automation and drives simirel overview thermocouples resistance sensors selection criteria...

Automation and Drives

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Overview

Thermocouples

Resistance Sensors

Selection Criteria

Controlling

Controlling & Monitoring

Product Overview

92 Definitions

Temperature Monitoring Guidelines

for

SIMIRELSIMIREL3RS10/3RS113RS10/3RS11

SIMIREL: Relays for All Applications

Overview


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92 Definitions

Temperature:

One of the most important industrial measurements.

Physically speaking, heat is a means to measure the energy within a body. Such energy is stored in the disordered molecular and atomic movements of a body and increases with a simultaneous increase in temperature.The unit of measurement for temperature is Kelvin [K]. At 0°K (-273.5°C), all molecules within a body are at rest, i.e. its heat capacity is zero. The measurement of absolute temperature is generally stated in [°C] and temperature differences are stated in [K].

Thus, with many applications, temperature monitoring equals the (energy) monitoring of materials and system components.

Overview: The Definition of Temperature

Overview


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92 Definitions

Sensors:

Thermocouples: Two interconnected metals which deliver a thermoelectric voltage independent of the ambient temperature. This voltage is a direct means of measurement for the difference between the measuring junction temperature T1 and the reference junction temperature T2.

Resistance sensors: These sensors change their resistance independent of the ambient temperature. They are generally made of platinum wire which is either fixed to a ceramic mould body (thin-film resistor) or is coiled onto a support within an oversheath. Resistance sensors are available as PTC resistors or as NTC resistors.

Sensors for electrical temperature monitoring can be divided into:

Overview: The Most Important Sensors

Overview


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Resistance Sensors

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92 Definitions

Thermocouples

Mode of Operation

Overview

Reference JunctionCompensation

Application Areas

Colour Codes

Thermocouples


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92 Definitions

The thermoelectric effect is the generation of an electromotive force (EMF) by ways of a temperature difference between the two connection junctions of two different metals which are part of a joint electric circuit.

A thermocouple generates a thermoelectric voltage independent of the used materials and the temperature difference between the measuring point and the reference junction.

No absolute temperatures can be measured with thermocouples.

The measuring point is the point at which the two metals are soldered, welded or twisted.

The reference junction is the point at which the two different conductors are connected to a further metal (e.g. copper).

T1

NiCr

NiMeasuring point

Umeas

Reference junction

T2

Umeas = Uth T1 - Uth T2

The Seebeck Effect: Thermoelectric Effect Regarding Thermoelectric Couples

Thermocouples


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92 Definitions

A “mere” temperature difference measurement between the measuring point and the reference junction can be carried out with the help of the thermoelectric effect.

To be able to evaluate the absolute temperature at the measuring junction, the ambient temperature of the reference junction must be established and added (e.g. with the help of a PT100).

Tabs= T1 (from Umeas = Uth T1 - Uth T2 ) + T2 (from RPT100 )

T1

NiCr

NiMeasuring point

Internalreference junction

T2

PT100

All SIMIREL 3RS11 monitoring relays for thermocouples are already equipped with an internal reference junction compensation.

Thus, the ambient temperature of the evaluation device need not be taken into account.

A length extension of the thermoconductors is only permissible with the use of suitable conductors.

Measuring Absolute Temperatures with the Help of “Reference Junction Compensation”

Thermocouples


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92 Definitions

DIN EN 60584-2 (1994), IEC 584-2 (1992)

K

T

J

N

E

Element/ alloy

Voltage changes per °C in µV

at °C: Properties / Notes

100 500 1000

Applicationtemperatures

Long-termShort-term

Nickel-Chrome / Nickel-

Aluminium

Copper / Copper-Nickel

Iron / Copper-Nickel

Nickel-Chrome-Silicium /

Nickel-Silicium

Nickel-Chrome / Copper-Nickel

42

46

54

30

68

43

-

56

38

81

39

-

59

39

-

0°C up to 1100°C

-185°C up to 300°C

20°C up to 700°C

0°C up to 1100°C

0°C up to 800°C

-180°C up to 1350°C

-250°C up to 400°C

-180°C up to 750°C

-270°C up to 1300°C

-40°C up to 900°C

• The most commonly used thermocouple

• For oxidising atmospheres with a large application temperature range

• Large hysteresis

• Rarely used• For low application temperatures • Good properties concerning high humidity

