automation and drives simirel overview thermocouples resistance sensors selection criteria...
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Automation and Drives
simirel
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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Overview
Thermocouples
Resistance Sensors
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Controlling
Controlling & Monitoring
Product Overview
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
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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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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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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
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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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Resistance Thermometers
Color Codes
Connection Methods
2-Conductor Method
3-Conductor Method
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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)
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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
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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
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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.
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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
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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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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
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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)
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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
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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
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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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Controlling & Monitoring
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.
Final controlling element(heating)
Control path(system)
Measuring device(sensor)
Intensifier(SC-contactor)
Control Circuit
Setpoint value
Disturbance variables
ZControl point
Measuring junction
Reference junction
Interruption,e.g. breakage
Controlling & Monitoring
Setpoint value adjusterreference input element
(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.
Final controlling element(heating)
Control path(system)
Measuring devices(2 sensors)
Intensifier(SC-contactor)
Control Circuit
Disturbance variables
ZControl point
Measuring junction
Reference junction
Temperature monitoring relay(3RS10/3RS11) Warning light
Controller Devices with Additional Temperature Monitoring and Second Sensor
Controlling & Monitoring
Setpoint value adjusterreference input element
(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
Final controlling element(heating)
Control path(system)
Measuring device(1 sensor)
Intesifier(SC-contactor)
Control Circuit
Disturbance variables
ZControl point
Measuring junction
Referencejunction
Temperaturemonitoring relay
(3RS17) Warning light
0/4-20mA, 0-10VControlling & Monitoring
Setpoint value adjusterreference input element
(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
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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
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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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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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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
Mode of operation: working current principle
Mode of operation: closed current principle
DelayDelay
Delay Delay
Function Diagram: Temperature Undershoot
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Mode of operation: working current principle
Mode of operation: closed current principle
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
92 Definitions
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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