Beckhoff EPP3314-0002 User Manual

Documentation | EN

EPP3314-0002

4-channel analog input thermocouple

2021-02-11 | Version: 1.2

Table of contents

Table of contents

1 Foreword ....................................................................................................................................................5

1.1 Notes on the documentation..............................................................................................................5

1.2 Safety instructions .............................................................................................................................6

1.3 Documentation issue status ..............................................................................................................7

2 Product group: EtherCATP Box modules ..............................................................................................8

3 Product overview.......................................................................................................................................9

3.1 Introduction........................................................................................................................................9

3.2 Technical data .................................................................................................................................10

3.3 Process image.................................................................................................................................12

3.4 Scope of supply ...............................................................................................................................13

3.5 Basics of thermocouple technology.................................................................................................14

4 Mounting and connections.....................................................................................................................21

4.1 Mounting..........................................................................................................................................21

4.1.1 Dimensions ...................................................................................................................... 21

4.1.2 Fixing ............................................................................................................................... 22

4.1.3 Functional earth (FE) ....................................................................................................... 22

4.1.4 Tightening torques for plug connectors ........................................................................... 22

4.2 Connections.....................................................................................................................................23

4.2.1 EtherCATP...................................................................................................................... 23

4.2.2 Thermocouples ................................................................................................................ 26

4.3 UL Requirements.............................................................................................................................27

5 Commissioning/Configuration ...............................................................................................................28

5.1 Integration in TwinCAT ....................................................................................................................28

5.2 Settings............................................................................................................................................29

5.2.1 Presentation, index 0x80n0:02 ........................................................................................ 29

5.2.2 Siemens bits, index 0x80n0:05........................................................................................ 30

5.2.3 Underrange, Overrange................................................................................................... 30

5.2.4 Filter................................................................................................................................. 30

5.2.5 Limit 1 and Limit 2............................................................................................................ 30

5.2.6 Calibration........................................................................................................................ 31

5.3 Object overview ...............................................................................................................................33

5.4 Object description and parameterization .........................................................................................39

5.4.1 Objects to be parameterized during commissioning........................................................ 39

5.4.2 Objects for regular operation ........................................................................................... 45

5.4.3 Standard objects (0x1000-0x1FFF) ................................................................................. 45

5.4.4 Profile-specific objects (0x6000-0xFFFF) ........................................................................ 51

5.5 Restoring the delivery state .............................................................................................................56

5.6 Decommissioning ............................................................................................................................57

6 Appendix ..................................................................................................................................................58

6.1 General operating conditions...........................................................................................................58

6.2 Accessories .....................................................................................................................................59

6.3 Version identification of EtherCAT devices .....................................................................................60

6.3.1 Beckhoff Identification Code (BIC)................................................................................... 64

EPP3314-0002 3Version: 1.2

Table of contents

6.4 Support and Service ........................................................................................................................66

EPP3314-00024 Version: 1.2

Foreword

1 Foreword

1.1 Notes on the documentation

Intended audience

This description is only intended for the use of trained specialists in control and automation engineering who
are familiar with the applicable national standards.
It is essential that the documentation and the following notes and explanations are followed when installing
and commissioning these components.
It is the duty of the technical personnel to use the documentation published at the respective time of each
installation and commissioning.

The responsible staff must ensure that the application or use of the products described satisfy all the
requirements for safety, including all the relevant laws, regulations, guidelines and standards.

Disclaimer

The documentation has been prepared with care. The products described are, however, constantly under
development.

We reserve the right to revise and change the documentation at any time and without prior announcement.

No claims for the modification of products that have already been supplied may be made on the basis of the
data, diagrams and descriptions in this documentation.

Trademarks

Beckhoff®, TwinCAT®, EtherCAT®, EtherCATG®, EtherCATG10®, EtherCATP®, SafetyoverEtherCAT®,
TwinSAFE®, XFC®, XTS® and XPlanar® are registered trademarks of and licensed by Beckhoff Automation
GmbH. Other designations used in this publication may be trademarks whose use by third parties for their
own purposes could violate the rights of the owners.

Patent Pending

The EtherCAT Technology is covered, including but not limited to the following patent applications and
patents: EP1590927, EP1789857, EP1456722, EP2137893, DE102015105702 with corresponding
applications or registrations in various other countries.

EtherCAT® is registered trademark and patented technology, licensed by Beckhoff Automation GmbH,
Germany.

Copyright

© Beckhoff Automation GmbH & Co. KG, Germany.
The reproduction, distribution and utilization of this document as well as the communication of its contents to
others without express authorization are prohibited.
Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a
patent, utility model or design.

EPP3314-0002 5Version: 1.2

Foreword

1.2 Safety instructions

Safety regulations

Please note the following safety instructions and explanations!
Product-specific safety instructions can be found on following pages or in the areas mounting, wiring,
commissioning etc.

Exclusion of liability

All the components are supplied in particular hardware and software configurations appropriate for the
application. Modifications to hardware or software configurations other than those described in the
documentation are not permitted, and nullify the liability of Beckhoff Automation GmbH & Co. KG.

Personnel qualification

This description is only intended for trained specialists in control, automation and drive engineering who are
familiar with the applicable national standards.

Description of instructions

In this documentation the following instructions are used.
These instructions must be read carefully and followed without fail!

DANGER

Serious risk of injury!

Failure to follow this safety instruction directly endangers the life and health of persons.

WARNING

Risk of injury!

Failure to follow this safety instruction endangers the life and health of persons.

CAUTION

Personal injuries!

Failure to follow this safety instruction can lead to injuries to persons.

NOTE

Damage to environment/equipment or data loss

Failure to follow this instruction can lead to environmental damage, equipment damage or data loss.

Tip or pointer

This symbol indicates information that contributes to better understanding.

EPP3314-00026 Version: 1.2

Foreword

1.3 Documentation issue status

Version Comment

1.2 • Terminology update

• Structure update

1.1 • CoE parameters updated

1.0 • First release

Firmware and hardware versions

This documentation refers to the firmware and hardware version that was applicable at the time the
documentation was written.

The module features are continuously improved and developed further. Modules having earlier production
statuses cannot have the same properties as modules with the latest status. However, existing properties
are retained and are not changed, so that older modules can always be replaced with new ones.

Documentation Firmware Hardware

1.2 06 04

1.1 06 04

1.0 06 04

The firmware and hardware version (delivery state) can be found in the batch number (D-number) printed on
the side of the EtherCAT Box.

Syntax of the batch number (D-number)

D: WW YY FF HH

WW - week of production (calendar week)
YY - year of production
FF - firmware version
HH - hardware version

Further information on this topic: Version identification of EtherCAT devices [}60].

Example with D no. 29 10 02 01:

29 - week of production 29
10 - year of production 2010
02 - firmware version 02
01 - hardware version 01

EPP3314-0002 7Version: 1.2

Product group: EtherCATP Box modules

2 Product group: EtherCATP Box modules

EtherCATP

EtherCATP supplements the EtherCAT technology with a process in which communication and supply
voltages are transmitted on a common line. All EtherCAT properties are retained with this process.

Two supply voltages are transmitted per EtherCATP line. The supply voltages are electrically isolated from
each other and can therefore be switched individually. The nominal supply voltage for both is 24 VDC.

EtherCAT P uses the same cable structure as EtherCAT: a 4-core Ethernet cable with M8 connectors. The
connectors are mechanically coded so that EtherCAT connectors and EtherCATP connectors cannot be
interchanged.

EtherCATP Box modules

EtherCATP Box modules are EtherCATP slaves with IP67 protection. They are designed for operation in
wet, dirty or dusty industrial environments.

Fig.1: EtherCATP

EtherCAT basics

A detailed description of the EtherCAT system can be found in the EtherCAT system documentation.

