Basic function principles

The KL3351 analog input terminal permits direct connection of a resistor bridge. The bridge voltage, UD, and the supply voltage, Uref, to the bridge are digitized with 16-bit resolution, and are transmitted, electrically isolated, to the higher-level automation device. The input channels are available in the form of two 16-bit values for further processing.

The measurement result can be calculated from the formula: measured value = UD / Uref.

Precise acquisition of the supply voltage along with the bridge voltage in a converter compensates for long-term and temperature drift.

LED display

The green Run LEDs indicate the operating state of the associated terminal channel.

The red error LEDs indicate an overflow (range exceeded):

Output of the measured value

The bridge voltage between +UD and -UD is output with a resolution of 500 nV/digit, so that 10 mV corresponds to an output value of 20000 in the data bytes D0 and D1 of channel 1.

The supply voltage for the measuring bridge is output with a resolution of 500 µV/digit, so that 10 V corresponds to the output value 20000 in the data bytes D0 and D1 of channel 2.

The resolution can be adjusted by means of gain register R38.


A load cell was connected to the KL3351 in an experimental test bed.

The load cell was fed with the terminal’s 5 V supply voltage (UV), while the reference voltage (Uref) and the bridge voltage were captured with the Uref and UD channels respectively.

Technical data for the load cell:

5 kg = 2 mV / V

The weight is calculated as follows:

Weight = UD / Uref * 5 / 0.002 [kg]

Bridge supply

If the internal supply voltage is overloaded (I_load > 20 mA), the use of a KL9505 or a KL9510 it is recommended.