

The power to the bath heater is precisely controlled by the temperature control

­ler to maintain a constant bath temperature. Power is controlled by periodically
switching the heater on for a certain amount of time using a solid-state relay.

The front panel heater mode indicator shows the state of the heater. The indica

­tor glows red when the heater is on and is off when the heater is off. The indi

-

cator will pulse constantly when the bath is maintaining a stable temperature.

8.5 Refrigeration

This bath uses a two-stage refrigeration system which requires special refriger

­ants to enable it to reach low temperatures. This section describes some aspects
of the cooling system and provides important information regarding its
refrigerants.

8.5.1 Operation

The bath controller automatically switches off cooling when the bath is oper­ated above 50°C to protect the system from extreme pressures. The refrigera­tion system is also protected by a brownout and over voltage protection device
that switches off power to the system when the line voltage is outside the safe
operating range. The display indicates “LoLinE” when this condition exists. A
time delay prevents the refrigeration from restarting for a short time after ade­quate line voltage has been restored.

8.5.2 Important Refrigerant Information

The refrigeration system in this bath has been designed to perform at ultra-low
temperatures. As a result, aspects of the design are uncommon and the refriger

-

ants are non-standard.

The system is cascaded, meaning there are two separate systems with the first
one chilling the second. This is required to reach temperatures below –40°C.
Normal refrigeration does not use a cascading technique, and many refrigera

-

tion technicians are not familiar with such systems.

The high stage (first compressor) refrigerant is an HFC known as R-507. The
low stage (second compressor) performs the ultra-low cooling. Its refrigerant is
an HFC R-508B. Also, known as SUVA-95.

What this means to you:

•

The cascade system is complex and its uncommon nature means that
many local refrigeration service technicians may not be able to service it.
If your bath needs service, contact a Hart Authorized Service Center (see

7380 Ultra Low Temp Bath

User’s Guide

32

Section 1.3). If you desire to use your own refrigeration technician, a Ser

-

vice Center can try to assist by phone.

•

The compressor manufacturer does not warranty their compressors when
used with non-standard refrigerants. Warranty of these compressors must
be handled through a Hart Authorized Service Center only. There is no
other way for you to receive parts or service on your compressor. You
must receive your parts or service from a Hart Authorized Service Center.

8.6 Temperature Controller

The bath temperature is controlled by Hart Scientific’s special digital tempera

­ture controller. The controller features a 24-bit analog-to-digital converter
(DAC) that gives it remarkable accuracy and stability.

The bath temperature is monitored with a platinum resistance sensor in the con

-

trol probe. The controller uses a proportional-integral-derivative (PID) algo

­rithm to determine how much heat the bath needs. The bath is heated by a
solid-state relay (SSR) controlled 500W heater.

The bath is operable within the temperature range given in the specifications.
For protection against solid-state relay failure or other circuit failure, a thermo­couple cutout automatically turns off the heater anytime the bath temperature
exceeds the maximum temperature.

The controller allows the operator to set the bath temperature with high resolu­tion, adjust the proportional band, monitor the heater output power, and pro­gram the controller configuration and calibration parameters. The controller
may be operated in temperature units of degrees Celsius or Fahrenheit. The
controller is operated and programmed from the front control panel using the
four key switches and digital LED display. The controller is equipped with a
serial RS-232 digital interface for remote operation. Operation of the controller
using the front control panel is discussed in Section 9, Controller Operation.
Operation using the digital interfaces is discussed in Section 10, Digital Com

-

munication Interface.

When the controller is set to a new set-point the bath heats or cools to the new
temperature. Once the new temperature is reached the bath usually takes 15-20
minutes for the temperature to settle and stabilize. There may be a small
amount of overshoot or undershoot.

33

8 General Operation

Temperature Controller

9 Controller Operation

This section discusses in detail how to operate the bath temperature controller
using the front control panel. Using the front panel key-switches and LED dis

­play the user may monitor the bath temperature, set the temperature set-point in
degrees C or F, monitor the heater output power, adjust the controller propor

­tional band, and program the calibration parameters, operating parameters, and
serial interface configuration. Operation of the functions and parameters are
shown in the flowchart in Figure 4 on page 36. This chart may be copied for
reference.

In the following discussion a button with the word SET, UP, EXIT or DOWN
inside indicates the panel button while the dotted box indicates the display
reading. Explanation of the button or display reading are to the right of each
button or display value.

9.1 Bath Temperature

The digital LED display on the front panel allows direct viewing of the actual
bath temperature. This temperature value is what is normally shown on the dis­play. The units, C or F, of the temperature value are displayed at the right. For
example,

10.00C

Bath temperature in degrees Celsius

The temperature display function may be accessed from any other function by
pressing the “EXIT” button.

9.2 Temperature Set-point

The temperature set-point can be set to any value within the range and resolu

­tion as given in the specifications. Be careful not to exceed the safe temperature
limits of any devices inserted into the bath.

Setting the temperature involves two steps: (1) select the set-point memory and
(2) adjust the set-point value.

To protect the refrigeration system from excessive pressures, it will not operate
above 50°C.

9.2.1 Programmable Set-points

The controller stores 8 set-point temperatures in memory. The set-points can be
quickly recalled to conveniently set the calibrator to a previously programmed
temperature set-point.

To set the temperature one must first select the set-point memory. This function
is accessed from the temperature display function by pressing “SET”. The

35

9 Controller Operation

Bath Temperature

7380 Ultra Low Temp Bath

User’s Guide

36

UP

UP

DOWN DOWN

SET

Operating

Parameters

Menu

SET

SET

Cal

Menu

ALPHA

Adj. R0

DO NOT CHANGE THESE VALUES. SEE MANUAL

DO NOT CHANGE THESE VALUES. SEE MANUAL

Serial

Interface

Menu

BAUD

Rate

Adjust

BAUD Rate

Sample

Period

Adj. Sample

Period

DE LTA

Duplex

Mode

Adj. Duplex

Mode

Linefeed

BETA

Adjust

Linefeed

Adjust

BETA

EXITEXIT

EXIT

EXIT

EXIT

UP

DOWN

SET

SET

SET

+

+

+

Display Power

Toggles °C / °F

SET

SET

Select Setpoint

Adjust Setpoint

Units °C/°F

Scan On/Off

Scan Rate

Display

Temperature

Configuration Menu

Secondary Functions

X5

HL

LL

Adj. HL

Adj. LL

Display of Rs

EXIT

Set Proportional Band

R0

Hard

Cut-out

Adj. Hard

Cut-out

Adj. ALPHA

Adj. DELTA

Menu Legend:

Press “SET” to step through the menu
and to store the parameter value.

Press “EXIT” briefly to skip a parameter
without storing the parameter value.

Hold “EXIT” to exit the menu and
display the temperature

Set Cut-out Temp

Cool

Adj. Cool

Figure 4 Controller Operation Flowchart

number of the set-point memory currently being used is shown at the left on the
display followed by the current set-point value.

10.00C

Bath temperature in degrees Celsius

S

Access set-point memory

1. 25.0

Set-point memory 1, 25°C currently used

To change the set-point memory press “UP” or “DOWN”.

4. -25.0

New set-point memory 4, –25°C

Press “SET” to accept the new selection and access the set-point value.

S

Accept selected set-point memory

9.2.2 Set-point Value

The set-point value may be adjusted after selecting the set-point memory and

pressing “SET”.

4 -25.0

Set-point 4 value in°C

If the set-point value is correct, hold “EXIT” to resume displaying the well
temperature. Press “UP” or “DOWN” to adjust the set-point value.

-28.00

New set-point value

When the desired set-point value is reached press “SET” to accept the new
value and access the temperature scale units selection. If “EXIT” is pressed in

-

stead of “SET”, any changes made to the set-point are ignored.

S

Accept new set-point value

9.2.3 Temperature Scale Units

The temperature scale units of the controller can be set by the user to degrees
Celsius (°C) or Fahrenheit (°F). The selected units are used in displaying the
well temperature, set-point, and proportional band.

Press “SET” after adjusting the set-point value to change display units.

Un= C Scale units currently selected

37

9 Controller Operation

Temperature Set-point

Press “UP” or “DOWN” to change the units.

Un= F New units selected

9.3 Scan

The scan rate can be set and enabled so that when the set-point is changed the
bath heats or cools at a specified rate (degrees per minute) until it reaches the
new set-point. With the scan disabled the bath heats or cools at the maximum
possible rate.

9.3.1 Scan Control

The scan is controlled with the scan on/off function that appears in the main
menu after the set-point function.

Sc=OFF

Scan function off

Press “UP” or “DOWN” to toggle the scan on or off.

Sc=On

Scan function on

Press “SET” to accept the present setting and continue.

S

Accept scan setting

9.3.2 Scan Rate

The next function in the main menu is the scan rate. The scan rate can be set
from .1 to 99.9°C/min. The maximum scan rate is actually limited by the natu

-

ral heating or cooling rate of the instrument and is less than 10°C/min.

The scan rate function appears in the main menu after the scan control function.
The scan rate units are in degrees per minute, degrees C or F depending on the
selected units.

Sr= 5.0

Scan rate in°C/min

Press“UP”or“DOWN”tochangethescanrate.

Sr= 2.0

New scan rate

Press “SET” to accept the new scan rate and continue.

S

Accept scan rate

7380 Ultra Low Temp Bath

User’s Guide

38

9.4 Secondary Menu

Functions which are used less often are accessed within the secondary menu.
The secondary menu is accessed by pressing “SET” and “EXIT” simulta

­neously and then releasing. The first function in the secondary menu is the
heater power display. (See Figure 4 on page 36.)

9.5 Heater Power

The temperature controller controls the temperature of the bath by pulsing the
heater on and off. The total power being applied to the heater is determined by
the duty cycle or the ratio of heater on time to the pulse cycle time. By knowing
the amount of heating the user can tell if the calibrator is heating up to the
set-point, cooling down, or controlling at a constant temperature. Monitoring
the percent heater power allows the user to determine the stability of the bath
temperature.

The heater power display is accessed in the secondary menu. Press “SET” and
“EXIT” simultaneously and release. The heater power displays as a percentage
of full power.

10.00C

Bath temperature

S+E

Access heater power in secondary menu

SEC Flashes

12.0 P

Heater power in percent

To exit out of the secondary menu hold “EXIT”. To continue on to the propor

-

tional band setting function press “EXIT” momentarily or “SET”.

9.6 Proportional Band

In a proportional controller such as this the heater output power is proportional
to the well temperature over a limited range of temperatures around the
set-point. This range of temperature is called the proportional band. At the bot

-

tom of the proportional band the heater output is 100%. At the top of the pro

­portional band the heater output is 0. Thus as the temperature rises the heater
power is reduced, which consequently tends to lower the temperature back
down. In this way the temperature is maintained at a fairly constant
temperature.

The temperature stability of the bath and response time depend on the width of
the proportional band.

39

9 Controller Operation

Secondary Menu

If the band is too wide, the temperature deviates excessively from the set-point
due to varying external conditions. This is due to the power output changing
very little with temperature and the controller cannot respond very well to
changing conditions or noise in the system.

If the proportional band is too narrow, the temperature may swing back and
forth because the controller overreacts to temperature variations.

For best control stability, the proportional band must be set for the optimum
width. This value is usually two to three times the largest value at which the
bath temperature oscillates.

The proportional band width is set at the factory to a value between 0.5 and

1.0°C. The proportional band width may be altered by the user if he desires to
optimize the control characteristics for a particular application.

The proportional band width is easily adjusted from the front panel. The width
may be set to discrete values in degrees C or F depending on the selected units.
The proportional band adjustment is be accessed within the secondary menu.
Press “SET” and “EXIT” to enter the secondary menu and show the heater
power. Then press “SET” to access the proportional band.

S+E

Access heater power in secondary menu

12.0 P

Heater power in percent

S

Access proportional band

ProP Flashes “ProP” and the setting

15.0 Proportional band setting

To change the proportional band press “UP” or “DOWN”.

1.5

New proportional band setting

To store the new setting press “SET”. Press “EXIT” to continue without storing
the new value.

S

Accept the new proportional band setting

9.7 Cutout

As a protection against software or hardware fault or user error, the bath is
equipped with an adjustable cutout device that shuts off power to the heater if
the temperature exceeds a set value. This protects the instrument, probes, and

7380 Ultra Low Temp Bath

User’s Guide

40

fluid from excessive temperatures. The cutout temperature is programmable by
the operator from the front panel of the controller. The cutout should be set to
the temperature limits of the selected fluid.

If the cutout is activated because of excessive temperature then power to the
heater shuts off and the instrument cools. The bath cools until it reaches a few
degrees below the cutout set-point temperature. At this point the cutout resets
and allows normal operation.

The cutout set-point may be accessed within the secondary menu. Press "SET"
and "EXIT" to enter the secondary menu and show the heater power. Then
press "SET" twice to access the cutout set-point.

S+E

Access heater power in secondary menu

12.0 P Heater power in percent

S

Access proportional band

Pb= 0.05C Proportional band setting

S

Access cutout set-point

CO= 80C Cutout set-point

To change the cutout set-point press "UP" or "DOWN".

CO= 70C New cutout set-point

To accept the new cutout set-point press "SET".

S

Accept cutout set-point

The next function is the configuration menu. Press "EXIT" to resume display

-

ing the temperature.

9.8 Controller Configuration

The controller has a number of configuration and operating options and calibra

-

tion parameters which are programmable via the front panel. These are ac

­cessed from the secondary menu after the proportional band function by
pressing “SET”. Pressing “SET” again enters the first of three sets of configu

-

ration parameters: operating parameters, serial interface parameters, and cali

-

41

9 Controller Operation

Controller Configuration

bration parameters. The menus are selected using the “UP” and “DOWN” keys
and then pressing “SET”. (See Figure 4 on page 36.)

9.9 Operating Parameters

The operating parameters menu is indicated by,

PAr

Operating parameters menu

The operating parameters menu contains the High Limit, Stir Speed, and Cool

-

ing parameters.

9.9.1 High Limit

The High Limit Parameter adjusts the upper set-point temperature. The factory
default and maximum temperature are set to 100°C. For safety, a user can ad

-

just the High Limit down so the maximum temperature set-point is restricted.

HL High Limit parameter

Press “SET” to enable adjustment of HL.

HL Flashes “HL” and then displays the setting

H=100 Current HL setting

Adjust the HL parameter using “UP” or “DOWN”.

H=90 New HL setting

Press “SET” to accept the new temperature limit.

9.9.2 Low Limit

The Low Limit (LL) Parameter adjusts the lower set-point temperature limit.
The factory default and minimum temperature are set to –90°C. For safety, a
user can adjust the Low Limit up so the minimum temperature set-point is
restricted.

LL Low Limit parameter

Press “SET” to enable adjustment of LL.

LL Flashes “ ” and then displays the setting

L=-90 Current LL setting

7380 Ultra Low Temp Bath

User’s Guide

42

Adjust the LL parameter using “UP” or “DOWN”.

