GXAM06_技术文档

MICROTEMP^®Thermal Cutoffs:

INTRODUCTION

Upper Limit Temperature Protection

MICROTEMP^®thermal cutoffs from Therm-O-Disc offer an accurate, reliable solution to the need

for upper limit temperature protection. Known as a thermal fuse, thermal link, or TCO, the

MICROTEMP^®thermal cutoff provides protection against overheating by interrupting an electrical

circuit when operating temperatures exceed the rated temperature of the cutoff.

MICROTEMP^®Features:

•

One-shot operation cuts off electrical power

Current interrupt capacity up to 25 amps @ 250VAC

Low resistance

Compact size

Operating Principle of the MICROTEMP^®TCO

The active trigger mechanism of the thermal cutoff is an exclusively formulated, electrically

nonconductive pellet. Under normal operating temperatures, the solid pellet holds spring-loaded

contacts closed.

When a predetermined temperature is reached, the pellet melts, allowing the compression spring

to relax. The trip spring then slides the contact away from the lead and the circuit is opened (see

figures 1 and 2).

After a MICROTEMP^®thermal cutoff opens a circuit, the TCO needs to be replaced. This

replacement procedure must include correction of the fault condition before the product is

operated again.

135

MICROTEMP^®G4, G6 & G7 Series TCO

Before Operation

After Operation

CASE AND LEAD

ASSEMBLY

CASE AND LEAD

ASSEMBLY

THERMAL

PELLET

DISCS

COMPRESSION

SPRING

DISCS

COMPRESSION

SPRING

STAR CONTACT

TRIP SPRING

STAR CONTACT

TRIP SPRING

CERAMIC

BUSHING

CERAMIC

BUSHING

ISOLATED

LEAD

ISOLATED

LEAD

EPOXY

SEAL

EPOXY

SEAL

Grey area shows

current path

Grey area shows opened or

broken current path

Figure 1

MICROTEMP^®G5 & G8 Series TCO

Before Operation

After Operation

CASE AND LEAD

ASSEMBLY

CASE AND LEAD

ASSEMBLY

THERMAL

PELLET

DISCS

COMPRESSION

SPRING

COMPRESSION

SPRING

DISCS

STAR CONTACT

TRIP SPRING

FLOATING

CONTACT

FLOATING

CONTACT

CERAMIC

BUSHING

CERAMIC

BUSHING

ISOLATED LEAD

EPOXY

SEAL

EPOXY

SEAL

Grey area shows opened or

broken current path

Grey area shows

current path

Figure 2

136

MICROTEMP^®Thermal Cutoffs:

TYPES & SPECIFICATIONS

MICROTEMP^®thermal cutoffs are available in a range of temperatures and electrical ratings to

meet application requirements (see figure 3). There are five primary types of thermal cutoffs

available. Standard dimensions of each TCO series are shown in figure 4.

G4 Series

Rated for continuous operating currents up to 10 amps @ 250VAC (15 amps @ 120VAC), the G4

series MICROTEMP^®TCO is the industry standard for over-temperature protection. The G4 series is

applied to millions of appliances and personal care products each year, providing reliable back-up

protection for temperature controlling thermostats and other over-temperature conditions. The

G4 series is also widely applied in office machines, portable heaters and industrial equipment as a

thermal safeguard.

G5 Series

Designed for higher current applications, the G5 series MICROTEMP^®TCO is rated for operating

currents up to 16 amps @ 250VAC (20 amps @ 250VAC and 25 amps @ 120VAC at UL/CSA).

Similar in appearance to the G4 series, the G5 series has a different internal construction designed

for interrupting higher currents.

G6 Series

The G6 series MICROTEMP^®TCO can be utilized in applications where a higher maximum-overshoot

temperature rating is not required, yet it is rated for operating currents up to 16 amps @ 250VAC.

It is the same physical size as the G4, G5 and G8 series TCOs.

G7 Series

The G7 series MICROTEMP^®TCO is designed to satisfy applications requiring miniaturized components

that do not need maximum current interrupt capability. The G7 is just 2/3 the size of the G4 and

G5, and with a current interrupting capability of 5 amps @ 250VAC, it is capable of meeting the

requirements of transformers, motors, battery packs and electronic circuit applications.

G8 Series

Designed for very high-current applications such as major appliances and high-wattage electric

heat packages, the G8 series MICROTEMP^®TCO is rated for operating currents up to 25 amps @

250VAC. More economical than electromechanical bimetal-type one shot devices, it can be

utilized in applications where its small size is an advantage in terms of mounting (it’s the same

physical size as the G4, G5 and G6 series TCOs) and thermal response.

137

MICROTEMP^®TCO Operating Temperature Summary

Max.

Open

Temp

Holding

Temp

Maximum Overshoot Temperature

T_m°C T_m°C T_m°C

T

T_m°C

h

T °C

°C

G4 Series G5 Series G6 Series G7 Series G8 Series R9 Series R7 Series

f

072

077

084

093

098

104

110

117

121

128

144

152

167

184

192

216

229

240

47

52

59

68

73

79

85

92

96

103

119

127

142

159

167

191

200

100

125

140

150

160

175

210

375

175

200

215

225

235

250

285

350

375

100

125

—

140

150

—

160

175

—

210

—

175

200

215

225

235

250

—

285

350

—

375

100

125

140

150

160

175

210

375

—

125

140

—

140

150

175

200

—

125

140

—

140

150

175

200

—

T_M– Maximum overshoot

temperature: temperature

up to which TCO will not

change status

T_F– Functioning open

temperature

tolerance: +0, -5°C

T_H– Holding temperature:

Maximum continuous

exposure temperature

C.T.I. – Comparative tracking

index (all primary thermal

cutoffs): 250VAC

NOTE: G4, G5, G6,G7 and G8

series TCOs with T_F≥ 184°C

comply with UL conductive

heat aging (CHAT)

—

375

—

requirements.

Electrical Rating Summary

Maximum Overshoot Temperature

Agency

G4 Series

Resistive Inductive

G5 Series

Resistive

G6 Series

Resistive

G7 Series

Resistive Inductive

G8 Series

Resistive

R9 Series

Resistive

R7 Series

Resistive

10A/250VAC 8A/250VAC 16A/250VAC

15A/120VAC 14A/120VAC 25A/120VAC

21A/240VAC

5A/250VAC 4.5A/250VAC

5A/24VDC 4.5A/120VAC

UL/CSA

IEC

16A/250VAC

25A/250VAC

—

10A/250VAC 8A/250VAC

15A/120VAC 14A/120VAC

4.5A/250VAC

4.5A/120VAC

16A/250VAC 16A/250VAC 5A/250VAC

25A/250VAC

—

5A/250VAC

15A/250VAC 15A/250VAC

5A/24VDC

7A/250VAC

7A/24VDC

METI 10A/250VAC

—

15A/250VAC

Figure 3

MICROTEMP^®TCO

Standard Dimensions

`

Dimensions – Inches (millimeters)

G4, G5, G6 & G8 Series

G7 Series

A

B

C

Overall Length .12 ( 3.0)

Epoxy Lead Length (Reference)

Case Lead Length .06 ( 1.5)

2.51 (63.8)

0.55 (14.0)

1.38 (34.9)

N/A

Standard

Leads

A

B

C

Overall Length .12 ( 3.0)

Epoxy Lead Length (Reference)

Case Lead Length .06 ( 1.5)

3.26 (82.8)

1.30 (33.0)

1.38 (34.9)

3.26 (82.8)

1.50 (38.1)

1.38 (34.9)

Long Leads

D

E

Case Lead Diameter

Case Lead Material

Epoxy Lead Diameter

Epoxy Lead Material

.040 (1.0)

Tin-Plated Copper

.040 (1.0)

.023 (.57)

Tin-Plated Copper

.023 (.57)

Lead Material

and Diameter

E

Silver-Plated Copper

Case

Dimensions

F

G

Case Length (Reference)

Case Diameter (Reference)

.58 (14.7)

.158 (4.0)

.38 (9.6)

.118 (3.0)

Figure 4

138

Packaged Thermal Cutoffs

Therm-O-Disc also offers a variety of packaging options for MICROTEMP^®thermal cutoffs.

Therm-O-Disc offers two standard packages with wide application in the HVAC industry. Primarily

designed for heating applications, the GXAM04 and GXAM06 packages mount a standard G4 or

G5 TCO in a high temperature ceramic base (see figure 5).

The popular GXAP Potted TCO packages consist of a TCO epoxy-potted into a plastic insulating

mounting case. The assembly can be supplied with various case materials, shapes and terminations.