• Commonly used in the plastics industry• Also used with exposed measuring junctions in reduced atmospheres• Corrodes with low temperatures, oxidises with high temperatures

• (Still) rarely used• Extremely stable output signal• High resistance against temperature change strains

• Largest thermoelectric voltage per °C• Also used with exposed measuring junctions within a vacuum or slightly oxidising atmospheres

Overview:Thermocouples

Thermocouples


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92 Definitions

Max. temperature of the conducting

wires

Temperature range of

performanceProperties / Notes

DIN 43722 (1994), IEC 584-3 (1989)

KThermo-conductor KX

Extension conductor KCB

T Thermo-conductor TX

J Thermo-conductor JX

NThermo-conductor NX

Extension conductor NC

E Thermo-conductor EX

900°C

900°C

300°C

500°C

900°C

900°C

500°C

-25°C up to +200°C

0°C up to +100°C

-25°C up to +200°C

-25°C up to +200°C

-25°C up to +200°C

0°C up to +150°C

-25°C up to +200°C

The extension wire is made of the same material as the thermoelectric couple, i.e. thermal faults are minimized.

Cost-favorable alternative for applications within these temperature limits (Copper - Copper/Nickel).

The extension wire is made of the same material as the Thermocouple. Extension wire is not accounted for (cost-favorable).

The extension wire is made of the same material as the Thermocouple. Extension conductors are not accounted for (cost-favorable).

The extension wire is made of the same material as the thermocouple.

Extension wires are not normally used. The accuracy advantage of this thermocouples would be lost.

The extension wire is made of the same material as the thermocouple. Extension conductors are not accounted for.

International identification letters

Application Areas of Thermocouple and Extension- Wires

Thermocouples


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Color Codes for Thermocouples and Extension Wires

KThermo-wire KX

Equalising- wire KCB

T Thermo-wire TX

J Thermo-wire JX

NThermo-wire NX

Equalising- wire NC

E Thermo-wire EX

German and international color codes

Intern. color codes for intrinsically safe

electric circuitsUnited States

DIN 43722 (1994), IEC 584-3 (1989) ANSI MC96.1

International identification letters

+ -

+ -

+ -

+ -

+ -

+ -

+ -

+ -

+ -

+ -

+ -

+ -

+ -

+ -

+ -

+ -

+ -

Green Green

Green Green

Brown Brown

BlackBlack

Pink Pink

Pink Pink

Purple Purple

BlueGreen

BlueGreen

BlueBrown

BlueBlack

Blue Pink

Blue Pink

Blue Purple

Brown Yel

BrownBlue

Brown White

Thermocouples

+ -

Brown Purple

Red

Red

Red

Red


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92 Definitions

Resistance Thermometers

Color Codes

Connection Methods

2-Conductor Method

3-Conductor Method

Resistance Sensors


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92 Definitions

Color Codes of Resistance Thermometers

RT

Red

White

RT

Red

White

Red

RT

Red

White

Red

WhiteRT

Blue

White

Blue

Red

In general, four different connection methods for resistance thermometers are possible:

2-conductor circuit 3-conductor circuit 4-conductor circuit4-conductor circuit

with blind loop

In accordance with DIN 60751 (1996) and IEC751 (1983)

Resistance Sensors


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Overview of the Connection Methods for Resistance Sensors

Conductor resistance and sensor resistance are added together

Systematic fault(dependent of:conductor length, conductor cross section and conductive material)

I

PT 100

I

U

RL

RL

2-conductor measuring 3-conductor measuring 4-conductor measuring

I

PT 100

I

U

RL

RL

RL

I

PT 100

I

U

RL

RL

RL

RL

State of the art solution

Conductor resistance is not included in the measurement

Precondition:All conductors have the same resistance

Decreasing use

Conductor resistance is not included in the measurement

Conductors may have a differing resistance

Resistance Sensors


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Two-Conductor Method for Resistance Sensors

Example: Classical Wheatstone-bridge with the two voltage dividers R1 and RT as well as R2 and R3 .

