BECKHOFF EL31xx Series 16 Bit EtherCAT Analog Input Terminal Manual

BECKHOFF EL31xx High speed Analog Input Terminal: On site Diagnosis, Troubleshooting, and Maintenance Guide

The Beckhoff EL31xx series EtherCAT analog input terminal is a high-speed 16 bit acquisition module designed for high-performance measurement applications. Compared to the EL30xx series, its conversion time is significantly reduced (up to about 35 µ s), it supports distributed clock (DC) synchronization, and offers differential or single ended input options. The product covers multiple signal types such as ± 10   V, 0... 20   mA, 4... 20   mA, including EL310x, EL311x, EL312x, EL314x, EL315x, EL316x, and configurable EL3174 sub models.

When on-site engineers use these terminals, they may encounter issues such as measurement value jumps, over range alarms, disconnection indications, terminals unable to enter the OP state, or synchronization errors. This document aims to provide a comprehensive hardware diagnostic and parameter configuration guide for the EL31xx series, based entirely on official technical documentation, focusing on practical operational scenarios, covering the entire process from installation and wiring, LED status interpretation, process data analysis to filter settings and factory reset.

1. Overview of Product Series and Key Selection Points

EL31xx terminals are classified into the following main categories based on signal type and input structure:

Model Series Signal Range Input Type Typical Model

EL310x -10...+10   V differential EL3101/2/4

EL311x 0... 20 mA differential EL3111/2/4; EL3112-0011 is ± 20 mA

EL312x 4... 20mA differential EL3121/2/4; EL3124-0090 with TwinSAFE SC

EL314x 0... 20   mA single ended EL3141/2/4; EL3142-0010 is ± 10 mA

EL315x 4... 20   mA single ended EL3151/2/4

EL316x 0... 10   V single ended EL3161/2/4

EL3174-10/0...+10   V/-20/0/+4...+20   mA configurable (U/I) EL3174-0002 (differential isolation), EL3174‑0090（TwinSAFE SC）

Key differences in selection:

Differential input (EL310x/311x/312x): Each channel has independent signal pairs (+/-), strong resistance to common mode interference, and supports long-distance transmission. Common mode voltage (Ucm) limit: EL310x is ± 35   V (for internal GND), EL311x/EL312x is ± 10   V.

Single ended input (EL314x/315x/316x): The signal reference ground is either the 0   V power contact or the internal GND. The wiring is simple and suitable for situations where the sensor and terminal ground potential are consistent. Some models (such as EL3154) provide 24V output to power two-wire sensors.

EL3174 series: Each channel can be independently configured with voltage or current mode. EL3174-0002/0032 adopts differential input and electrical isolation between channels (test voltage 2500   VDC), while EL3174-0090 supports safe single channel (TwinSAFE SC).

2. Key points for installation and wiring

2.1 Mechanical Installation and ESD Protection

The terminal is installed vertically on a 35 mm DIN rail, with at least 30 mm ventilation gap reserved above and below.

EL9011/EL9012 end caps must be used to seal the ends to ensure protection level and ESD protection.

ESD sensitivity: Avoid direct contact with spring contacts; Workbenches, packaging, and personnel should be grounded.

2.2 Power contacts and E-bus power supply

The E-bus (5   V) is provided by the left coupler, and the total current should not exceed 2   A. When exceeding the limit, the EL9410 and other power supply input terminals need to be inserted.

The power contacts transmit 24V on-site power supply, but some terminals' input reference ground is not connected to the power contacts (such as EL3101/3102, EL3111/3112, etc.), which requires special attention.

The PE contact (protective grounding) is the first to connect and can carry a short-circuit current of 125 amperes. During insulation testing, the PE connection should be disconnected.

2.3 Common mode voltage processing for differential current input (0/4... 20 mA)

For differential current inputs such as EL311x/EL312x, internal measurement is carried out through a 33 Ω shunt resistor, and the potential difference (Ucm) between the midpoint of the resistor (CMP) and the internal GND (GND_int) must not exceed the specification (usually ± 10   V). The 1/2 channel terminal leads GND_int to the terminal point and can be externally wired to stabilize the common mode potential.

Correct wiring example: Both sensors use low side measurement (negative terminal connected to GND) - CMP potential is about 0.33   V, Ucm<0.5   V, which meets the requirements.

Example of incorrect wiring: A low side measurement (5   V) and a high side measurement (12   V) - the potential difference between the two CMP channels is greater than 10   V, resulting in measurement errors. At this point, GND_int should be connected to an auxiliary potential (such as 6V) to center CMP.

4-channel terminals (EL3114/EL3124): GND_int is internally connected to the 0   V power supply contact, and it must be ensured that the common mode potential of all channels meets Ucm, Max.