EPP3314-00028 Version: 1.2

3 Product overview

3.1 Introduction

Product overview

Fig.2: EPP3314-0002

4-channel analog input thermocouple

The EPP3314 EtherCAT P Box with analog inputs permits four thermocouples to be directly connected. The
module’s circuit can operate thermocouple sensors using the 2-wire technique. Linearisation over the full
temperature range is realised with the aid of a microprocessor. The temperature range can be selected
freely. The error LEDs indicate a broken wire. Compensation for the cold junction is made through a
temperature measurement in the connecting plugs. This means that standard extension leads can be
connected. The EPP3314 can also be used for mV measurement.

The module is quite versatile, but the default values are selected in such a way that in most cases it is not
necessary to perform configuration. The input filter and associated conversion times can be set within a wide
range; several data output formats may be chosen. If required, the inputs can be scaled differently.
Automatic limit monitoring is also available. Parameterisation is carried out via EtherCAT. The parameters
are stored in the module. For the temperature compensation a Pt1000 element is needed. Beckhoff offers a
connector with temperature compensation (ZS2000-3712).

Quick links

Technical data

Process image [}12]
Signal connection [}26]

EPP3314-0002 9Version: 1.2

Product overview

3.2 Technical data

All values are typical values over the entire temperature range, unless stated otherwise.

EtherCATP

Connection 2xM8 socket, 4-pin, P-coded, red

Supply voltages

Connection See EtherCAT P connection
US nominal voltage 24VDC (-15%/ +20%)
US sum current: I
Current consumption from U
Rated voltage U
UP sum current: I
Current consumption from U

S,sum

S

P

P,sum

P

Thermocouple inputs

Number 4
Connector 4 x M12 socket
Cable length to thermocouple max. 30m
Sensor types

Electrical isolation The measuring channels have a common isolated ground

Measuring ranges

Measuring error Thermocouple type K: max. ±0.3%,

Digital resolution 16-bit
Value of an LSB Thermocouple: 0.1°C

Filter Digital filter. Filter frequency adjustable from 5Hz… 30kHz
Conversion time approx. 2.5 s to 20 ms, depending on configuration and filter

Diagnostics • Open-circuit recognition

max. 3A
100mA
24VDC (-15%/ +20%)
max. 3A
None. UP is only forwarded.

• Thermocouples [}11]

• Sensors with a voltage output of up to ±75mV

potential.

Thermocouples: depending on type [}11].

Voltage measurement: ±30mV, ±60mV, ±75mV

relative to the full scale value

Voltage measurement:
Measuring range 30mV: 1µV
Measuring range 60mV: 2µV
Measuring range 75mV: 4µV

setting.

Default: approx. 250ms

• Limit value monitoring

Housing data

Dimensions WxHxD 30mmx 126mmx 26.5mm (without connectors)
Weight approx. 165 g
Installation position variable
Material PA6 (polyamide)

EPP3314-000210 Version: 1.2

Environmental conditions

Ambient temperature during operation -25…+60°C

-25…+55°C according to cULus
Ambient temperature during storage -40…+85°C
Vibration resistance, shock resistance conforms to EN 60068-2-6 / EN 60068-2-27

Additional checks [}11]

EMC immunity / emission conforms to EN 61000-6-2 / EN 61000-6-4
Protection class IP65, IP66, IP67 (conforms to EN 60529)

Approvals

Approvals

Additional checks

The boxes have been subjected to the following checks:

Verification Explanation

Vibration 10 frequency sweeps in 3 axes

5Hz<f<60Hz displacement 0.35mm, constant amplitude

60.1Hz<f<500Hz acceleration 5g, constant amplitude

Shocks 1000 shocks in each direction, in 3 axes

35g, 11ms

CE, cULus [}27]

Product overview

Overview of suitable thermocouples

The following thermocouples are suitable for temperature measurement:

Type (according
to EN60584-1)

B Pt30%Rh-Pt6Rh 600°C to 1800°C grey - grey - white
C * W5%Re-W25%Re 0°C to 2320°C n.d.
E NiCr-CuNi -100°C to 1000°C violet - violet - white
J Fe-CuNi -100°C to 1200°C black - black - white
K NiCr-Ni -200°C to 1370°C green - green - white
L ** Fe-CuNi 0°C to 900°C blue - red - blue
N NiCrSi-NiSi -100°C to 1300°C pink - pink - white
R Pt13%Rh-Pt 0°C to 1767°C orange - orange - white
S Pt10%Rh-Pt 0°C to 1760°C orange - orange - white
T Cu-CuNi -200°C to 400°C brown - brown - white
U ** Cu-CuNi 0°C to 600°C brown - red - brown

* not standardized according to EN60584-1
** according to DIN 43710

Element Implemented temperature

range

Color coding (sheath - plus
pole - minus pole)

EPP3314-0002 11Version: 1.2

Product overview

3.3 Process image

Fig.3: Process image

TC Inputs Channel1

• Underrange
Measurement is below range

• Overrange
Measuring range exceeded

• Limit 1
Status variable of the limit value monitoring
0: The limit value monitoring is disabled
1: The measured value is smaller than the limit value
2: The measured value is greater than the limit value
3: The measured value is exactly the same size as the limit value

• Limit 2
Status variable of the limit value monitoring

• Error
The current measured value "Value" is invalid.
Possible reasons: Wire breakage, Underrange, Overrange

• TxPDO State
If this bit is TRUE, the current measured value "Value" is invalid.

• TxPDO Toggle
The box inverts this bit every time it updates the measured value "Value" in
the process data.
This allows the currently required conversion time to be derived.

Value

The current measured value. Unit: 1/10°C.

TC Inputs Channel2 bis 4

The process data objects of channels 2…4 have exactly the same structure as those of channel 1.

EPP3314-000212 Version: 1.2

3.4 Scope of supply

Make sure that the following components are included in the scope of delivery:

• 1x EPP3314-0002 EtherCAT P Box

• 2x protective cap for EtherCATP socket, M8, red (pre-assembled)

• 10x labels, blank (1 strip of 10)

Pre-assembled protective caps do not ensure IP67 protection

Protective caps are pre-assembled at the factory to protect connectors during transport. They may
not be tight enough to ensure IP67 protection.

Ensure that the protective caps are correctly seated to ensure IP67 protection.

Product overview

EPP3314-0002 13Version: 1.2

Product overview

3.5 Basics of thermocouple technology

Thermocouples are temperature sensors. The application areas of thermocouples are very diverse due to
their low cost, fast detection of temperature differences, wide temperature ranges, high temperature limits
and availability in a wide range of types and sizes.

Measuring principle and configuration

Temperature measurement with a thermocouple is based on the Seebeck effect, which was discovered in
the 1820s by the German physicist Thomas Johann Seebeck. The Seebeck effect, also known as
thermoelectric effect, describes a charge shift in a conductive material due to a temperature gradient along
the conductor. The magnitude of the charge shift depends on the magnitude of the temperature difference
and the respective conductor material.

In thermocouples this charge shift is used to generate a voltage. Two different conductor materials are
connected at one end. This is the measuring point at which the temperature is to be determined. At the other
end the conductors are not connected. This open end, where the transition to the measuring electronics is
located, is the cold junction. A temperature difference occurs between the cold junction and the measuring
point, which can be measured via the voltage between the conductors at the open end. The voltage depends
on the conductor materials used and the temperature difference. It is in the range of a few mV.

Fig.4: Structure and principle of a thermocouple

If only one material were used for a thermocouple, the charge shift in both conductors would be identical, so
that no potential difference between the two conductors at the open end could be measured.

The temperature measurement with thermocouples is therefore actually a voltage measurement, based on
which a temperature can be determined from the known characteristic curve. In addition, the measuring
procedure is not absolute but differential, since no absolute temperature (with the reference point 0 °C) is
determined, but the temperature difference between the measuring point and the cold junction.

EPP3314-000214 Version: 1.2

Product overview

For the evaluation of thermocouples, measuring electronics are required that can evaluate small voltages in
the mV range with sufficiently high resolution and accuracy. Thermocouples are active sensors, which
means that no sensor supply is required to measure the temperature.

Thermocouple types

There are different types of thermocouples, which consist of different combinations of conductor materials.
Each material combination has specific properties and is suitable for certain applications. The different
thermocouple types are distinguished by letters.

Due to the different material combinations, the different thermocouple types have different characteristic
values. They differ in the temperature limits and the characteristic voltage/temperature curve. In order to be
able to differentiate between the thermocouple types, the color codes for the sheath, the positive pole and
the negative pole are defined in various standards.

The following table shows common thermocouple types with the specification of the materials used, the
defined temperature ranges and the color coding.

Type (con­forms to
EN60584-1)

B Pt30%Rh-Pt6Rh 600°C 1820°C 6µV/K 13.820mV grey - grey - white
C ** W5%Re-

E NiCr-CuNi -270°C 1000°C 65µV/K 76.373mV violet - violet - white
J Fe-CuNi -210°C 1200°C 54µV/K 69.553mV black - black - white
K NiCr-Ni -270°C 1372°C 42µV/K 54.886mV green - green - white
L *** Fe-CuNi -200°C 900°C 54µV/K 53.140mV blue - red - blue
N NiCrSi-NiSi -270°C 1300°C 27µV/K 47.513mV pink - pink - white
R Pt13%Rh-Pt -50°C 1768°C 10µV/K 21.101mV orange - orange - white
S Pt10%Rh-Pt -50°C 1768°C 10µV/K 18.693mV orange - orange - white
T Cu-CuNi -270°C 400°C 40µV/K 20.872mV brown - brown - white
U *** Cu-CuNi -200°C 600°C 40µV/K 34.310mV brown - red - brown

*The specified measuring range refers to the maximum possible measuring range of the specified
thermocouple type. The possible measuring range with the thermocouple module may be limited. The
specification of the possible measuring range of the thermocouple module can be taken from the technical
data in the documentation.

**not standardized according to EN60584-1

Element Measuring range * Average

min max

-18°C 2316°C 15µV/K 37.070mV n.d.

W25%Re

temperature
coefficient

Voltage at
FSV

Color coding (sheath ­plus pole - minus pole)

***conforms to DIN 43710

The thermocouple must be selected according to the operating conditions. Therefore, not only the
uncertainty must be taken into account, but also the other properties of the different thermocouple types. For
an application with small temperature fluctuations, it is advantageous to select a thermocouple type with a
high thermovoltage per temperature change. In an application where the temperature to be measured is very
high, it is important to observe the maximum operating temperature.

Characteristic curve

Type-specific reference tables are available for determining the temperature difference to a measured
thermovoltage. A simple conversion of the voltage into a temperature with a temperature coefficient, as is
often approximated in resistance thermometers, is not possible because the relationship between voltage
and temperature is clearly non-linear over the entire measuring range. The changing temperature coefficient
results in a non-linear characteristic voltage/temperature curve. This characteristic curve is in turn dependent
on the thermocouple type, so that each type has its own non-linear characteristic voltage/temperature curve.
As an example, the characteristic curves for typical thermocouple types are shown in the following diagram.
The non-linearity is particularly evident in the temperature range below 0°C.

EPP3314-0002 15Version: 1.2

Product overview

Fig.5: Characteristic voltage/temperature curves of different thermocouple types

Thermocouples are subject to unavoidable and irreversible changes during practical application, which leads
to ever-increasing measurement uncertainties over time. In other words: the measurement becomes more
and more incorrect over time. These changes are also referred to as aging and depend on various
influencing factors. Examples of these influences are mechanical and chemical stresses on the
thermocouples. Mechanical stresses are deformations of the conductors, which change the crystal structure
of the metals. This leads to incorrect thermovoltages. Chemical stresses are also changes in the crystal
structure of the metals or oxidation, which change the thermal properties of the conductors, resulting in a
change in the characteristic curve. This influence can be reduced by installation in gas-tight protection tubes.

Pluggable connections

Open wire ends or suitable thermocouple connectors can be used to connect thermocouples to measuring
devices and evaluation electronics or to connect a thermocouple to thermo or compensating cables.

Ideally, the contacts of such a thermocouple connector are made of the material of the respective
thermocouple. This results in a thermovoltage-free transition at the connection points. The plugs are color­coded depending on the type, e.g. type K is green. Labelling on the housing and different contact shapes are
intended to avoid polarity reversal.

There are several common sizes: standard, mini, micro.

A special feature is the white connector, which is designed with normal copper contacts, almost like a normal
non-thermocouple connector. This makes it universally applicable for all thermocouple types, although it has
the disadvantage that it does not create a thermovoltage-free transition. Far more common than the white

EPP3314-000216 Version: 1.2

Product overview

plug is the white "universal" socket on the measuring device. This allows any thermocouple plug to be
plugged into the device. In the measuring device, the cold junction temperature must then be determined at
this plug transition.

Extensions and connection of thermocouples

In some cases it is useful to extend the thermocouple and thus to move the cold junction to a particular
location, where the temperature can be kept constant or measured by simple means. For this purpose the
thermocouple must be extended. This can be done with a thermo or compensation wire. Thermo cables are
made of the same material as the thermocouple itself. Compensating cables, on the other hand, are usually
made of cheaper materials with similar thermal properties. Both types are therefore suitable for extending a
thermocouple to a remote cold junction. The wires for thermo and compensating cables are standardized by
DIN 43713.

With compensating cables, care must be taken to ensure that the material used has similar thermal
properties but not identical properties. The thermal properties only apply in a narrowly limited temperature
range. At the transition from thermocouple to compensation wire, another thermocouple is created. This
results in small thermovoltage distortions, which influence the measurement result. If the compensating
cables are used outside the specified temperature range, the accuracy of the temperature measurement will
be further affected and the measurement result will deteriorate.

For both thermal and compensation wires, there are two accuracy classes that indicate the limit deviations.
These are defined in DIN43722. When selecting the thermocouple extension, the resulting uncertainty
should be considered and evaluated.

Sensor circuit

Changing the sensor circuit through additional elements such as selector switches or multiplexers
can affect the measuring accuracy. In such switches, small local thermovoltages can be generated
which distort the measurement. If such components cannot be avoided in the application, their influ­ence should be carefully examined.

Maximum cable length to the thermocouple

Without additional protective measures, the maximum cable length from the measuring module (ter­minal, box) to the thermocouple is 30m. For longer cable lengths, suitable surge protection should
be provided.

Determination of the absolute temperature

Temperature measurement with a thermocouple is a differential temperature measurement, in which the
temperature difference between the measuring point and the reference junction, also known as cold junction,
is determined. To determine the absolute temperature at the measuring point, the measured thermovoltage
must therefore be corrected by the thermovoltage at the cold junction. With the corrected thermovoltage, the
temperature at the measuring point can then be determined from suitable tables or characteristic curves.
Due to the non-linearity of the characteristic curve, it is imperative that this calculation is carried out with the
voltages and not with the temperature. Otherwise, there would be a significant error in the measurement.

Difficulties in measuring temperature with thermocouples

- Linearization

- Cold junction compensation

In general, the absolute temperature is calculated using the following relationship:

U

measuring point

T

measuring point

= U

= f(U

+ U

thermo

measuring point

cold junction

)

In the following section, the absolute temperature is determined as an example based on correction of the
thermovoltages and the temperature. The example calculation can be used to illustrate the error resulting
from incorrect correction.