Precondition: The conductor resistance values RL are negligible.

For R1 / RT = R2 / R3 it is assumed that: UB = 0

The bridge is assumed to be balanced when : UB = 0. If the resistance RT changes, the measuring voltage UB changes proportionally.

Advantage of the Wheatstone-bridge: The value of the supply voltage is not included in the measurement.

Uv

R1 R2

R3

RT

UB

IT

IR

I

RL

RL

Resistance Sensors


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92 Definitions

Three-Conductor Method for Resistance Sensors

Example: Classical Wheatstone-bridge with three-conductor circuit and the two voltage dividers R1 and RT as well as R2 and R3, each of which also comprises the conductor resistance RL.

Precondition: All conductor resistance RL values are equally high.

Uv

R1 R2

R3

RT

UBRL

RL

RL

IT

IR

I

For R1= R2 and the balanced bridge it is assumed that: UB= 0 and IT= IR

Advantages: The value of the supply voltage is not included in the

measurement.The conductor resistance has no influence on UB as each of

the two voltage dividers comprise a conductor resistance RL.

Resistance Sensors


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92 Definitions

Selection Criteria for Thermocouples and Resistance Thermometers

Properties in Comparison

Types of Construction

Application Areas

Characteristic Curves

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Properties of Thermoelectric Cells and Resistance Thermometers

Accuracy Good Very good

Application Areas Large temperature range Small temperature range

Price Cost-favorable More expensive

Measuring Point Small, point-shapedCovering the length of the

measuring resistance

Response Times Very short Relatively long

Reference Junction Required Not required

Surface Measurement Very good suitability Limited suitability

Vibration Resistance Very robust Limited suitability

Supply of Measuring Current

Not required Required

Spontaneous Heating Does not occur Insignificant fault occurrence

Long-Term Stability Satisfactory Excellent

Robustness Very good Good

Connection Lines Special materials Standard cables

Thermocouples Resistance Sensors

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Selection of Some Types of Construction of Temperature Sensors

Sheathed thermocouples(bendable)

Angular thermocouples

Resistancethermometer

Thermocouples

Embedded resistance thermometer

Wire-coiledPT100

Foil thermocouples

Sheathed resistancethermometer

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92 Definitions

Application Areas of Thermocouples and Resistance Thermometers

Co

oli

ng

an

d

ve

nti

lati

on

te

ch

no

log

y

Am

bie

nt

tem

pe

ratu

res

Bo

ile

r p

lan

ts

So

lid

bo

die

s

(e.g

. fi

lm s

ea

lin

g

jaw

s)

Ex

ha

us

t te

mp

era

ture

s

En

am

el

an

dc

era

mic

te

mp

eri

ng

fu

rna

ce

s

Me

tal

we

ldin

g,

sa

lt b

ath

s

Co

mb

us

tio

n

ch

am

be

r m

on

ito

rin

g

Resistance thermometers

Sheathed resistance thermometers (bendable)

Thermo-couples

Sheathed thermo-couples(bendable)

Angular thermo-couples

X X X X X

X X X X

X X X X

X X X X X

X

Temperature

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0 250 500 750

1000

R []

2000

3000

4000

20

U [mV]

40

60

80

T [°C]

NTC

PT100

PT1000

Type E

Type J

Type K

Characteristic Curves of Some Thermocouples and Resistance Thermometers

Conversion of °C to °F: °C = (°F-32)/1.8 °F = 1.8°C+32

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Controlling

The Control Circuit

2-Position Controllers

3-Position Controllers

PID Controllers with Clocking Output

PID Controllers with Analogue Output

Controllers with Integrated Automatic Adjustment

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The Control Circuit

Controlling means:A constant comparison between the measured and required value and, in cases of deviations, the necessary correction of such deviation with the help of the final controlling element.

The control circuit serves the adjustment of a pre-specified measurement to the desired value and the limitation of such realised value within a reasonable tolerance range.

Controlling

Final controlling element(heating)

Measuring device

(sensor)

Control path(system)

Intensifier(SC-contactor)

Control Circuit

Setpoint value

Disturbance variables

ZControl point

Measuring junction

Referencejunction

Setpoint value adjusterreference input element

(SPC)


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Two-Position Controller with Hysteresis, Shown in a “Heating” Application

When the TSetpoint temperature is attained, the two-position controller switches off the heating. As soon as the temperature has attained the hysteresis value, the heating is switched back on again.

Examples: Heating chambers for stress tests of electronic modules Water heating within instantaneous water heaters, pipe heat tracings

for frost protection, ... Can analogously also be used for cooling applications, e.g. with cooling and

air-conditioning systems, switchgear cabinets, water-cooled operating mechanisms and lasers, ...

Hysteresis range

TMax

t Start t 0

TMax = Maximum attainable temperature;

limited by the heating power

TSetpoint = Switch-off temperature

t Start = Preheating time

t 0 = Controlling clocking time

t

TSetpoint e.g. 80°C

Hysteresisvalue

Controlling


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Example of a 2-Position Controller with Hysteresis: Frost Protection with Pipe Heat Tracings

The two-position controller switches on the pipe heat tracing at 5°C. As soon as the temperature has reached the hysteresis value of 7°C, the pipe heat tracing is switched back off again.

S1

11

K1

L1

L2 H1

12

A2NSB01333b

A1

T1

T2

T3

K1

1113

1412

A3

Switch-on value

Hysteresis value

Advantages of Simirel 3RS1010-1CD00: Cost-favorable solution Simple construction, easy setting Can also be used for cooling applications, e.g. with cooling and air-

conditioning systems, switchgear cabinets, water-cooled operating mechanisms and lasers, ...

(Illustration with appliedsupply voltage, temperaturelies above the threshold value)

Controlling


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TMax = Maximum attainable temperature;

limited by the heating power

TSetpoint = Switch-off temperature of the

second heating

T1 = Switch-off temperature of the

first heating

t Start = Preheating time

t 0 = Controlling clocking time

TMax

t

Hysteresis range

Hysteresis range

TSetpoint e.g. 130°C

T1 e.g. 110°C

t Start t 0

3-Position Controller with Two Filament Windings and Hysteresis, Shown in a “Heating” ApplicationThe three-position controller switches the first heating off when the temperature T1 is attained and the second heating when the temperature TSetpoint is attained.

(TSetpoint approx. 50 % of TMax (two heatings) and approx. 90 % of TMax (one heating).)

Advantage: Short preheating time and long

clocking time with few switching cycles and little current variations

Example: Heat treatment ovens for

metal processing Decompression furnaces

Controlling


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Example of a 3-Position Controller with Hysteresis:Temperature Controlling in Heat Treatment Ovens

Solution with SIMIREL 3RS1040/3RS1140 :

In contrast to the classical two-position controller with only one filament winding, this principle both works with a heating power whose power only generates slow temperature changes in a stationary process state as well as with a second, stronger filament winding which is able to generate fast heating processes. After the preheating phase, i.e. after the process temperature has been attained, the second filament winding may be switched off. The controller will only switch the second heating back on again if the first off-switching temperature is undershot, e.g. when opening the oven door. During normal operation, merely the poorer performing heating is switched on in accordance with the heating requirements.

Advantages and special characteristics:

- The preheating phase is significantly shortened. -Current and temperature fluctuations are kept insignificant during the entire course of operation. - The switching frequency is reduced as the heating power can be adjusted to the process requirements relatively accurately.

Temperature control of two filament windings within a heat treatment oven with the help of a three-position controller.

Required task: Mode of Operation:

Wiring diagram of 3RS1040:

S1

16 18

15

K15

33

34

H33

L1

L2

H11

28

25

26

K25

H15 H25

Controlling


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Intervals are thus continuously becoming longer while heating times become shorter.

PID Controller with On-Off Control

The PID controller with On-Off Control changes its On-Off ratio depending on the difference between the setpoint value and the actual value.

T T Setpoint

t

T Actual

Relay “On”

Relay “Off”

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Correcting values are thus continuously becoming smaller. Umin keeps the temperature at TSetpoint .