They can be used to accurately sense temperature as probes and as surface, airstream and ambient

sensors (see figure 6). They can be easily replaced in the field without disturbing the rest of the circuit.

Custom packages, insulations or special assemblies may be specified to meet specific unique

application needs. By taking advantage of our technical expertise and high volume production

methods and equipment, we can provide significant savings on custom packages.

Packaged TCO Material Specifications

Type

Base Material

Material Rating

Temperature °C

Maximum TCO

Temperature °C

GXAP01

GXAP02

GXAP04

GXAP05

GXAP08

GXAP10

GXAP12

GXAM04

GXAM06

Valox DR48

Ryton R-4

120

220

120

220

120

>250

128

152

128

184

128

240

Valox DR48

Ryton R-7

Valox DR48

Ceramic DIN VDE 0335, C 221

GXAM06

GXAP04

GXAP02

GXAM04

Figure 5

GXAP12

GXAP08

GXAP05

Figure 6

139

Lead Configurations

The MICROTEMP^®TCO can be furnished with virtually any lead configuration specified for an

application. Lead curls are available to match most sizes of screws along with varying lead lengths

and lead forms.

All types of terminations, such as quick connects, ring terminals and blade terminals, are available

at additional cost. In addition, tape and reel packaging can be specified to meet high volume

requirements.

Temperature Ratings

MICROTEMP^®thermal cutoffs are available in a wide range of opening temperatures, providing

designers a high degree of flexibility (see figure 3). Determining the correct TCO temperature

calibration requires significant application testing.

The proper calibration will be affected by application variables such as I²R self heating of the TCO,

heat transfer through insulation and heat dissipation due to heat sinking and air flow.

Thermocoupled “dummy” TCOs, that match the physical and electrical characteristics of a

functional TCO, are available to help evaluate application specific variables.

For more information on testing and installing MICROTEMP^®TCOs, please review the

MICROTEMP^®thermal cutoff technical information section beginning on page 143.

Direct Current (DC) Applications

MICROTEMP^®thermal cutoffs do not have published electrical ratings for direct current (DC)

applications. Current interruption capacity in DC circuits is highly application sensitive.

Therm-O-Disc recommends thorough testing of DC electrical applications using the testing

guidelines in Therm-O-Disc’s MICROTEMP^®thermal cutoff technical information section.

Samples and Quotations

MICROTEMP^®TCO samples and thermocoupled “dummies” are readily available for determining

the correct response and desired performance in an application. For more information on

MICROTEMP^®TCOs, call a Therm-O-Disc sales engineer at 419-525-8300.

140

Lead Cutting

Minimum Dimensions

Inches (millimeters)

DIM. A

DIM. C

DIM. B

` Dimension A

Dimension B

Dimension C

0.95 (24.2)

0.22 (5.6)

0.73 (18.6)

Tape and Reel Packaging

Dimensions – Inches (millimeters)

`

Item

Dim. A

Dim. B

Dim. C

Dim. D

Dim. E

Dim. F

GXAA0900TTTC

G7FA0900TTTC

1.66 (42.1)

2.80 (71.1)

1.38 (35.1)

3.26 (82.8)

3.60 (91.4)

0.200 (5.1)

0.197 (5.0)

0.031(0.8)

F

DIM. E

0.060(1.5)

F

REF.

Ø 1.25(3.2)

REF.

Ø 0.551(14.0)

DIM. A

DIM. D

TAPING CORRUGATION

THIS SIDE

DIM. B

DIM. C

SPOOL ROTATION

REF.

Ø 0.026(0.7)

DIM. F

(PITCH MEASURED AT TAPE ON MICROTEMP SIDE)

NOT TO SCALE

TCO ORIENTATION

141

Product Nomenclature

MICROTEMP^®TCO

G

Z X XX TTTC

TTTC – Maximum

open temperature in °C

G – Rating type

(G – Global, Y – Non Agency, R – Regional)

XX – Modification of basic TCO

(Plating, lead material,

lead length, stenciling)

Z – Internal construction

X – Case material and lead wire

(A, C, D, E, F)

(4, 5, 6, 7, 8, 9)

MICROTEMP^®TCO Packages

G

Z

X

X XX RR TTTC

TTTC – Maximum

open temperature in °C

G – Rating type

(G – Global, Y-Non Agency)

RR – Assembly modifications

(Plating, terminal bend, stenciling)

Z – Internal construction

XX – Specific package construction

(00-99)

(4, 5, 6, 7, 8, 9)

X – Case material and lead wire

X – General packages TCO type

(Configuration, potted, mounting base, etc.)

(A, C, D, F)

Figure 7

As shown in figure 7, Therm-O-Disc MICROTEMP^®TCOs follow a consistent product nomenclature that identifies the

basic product type, lead wire size, special features and packaging options. For example, a standard G4 series TCO

calibrated to open at 192°C would have a part number G4A00192C.

MICROTEMP^®TCO Product Markings

Primary TCOs

Secondary Packages

XXXXXXXX

Special customer identification

XXXXXXXXX

Special customer identification

(when required, up to 9 characters)

MICROTEMP^®

P ZZZZZ

Registered trademark

MICROTEMP^®

Registered trademark

(may be T-O-D)

(P) Manufacturing plant;

(ZZZZZ) Date code

G Z X X XX RR

T_FTTTC P ZZ

Part number (see figure 7)

G Z X XX

T_FTTTC

Part number (see figure 7)

(T_FTTTC) Maximum open temperature °C;

(

) Underwriters Labs logo;

(P) Manufacturing plant location;

(ZZ) Manufacture date code;

(T_FTTTC) Maximum open

temperature °C

(

) Underwriters Labs logo

142

MICROTEMP^®Thermal Cutoffs:

TECHNICAL DATA

MICROTEMP^®thermal cutoffs, available in a variety of standard and custom configurations, pro-

vide reliable one-shot, over-temperature protection in a wide range of applications. Performance

can be affected by installation method and proper location of the thermal cutoff. Both application

and installation are important in the overall performance of the product, and thorough testing is

necessary for both AC and DC applications. The following guidelines will answer most questions

concerning these two subjects.

Application of Thermal Cutoffs

A thermal measurement procedure that utilizes a “dummy” thermal cutoff can assist in determining

the appropriate calibration temperature and design location of MICROTEMP^®thermal cutoffs. The

dummy matches the electrical characteristics of the thermal cutoff but does not have thermally

responsive parts. The dummy is supplied with a thermocouple attached to the case of the thermal

cutoff (see figure 8).

Figure 8

View of required thermocouple attachment before soldering

Dummy cutoffs can be supplied with Type J, Type T or Type K thermocouples. Other thermocouple

types can usually be supplied upon request at a nominal charge.

Location

Sufficient time and effort must be used to determine the proper and most desirable location for a

thermal cutoff. The employment of infrared thermography, or a sufficient number of thermocouples

to identify the highest temperature areas in the product requiring protection during fault conditions,

should be considered.

143

Calibration Temperature

It is necessary to select a thermal cutoff rating above the maximum temperature experienced during

normal operation, including expected short-term temperature overshoots. The temperatures

experienced by the thermal cutoff during normal operation will determine the life expectancy for

the thermal cutoff. If the thermal cutoff rating is too close to the temperature experienced during

normal operation (including overshoot temperatures after opening of a thermostat, etc.), the

probability of a nuisance trip increases.

Nuisance trips are caused by pellet shrinkage due to repeated operation at temperatures near but

below calibration temperature, or excessive thermal gradients across the case of the TCO and its

leads (see “Thermal Gradients”). More information on nuisance tripping due to pellet aging is

available in U.L. Standard 1020, under the section on Thermal Element Stability Test. Therm-O-Disc

has compiled standard life curves by subjecting MICROTEMP^®thermal cutoffs to very controlled

temperatures for extended time periods under ideal laboratory conditions. Therefore, these

standard life curves should be used only as a guideline.

Comparison of measured temperatures to MICROTEMP^®thermal cutoff standard life curves should

not replace customer life testing using functional thermal cutoffs for the particular application.

The design engineer must make the trade-off between response and life of the TCO based on

product requirements. It is important to remember that temperatures experienced in actual

application will vary from unit to unit.

Test Procedure

Install the dummy cutoff in the electrical circuit to be opened in the event of a fault condition.