2.4 Shielded Connection

Analog sensors and encoders must use shielded twisted pair cables. The shielding layer should be single ended grounded through terminal point 4 or 8 (Shield) to avoid mixing with GND_int.

3. LED status indicator diagnosis

The RUN LED (green) on the EL31xx terminal indicates the status of the EtherCAT state machine (ESM):

LED Status ESM Status Description

Turn off the Initiat/BOOTSTRAP initialization or firmware update mode

Flashing PREOP email communication available, no process data available

Single flash SAFEOP output safe status, valid input data (limited to terminals with output)

The OP is running normally and the process data communication is normal

In addition, each channel of the current input terminals (EL311x/312x/314x/315x) is equipped with an ERROR LED (red):

Illuminated: Indicates over range or under range.

For the 4-20 mA terminals (EL312x/EL315x), the red LED also indicates a disconnection (current<2 mA typical value).

The diagnostic bit can be read through the Overrange (bit1), Underrange (bit0), and Error (bit6) in the status word.

4. Detailed explanation of process data and status words

EL31xx defaults to 4-byte process data per channel: 2-byte Status+2-byte Value. Compact mode (only 2-byte values) can also be selected through "Predefined PDO Assignment".

Definition of Status Word:

Name Description

0 Underrange input signal is below the lower limit of the measurement range. For example, set the ± 10   V terminal when it is below approximately -10.2   V.

1 Overlange is higher than the upper limit (approximately+10.2   V).

Comparison result between 3 Limit 1 and the user set Limit 1 (2-bit: 0=inactive, 1=less than, 2=greater than, 3=equal to)

5 Limit 2 Same as above

6 Error universal error bit, set when Overrange or Underrange.

13 Sync error in DC mode (supported starting from the revised version EL31xx 0000-0016)

Set 1 when there is an internal error in TxPDO State, indicating that the process data is invalid.

The 15 TxPDO toggle flips every time a new measurement value is updated to monitor the conversion cycle.

Value: A 16 bit signed integer corresponding to ± 32767 at full scale. It can be changed to an unsigned integer or signed amplitude representation through the CoE object 0x80n0:02. EL3174 supports Extended Range, with 100% corresponding to ± 30518 (0x7736) and a technical range of ± 107%.

5. Operation mode and synchronous configuration

EL31xx supports three operation modes, set through the CoE object 0x1C33:01:

Typical transition time for mode filter state synchronization method

FreeRun (default) can enable the internal timer of the FIR/IR terminal to asynchronously collect 50Hz FIR: 625 µ s (1ch)/1.25 µ ms (4ch)

Sync (SM2 event) must be disabled for each EtherCAT cycle, triggering a transition that is the same as the cycle and requires a minimum transition time (e.g. 80 µ s)

DC synchronization must be turned off. The minimum interruption period for the distributed clock SYNC 0/SYNC 1 is 100 µ s (1ch) and 150 µ s (4ch)

Filter settings:

Enable the filter through 0x8000:06 and select the type (0=50Hz FIR, 1=60Hz FIR, 2... 9=IIR 1... 8) through 0x8000:15. FIR provides notch characteristics (50/60Hz suppression>45 dB), while IIR is first-order low-pass (cutoff frequency reduced from 1 kHz to 3 Hz).

Important: The filter parameters must be set centrally through channel 1 (x800:15), and 0x80n0:15 for other channels is invalid.

Fast Mode:

By setting bit15=1 for 0x1C33:01 (e.g. 0x8001), CoE online access can be disabled, thereby reducing conversion time by approximately one-third.

When enabling Fast Mode, the filter must be turned off at the same time.

6. Common troubleshooting and diagnosis

6.1 Terminal cannot enter OP state

Possible reason: Invalid PDO configuration; Watchdog triggered; E-bus power supply is insufficient.

Solution: Check if the PDO combination in the "Process Data" tab is valid (if Legacy and Standard cannot be selected simultaneously). View the 'invalid SM cfg' information in the TwinCAT log. Calculate the total current of the E-bus (typically 130 mA per terminal), and if it exceeds 2 mA, insert the power supply input terminal.

6.2 The measured value is always 0 or a fixed value

Possible cause: Sensor wiring error; The 24V power supply is not connected (external power supply is required for the single ended current terminal); Range configuration error; Broken line.

solve:

For EL314x/EL315x single ended current input: Confirm that+24V has been connected to terminal point 2 (or the corresponding terminal), and the sensor is connected in series between 24V and the input.

For EL311x/EL312x differential current input: Check the polarity and ensure that GND_int is correctly connected (especially when multiple sensor power supplies are different).

Observe the ERROR LED: If it lights up, read the Overrange/Underrange bits of the status word. For 4-20 mA, if the current is less than 2 mA, the ERROR LED will remain on and the Underrange will be set, indicating a disconnection.