PID Controller with Analog Output

The PID controller with analog output changes its correcting variable depending of the difference between the setpoint value and the actual value.

T T Setpoint

t

T Actual

Umax

t

Correcting variable

Umin

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Temperature Controllers with Auto Tuning

Setpoint value

Alarm setpoint value

Proportional band

Dwell time

Lead time

Compensation variable

Input value deferral

Manualsetting

Automaticadjustment

Manualsetting

Many controllers are equipped with a system with which they can determine the required PID parameters independently. To do this, they switch the heating completely on and measure the proportional factor, dwell time and lead time (self-learning).

In addition, there are controller types which also continuously optimise these parameters (self-optimising).

ON/OFFThe PID constants

are determined

Controller reactionafter calculation of

PID constants

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Why isControl Monitoring Necessary?

Monitoring with 3RS17

Monitoring with3RS10/3RS11



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Why is Temperature Monitoring Necessary Despite Controller Devices?

The control circuit is made up of a chain of various hardware and software components.

In cases of component or connection line failures, in cases of software faults as well as in cases of too large disturbance variables, the controller can no longer guarantee a compliance with the temperature limits.



Measuring device(sensor)


Control Circuit

Setpoint value


ZControl point

Measuring junction

Reference junction

Interruption,e.g. breakage



(SPC)


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92 Definitions Advantages:The second sensor offers additional protection. The monitoring of second sensor operates in parallel with the

control circuit. Thus, the existing control system need not be altered.



Measuring devices(2 sensors)


Control Circuit


ZControl point

Measuring junction

Reference junction

Temperature monitoring relay(3RS10/3RS11) Warning light

Controller Devices with Additional Temperature Monitoring and Second Sensor



(SPC)


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Controller Devices with 3RS17 Temperature Converter and One Sensor (Planned)

Advantages:SPC connection and temperature limiter within one deviceWarning signal when the first temperature limit is reachedDisruption of the control system‘s energy supply when the

set maximum temperature is exceeded



Measuring device(1 sensor)

Intesifier(SC-contactor)

Control Circuit


ZControl point

Measuring junction

Referencejunction

Temperaturemonitoring relay

(3RS17) Warning light

0/4-20mA, 0-10VControlling & Monitoring


(SPC)


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3RS10/3RS11 Device Overview

Overview Split by Sensors

Overview Split by Scopes of Functionality

Product DetailsAnalog devices with 1 threshold valueAnalog devices with 2 threshold valuesDigital devices with 2 threshold values

Setting Parameters

Function Diagrams

Establishment of an Average Temperature

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For Thermocouples Voltage potential proportional to the temperature

- Type J -99°C up to + 999°C - Type K -99°C up to + 999°C - Type N -99°C up to + 999°C - Type T -99°C up to + 400°C - Type E -99°C up to + 999°C

For Resistance Sensors Resistance value proportional to the temperature

- PT100 -50°C up to + 500°C

- PT1000 -50°C up to + 500°C- KTY 83 -50°C up to + 175°C- KTY 84 -40°C up to + 300°C- NTC +80°C up to + 160°C

Product Overview Split by Sensors

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Working/closed currentprinciple

2- or 3-position controller

Closed current principle

Setting of limit values and hysteresis via a rotary potentiometer

Very easy parameterisation with rotary switch

and two pushbuttons

Analog Devices with Two Setpoint Values

Digital Devices

Product Overview Split by Functionality

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Analog Devices with One Setpoint Value


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Product Details: Analog Devices with One Threshold Value

The top-seller The top-seller PT100, Type J, Type K Closed current principle Overflow or underflow Different temperature ranges

One threshold value with adjustable hysteresis

-K1

11A1

12T1/+ T2/- A2

3RS1000/1010 1100/1101 1110/1111

L1

13

-H2

14

TC / RS

Trip Signal

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92 Definitions Warning and

off-switching

PT100, Type J, Type K Working or closed current principle Overflow or underflow Different temperature ranges

-K1

A1

T1/+ T2/- A2

3RS1020/1030 1120/1121 1130/1131

L1

23

-H2

24

TC / RS

11

12 14

-H3

Trip

Signal

Alarm

Two threshold values and adjustable hysteresis

Product Details: Analog Devices with Two Setpoint Values

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92 Definitions The expert

For all common sensors LED display Overflow, underflow,

window monitoring Adjustable hysteresis and delay time 1CO + 1CO + 1NO

-K2

A1

T1/+ T2/- A2

3RS1040/1041 1140

L1

-H2TC / RS

2515

16 18 26 28

33

34

-K1

-H1-H3

Wire breakage/Short circuit

Display

Trip

Product Details: Digital Devices with Two Setpoint Values

Two threshold values and ajdustable hysteresisProduct Overview


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Digital Devices:Parameterisation Example: 3RS1040

Down Up

Parameter selection

PT100 PT1000 KTY83 KTY84 NTC

OVERFLOWUNDERFLOW WINDOW

WORKING CLOSED

1. Threshold value

2. Threshold value

3. Hysteresis

4. Delay time

5. Working principle

6. Mode of operation

7. Sensor type

8. Operation (RUN)

Rotary selector switch for parameter selection

Pushbutton for“Up” or “Down”

ACTUAL TEMPERATURE

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Function Diagram:Temperature Overshoot

Us

K1

K2

DelayDelay

Us

K1

K2Delay

Delay

Mode of operation: working current principle

Mode of operation: closed current principle

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Us

K1

K2

Us

K1

K2



DelayDelay

Delay Delay

Function Diagram: Temperature Undershoot

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Us

K1

K2Delay Delay

Delay

Function Diagram:Window Monitoring

Delay

Us

K1

K2

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Establishing the Average Temperature Within a Medium with the Help of Several Sensors

Tips & Tricks

In many cases, the average temperature within a medium or that on a specific surface is of special interest. Such measurement can easily be realised with the use of the wiring diagram illustrated below as well as a 3RS11 temperature monitoring relay.

Measuring point 1

T1

Measuring point 2

T2

Measuring point 3

T3

Mode of operation:As soon as different temperatures are detected between the thermoelectric cells, equalising currents will flow within the conductors. They serve to ensure that the average value of the single voltages is realised at the connection junction, given that all conductors have the same conductive resistance.


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92 Definitions: Would You Have Known Them?

Almost everything you needto know about temperaturemonitoring relevant definitions

From A - Z

92 Definitions


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Definition of Terms Abs - Com

Absolute zeroThe lowest temperature a substance can have. It is also the starting point of the Kelvin scale (-273.15°C).

AlumelTrading name of the high-temperature resistant nickel alloy NiAl which, together with chromel, forms the Type K thermocouple.

Blind loopAdditional conductor loop from the measuring device to the sensor used to compensate conductor resistance and parasitic voltages.

ChromelTrading name of the high-temperature resistant nickel alloy NiAl which, together with alumel, forms the Type K thermoelectric couple. 92 Definitions

Adjustment timeTime period between a sudden change of the input size and the adjustment of the output size to its balancing setpoint value.

Black bodyA body which absorbs all occurring radiation and emits the maximum thermal radiation.

Calorie [cal] Quantity of energy required to heat 1 gram of water from 14°C to 15°C.

Ceramic insulationHigh-temperature resistant ceramics (sintered aluminium oxide, corundum, silmanite or magnesium oxide). It is used as a material for protective pipes or for small insulating rods of thermometers.

Compensation device

Ensures that the measured value is largely independent of influential variables (disturbance variables).


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Definition of Terms Con - Ext

Depth of immersionThe length of the thermometer component which is exposed to the measuring value.

EMFElectromotive Force which, e.g., effects a voltage difference by ways of thermoelectric energy within a conductor.

Emissivity coefficient

Ratio of the optical radiated power of a substance compared with a black body of the same temperature.

External reference junction temperature

Reference junction temperature which is used for the determination or establishment of the signal voltage when thermocouples are applied.

Earthed measuring junction

Thermocouples whose measuring junction is welded with the protective cover (same potential as the system).

92 Definitions

Connecting headCover or casing for sealing protective pipes used with thermocouples or resistance thermometers.

ConstantanCopper-Nickel alloy which was developed as a material for electric resistance. Yet, it is also used as a negative arm for the Type K and Type T thermoelectric couples.

Drift Shift of a measuring signal over a long period of time.

Equalising conductors

Conductors for a cost-favourable length expansion of measuring conductors for thermocouples (limited measuring ranges).

Exposed measuring junction

The measuring junction of a thermocouples is in direct contact with the medium to be measured without any mechanical protection (to facilitate a fast response behaviour).


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Definition of Terms Fah - Kel

Hot junction Designation for the measuring junction of a thermocouple.

Internal conductorsElectrical connection between the actual measuring resistance and the external connections of the sensor element.

Insulated measuring junction

The hot junction of thermocouples which is electrically insulated against the protective cover or the tubular jacket.

Isothermal State of a homogeneous and constant temperature.

IST- 90 International temperature scale of 1990.

Joule Unit of measurement for energy.

92 Definitions

Fahrenheit Anglo-Saxon temperature scale (32°F = 0°C / 212°F = 100°C).

Indicial responseRepresentation of the temporal course of a measured value or the output signal after a sudden change of the measured variable.

Intrinsically safe electric circuits

The switching circuit is arranged in such a way that sufficient electric energy for the igniting of flammable substances can under no circumstances whatsoever be transferred or saved.

Kelvin scaleTemperature scale for the measured variable of the thermodynamic temperature. The scale definition starts with absolute zero (-273.15°C).


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Definition of Terms Lif - Mea

Life zeroThis minimum current of 4mA is normally used for power supply and conductor monitoring; values of under 4mA are a proof for occurred faults.

LinearityDirectly proportional ratio of an instrument‘s display value and the measured value.

92 Definitions

Limit conditionsMaximum ambient conditions a thermometer can be exposed to without consequential damage or deterioration.

Loop resistanceTotal resistance of the measuring loop, including the measuring element, contact resistance and conductor resistance.

Measured valueValue of a measuring unit determined by way of a measurement. It is made up of the product of numeric value and unit.

Measured value hysteresis value

Hysteresis: Differential sum of the measured values for the same value of the measured variable when this value is reached in increasing or decreasing direction.

Measured variableA feature whose value is to be determined with the help of a measurement (e.g. temperature).

Measuring faultUndesired deviation between the actual value of a measuring device and its setpoint value.

Measuring junctionConnection points of the welded, soldered or twisted thermoelectric arms of a thermocouple.

Measuring pointPoint within a medium or a substance at which the measurement is carried out.


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Definition of Terms Mea - Ove

Measuring range Maximum value range of a measuring device.

Measuring resistorSensor element of a resistance thermometer whose electric resistance depends on the temperature.

Medium temperature coefficient

Medium relative resistance change per Kelvin within the range of 0°C and 100°C.

Müller bridgeHighly precise measuring bridge configuration for resistance thermometers with 3-conductor circuits.

92 Definitions

Negative temperature coefficient (NTC)

Ratio of the temperature difference and the resistance difference of NTC resistors. With an increase in temperature, the resistance decreases.

Nicrosil-NisilType N thermoelectric couple which is made of a Nickel-Chrome alloy and a Nickel-Silicium alloy.

NoiseUndesired effect caused by electromagnetic radiation of the signal conductors.

Nominal resistance Setpoint value of the temperature-dependent resistance at 0°C.

NTC resistors Sensors with a negative temperature coefficient. With an increase in temperature, the electric resistance decreases (NTC).

Overtravel deviation

Measuring deviation due to a temporal overtravel of the measured value or the output signal compared with a sudden change of the measured variable.


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Definition of Terms Pel - Ref

Peltier effectReversion of the Seebeck effect. With a current-imposed conductor consisting of two metals, one connection junction is supplied with heat while the other one is subjected to heat dissipation.

Polarity Designation of the plus and minus arms of thermocouples.

92 Definitions

Positive temperature coefficient (PTC)

Ratio of the temperature difference and the resistance difference of PTC resistors. With an increase in temperature, the resistance increases.

PT100 Platinum resistor element with a nominal resistance of 100 Ohm at 0°C.

PTC resistorSensors with a positive temperature coefficient. With an increase in temperature, the electric resistance also increases (PTC).

PyrometryTemperature measurement with the help of radiation pyrometers. The thermal radiation of a body is used for temperature measurement.

Reference junctionConnection junction of the thermocouples lying on the reference temperature.

Reference junction compensation

Adjustment of the output signal of a thermocouple if the reference junction is not specified at 0°C.

Reference junction thermostat

Externally tempered measuring circuit with a constant and known temperature which is taken as a reference for reference junction compensation.


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Definition of Terms Ref - See

Reference valueValue which is based on the incorporation of measurement results, the determination of fault limits or other conditions.

92 Definitions

RepeatabilityThe capability of a sensor or a measuring system to reproduce the same measuring signal under identical conditions.

Resistance element Is used within resistance thermometers for measuring the temperature.

Resistance temperature sensor

Consisting of a measuring resistor within a protective cover, the internal conductors and the external connections.

Resistancethermometer

An instrument or measuring system consisting of one measuring device and one resistance temperature sensor which has a known ratio of resistance and temperature. The temperature is determined on the basis of the resistance measurement.

Response timeTime period between a temperature change of the medium to be measured and the sensor output signal.

Seebeck coefficientInitial derivation of the thermal EMF with regard to the temperature, stated in [V/°C].

Seebeck effectGeneration of an electromotive force (EMF) by way of the temperature difference between the two connection junctions of two different metals which are part of an electric circuit.


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Definition of Terms See - The

92 Definitions

SensitivityThe response behaviour of a temperature sensor as regards the time period or signal size of a given temperature difference.

Sensor elementDesignation of a serviceable sensor which is integrated in a protective fitting.

Sheathed thermoelectric cells

Thermocouples with mineral-insulated sheathed conductor. The thermoelectric arms are embedded in pressed magnesium oxide within a tubular jacket made of stainless steel.

Spontaneous heating

Influential effect which is generated by the electric power transferred by the measuring current within the measuring resistance.

Stabilisation Artificial weathering of measuring sensors based on heat treatment.

Temperature gradient

Temperature variation within a substance.

Temperature sensor

The part of the thermometer which is directly exposed to the temperature.

Thermal conductivity

Measurement for the heat quantity per temporal unit which flows between bodies of differing temperatures during heat transmission.

Thermal expansion Expansion of a body with an increase in temperature.

Thermal radiationElectromagnetic radiation which is emitted by a body with a temperature of above absolute zero.


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Definition of Terms The - Tra

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ThermistorSemiconductor-sensor with a non-linear ratio of resistance change and temperature change (PTC).

ThermoconductorConductor couple for the expansion of the thermoelectric arm to the reference junction consisting of the same material as the thermoelectric arm.

Thermoelectric armSingle conductor of a thermocouple. Depending on the polarity, “plus” and “minus” thermoelectric arms are differentiated.

Thermoelectric cells

Temperature sensors which supply a direct electric voltage or electric current by utilising their thermoelectric properties.

Thermoelectric couples

Two interconnected electric conductors made of different materials which supply a thermal voltage or a thermal current on the basis of the Seebeck effect.

Thermometer resistance

The sum of the entire resistance within a resistance thermometer (internal conductors and measuring resistance).

Thomson effectEffects a change of the heat concentration within a current-imposed conductor within a temperature gradient.

TransducerTransformer which transforms a physical measurement, e.g. temperature, into a current or voltage signal.

Transition pointSealing which covers the connection junction of the thermoelectric arms with the thermowires or equalisinwires.


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Definition of Terms Tra - Zer

Wheatstone bridgeA measuring bridge consisting of four resistors and serving the precise determination of resistance within a measuring circuit.

Two-, three- or four-conductor circuits

Type of connection of a resistance temperature sensor to a display device with two-, three- or four-conductor incoming supply.

92 Definitions

TransmitterTransformer which transforms any voltage or current signals into standardised voltage or current signals.

Triple pointTemperature at which a substance can exist stable in all three phase conditions. The triple point of water lies at 0.01°C.

Zero suppressionMeasuring range shift to receive a higher accuracy in a measuring device‘s relative measuring range.

Zero shift Difference between the displayed zero value and the actual zero.


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