Position it in the area that has been selected to be protected within the product based on prior

determinations of the maximum permissible temperatures to be allowed. The dummy cutoff

should be installed using the same mounting and electrical connection that will be used for

functional TCOs in production. Connect the thermocouple leads to a digital temperature

measuring device to record temperatures. The product to be protected can now be operated,

and the normal operating temperature monitored. Note that the thermal cutoff dummy is not a

functional TCO and therefore will not open the circuit in the test setup.

144

TEMPERATURE OR VOLTAGE MEASURING DEVICE

THERMOCOUPLE

CONNECTNG CONDUIT WIRE

THERMAL CUTOFF "DUMMY"

TERMINAL OR SPLICE

ELECTRICAL INSULATOR

Figure 9

Figure 9 illustrates a typical installation of a thermocoupled cutoff. Note that the body of the thermal

cutoff is at the same potential as the connecting circuit; therefore, it must be electrically isolated

from the surface against which the cutoff is mounted. Also note that the thermocouple wire is at

the same potential as the connecting circuit.

CAUTION . . . To avoid a false reading of the unit under test, thermocouple wires must not make

contact with each other except at the temperature sensing junction.

CAUTION . . . Ensure that the thermocouple wire insulation will provide isolation against short-

circuiting and shock hazards.

CAUTION . . . The terminal of the temperature measuring instrument, to which the thermocouple

is attached, will be at the same potential as the connecting circuit wire. This instrument must be

electrically isolated and considerable caution must be exercised in its use, since one of the

thermocouple terminals is frequently grounded to the instrument chassis.

Before using measuring equipment powered directly from standard line voltages, check operation

manuals. Be sure line voltages impressed on the thermocouple wires by the dummy cutoffs will

not cause damage to the instrument.

The more closely the actual operating and ambient conditions can be simulated during test, the

more valid the test results will be. These tests are necessary to empirically include the variable

factors that need to be considered to select the properly rated thermal cutoffs. These factors

include, but are not limited to, the heating effect of the current through the cutoff, adjoining

145

terminals and leads, heating or cooling effect of the terminals and external leads, rate of

temperature rise, air flow, shock, vibration and other environmental and operating conditions

unique to the application.

The product and application being tested will determine the number of cycles that must be run to

determine the maximum “normal” operating temperature. “Overshoot” temperatures should be

included in the determination of the maximum “normal” operating temperature. The overshoot

temperature is often considerably higher than the temperature reached at the moment the

thermostat opens. The conclusion of these tests will provide the maximum “normal” operating

temperature at the thermal cutoff (at maximum anticipated voltage, ambient temperature, etc).

The overshoot temperature seen by the thermal cutoff after the thermal cutoff opens in the

application must also be carefully examined.

Manufacturing tolerances and variations should be carefully considered, and a sufficient number

of units evaluated, to provide a statistical basis on which to determine the operating overshoot

temperatures.

After obtaining the above information, test the product under fault conditions and monitor to

determine that desired fault condition temperatures are not exceeded.

Where there are a variety of fault conditions, (e.g., short-circuited thermostats and transformer

secondaries, locked motor rotors and solenoids, high ambient temperatures, restricted or

blocked airflow, etc.), consideration should be given to multiple fault conditions which could

occur simultaneously during the lifetime of the product, and to faults which may cause localized

overheating in areas away from the TCO.

When the fault conditions have been set up, note the temperature of the dummy cutoff when the

maximum desired temperature limit is reached. At this point the circuit is manually interrupted.

This test should be run several times, in several different units. In some applications, it will not be

possible to “save” the tested item from damage, but only prevent the product from creating an

external fire or electrical hazard. Damaged products should not be retested, since the results may

not be the same as with undamaged units. The MICROTEMP^®thermal cutoff ratings selected

should be equal to or less than the temperature recorded at the dummy thermal cutoffs at the

time the maximum desired temperature is reached.

CAUTION . . . Excessive overshoot temperatures after the opening of the thermal cutoff may cause

dielectric breakdown of the thermal cutoff and allow reconduction to occur. Functional thermal

cutoffs should be tested to verify proper operation of the thermal cutoffs in the application (see

figure 3).

146

Substitute actual thermal cutoffs in a sufficient number of finished products and re-run the

tests to obtain statistical verification of the results. For multiple TCO applications, test functional

thermal cutoffs under fault conditions so that the product overheats and each thermal cutoff is

independently called upon to interrupt the flow of current. Each thermal cutoff should open the

circuit independently of any other over-temperature limit controls, with product damage not

exceeding an acceptable level. This test should be run using the maximum voltage and current;

the thermal cutoff will be expected to interrupt and hold open.

Installation of Thermal Cutoffs

The performance of a MICROTEMP^®thermal cutoff can be affected by installation methods such

as soldering, welding, splicing, lead bending, insulation, clamping and mounting. Certain precautions

should be taken during installation to ensure that the MICROTEMP^®thermal cutoff is not damaged,

which may cause it to not operate in its intended manner. Likewise, care should be taken during

installation to ensure that the TCO in every unit experiences the expected temperature range

environment previously determined during the calibration temperature selection. The following

guidelines should be used to minimize undesirable conditions that can result from improper

installation practices.

Soldering Leads

Thermal cutoff leads should be heat sinked during the soldering operation (see figure 10). If

excessive heat is conducted by the leads into the thermal cutoff, it can shorten the life of the TCO.

In addition, excessive lead temperatures can damage the epoxy and possibly result in the TCO

failing to open. More heat sinking is necessary for thermal cutoffs with low temperature ratings.

HEAT SINK HERE

SOLDER

Figure 10

147

Test samples should be x-rayed before and after the soldering operation. The size of the chemical

pellet should be measured with an optical comparator or a toolmaker’s microscope to verify that

no shrinkage has occurred during the soldering operation (see figure 11). The epoxy seal should

retain its size and shape and not discolor. If the chemical pellet or the epoxy have changed size as

a result of the soldering operation more heat sinking is required.

BARREL

SPRING

EPOXY SEAL

THERMAL PELLET

ISOLATED

LEAD

CASE &

LEAD ASSEMBLY

TRIP

SPRING

Figure 11

Welding Leads

The thermal cutoff leads may also need to be heat sinked during a welding operation (see figure

12). The same precautions and tests described in the soldering section should also be followed for

welded leads.

HEAT SINK HERE

WELD POINTS

Figure 12

To avoid damaging or welding internal parts, care should be taken that none of the welding current

is conducted through the TCO. A welding current of hundreds of amperes can weld the internal

parts together, resulting in the TCO failing to open.

TCO leads must be supported during the weld operation to prevent breaking the thermal cutoff

epoxy seal.

148

Splices & Terminals

Insecure splices and terminations may produce high resistance junctions which can cause self

heating (I²R) as power is dissipated across these junctions during product operation.

Heat from these hot spots can flow down the thermal cutoff leads and increase the temperature

of the thermal cutoff (see figure 13). Nuisance openings of the thermal cutoffs or degradation of

the epoxy seal can occur as a result of the heat generated by high resistance junctions. The splice

or termination junction may initially measure low resistance, but can change to a much higher

resistance after several temperature cycles. It is generally better to splice MICROTEMP^®thermal

cutoff leads to stranded lead wires rather than solid wires as the stranded wire may be crimped

tighter and maintain better electrical contact during temperature cycling.

NUT

SPLICE

HEAT FLOW

LOCK

WASHER

SPLICE

BOLT

TERMINATION

Figure 13

The temperature capabilities of the splice and/or termination should be considered. For example,

solder back-up should be considered for splices of terminations in applications cycled at temperatures

exceeding 150°C.

Bending Leads

When configuring leads, special care must be exercised in supporting the leads at each end near

the body of the thermal cutoff so that the case will not be distorted or the epoxy will not be

cracked or broken. At least 0.125” (3mm) should be maintained between the epoxy seal and any

lead bends (see figure 14).

149

.70 MIN. (17.8 mm)

.09 MIN.

(2.3 mm)

.04 MIN. RAD.

(1.0 mm)

Figure 14

Dimensions are shown in inches (millimeters).

Thermal Gradients

Ideal TCO placement subjects the entire TCO case, leads, epoxy seal and internal components to a

uniform temperature environment.

Care should be exercised in the placement of the TCO to minimize thermal gradients across the

TCO body. In certain applications, the TCO can be mounted in a position where heat is conducted

to the body of the TCO through one of the leads, resulting in thermal gradients across the TCO.

Over time, the TCO life can be reduced by thermal gradients if the isolated (epoxy) lead is at a

consistently lower temperature than the case lead. Long term testing is recommended in

determining whether these conditions exist in the application.

To minimize the effects of thermal gradients and the temperature increase of the TCO body from

this heat flow, attach the isolated (epoxy) lead, rather than the case lead, to the heat source.