6.3 Common mode voltage (Ucm) issue causing measurement drift (differential input only)

When two channels of sensors use different power sources (such as one low side and one high side), the potential difference between the two CMPs may exceed Ucm, max (± 10   V), causing internal balancing current and measurement errors.

Solution:

For EL3111/3112/3121/3122: Connect terminal point 3 or 7 (GND_int) to an external low impedance potential (such as 0V or sensor common terminal) to center the CMP potential of all channels.

For EL3114/3124: GND_int connected to the 0   V power supply contact, ensure that the sensor reference potential of all channels is close to 0   V. Mixing high and low side measurements is strictly prohibited.

6.4 Measurement values with high noise or jumping

Possible reasons: electromagnetic interference; The filter is not turned on; Poor grounding.

Solution: Use shielded twisted pair cables and connect the shielding layer to the Shield terminal. Enable 50/60 Hz FIR filter (via x800:06 and x800:15). Ground the sensor power supply and terminal power supply together. For devices with severe interference (such as frequency converters), use an independent power supply to power the terminals.

6.5 Firmware/hardware revision number mismatch (blue/red entries displayed during scanning)

When TwinCAT scans the actual hardware, if the actual revision number is higher than the one in the configuration, it will be displayed in blue (usually compatible, but it needs to be confirmed that the new feature does not affect the original logic). If the actual revision number is lower than the one in the configuration, it will be displayed in red (possibly incompatible).

Principle: The revision number of the actual terminal used should be ≥ the revision number in the configuration.

Solution: Use "Copy Before" in the "Correction Dialog" to update the configuration to the actual revision number or replace it with matching hardware.

6.6 CoE parameter cannot be saved or EEPROM lifespan issue

Beckhoff terminal saves CoE changes to EEPROM (with a typical lifespan of 100000 write operations). If the program frequently modifies parameters (such as multiple times per second), it will exhaust its lifespan.

Solution: For parameters that require frequent changes, use the NoCoeStorage function (if supported by the firmware): write the code word 0x12345678 to the object 0xF008, and the changed CoE value will no longer be written to the EEPROM. This function fails after the device is restarted.

7. Key parameter configuration and calibration

7.1 User Scaling

By enabling 0x80n0:01, the gain 0x80n0:12 (Q16 fixed-point format, default 65536 corresponds to 1.0) and offset 0x80n0:11 (INT16) can linearly transform the measured values. Formula: YS=(YH × AS/2 ^ 16)+BS. The gain is limited within ± 0x7FFFF, exceeding it will trigger error 0x06090031/32.

7.2 Limit Monitoring (Limit 1/Limit 2)

Enabled by 0x80n0:07/08, the limit value is set by 0x80n0:13/14 (INT16, consistent with the process numerical representation). The status bits 0x60n0:03 and 0x60n0:05 are output in a 2-bit format. The logic of greater/less can be reversed using 0x80n0:0E (Swap limit bits).

7.3 User Calibration

Enabling through 0x80n0:0A, offset 0x80n0:17 and gain 0x80n0:18 (INT16, default 16384 corresponds to 1.0) can compensate for sensor or system errors. Starting from a specific firmware version (see document compatibility table), user calibration is password protected: write 0x12345678 to 0xF009 to activate protection (read-only), and write 0x11223344 to remove protection.

7.4 Factory reset

Find object 0x1011:01 in CoE Online, write value 0x64616F6C (ASCII "load"), and all BackUp objects will be reset to the delivery state. Partial old terminals require the use of substitute value 0x6C6F6164.

8. Firmware updates and ESI description files

8.1 Precautions for firmware update

Only using TwinCAT 3, the system is in Config/FreeRun mode, with a cycle time of ≥ 1ms.

It is necessary to ensure that EtherCAT communication has no CRC errors or frame loss.

During the update process, it is absolutely forbidden to power off or disconnect the network, otherwise the terminals may be permanently damaged.

Confirm that the new firmware is compatible with the hardware version before updating (refer to the compatibility table in the documentation). If using Bundle firmware (file name containing REV and SW) and entering password 1 in the download dialog box, the controller firmware (*. efw) and ESI description can be updated simultaneously.

8.2 ESI/EEPROM Update

Right click on the online terminal, select "EEPROM Update", and choose the new ESI file (XML). After the update, the terminal needs to be powered off and restarted to take effect. Attention: Some terminals (such as EL3174-0002) store production calibration data, and updating ESI may overwrite this data. Please consult Beckhoff support.

9. Maintenance suggestions

Suggested inspection period notes

The tightening of terminal wiring may cause spring terminals to loosen due to annual vibration

Ventilation openings should be cleaned every six months using a vacuum cleaner, and compressed air is prohibited

Parameter backup (startup list) saves the CoE configuration to the startup list after each modification, facilitating quick terminal replacement

Firmware version check: Visit the Beckhoff website every 2 years to obtain updates and fix known issues