Voltage measurement

EL3356 and special versions Unless stated otherwise, the designation “EL3356” always refers also to special versions such as the EL3356-0010.

The EL3356 principally offers a 2-channel voltage measurement on one terminal with two very different measuring ranges of ±25 mV and ±12 V nominal voltage. The load on the one connected strain gauge can be calculated from the two simultaneously measured voltages; the EL3356 already performs this calculation in the terminal and thus represents a 1-channel terminal in the sense of load calculation.

Notice: The Ctrl PDO (CoE 0x7000:0) Start/Disable calibration, Input freeze, Sample Mode and Tara have no function in this case.

The following applies to the individual channels:

• Channel 1
• Typical measuring range approx. -13.5 V to 0 to +13.5 V (equivalent to process value 0x80.00.00.00...0...0x7F.FF.FF.FF)
• Nominal measuring range: -12 V...0...+12 V
• max. permissible voltage - U_ref vs. +U_ref: ±13.5 V
• Measuring error< ±0.1% of the full scale value, 50 Hz filter active
• Channel 2:
• Typical measuring range approx. -27 mV to 0 to +27 mV (equivalent to process value 0x80.00.00.00...0...x07F.FF.FF.FF)
• Nominal measuring range: -25 mV...0...+25 mV
• max. permissible voltage -U_D vs. +U_D: ±27 mV
• Measuring error< ±0.1% of the full scale value, 50 Hz filter active
• in strain gauge mode the connected strain gauge guarantees that no impermissibly high potential differences arise inside and outside the circuit.

In the standard setting the EL3356 operates as a 1-channel strain gauge monitor with the process image; the terminal can be switched to 2-channel voltage measurement by changing the process data. See the notes on the process image regarding this.

If the EL3356 is not used as a load measuring terminal, but rather as a 2-channel analog input measuring terminal, the following must be observed:

• The CoE settings are to be found for
• Channel 1: objects under 0x8010:xx
• Channel 2: objects under 0x8020:xx
• the strain gauge objects under 0x8000:xx have no function
  Exception: the averager (0x8000:03) can also be used in voltage measuring mode and applies to both channels simultaneously.
• Self-calibration is not possible and useful.
• The two analog channels are not calibrated by the manufacturer, since this is not required for the relative measurement in strain gauge mode.
  This means, for example, for channel 1 with a nominal measuring range of  ±12 V or a typical measuring range of ±13.5 V, that the maximum measured value 0x7F.FF.FF.FF can be output by one terminal for example as 13.4 V and by another as 13.6 V.
  If terminals output identical process values for identical applied voltages, meaning that they are exchangeable, each channel must be calibrated by the user by making settings for each channel in the CoE. The user calibration (CoE 0x80n0:17 [offset], 0x80n0:18 [gain]) or the user scaling (CoE 0x80n0:11 [offset], 0x80n0:12 [gain]) can be used for this.

Voltage measurement In the voltage measuring mode the EL3356 is to be connected to external GND with a single-ended connection. In addition the internal GND reference is to be closed by the CoE switch SymmetricReferencePotential, see the following figure.

Fig.38: EL3356 voltage measurement - symmetric reference potential