BECKHOFF EL31xx Series 16 Bit EtherCAT Analog Input Terminal Manual

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: