AKT2G-AN-400-000

4-channel thermocouple input terminal, preset to type K, with wire breakage detection, 16 bit

See also:Notices on Analog Specifications for information on

Related Topics: Map Input and Output to Variables

Thermocouple Technology Basics

The thermocouple terminals can evaluate thermocouples of the types B, C, E, J, K, L, N, R, S, T and U. The characteristic curves are linearized and the reference temperature determined directly within the terminal.

Temperatures are output in 1/10°C, for example (device-dependent). The terminal is fully configurable via the Bus Coupler or the control system. Different output formats may be selected or own scaling activated. In addition, linearization of the characteristic curve and determination and calculation of the reference temperature (temperature at the terminal connection contacts) can be switched off.

Measuring principle of the thermocouple

Thermocouples can be classified as active transducers. They exploit the thermo-electric effect (Seebeck, Peltier, Thomson). A voltage referred to as thermovoltage occurs over the length of a cable with different temperatures at both ends. It is an unambiguous function of the temperature and the material. In a “TC element” this effect is utilized by operating two different conductor materials in parallel.

Figure 9-17: Principle of the thermocouple

Example: In the following example, the voltage Uth is given which is present at a type-K thermocouple at the temperature Tm.

Uth = (kNiCr - kNi) x ΔT

with

ΔT = Tm - Tv

A type-K thermocouple consists of a junction of a nickel-chrome alloy and nickel, where kNiCr and kNi represent the thermoelectric coefficients of nickel-chrome and nickel respectively. By adapting the equation according to Tm, the sought-after temperature can be calculated from the voltage measured across the thermocouple. Based on the difference to the cold junction temperature, the temperature at the measurement point can be determined to an accuracy of better than one tenth of a Kelvin with the aid of the above thermocouple equation.

Internal conversion of the thermovoltage and the reference voltage

Since the coefficients are determined at a reference temperature of 0°C, it is necessary to compensate for the effect of the reference temperature. This is done by converting the reference temperature into a reference voltage that depends on the type of thermocouple, and adding this to the measured thermovoltage. The temperature is found from the resulting voltage and the corresponding characteristic curve.

Uk = Um+ Ur

Tout = f(Uk)

Overview of suitable thermocouples

The following thermocouples are suitable for temperature measurement:

Type (according
to EN60584-1)

Element

Implemented temperature
range

Color coding
(sheath - plus pole - minus pole)

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

LEDs

LED

Color

Meaning

RUN

green

This LED indicates the terminal's operating state:

off

State of the EtherCAT State Machine: INIT = initialization of the terminal

flashing uniformly

State of the EtherCAT State Machine: PREOP = function for mailbox communication and different standard-settings set

flashing slowly

State of the EtherCAT State Machine: SAFEOP = verification of the sync manager channels and the distributed clocks.

Outputs remain in safe state

on

State of the EtherCAT State Machine: OP = normal operating state; mailbox and process data communication is possible

flashing rapidly

State of the EtherCAT State Machine: BOOTSTRAP = function for terminal firmware updates

ERROR1-4

red

Short circuit or wire breakage. The resistance is in the invalid range of the characteristic curve.

Connection Instructions for Earthed/Potential-Free Thermocouples

Due to the differential inputs of the terminals, different connection types are recommended depending on the type of thermocouple used. For earthed thermocouples, ground is not connected to the shielding. If the thermocouple does not have a ground connection, the ground and shielding contacts can be connected (see AKT2G-AN-400-000).


  • Connection instructions for thermocouples

    • Earthed thermocouple
      • Do not connect GND to the shielding
    • Potential-free / earth-free thermocouple
      • GND can be connected to the shielding
      • or: GND can connected to any potential, max. 35 V to 0 V power
    • Non-potential-free thermocouple
      • Do not connect GND to the shielding
      • Do not connect GND to thermocouple potential.
      • Thermocouple-potential max. 35 V to 0 V power
    • Unused inputs
      • Unused inputs should be short-circuited (low-resistance connection of +TC, -TC)

Shielding Measures


  • Shielding Measures

    Due to the complexity in the "EMC" area, there is no generally applicable guideline, but only technical measures in accordance with the state of the art, which can sometimes contradict each other. These must be checked for feasibility and effectiveness, taking into account the plant specifications, and applied by the plant installer following assessment.

    The following notes on shielding are to be understood as technical suggestions that have proven themselves from time to time in practical use. It must be checked in each case which measures can be applied, depending on the installation and plant. The effectiveness of each measure must be checked individually. The formal transferability of measures to other types of plant is in general not possible.

    Priority is to be given to typical national or general normative specifications.

A shielding approach is described below that in many cases improves the measurement quality. The suggested measures must be checked for feasibility and effectiveness in the actual plant.

  • Apply the shield with a low resistance and enveloping the cable by 360°
  • at the entry point into the control cabinet, the shield should be earthed conductively
  • the shield should be earthed again at the terminal
    • at the terminal connection point, if present
    • if no terminal connection point is available, earth the shield as close to the terminal as possible.
    • to avoid ground loops the shield can be undone after entry into the control cabinet. A capacitive connection to the terminal shield contact is possible.
    • avoid unshielded cable lengths of > 50 cm!
AN-240 Shield Connection with Shield Contact Examples
In the case of potential interference sources inside the control cabinet In the case of potential interference sources inside and outside the control cabinet

Data Processing - TC Temperature

Settings

Presentation

index 0x80n0:02

In the delivery state, the measured value is output in increments of 1/10° C in two's complement format (signed integer).

Index 0x80n0:02 offers the possibility to change the method of representation of the measured value.

Measured value

Output (hexadecimal)

Output (signed integer, decimal)

-200.0 °C

0nF830

-2000

-100.0 °C

0nFC18

-1000

-0.1 °C

0nFFFF

-1

0.0 °C

0n0000

0

0.1 °C

0n0001

1

100.0 °C

0n03E8

1000

200.0 °C

0n07D0

2000

500.0 °C

0x1388

5000

850.0 °C

0x2134

8500

1000.0 °C

0x2170

10000

Table 9-5: Output of measured value and process data

  • Signed Integer:

    The measured value is presented in two’s complement format.
    Maximum presentation range for 16 bit = -32768 .. +32767

    Example:

    • 1000 0000 0000 0000bin = 0x8000hex = - 32768dec
    • 1111 1111 1111 1110bin = 0nFFFEhex = - 2dec
    • 1111 1111 1111 1111bin = 0nFFFFhex = - 1dec
    • 0000 0000 0000 0001bin = 0n0001hex = +1dec
    • 0000 0000 0000 0010bin = 0n0002hex = +2dec
    • 0111 1111 1111 1111bin = 0x7FFFhex = +32767dec
  • Absolute value with MSBClosed"Most significant bit" Sometimes abbreviated as MSB, the most significant bit is the bit position in a binary number having the greatest value as sign:

    The measured value is output in magnitude-sign format.
    Maximum presentation range for 16 bit = -32767 .. +32767

    Example:

    • 1111 1111 1111 1111bin = 0nFFFFhex = - 32767dec
    • 1000 0000 0000 0010bin = 0x8002hex = - 2dec
    • 1000 0000 0000 0001bin = 0x8001hex = - 1dec
    • 0000 0000 0000 0001bin = 0n0001hex = +1dec
    • 0000 0000 0000 0010bin = 0n0002hex = +2dec
    • 0111 1111 1111 1111bin = 0x7FFFhex = +32767dec
  • High resolution (1/100 C°):

    The measured value is output in 1/100 °C steps.

Siemens bits

index 0x80n0:05

If the bit in index 0x80n0:05 is set, status displays are shown for the lowest 3 bits. In the error case "overrange" or "underrange", bit 0 is set.

Underrange, Overrange

Undershoot and overshoot of the measuring range (underrange, overrange), index 0x60n0:02, 0x60n0:03

  • Uk > Ukmax: Index 0x60n0:02 and index 0x60n0:07 (overrange and error bit) are set. The linearization of the characteristic curve is continued with the coefficients of the overrange limit up to the limit stop of the A/D converter or to the maximum value of 0x7FFF.
  • Uk < Ukmax: Index 0x60n0:01 and index 0x60n0:07 (underrange and error bit) are set. The linearization of the characteristic curve is continued with the coefficients of the underrange limit up to the limit stop of the A/D converter or to the minimum value of 0x8000.

For overrange or underrange the red error LED is switched on.

Notch filter (conversion times)

Notch filter, index 0x80n0:06

The AN-400 terminals are equipped with a digital filter. The filter performs a notch filter function and determines the conversion time of the terminal. It is parameterized via the indices 0x80n0:15. The higher the filter frequency, the faster the conversion time.


  • Index 0x80n0:06

    The filter function is always active even if the bit is not set, since this is obligatory for the measurement process!


  • The filter characteristics are set via index 0x8000:15

    The filter frequencies are set for all channels of the AN-400 terminals centrally via index 0x8000:15 (channel 1, see "80n0:15"). The corresponding indices 0x8010:15, 0x8020:15, 0x8030:15 have no parameterization function.


  • Conversion time

    The conversion time is determined as follows:

    No. of active channels * no. of measurements * no. of filter periods + computing time = conversion time

Example: (2 channels), 3 measurements (thermocouple, wire breakage, cold junction), filter 50 Hz

2 channels * 3 measurements * (1/50 Hz) + 6 ms ≈ 126 ms

Example: (4 channels), 3 measurements (thermocouple, wire breakage, cold junction), filter 50 Hz

4 channels * 3 measurements * (1/50 Hz) + 12 ms ≈ 252 ms

Typical conversion times with 3 measurements (thermocouple, broken wire, cold junction)

Filter frequency

AKT2G-AN-400

5 Hz

2.4 s

10 Hz

1.2 s

50 Hz

250 ms

60 Hz

210 ms

100 Hz

130 ms

500 Hz

33 ms

1000 Hz

24 ms

2000 Hz

20 ms

3750 Hz

19 ms

7500 Hz

19 ms

15000 Hz

19 ms

30000 Hz

19 ms

mV range

12 ms

Table 9-6: Conversion times in relation to the filter frequencies

Limit 1 and Limit 2

Limit 1 and limit 2, index 0x80n0:13, index 0x80n0:14

A temperature range can be set that is limited by the values in the indices 0x80n0:13 and 0x80n0:14. If the limit values are overshot, the bits in indices 0x80n0:07 and 0x80n0:08 are set.

The temperature value is entered with a resolution of 0.1 °C.

Example:

Limit 1= 30 °C

Value index 0x80n0:13 = 300

Calibration

User calibration

index 0x80n0:0A

User calibration is enabled via index 0x80n0:0A. Parameterization takes place via the indices

User scaling

index 0x80n0:01

The user scaling is enabled via index 0x80n0:01. Parameterization takes place via the indices

  • 0x80n0:11
    User scaling offset

    The offset describes a vertical shift of the characteristic curve by a linear amount.

    At a resolution of 0.1°, 1 digit(dec) corresponds to an increase in measured value by 0.1° At a resolution of 0.01°, 1 digit(dec) corresponds to an increase in measured value by 0.01

  • 0x80n0:12
    User scaling gain

    The default value of 65536(dec) corresponds to gain = 1.

    The new gain value for 2-point user calibration after offset calibration is determined as follows:

    Gain_new = reference temperature / measured value x 65536(dec)

Calculation of process data

The concept "calibration" is used here even if it has nothing to do with the deviation statements of a calibration certificate. Actually, this is a description of the vendor or customer calibration data/adjustment data used by the device during operation in order to maintain the assured measuring accuracy.

The terminal constantly records measured values and saves the raw values from its A/D converter in the ADC raw value objects 0x80nE:01, 0x80nE:02. After each recording of the analog signal, the correction calculation takes place with the vendor and user calibration data as well as the user scaling, if these are activated (see following picture).

Figure 9-18: Calculation of process data

Calculation

Designation

XADC

Output of the A/D converter

XF

Output value after the filter

YH = (XADC – BH) x AH x 2-14

Measured value after vendor calibration,

YA = (YH – BA) x AA x 2-14

Measured value after vendor and user calibration

YS= YA x AS x 2-16 + BS

Measured value following user scaling
Legend for previous table

Name

Designation

Index

XADC

Output value of the A/D converter

0x80nE:01

XF

Output value after the filter

-

BH

Vendor calibration offset (not changeable)

0x80nF:01

AH

Vendor calibration gain (not changeable)

0x80nF:02

BA

User calibration offset (can be activated via index 0x80n0:0A)

0x80n0:17

AA

User calibration gain (can be activated via index 0x80n0:0A)

0x80n0:18

BS

User scaling offset (can be activated via index 0x80n0:01)

0x80n0:11

AS

User scaling gain (can be activated via index 0x80n0:01)

0x80n0:12

YS

Process data for controller

-

  • Measurement Result

    The accuracy of the result may be reduced if the measured value is smaller than 32767 / 4 due to one or more multiplications.

Producer Codeword


  • Producer Codeword

    The vendor reserves the authority for the basic calibration of the terminals. The Producer codeword is therefore at present reserved.

Operation with an external cold junction

The AKT2G-AN-400 supports operation with an internal cold junction as standard. This means that the thermocouple is attached to the terminal points at the front of the terminal housing, so that the material transition and the cold junction are located at the front of the terminal housing. The terminal measures the cold junction temperature with its own internal temperature sensor and calculates the desired measuring point temperature value.

In special applications, operation with an external cold junction is required. The external cold junction is connected to the AN-400 with a normal copper connection cable, the material transition then takes place in the external connection point.

Figure 9-19: External cold junction

For this operation the following must be set

  • all CJCompensation PDO of the terminal must be activated, even if the "external cold junction" function is only used on isolated channels

  • In CoE 0x80n0:0C of the desired channel, the external cold junction calculation must be activated by the value "2" (external process data).

The cold junction temperature Tv must now be recorded by a separate temperature sensor at the cold junction and fed to the terminal via the fieldbus master and the fieldbus as a linked variable ("external") (see Figure 9-19: External cold junction).

The separate measurement can technically be done via another thermocouple connected to an AN-400, or any other temperature measurement whose value is known to the controller.

The AN-400 then supplies the measured value Value, taking into account the temperature value supplied with CJCompensation:

The comparison data is written to CoE 0x70n0:11.


  • Alternative to cold junction measurement

    As an alternative to the procedure described above, the cold junction can be maintained at a defined temperature through ice water (0° C), for example. In this case, the temperature is known without measurement of the cold junction temperature (Figure 9-19: External cold junction) and can be reported to the AN-400 via the process data.

Interference From Equipment

When operating the AKT2G-AN-400 analog EtherCAT terminals, high frequency superimposed signals from interfering devices (e.g. proportional valves, stepper motors or DC motor output stages) can be picked up by the terminal. In order to guarantee interference-free operation, we recommend the use of separate power supply units for the terminals and the interference-causing devices.

Wire Break Detection

The AKT2G-AN-400 terminals provide a wire break detection of the connected thermocouple. A periodical testing current of several µA will be given to the thermocouple for detection. No voltage measurement takes place during test.

Due to particular cases, the testing current could have a disturbing effect, the wire break detection can be disabled by CoE (object 0x80n0:0E, "Disable wire break detection") since following firmware versions:

  AKT2G-AN-400
Firmware 04
ESI / Revision 0023

Status Word

The status information for each channel of the AN-400 is transmitted cyclically from the terminal to the EtherCAT Master as process data (PDO). Two versions of the device description are available for the AN-400, representing the process image in individual and extended forms.

The AN-400 transmits the following process data:

  • Underrange: Measurement is below range
  • Overrange: Range of measurement exceeded ("Cable break" together with "Error")
  • Limit 1: Limit value monitoring 0: ok, 1: Limit value overshot , 2: limit range undershot
  • Limit 2: Limit value monitoring 0: ok, 1: Limit value overshot , 2: limit range undershot
  • Error: The error bit is set if the process data is invalid (cable break, overrange, underrange)
  • TxPDO State: Validity of the data of the associated TxPDO (0 = valid, 1 = invalid).
  • TxPDO Toggle: The TxPDO toggle is toggled by the slave when the data of the associated TxPDO isupdated. This allows the currently required conversion time to be derived.

The limit evaluation is set in the "8000" objects in the CoE directory.

Technical Data

Technical Data

AKT2G-AN-400-000

Number of inputs

4

Thermocouple sensor types

Types J, K, L, B, E, N, R, S, T, U, C (default setting type K), mV measurement

Input filter limit frequency

1 kHz typ.; depending on sensor length, conversion time, sensor type

Connection technology

2-wire

Maximum cable length to the thermocouple

30 m

Measuring range, FSV

in the range defined in each case for the sensor (default setting: type K; -200 … +1370°C)

Voltage: ± 30 mV (1 µV resolution) up to ± 75 mV (4 µV resolution)

Resolution

Internal: 16 bit

Temperature representation: 0.1/0.01 °C per digit, default 0.1°C

Note: 16 bit is used for FSV calculation; so, value leaps >0.01°C will occur at resolution 0.01°C depending of which thermocouple is set; e.g. type K: approx. 0.04°C

Supports NoCoeStorage function

yes, from firmware 01

Wiring fail indication

yes

Conversion time

approx. 2.5 s to 20 ms,

depending on configuration and fil ter setting, default: approx. 250 ms

Measuring error

< ±0.3 % (relative to full scale value)

Voltage supply for electronics

via the E-bus

Distributed Clocks

-

Current consumption via E-bus

typ. 200 mA

Bit width in the process data image

max. 16 byte input, max. 8 byte output

Max. potential ±TC against ground

2 V, important e.g. when operating with grounded thermocouples

Max. differential voltage between the ±TC inputs

±15 V permanent

Electrical isolation

500 V (E-bus/field voltage)

Configuration

via TwinCAT System Manager

Weight

approx. 60 g

Permissible ambient temperature range during operation

-25°C ... +60°C (extended temperature range), from firmware 06

Permissible ambient temperature range during storage

-40°C ... +85°C

Permissible relative humidity

95%, no condensation

Dimensions (W x H x D)

approx. 15 mm x 100 mm x 70 mm (width aligned: 12 mm)

Mounting

on 35 mm mounting rail conforms to EN 60715

Vibration/shock resistance

conforms to EN 60068-2-6 / EN 60068-2-27,

see also installation instructions for terminals with increased mechanical load capacity

EMC immunity/emission

conforms to EN 61000-6-2 / EN 61000-6-4

Protection class

IP20

Installation position

variable

Approval

CE, ATEX, cULus, IECEx