Beckhoff KL3351 Bedienungsanleitung PDF herunterladen (Seite 6)

Description of functions

6 KL3351

Description of functions

The KL3351 analogue input terminal permits direct connection of a

resistance bridge. The bridge voltage, U

, and the supply voltage, U

ref

, to

the bridge are digitised with 16 bits resolution, and are transmitted over an

electrically isolated channel to the supervising automation system. The

input channels are available in the form of two 16 bit values for further

processing. The resulting measurement can be calculated from the

formula: measurement = U

/ U

ref

. Precise acquisition of the supply voltage

along with the bridge voltage compensates for long-term and temperature

drift.

Output of the measurement

The bridge voltage between +U

and –U

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 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.

Example

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 (U

), while the

reference voltage (U

ref

) and the bridge voltage were captured with the U

ref

and U

channels respectively.

Technical data for the load cell:

5 kg = 2 mV/V

The weight is calculated as follows:

Weight = U

/ U

ref

* 5/0.002 [kg]

Bridge supply

If the internal voltage supply is overloaded (I_load > 20 mA), it is

recommended that a KL9505 or a KL9510 be used.

LED display

The four LEDs indicate the operating state of the associated terminal

channels.

Green LEDs: RUN

On: normal operation

Off: Watchdog-timer overflow has occurred. If no process data is

transmitted to the bus coupler for 100 ms, the green LEDs go out.

Red LEDs: ERROR

Error LED1: outside the acceptable range for the signal voltage (U

), or

broken wire

Error LED2: outside the acceptable range for the reference voltage (U

ref

)

1 2 3 4 5 6 7 8 9 10 11 ... 17 18

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