L=-20 New LL setting

Press “SET” to accept the new temperature limit.

9.9.3 Cooling

This menu function allows the operator to disable cooling and corresponds to
the remote cooling control function (see Table 3). Switching the cooling off
temporarily allows the bath to heat up more quickly from a low temperature.
Cooling can be manually switched off using the cooling switch on the front
panel or automatically switched off any time the bath temperature or set-point
is higher than about 35°C. As a result, cooling is ON only if the cooling func

­tion is ON, the cooling switch is ON, and both the bath temperature and the
set-point are less than about 35°C. The cooling function is indicated by,

CooL Flashes "CooL" and then displays the setting

CooL=OFF Current cooling setting

The setting may be changed using "UP" or "DOWN" and pressing "SET".

CooL=On New cooling setting

9.10 Serial Interface Parameters

The serial RS-232 interface parameters menu is indicated by,

SErIAL

Serial RS-232 interface parameters menu

The serial interface parameters menu contains parameters which determine the
operation of the serial interface. These controls only apply to instruments fitted
with the serial interface. The parameters in the menu are — baud rate, sample
period, duplex mode, and linefeed. Press “UP” to enter the menu.

9.10.1 Baud Rate

The baud rate is the first parameter in the menu. The BAUD rate setting deter

-

mines the serial communications transmission rate.

The BAUD rate parameter is indicated by,

bAUd

Flashes “bAUd” and then displays the stetting

2400 b

Current BAUD rate

43

9 Controller Operation

Serial Interface Parameters

The BAUD rate of the serial communications may be programmed to 300, 600,
1200, 2400, 4800, or 9600 BAUD. Use “UP” or “DOWN” to change the BAUD
rate value.

4800 b

New BAUD rate

Press “SET” to set the BAUD rate to the new value or “EXIT” to abort the op

-

eration and skip to the next parameter in the menu.

9.10.2 Sample Period

The sample period is the next parameter in the serial interface parameter menu.
The sample period is the time period in seconds between temperature measure

-

ments transmitted from the serial interface. If the sample rate is set to 5, the in

­strument transmits the current measurement over the serial interface
approximately every five seconds. The automatic sampling is disabled with a
sample period of 0. The sample period is indicated by,

SPer

Flashes “SPEr” and then displays the setting

SP= 1

Current sample period (seconds)

Adjust the value with “UP” or “DOWN” and then use “SET” to store the sam­ple rate to the displayed value. “EXIT” does not store the new value.

SP= 60

New sample period

9.10.3 Duplex Mode

The next parameter is the duplex mode. The duplex mode may be set to full du

­plex or half duplex. With full duplex any commands received by the calibrator
via the serial interface are immediately echoed or transmitted back to the device
of origin. With half duplex the commands are executed but not echoed. The du

-

plex mode parameter is indicated by,

dUPL

Flashes “dUPL” and then displays the setting

d=FULL

Current duplex mode setting

The mode may be changed using “UP” or “DOWN” and pressing “SET”.

d=HALF

New duplex mode setting

7380 Ultra Low Temp Bath

User’s Guide

44

9.10.4 Linefeed

The final parameter in the serial interface menu is the linefeed mode. This pa

­rameter enables (on) or disables (off) transmission of a linefeed character (LF,
ASCII 10) after transmission of any carriage-return. The linefeed parameter is
indicated by,

LF

Flashes “LF” and then displays the setting

LF= On

Current linefeed setting

The mode may be changed using “UP” or “DOWN” and pressing “SET”.

LF= OFF

New linefeed setting

9.11 Calibration Parameters

The operator of the 7380 controller has access to the Hard Cutout and a number
of the bath calibration constants namely R

0

, ALPHA, DELTA, and BETA.

These values are set at the factory and should not be altered. The correct values
are important to the accuracy and proper and safe operation of the bath. Access
to these parameters is available to the user only so that in the event that the con­troller memory fails the user may restore these values to the factory settings.
The user should have a list of these constants and their settings with the
manual.

CAUTION: DO NOT change the values of the bath calibration constants

from the factory set values. The correct setting of these parameters is im

-

portant to the safety and proper operation of the bath.

The calibration parameters menu is indicated by:

CAL Calibration parameters menu

Press “SET” five times to enter the menu.

The calibration parameters R

0

, ALPHA, DELTA, and BETA characterize the

resistance-temperature relationship of the platinum control sensor. These pa

­rameters may be adjusted by an experienced user to improve the accuracy of
the bath.

9.11.1 Hard Cutout

This parameter is the temperature above which the unit shuts down automati

­cally. The parameter is set at the factory to approximately 120°C and can be
changed only through the variable resistor. This parameter cannot be changed

45

9 Controller Operation

Calibration Parameters

through the instrument menu or the communications port and is not user
settable.

9.11.2 R0

This probe parameter refers to the resistance of the control probe at 0°C. The
value of this parameter is set at the factory for best instrument accuracy.

9.11.3 ALPHA

This probe parameter refers to the average sensitivity of the probe between 0
and 100°C. The value of this parameter is set at the factory for best instrument
accuracy.