TCO dummies can be supplied with thermocouples on both ends to facilitate gradient evaluations.

Temperature Limits

The temperatures experienced during normal operation, including expected temperature overshoots,

will determine the life expectancy of the TCO. Nuisance trips can result if the thermal cutoff rating

is too close to the temperatures experienced during normal operation. Thermal cutoffs of any

temperature rating should not be subjected to continuous normal temperatures in excess of

200°C. Additionally, overshoot temperatures after the opening of the thermal cutoff should be

minimized to avoid dielectric breakdown and reconduction of the thermal cutoff.

150

CAUTION . . . The thermal cutoff may fail to open the electrical circuit under certain conditions.

Distortion of the case, breaking or cracking the seal, exposing the epoxy seal to cleaning solvents,

compression of the leads and current surges that exceed the operating specifications of the thermal

cutoff may cause the thermal cutoff not to open. In addition, pellet shrinkage due to thermal

aging under some circumstances may also result in failure to open. Finally, a very low rate of

temperature rise may produce conditions that may also result in failure to open. Care must be

taken to avoid any mishandling or misapplication of the thermal cutoff.

CAUTION . . . Although TCOs are highly reliable devices, a TCO may fail to open in operation for

one or more of the reasons set forth above. These conditions must be taken into account by the

product design engineer in determining the level of reliability needed for the application. If failure

of the TCO to open could result in personal injury or property damage, the product design engineer

may want to consider using one or more redundant TCOs of different ratings to achieve the

desired level of reliability. A number of consumer product design engineers have incorporated

redundant TCOs of different ratings in their designs for this reason.

Definition of Terms

f

F

Maximum Open Temperature or Rated Functioning Temperature (T , T ):

The maximum temperature at which the thermal cutoff changes its state of conductivity to open

circuit with detection current as the only load. The rated functioning temperature is measured

during a temperature rise of approximately 0.5°C per minute.

h

H

Holding Temperature (T , T ):

The maximum temperature at which, when applying the rated current to the thermal cutoff, the

state of conductivity will not change during a period of one week.

m

M

Maximum Overshoot Temperature or Maximum Temperature Limit (T , T ):

The maximum temperature at which the thermal cutoff, having changed its state of conductivity,

can be maintained for a specified period of time, during which its mechanical and electrical

properties will not be impaired.

Rated Voltage:

The maximum voltage that can be applied to the circuit in which the thermal cutoff is used.

Rated Current:

The maximum current that the thermal cutoff is rated to interrupt at the rated voltage.

151

Agency Recognition

MICROTEMP^®thermal cutoffs are recognized by the following major agencies:

PS

E

UL

BEAB

METI

CSA

VDE

Underwriters

Laboratories Inc.

(USA)

British

Electrotechnical

Approvals Board

Ministry of

Economy, Trade

and Industry of

Japan

Canadian

Standards Association

Varband

Deutscher

Electrotechniker e.V.

(F. R. G.)

MICROTEMP^®thermal cutoffs are recognized by the major approval agencies throughout the world

for AC circuit applications (they do not have recognition for DC circuit applications). These agency

electrical ratings can be used as a guideline when evaluating specific thermal cutoff applications.

However, the electrical and thermal conditions to which the thermal cutoff may be exposed in an

application may differ significantly from agency test conditions. Accordingly, customers should

not rely solely on agency ratings but rather must perform adequate testing on the particular

application to confirm that the TCO selected is appropriate for that application and will operate as

intended.

Important Notice

Users must determine the suitability of the control for their application, including the level of

reliability required, and are solely responsible for the function of the end-use product.

These controls contain exposed electrical components and are not intended to withstand

exposure to water or other environmental contaminants which can compromise insulating

components. Such exposure may result in insulation breakdown and accompanying localized

electrical heating.

A control may remain permanently closed or open as a result of exposure to excessive mechanical,

electrical, thermal or environmental conditions or at normal end-of-life. If failure of the control to

operate could result in personal injury or property damage, the user should incorporate supplemental

system control features to achieve the desired level of reliability and safety. For example, backup

controls have been incorporated in a number of applications for this reason.

152


型号：	GXAM06
厂家：	ETC
描述：	MICROTEMP Thermal Cutoffs INTRODUCTION
文件：	总22页 (文件大小：515K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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