Process data

Data flow

The amplitude values are measured with 16-bit resolution and provided as oversampling packets in the process image for cyclic transmission.

Data processing

The data processing is done simultaneously for all channels in the EL3773 with 16-bit conversion in the ADC
Scaling related to the respective (constant) measuring range:

1. Vendor calibration (0x80p0:0B)

Activation: CoE 0x80p0:0B
X₁ = (X_ADC - Offset_Vendor) * Gain_Vendor

This produces the following signed integer value representation:

Signed integer: the negative output value is represented in two’s complement (negated + 1). Maximum representation range for 16 bits = -32768 to +32767_dec.

2. User calibration (0x80p0:0A)

Activation: CoE 0x80n0:0A
X₂ = (X₁ - Offset_User) * Gain_User

3. Limit value evaluation (0x80p0:13, 0x80p0:14)

Display in the status word of the channel

If the value exceeds or falls below these values, which can be entered in the indices 0x80p0:13 and 0x80p0:14, then the bits in the indices 0x60p0:03 and 0x60p0:05 are set accordingly (see example below).
The entry 0x80p0:07 serves to activate the limit value monitoring.

Output limit n (2-bit):

• 0: not active
• 1: One or more values <= Limit n
• 2: One or more values >= Limit n
• 3: Cases 1 and 2 simultaneously

Linking in the PLC with 2-bit values The limit information consists of 2 bits. Limitn can be linked to the PLC or a task in the System Manager: PLC: IEC61131-PLC contains no 2-bit data type that can be linked with this process data directly. In order to transmit the limit information, therefore, define an input byte, e.g. and link the limit with the VariableSizeMismatch dialog. Additional task 2-bit variables can be created in the System Manager.

Example of voltage measurement with EL3773:

Channel 1; Limit 1 and Limit 2 enabled, Limit 1 = 100 V, Limit 2 = 200 V, representation: signed integer

Entry in index (Limit 1): 0x8000:13
(100 V / 410 V) x 2¹⁶ / 2 - 1 = 7991_dec

Entry in index (Limit 2): 0x8000:14
(200 V / 410 V) x 2¹⁶ / 2 - 1 = 15983_dec

Output:

4. Provision in the process data

The influencing parameters can be changed in the CoE of the respective channel.

Changes in the CoE directory In case of changes to the CoE default parameters, it is essential that corresponding values are entered in the start-up list, so that in the case of exchange the EL3773 operates again as foreseen in the application.

Predefined PDO Assignment

The "Predefined PDO Assignment" enables a simplified selection of the process data.
The desired function is selected on the lower part of the "Process Data" tab. As a result, all necessary PDOs are automatically activated and the unnecessary PDOs are deactivated.
8 PDO assignments are available: 

Process image

The EL3773 is inserted into the configuration by default with the 10-fold oversampling process image and DC timestamp:

It is urgently recommended to evaluate the offered diagnostic values in the controller, e.g. see the Notes page.

In particular the EL3773 offers the following cyclic information:

Correlation between timestamp and process data

The figure "Timing relationship between SYNC signals and SyncManager interrupt" illustrates the function and the timing relationship between time stamp and measured values.

For explanation::

• shown is an example for oversampling factor = 5
• the SYNC0 signal in the terminal triggers the AD conversion and fills the internal buffer with 5 measured values (A)
• SYNC1 runs synchronously with the cycle time, which triggers the supply of the filled buffer as process date and simultaneously fetches the StartTimeNextLatch from the local DistributedClock (B)
• the data block is assembled together with the next LatchTime
• the next EtherCAT cycle fetches this data (C)

Since different input filters (see CoE setting 0x8000:15 [95]) also result in different propagation delays within the terminal, these can be compensated again via CoE object 0x805D:12 so that the time stamp continues to match the measured values. Please refer to the following table to find the appropriate value for your input filter.

However, since only one DCTimeStampShift value can be set per terminal, it may make sense to perform this conversion in the PLC first if the input filters are different for each channel.

Control/status word

Status word

The status word (SW) is located in the input process image, and is transmitted from terminal to the controller.

Control word

The EL3773 has no control word

Synchronization, trigger and conversion time

The EL3773 generally operates in oversampling mode. It can be operated with and without Distributed Clocks activated.

Distributed Clocks activated

• the EtherCAT system-wide synchronized Distributed Clocks also encompass this EL3773
• the terminal then operates synchronously with all other DC devices
• the sampling clock is derived from the local DC in the EtherCAT slave controller (SYNC0: Oversampling, SYNC1: Provision of the data)

Advantages

• several EL3773 record the measured values of all their channels synchronously
• accurate time stamp of the individual samples

The following limit values are to be observed

• minimum sampling time 100 µs (10,000 kSps)
• only non-periodic values are permissible for the sampling rate
• the PDO StartTimeNextlatch can only be used/activated with cycle times > 100 µs

Table of sampling times

Supported configurations Configurations that require sampling times that are not divisible by 500 ns are not supported. The above table "Sampling times" does not show all possible cycle times.

Example: a 4000µs-cycle can be used with an oversampling factor of 64, since the sampling time is 62.5µs and therefore divisible by 500ns.

The minimum EtherCAT cycle time for the EL3773 is 100 µs. In order to activate Distributed Clocks, "DC" is to be selected in the Predefined PDO list, so that amongst others the time stamp PDO is selected

The permissible oversampling rates are set via the System Manager DC tab:

Distributed Clocks not activated

• the EL3773 operates according to an internal clock, which is synchronized to the EtherCAT cycle time. The trigger point in this case is the access to the input Sync Manager SM3.
• As a result the EL3773 can compensate fluctuations in the cycle time to a large extent
• The EL3773 can thus be used in systems that have no Distributed Clocks functionality. The time accuracy of the measured values is reduced, however.

The EtherCAT cycle time must be selected such that

• it is not less than 100 µs
• the oversampling interval does not produce a non-periodic time value – for example, 33.3 µs is not allowed for the oversampling cycle

The Distributed Clock is to be deactivated in the DC tab

The permissible oversampling rates are then set via the System Manager: