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Single-ended/differential typification. Beckhoff EL3314-0002, EL3314-0090, EL3312, EL3318, EL3311, EL33-00 Series, EL3314-0010, EL3314
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Commissioning
5.12.4
Single-ended/differential typification
For analog inputs Beckhoff makes a basic distinction between two types: single-ended (SE) and differential
(DIFF) , referring to the difference in electrical connection with regard to the potential difference.
The diagram shows two-channel versions of an SE module and a DIFF module as examples for all multichannel versions.
Fig. 181: SE and DIFF module as 2-channel version
Note: Dashed lines indicate that the respective connection may not necessarily be present in each SE or
DIFF module. Electrical isolated channels are operating as differential type in general, hence there is no direct relation (voltaic) to ground within the module established at all. Indeed, specified information to recommended and maximum voltage levels have to be taken into account.
The basic rule:
• Analog measurements always take the form of voltage measurements between two potential points.
For voltage measurements a large R is used, in order to ensure a high impedance. For current measurements a small R is used as shunt. If the purpose is resistance measurement, corresponding considerations are applied.
◦ Beckhoff generally refers to these two points as input+/signal potential and input-/reference potential.
◦ For measurements between two potential points two potentials have to be supplied.
◦ Regarding the terms "single-wire connection" or "three-wire connection", please note the following for pure analog measurements: three- or four-wire connections can be used for sensor supply, but are not involved in the actual analog measurement, which always takes place between two potentials/wires.
In particular this also applies to SE, even though the term suggest that only one wire is required.
• The term "electrical isolation" should be clarified in advance.
Beckhoff IO modules feature 1..8 or more analog channels; with regard to the channel connection a distinction is made in terms of:
◦ how the channels WITHIN a module relate to each other, or
◦ how the channels of SEVERAL modules relate to each other.
The property of electrical isolation indicates whether the channels are directly connected to each other.
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◦ Beckhoff terminals/ boxes (and related product groups) always feature electrical isolation between the field/analog side and the bus/EtherCAT side. In other words, if two analog terminals/ boxes are not connected via the power contacts (cable), the modules are effectively electrically isolated.
◦ If channels within a module are electrically isolated, or if a single-channel module has no power contacts, the channels are effectively always differential. See also explanatory notes below.
Differential channels are not necessarily electrically isolated.
• Analog measuring channels are subject to technical limits, both in terms of the recommended operating range (continuous operation) and the destruction limit. Please refer to the respective terminal/ box documentation for further details.
Explanation
• differential (DIFF)
◦ Differential measurement is the most flexible concept. The user can freely choose both connection points, input+/signal potential and input-/reference potential, within the framework of the technical specification.
◦ A differential channel can also be operated as SE, if the reference potential of several sensors is linked. This interconnection may take place via the system GND.
◦ Since a differential channel is configured symmetrically internally (cf. Fig. SE and DIFF module as
2-channel variant), there will be a mid-potential (X) between the two supplied potentials that is the same as the internal ground/reference ground for this channel. If several DIFF channels are used in a module without electrical isolation, the technical property V
CM
(common-mode voltage) indicates the degree to which the mean voltage of the channels may differ.
◦ The internal reference ground may be accessible as connection point at the terminal/ box, in order to stabilize a defined GND potential in the terminal/ box. In this case it is particularly important to pay attention to the quality of this potential (noiselessness, voltage stability). At this GND point a wire may be connected to make sure that V
CM,max
is not exceeded in the differential sensor cable.
If differential channels are not electrically isolated, usually only one V
CM, max
is permitted. If the channels are electrically isolated this limit should not apply, and the channels voltages may differ up to the specified separation limit.
◦ Differential measurement in combination with correct sensor wiring has the special advantage that any interference affecting the sensor cable (ideally the feed and return line are arranged side by side, so that interference signals have the same effect on both wires) has very little effect on the measurement, since the potential of both lines varies jointly (hence the term common mode). In simple terms: Common-mode interference has the same effect on both wires in terms of amplitude and phasing.
◦ Nevertheless, the suppression of common-mode interference within a channel or between channels is subject to technical limits, which are specified in the technical data.
◦ Further helpfully information on this topic can be found on the documentation page Configuration of 0/4..20 mA differential inputs (see documentation for the EL30xx terminals, for example).
• Single Ended (SE)
◦ If the analog circuit is designed as SE, the input/reference wire is internally fixed to a certain potential that cannot be changed. This potential must be accessible from outside on at least one point for connecting the reference potential, e.g. via the power contacts (cable).
◦ In other words, in situations with several channels SE offers users the option to avoid returning at least one of the two sensor cables to the terminal/ box (in contrast to DIFF). Instead, the reference wire can be consolidated at the sensors, e.g. in the system GND.
◦ A disadvantage of this approach is that the separate feed and return line can result in voltage/ current variations, which a SE channel may no longer be able to handle. See common-mode interference. A V
CM
effect cannot occur, since the module channels are internally always 'hardwired' through the input/reference potential.
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Typification of the 2/3/4-wire connection of current sensors
Current transducers/sensors/field devices (referred to in the following simply as ‘sensor’) with the industrial
0/4-20 mA interface typically have internal transformation electronics for the physical measured variable
(temperature, current, etc.) at the current control output. These internal electronics must be supplied with energy (voltage, current). The type of cable for this supply thus separates the sensors into self-supplied or externally supplied sensors:
Self-supplied sensors
• The sensor draws the energy for its own operation via the sensor/signal cable + and -.
So that enough energy is always available for the sensor’s own operation and open-circuit detection is possible, a lower limit of 4 mA has been specified for the 4-20 mA interface; i.e. the sensor allows a minimum current of 4 mA and a maximum current of 20 mA to pass.
• 2-wire connection see Fig. 2-wire connection , cf. IEC60381-1
• Such current transducers generally represent a current sink and thus like to sit between + and – as a
‘variable load’. Refer also to the sensor manufacturer’s information.
Fig. 182: 2-wire connection
Therefore, they are to be connected according to the Beckhoff terminology as follows: preferably to ‘single-ended’ inputs if the +Supply connections of the terminal/ box are also to be used connect to +Supply and Signal they can, however, also be connected to ‘differential’ inputs , if the termination to GND is then manufactured on the application side – to be connected with the right polarity to +Signal and –Signal
It is important to refer to the information page Configuration of 0/4..20 mA differential inputs (see documentation for the EL30xx terminals, for example)!
Externally supplied sensors
• 3- and 4-wire connection see Fig. Connection of externally supplied sensors , cf. IEC60381-1
• the sensor draws the energy/operating voltage for its own operation from 2 supply cables of its own.
One or two further sensor cables are used for the signal transmission of the current loop:
◦ 1 sensor cable: according to the Beckhoff terminology such sensors are to be connected to
‘single-ended’ inputs in 3 cables with +/-/Signal lines and if necessary FE/shield
◦ 2 sensor cables: for sensors with 4-wire connection based on +supply/-supply/+signal/-signal, check whether +signal can be connected to +supply or –signal to –supply.
- Yes: then you can connect accordingly to a Beckhoff ‘single-ended’ input .
- No: the Beckhoff ‘differential’ input for +Signal and –Signal is to be selected; +Supply and –
Supply are to be connected via additional cables.
It is important to refer to the information page Configuration of 0/4..20 mA differential inputs
(see documentation for the EL30xx terminals, for example)!
Note: expert organizations such as NAMUR demand a usable measuring range <4 mA/>20 mA for error detection and adjustment, see also NAMUR NE043.
The Beckhoff device documentation must be consulted in order to see whether the respective device supports such an extended signal range.
Usually there is an internal diode existing within unipolar terminals/ boxes (and related product groups), in this case the polarity/direction of current have to be observed.
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Fig. 183: Connection of externally supplied sensors
Classification of the Beckhoff terminals/ boxes - Beckhoff 0/4-20 mA terminals/ boxes (and related product groups) are available as differential and single-ended terminals/ boxes (and related product groups):
Single-ended
EL3x4x: 0-20 mA, EL3x5x: 4-20 mA; KL and related product groups exactly the same
Preferred current direction because of internal diode
Designed for the connection of externally-supplied sensors with a
3/4-wire connection
Designed for the connection of self-supplied sensors with a 2-wire connection
Differential
EL3x1x: 0-20 mA, EL3x2x: 4-20 mA; KL and related product groups exactly the same
Preferred current direction because of internal diode
The terminal/ box is a passive differential current measuring device; passive means that the sensor is not supplied with power.
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Commissioning
Single-ended Differential
Fig. 184: 2-, 3- and 4-wire connection at single-ended and differential inputs
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Table of contents
- 7 1 Foreword
- 7 Product overview Analog Thermocouple Input Terminals
- 7 Notes on the documentation
- 9 Safety instructions
- 10 Documentation issue status
- 12 Version identification of EtherCAT devices
- 16 2 Product overview
- 16 EL3311, EL3312, EL
- 16 Introduction
- 20 Technical data
- 21 Introduction
- 22 Technical data
- 23 Introduction
- 25 Technical data
- 26 Introduction
- 27 Technical data
- 28 Introduction
- 29 Technical data
- 30 TC technology basics
- 31 Use of EL33xx in the TwinCAT System Manager
- 32 Start
- 34 3 Basics communication
- 34 EtherCAT basics
- 34 EtherCAT cabling – wire-bound
- 35 General notes for setting the watchdog
- 37 EtherCAT State Machine
- 39 CoE Interface
- 44 Distributed Clock
- 45 4 Mounting and wiring
- 45 Safety instructions
- 45 Environmental conditions
- 45 Transport / storage
- 45 Control cabinet / terminal box
- 46 Instructions for ESD protection
- 46 Installation on mounting rails
- 49 Installation instructions for enhanced mechanical load capacity
- 50 Connection
- 50 Connection system
- 52 Wiring
- 53 Shielding
- 54 Positioning of passive Terminals
- 54 4.10 Installation positions 331x
- 56 4.11 Prescribed installation position EL3314-0002/ EL
- 58 4.12 LEDs
- 58 EL3311 - LEDs
- 59 EL3312 - LEDs
- 60 EL3314, EL3314-00xx - LEDs
- 63 EL3318 - LEDs
- 64 4.13 Terminal assignment
- 64 EL3311 - Connection
- 65 EL3312 - Connection
- 66 EL3314-00x0 - Connection
- 69 EL3318 - Connection
- 70 Connection instructions for earthed/potential-free thermocouples
- 71 4.14 UL notice
- 72 4.15 ATEX - Special conditions (standard temperature range)
- 73 4.16 ATEX - Special conditions (extended temperature range)
- 74 4.17 ATEX Documentation
- 75 5 Commissioning
- 75 TwinCAT Quick Start
- 77 TwinCAT
- 99 TwinCAT Development Environment
- 99 Installation of the TwinCAT real-time driver
- 105 Notes regarding ESI device description
- 109 TwinCAT ESI Updater
- 109 Distinction between Online and Offline
- 110 OFFLINE configuration creation
- 115 ONLINE configuration creation
- 123 EtherCAT subscriber configuration
- 133 General Notes - EtherCAT Slave Application
- 141 TwinSAFE SC
- 141 TwinSAFE SC - operating principle
- 141 TwinSAFE SC configuration
- 145 Process data
- 145 Sync Manager
- 146 Process data preselection (predefined PDOs)
- 148 Data processing
- 148 TwinSAFE SC process data EL
- 149 Settings
- 149 Presentation, index 0x80n
- 149 Siemens bits, index 0x80n
- 150 Underrange, Overrange
- 150 Notch filter (conversion times)
- 151 Limit 1 and Limit
- 151 Calibration
- 153 Producer Codeword
- 154 Operation with an external cold junction
- 155 Interference from equipment
- 155 Wire break detection
- 155 5.10 Object description and parameterization
- 156 Restore object
- 157 Configuration data
- 159 Profile-specific objects (0x6000-0xFFFF)
- 159 Configuration data (vendor-specific)
- 159 Input data
- 160 Output data
- 160 Information and diagnostic data
- 161 Standard objects (0x1000-0x1FFF)
- 166 5.11 Status word
- 170 5.12 Notices on analog specifications
- 170 Full scale value (FSV)
- 170 Measuring error/ measurement deviation
- 171 Temperature coefficient tK [ppm/K]
- 172 Single-ended/differential typification
- 177 Common-mode voltage and reference ground (based on differential inputs)
- 177 Dielectric strength
- 178 Temporal aspects of analog/digital conversion
- 182 6 Appendix
- 182 Sample program for individual temperature calculation in the PLC
- 185 EtherCAT AL Status Codes
- 185 Firmware Update EL/ES/EM/EPxxxx
- 186 Device description ESI file/XML
- 189 Firmware explanation
- 190 Updating controller firmware *.efw
- 191 FPGA firmware *.rbf
- 195 Simultaneous updating of several EtherCAT devices
- 196 Firmware compatibility
- 198 Restoring the delivery state
- 199 Support and Service