Sought: T

Known: Thermocouple type K, U

measuring point

= 24.255mV, T

thermo

cold junction

= 22°C

EPP3314-0002 17Version: 1.2

Product overview

Option 1: Correction of thermovoltages – CORRECT

The thermovoltage at the cold junction U

from the characteristic voltage/temperature curve or table for thermocouple type K:

junction

U

cold junction

= U(22°C) = 0.879mV

cold junction

must be determined based on the known temperature T

The thermovoltage at the measuring point can then be determined with reference to 0°C:

U

measuring point

= U

thermo

+ U

cold junction

= 24.255mV + 0.879mV = 25.134mV

The corresponding temperature value can then be determined for thermocouple type K based on the
determined thermovoltage from the characteristic voltage/temperature curve or table:

T

measuring point

= T(25.134mV) ≈ 605.5°C

Option 2: Temperature correction – WRONG

In principle, the temperature difference between the cold junction and the measuring point T
determined based on the known thermovoltage U

from the characteristic voltage/temperature curve or

thermo

thermo

could be

table for thermocouple type K:

T

= T(24.255mV) = 585°C

thermo

The temperature of the measuring point could then be determined with reference to 0°C:

T

measuring point

= T

thermo

+ T

cold junction

= 585°C + 22°C = 607°C

Note that there is a temperature difference of 1.5°C between the value with the proper correction (voltage
correction, option 1) and the value with the incorrect correction (temperature correction, option 2).

cold

Reference junction / Cold junction compensation / CJC

The correction of the thermovoltage value to determine the absolute temperature value is referred to as cold
junction compensation. In order to determine an absolute temperature value that is as accurate as possible,
the temperature at the cold junction must either be kept constant at a known value or measured continuously
during the measurement with the smallest possible uncertainty. In some applications, the cold junction may
be in an ice bath (0°C), for example. In this case the temperature determined via the thermovoltage
corresponds to both the temperature difference and the absolute temperature. In many applications,
however, this option cannot be implemented, so that cold junction compensation is necessary.

As a cold junction in thermocouple evaluation with Bus Terminals, the cold junction temperature is measured
at the transition from the thermocouple to the copper contacts. This value is measured continuously during
operation in order to correct the determined values internally.

Evaluation of thermocouples with thermocouple terminals

Beckhoff thermocouple modules (terminals, box) can evaluate thermocouples of different types. Linearization
of the characteristic curves and determination of the reference temperature takes place directly in the
module. The module can be fully configured via the Bus Coupler or the controller. Different output formats
may be selected or own scaling activated. Linearization of the characteristic curve and determination and
calculation of the reference temperature (temperature at the connection contacts of the module) can be
deactivated, so the module can be used as a [mV] measuring device or with an external cold junction. In
addition to the internal evaluation of the measured voltage for conversion into a temperature, the raw voltage
value can be transferred from the terminal to the control system for further processing.

Temperature measurement with thermocouples generally comprises three steps:

• Measuring the electrical voltage

• Optional: Temperature measurement of the internal cold junction

• Software-based conversion of the voltage into a temperature value according to the set thermocouple
type (K, J, …)

All three steps can take place locally in the Beckhoff measuring module. Module-based transformation can
be disabled if the conversion is to take place in the higher-level control system. Depending on the module
type, several thermocouple conversions are available, which differ in terms of their software implementation.

EPP3314-000218 Version: 1.2

Product overview

Uncertainties in the evaluation of thermocouples with thermocouple terminals

The thermocouple measurement consists of a chain of measuring and computing elements that affect the
attainable measurement deviation:

Fig.6: Concatenation of the uncertainties in temperature measurement with thermocouples

When measuring a temperature, there are various factors influencing the accuracy, from which the total
inaccuracy (total uncertainty) is then derived.

Uncertainty of the voltage measurement

First and foremost, measuring a temperature with thermocouples is not based on an actual temperature
measurement, but a voltage measurement with subsequent conversion into a temperature. The accuracy of
the voltage measurement is therefore the basis for the accuracy of the temperature determination. Since a
change of 1°C at the sensor causes a change in the single-digit µV range, depending on the thermocouple
type, even a small uncertainty of the voltage measurement has a large influence on the final result.

Uncertainty of the temperature conversion

The conversion of the measured voltage into a temperature is carried out during evaluation either by means
of value tables from the characteristic voltage/temperature curve of a thermocouple type or by approximation
based on a polynomial. Due to the non-linearity of the characteristic voltage/temperature curve, both options
are only approximations of the actual values, so that the conversion results in a further (small) transformation
uncertainty component.