9.11.4 DELTA

This probe parameter characterizes the curvature of the resistance-temperature
relationship of the sensor. The value of this parameter is set at the factory for
best instrument accuracy.

9.11.5 BETA

This probe parameter characterizes the low temperatures. The value of this pa­rameter is set at the factory for best instrument accuracy.

7380 Ultra Low Temp Bath

User’s Guide

46

10 Digital Communication Interface

The 7380 Bath calibrator is capable of communicating with and being con

-

trolled by other equipment through the digital serial interface.

With a digital interface the instrument may be connected to a computer or other
equipment. This allows the user to set the set-point temperature, monitor the
temperature, and access any of the other controller functions, all using remote
communications equipment. Communications commands are summarized in
Table 3 on page 50.

10.1 Serial Communications

The bath is installed with an RS-232 serial interface that allows serial digital
communications over fairly long distances. With the serial interface the user
may access any of the functions, parameters and settings discussed in Section 9
with the exception of the BAUD rate setting.

10.1.1 Wiring

The serial communications ca­ble attaches to the calibrator
through the DB-9 connector at
the back of the instrument. Fig­ure 5 shows the pin-out of this
connector and suggested cable
wiring. To eliminate noise the
serial cable should be shielded
with low resistance between the
connector (DB-9) and the
shield. If the unit is used in a
heavy industrial setting, the se

-

rial cable must be limited to
ONE METER in length.

10.1.2 Setup

Before operation the serial in

­terface must first be set up by
programming the BAUD rate
and other configuration parame

-

ters. These parameters are pro

­grammed within the serial
interface menu. The serial inter

-

face parameters menu is out

-

lined in Figure 4 on page 36.

47

10 Digital Communication Interface

Serial Communications

Figure 5 Serial Cable Wiring

To enter the serial parameter programming mode first press “EXIT” while
pressing “SET” and release to enter the secondary menu. Press “SET” repeat

­edly until the display reads “PAr”. Press “UP” until the serial interface menu
is indicated with“SErIAL”. Finally press “SET” to enter the serial parameter
menu. In the serial interface parameters menu are the BAUD rate, the sample
rate, the duplex mode, and the linefeed parameter.

10.1.2.1 BAUD Rate

The BAUD rate is the first parameter in the menu. The display prompts with
the BAUD rate parameter by showing “bAUd”. Press “SET” to choose to set
the BAUD rate. The current BAUD rate value is displayed. The BAUD rate of
the instrument serial communications may be programmed to 300, 600, 1200,
2400, 4800, or 9600 baud. The BAUD rate is pre-programmed to 2400 BAUD.
Use“UP”or“DOWN”tochangetheBAUDratevalue.Press“SET”tosetthe
BAUD rate to the new value or “EXIT” to abort the operation and skip to the
next parameter in the menu.

10.1.2.2 Sample Period

The sample period is the next parameter in the menu and prompted with
“SPEr”. The sample period is the time period in seconds between temperature
measurements transmitted from the serial interface. If the sample rate is set to
5, the instrument transmits the current measurement over the serial interface ap­proximately every five seconds. The automatic sampling is disabled with a
sample period of 0. Press “SET” to choose to set the sample period. Adjust the
period with “UP” or “DOWN” and then use “SET” to set the sample rate to the
displayed value.

10.1.2.3 Duplex Mode

The next parameter is the duplex mode indicated with “dUPL”. The duplex
mode may be set to half duplex (“HALF”) or full duplex (“FULL”). With full
duplex any commands received by the thermometer via the serial interface are
immediately echoed or transmitted back to the device of origin. With half du

-

plex the commands are executed but not echoed. The default setting is full du

-

plex. The mode may be changed using “UP” or “DOWN” and pressing “SET”.

10.1.2.4 Linefeed

The final parameter in the serial interface menu is the linefeed mode. This pa

-

rameter enables (“On”) or disables (“OFF”) transmission of a linefeed charac

­ter (LF, ASCII 10) after transmission of any carriage-return. The default setting
is with linefeed on. The mode may be changed using “UP” or “DOWN” and
pressing “SET”.

10.1.3 Serial Operation

Once the cable has been attached and the interface set up properly, the control

-

ler immediately begins transmitting temperature readings at the programmed

7380 Ultra Low Temp Bath

User’s Guide

48

rate. The serial communications uses 8 data bits, one stop bit, and no parity.
The set-point and other commands may be sent via the serial interface to set the
temperature set-point and view or program the various parameters. The inter

-

face commands are discussed in Section10.2. All commands are ASCII charac

-

ter strings terminated with a carriage-return character (CR, ASCII 13).

10.2 Interface Commands

The various commands for accessing the calibrator functions via the digital in

­terfaces are listed in this section (see Table 3). These commands are used with
the RS-232 serial interface. The commands are terminated with a carriage-re

­turn character. The interface makes no distinction between upper and lower
case letters, hence either may be used. Commands may be abbreviated to the
minimum number of letters which determines a unique command. A command
may be used to either set a parameter or display a parameter depending on
whether or not a value is sent with the command following a “=” character. For
example, “s”<CR> returns the current set-point and “s=150.0”<CR> sets the
set-point to 150.0 degrees.

In the following list of commands, characters or data within brackets, “[” and
“]”, are optional for the command. A slash, “/”, denotes alternate characters or
data. Numeric data, denoted by “n”, may be entered in decimal or exponential
notation. Characters are shown in lower case although upper case may be used.
Spaces may be added within command strings and are ignored. Backspace (BS,
ASCII 8) may be used to erase the previous character. A terminating CR is im­plied with all commands.

49

10 Digital Communication Interface

Interface Commands

7380 Ultra Low Temp Bath

User’s Guide

50

Command Description

Command
Format

Command
Example Returned

Returned
Example

Acceptable
Values

Display Temperature

Read current set-point s[etpoint] s set: 999.99 {C or F} set: 90.00 C

Set current set-point to n s[etpoint]=n s=80.00 Instrument

Range

Read temperature t[emperature] t t: 999.99 {C or F} t: 55.6 C

Read temperature units u[nits] u u: x u: C

Set temperature units: u[nits]=c/f

CorF

Set temperature units to Celsius u[nits]=c u=c

Set temperature units to
Fahrenheit

u[nits]=f u=f

Read scan mode sc[an] sc scan: {ON or OFF} scan:ON

Set scan mode sc[an]=on/off sc=on ON or OFF

Read scan rate sr[ate] sr srat: 99.9 {C or F}/min srat:12.4C/min

Set scan rate sr[ate]=n sr=1.1 .1 to 99.9

Secondary Menu

Read proportional band setting pr[opband] pr pb: 999.9 pb: 15.9

Set proportional band to

n

pr[opband]=n pr=8.83 Depends on

Configuration

Read cut-out setting cu[tout] c c: 9999 {C or F} c: 105C, in

Set cut-out setting to

n

degrees cu[tout]=n c=95 25 to 115°C

Read heater power

(duty cycle)

po[wer] po po: 999.9 po: 1.0

Configuration Menu

Operating Parameters Menu

Read high limit hl hl hl:999 hl:126

Set high limit hl=n hl=90 25 to 100

Read low limit ll ll ll:999 ll:-90

Set low limit ll=n ll=-90 –90 to 25

Read cooling setting co[ol] co cool: {ON or OFF} cool: ON

Set cooling setting co[ol]=on/of[f] co=ON ON or OFF

Serial Interface Menu

Read serial sample setting sa[mple] sa sa: 9 sa: 1

Set serial sampling setting to

n

seconds

sa[mple]=n sa=0 0 to 999

Set serial duplex mode: du[plex]=f[ull]/h[alf]

FULL or HALF

Set serial duplex mode to full du[plex]=f[ull] du=f

Set serial duplex mode to half du[plex]=h[alf] du=h

Set serial linefeed mode: lf[eed]=on/of[f]

ON or OFF

Set serial linefeed mode to on lf[eed]=on lf=on

Set serial linefeed mode to off lf[eed]=of[f] lf=of

Tabl e 3 Controller Communications Commands

51

10 Digital Communication Interface

Interface Commands

Command Description

Command
Format

Command
Example Returned

Returned
Example

Acceptable
Values

Calibration Menu

Read R0 calibration parameter r[0] r r0: 999.999 r0: 100.578

Set R0 calibration parameter to

n

r[0]=n r=100.324 90 to 110

Read ALPHA calibration
parameter

al[pha] al al: 9.9999999 al: 0.0038573

Set ALPHA calibration parameter
to

n

al[pha]=n al=0.0038433 .002 to .005

Read DELTA calibration
parameter

de[lta] de de:9.99999 de: 1.507

Set DELTA calibration parameter de[lta]=n de=1.3742 0–3.0

Read BETA calibration parameter be[ta] be be:99.999 be:03427

Set BETA calibration parameter be[ta]=n be=0.342 –20 to 20

Functions not on menu

Read firmware version number *ver[sion] *ver ver.9999,9.99 ver.7103,2.00

Read structure of all commands h[elp] h list of commands

Read all operating parameters all all list of parameters

Legend: [] Optional Command data

{} Returns either information

n Numeric data supplied by user

9 Numeric data returned to user

x Character data returned to user

Note:

When DUPLEX is set to FULL and a command is sent to READ, the command is returned followed by a
carriage return and linefeed. Then the value is returned as indicated in the RETURNED column.

Controller Communications Commands continued

11 Calibration Procedure

Note: This procedure is to be considered a general guideline. Each labo

­ratory should write their own procedure based on their equipment and
their quality program. Each procedure should be accompanied by an un

-

certainty analysis also based on the laboratory's equipment and environ

-

ment.

11.1 Calibration Procedure

Calibration of this instrument should be performed at regularly scheduled inter

-

vals by qualified authorized personnel in accordance with your company’s pol

-

icy. Following is the recommended procedure for calibrating this instrument.

11.1.1 Calibration Equipment

Calibration requires a standard thermometer that is adequately accurate and fits
properly into one of the reference holes in the block. Recommended equipment
includes a laboratory grade PRT with a length of 30 to 300 mm (9 to 12 inches)
and a diameter of 4.76 or 6.35 mm (3/16 or 1/4 inches). The combined accu­racy of the PRT and the readout which used to display the temperature should
be 0.025°C or better.

11.1.2 Calibration

The accuracy of the instrument over the full range is determined by the values
of the calibration parameters R0, ALPHA, DELTA, and BETA. The calibration
procedure involves measuring the error between the instrument and the refer­ence thermometer at several temperature throughout the range and adjusting the
calibration parameters as necessary to reduce the errors to within acceptable
limits. The stated accuracy of the instrument can be found in the specification
table in Section 3.1. Because of the way the calibration parameters affect the
temperature the simplest way to proceed is to measure the errors at 0°C, 100°C,
50°C, and –70°C and adjust R0, ALPHA, DELTA, and BETA at each point re

-

spectively. Be aware that you must use the appropriate fluid at each tempera

-

ture. Follow these steps:

•

Set the set-point to 0°C and allow adequate time for the bath to reach this
temperature and stabilize. Adjust the R0 calibration parameter (see Sec

­tion 9.11.2) to make the bath temperature as measured with the standard
thermometer match the set-point. The approximate ratio between a
change in R0 and a change in temperature at 0°C is about 0.4 to 1. For ex

­ample, if the bath temperature is high by 0.1°C at 0°C then decrease R0
by 0.04.

•

Set the set-point to 100°C and allow adequate time for the bath to reach
this temperature and stabilize. Adjust the ALPHA calibration parameter
(see Section 9.11.3) to make the bath temperature as measured with the

53

11 Calibration Procedure

Calibration Procedure

standard thermometer match the set-point. The approximate ratio between
a change in ALPHA and a change in temperature at 100°C is about

0.00004 to 1. For example, if the bath temperature is high by 0.1°C at
100°C then decrease ALPHA by 0.000004.

•

Set the set-point to 50°C and allow adequate time for the bath to reach
this temperature and stabilize. Adjust the DELTA calibration parameter
(see Section 9.11.4) to make the bath temperature as measured with the
standard thermometer match the set-point. The approximate ratio between
a change in DELTA and a change in temperature at 50°C is about 4.0 to 1.
For example, if the bath temperature is high by 0.1°C at 50°C then de

-

crease DELTA by 0.4.

•

Set the set-point to –70°C and allow adequate time for the bath to reach
this temperature and stabilize. Adjust the BETA calibration parameter
(see Section 9.11.5) to make the bath temperature as measured with the
standard thermometer match the set-point. The approximate ratio between
a change in BETA and a change in temperature at –70°C is about –1.0 to

1. For example, if the bath temperature is high by 0.1°C at –70°C then in

-

crease BETA by 0.1.

7380 Ultra Low Temp Bath

User’s Guide

54

12 Maintenance

•

The calibration instrument has been designed with the utmost care. Ease
of operation and simplicity of maintenance have been a central theme in
the product development. Therefore, with proper care the instrument
should require very little maintenance. Avoid operating the instrument in
dirty or dusty environments.

•

If the outside of the bath becomes soiled, it may be wiped clean with a
damp cloth and mild detergent. Do not use harsh chemicals on the surface
which may damage the paint.

•

Periodically check the fluid level in the bath to ensure that the level has
not dropped. A drop in the fluid level affects the stability of the bath.
Changes in fluid level are dependent upon several factors specific to the
environment in which the equipment is used. A schedule cannot be out

­lined to meet each environmental setting. Therefore, the first year the bath
should be checked weekly with notes kept as to changes in bath fluid.

• Heat transfer medium lifetime is dependent upon the type of medium and
the environment. The fluid should be checked at least every month for the
first year and regularly thereafter. This fluid check provides a baseline for
knowledge of bath operation with clean, usable fluid. Once some fluids
have become compromised, the break down can occur rapidly. Particular
attention should be paid to the viscosity of the fluid. A significant change
in the viscosity can indicate that the fluid is contaminated, being used out­side of its temperature limits, contains ice particles, or is close to a chemi­cal break-down. Once data has been gathered, a specific maintenance
schedule can be outline for the instrument. Refer to the General Operation
section (Section 8) for more information about the different types of flu­ids used in calibration baths.

•

If a hazardous material is spilt on or inside the equipment, the user is re

­sponsible for taking the appropriate decontamination steps as out-lined by
the national safety council with respect to the material. MSDS sheets ap

­plicable to all fluids used in the baths should be kept in close proximity to
the instrument.

•

If the mains supply cord becomes damaged, replace it with a cord with
the appropriate gauge wire for the current of the bath. If there are any
questions, call a Hart Authorized Service Center (see Section 1.3) for
more information.

•

Before using any cleaning or decontamination method except those rec

­ommended by Hart, users should check with a Hart Authorized Service
Center (see Section 1.3) to be sure that the proposed method does not
damage the equipment.

•

The condensing coil should be cleaned regularly. Inspect the coil through
the vented rear panel. If any dust or dirt accumulation is visible, remove
the rear panel to clean out the dust or dirt. Use a vacuum with a brush to

55

12 Maintenance

remove the dirt. Do not use compressed air as it might drive the dirt be

-

tween the fins where it may become lodged preventing airflow.

•

If the instrument is used in a manner not in accordance with the equip

­ment design, the operation of the bath may be impaired or safety hazards
may arise.

•

The over-temperature cutout should be checked every 6 months to see that
it is working properly. In order to check the user selected cutout, follow
the controller directions (Section 9.7, Cutout) for setting the cutout. Both
the manual and the auto reset option of the cutout should be checked. Set
the bath temperature higher than the cutout. Check to see if the display
flashes cutout and if the temperature is decreasing.

WARNING: When checking the over-temperature cutout, be sure that the

temperature limits of the bath fluid are not exceeded. Exceeding the tem

­perature limits of the bath fluid could cause harm to the operator, lab, and
instrument.

7380 Ultra Low Temp Bath

User’s Guide

56

13 Troubleshooting

If problems arise while operating the 7380, this section provides some sugges

-

tions that may help you solve the problem. A wiring diagram is also included.

13.1 Troubleshooting

Below are several situations that may arise followed by suggested actions to
take for fixing the problem.

Problem Possible Causes and Solutions

Incorrect tempera

-

ture reading

Incorrect R0, ALPHA, DELTA, and BETA parameters. Find the value for R0, AL

­PHA, DELTA, and BETA on the Report of Test that was shipped with the instrument.
Reprogram the parameters into the instrument (see Section 10.11, Calibration Pa

-

rameters). Allow the instrument to stabilize and verify the accuracy of the tempera

-

ture reading.

Controller locked up. The controller may have locked up due to a power surge or
other aberration. Initialize the system by performing the Factory Reset Sequence.

Factory Reset Sequence. Hold the SET and EXIT buttons down at the same time
while powering up the instrument. The instrument displays shows ‘-init-‘, the model
number, and the firmware version. Each of the controller parameters and calibration
constants must be reprogrammed. The values can be found on the Report of Test
that was shipped with the instrument.

Instrument heats
slowly

Incorrect scan and scan rate setting. The scan and scan rate settings may be set
to unwanted values. Check the Scan and Scan Rate settings. The scan may be off (if
the unit seems to be responding too quickly). The scan may be on with the Scan
Rate set low (if unit seems to be responding too slowly).

The display shows
an error

Controller problem. The error messages signify the following problems with the
controller.

Err 1

- RAM error

Err 2

- NVRAM error

Err 3

- Structure error

Err 4

- ADC setup error

Err 5

- ADC ready error

Err 6

- SENSOR error. Sensor is open, shorted , or otherwise damaged. Insure

that the probe is connected.

Err 7

- HtrCTL error
Initialize the system by performing the Factory Reset Sequence describe above.
LoLine. See the problem below labeled “The bath does not turn on.”

57

13 Troubleshooting

Troubleshooting

Problem Possible Causes and Solutions

The bath does not
turn on

If a fault condition exists upon application of power, the bath will not energize. The
bath needs to be plugged in to the line voltage for at least 2 minutes before turning
power on. This is only necessary for the first time that the bath is energized or when
it is moved from one location to another.

If a high or low voltage condition exists for longer than 5 seconds, the compressor is
de-energized. The controller flashes “Lo LinE” on and off while the condition exists.

Re-energization is automatic upon correction of the fault condition and after a delay
cycle of about 2 minutes.

High and low voltage protection limits at 115 VAC:

Voltage Cutout: ±12.5% (101 – 129 VAC)
Voltage Cutin: ±7.5% (106 – 124 VAC)

High and low voltage protection limits at 230 VAC:

Voltage Cutout: ±12.5% (203 – 257 VAC)
Voltage Cutin: ±7.5% (213 – 247 VAC)

See the Caution in the front of this manual for additional information.

Testing the Line Voltage – If the power line voltage is too low (90% of the compres­sor’s rated voltage), the compressor could be damaged. Place a DVM in the supply
line on the wall that feeds the bath. Measure the line voltage under load (with the
bath on). If the line voltage is low or marginal, disconnect any other devices that are
using the same line. Alternately, move the bath to a location where the supply volt­age is good. If none of these are possible, contact an electrician to re-route the cor­rect power. If necessary, you can inspect the operation of the line monitor by opening
the electronics cover. See the Caution at the front of this manual for a summary of
the ICM491 operation. Hart does not recommend adjustment of the operating volt­age in order to use the instrument. Instead, an electrician should be consulted to al­leviate the problem with the power source.

13.2 CE Comments

13.2.1 EMC Directive

Hart Scientific’s equipment has been tested to meet the European Electromag

­netic Compatibility Directive ( EMC Directive, 89/336/EEC). The Declaration
of Conformity for your instrument lists the specific standards to which the unit
was tested.

13.2.2 Low Voltage Directive (Safety)

In order to comply with the European Low Voltage Directive (73/23/EEC),
Hart Scientific equipment has been designed to meet the IEC 1010-1 (EN
61010-1) and IEC 1010-2-010 (EN 61010-2-010) standards.

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