Uncertainty of the cold junction evaluation

Cold junction compensation in thermocouple terminals must be carried out at the transition from the
thermocouple to the copper contacts of the electronics. However, in many cases the temperature at this
point cannot be measured directly for mechanical reasons. In this case the temperature of the cold junction
has to be approximated at a distance of a few millimeters or through an average value of the housing
temperatures. Since the exact value cannot be determined in this way, this results in further uncertainty.

Uncertainty of the sensor

The three factors influencing the uncertainty referred to above relate to the uncertainties in the evaluation of
the thermocouples. The accuracy of the thermocouple itself is another factor and must also be taken into
account.

Since temperature measurement with thermocouples is actually a voltage measurement and the
thermocouples have a non-linear characteristic voltage/temperature curve, it is not possible to simply add up
the individual temperature uncertainties to obtain the total uncertainty. To calculate the total uncertainty, all
temperature values must be converted into the corresponding voltage value of the respective thermocouple
type. When the temperatures are added together an error occurs, as described in the example in the chapter
on "Determination of the absolute temperature".

The following diagram shows an example of an analysis of the uncertainties associated with the evaluation
of a thermocouple for an EL331x thermocouple terminal with internal cold junction compensation and
conversion of the voltage into a temperature via a second degree polynomial. The diagram does not take
into account the uncertainty of the thermocouple itself, which is an additional factor.

EPP3314-0002 19Version: 1.2

Product overview

Fig.7: Example for an uncertainty analysis of the evaluation of thermocouples with thermocouple terminals

It is clear from the diagram that the uncertainty of the measured temperature depends on the temperature to
be measured. Especially in the lower temperature range, where there is a strong non-linearity of voltage and
temperature, the uncertainty of the temperature measurement increases significantly.

Beckhoff offers several products for the evaluation of thermocouples, including

• EL331x-0000: EtherCAT terminal, 1/2/4/8 channel analog input, temperature, thermocouple, 16 bit

• EL3314-0002: EtherCAT terminal, 4 channel analog input, temperature, thermocouple, 24 bit,
electrically isolated

• EL3314-0010: EtherCAT terminal, 4 channel analog input, temperature, thermocouple, 24 bit, high­precision

• EL3314-0030: EtherCAT terminal, 4 channel analog input, temperature, thermocouple, 24 bit, high­precision, external calibrated

• EL3314-0090: EtherCAT terminal, 4 channel analog input, temperature, thermocouple, 16 bit,
TwinSAFE SC

• ELM370x-xxxx: EtherCAT terminal, 2/4 channel analog input, multi-functional, 24 bit, 10ksps

• ELM334x-xxxx: EtherCAT measurement technology series, thermocouple input, mini thermocouple
connector

• EP3314-0002: EtherCAT Box, 4 channel analog input, temperature, thermocouple, 16bit, M12

• EPP3314-0002: EtherCAT P Box, 4 channel analog input, temperature, thermocouple, 16bit, M12

• KL331x: bus terminal, 1/2/4 channel analog input, temperature, thermocouple, 16 bit

• EJ3318: EtherCAT plug-in module, 8 channel analog input, temperature, thermocouple, 16bit

The current overview can be found at www.beckhoff.com

EPP3314-000220 Version: 1.2

4 Mounting and connections

119

126

23

3026.5

14

Ø 3.5

13.5

4.1 Mounting

4.1.1 Dimensions

Mounting and connections

Fig.8: Dimensions

All dimensions are given in millimeters.

Housing features

Housing material PA6 (polyamide)
Sealing compound polyurethane
Mounting two fastening holes Ø 3.5 mm for M3
Metal parts brass, nickel-plated
Contacts CuZn, gold-plated
Installation position variable
Protection class IP65, IP66, IP67 (conforms to EN 60529) when screwed together
Dimensions (H x W x D) approx. 126 x 30 x 26.5 mm (without connectors)
Weight approx. 165g

EPP3314-0002 21Version: 1.2