Bedienungsanleitung Weightec 348 (Seite 6 von 53) (Englisch)

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1.5 MEASURING PRINCIPLE

The A/D converter proceeds according to the unique continuous integrating principle and converts at 436 Hz

the analogue weight signal into a 21 bits digital value.

The 348 has 5 different types of filters for stabilizing the weight data. Amongst these 3 filters especial for the

setpoint comparison with automatic overshoot compensation and one manual settable filter.

The 3 filters for the setpoint comparison are selected in the start command for the setpoints.

The complete A/D conversion, as well as the analogue amplifier system, operates at 218 Hz (sine wave) speed.

The loadcell excitation and the sense return system operate at the same frequency and sine wave.

The measuring system is based upon synchronic detection of the AC signal and continuous integrating ratio

measurement by the A/D converter.

The big advantages of using alternating current with sine wave are the highly insensitivity for disturbances from

external interferences, a very stable zero without any drift and the feature that the loadcell connections may be

made with screw terminals in stead of soldered connections.

1.6 ACCURACY / SPEED

The internal resolution is 2,000,000 counts (21 bit) with a instability (noise)of max 3 count.

The EC legal approval allows for a minimum signal of 0.3 µV per scale division at 5.6 V loadcell excitation.

For a 2 mV/V loadcell this more than 37,000 counts / divisions, resulting in an accuracy of 0.003% of the

measuring range of the loadcell.

The EC Metrology Legislation for Class III weighing instruments limits this value to a maximum of 10,000 counts.

On the internal calibration display the digital weight signal is presented in max. 150,000 divisions.

In the data output max. 15,000 scale divisions available.

The high speed of the complete system, the setpoint comparators included, is 436 Hz (2.3 msec.) and

is independent of the setting of the amplifier (min. 0.25 mV/V full scale input).

1.7 LOADCELL CAPACITY, DEAD LOAD

The input sensitivity may be raised up to 1/8 part of the measuring capacity of a loadcell.

This does not effect the accuracy and the available resolution. The dead load on the loadcell may be

compensated up to 50 % (1 mV/V) of the loadcell capacity. This too does not effect the available resolution of

15,000 external divisions over the chosen input sensitivity.

This means that loadcells with an up to 8 times higher capacity as needed may be applied, moreover with 50%

dead load, without loss of speed or accuracy. This is very important for safeguarding a loadcell against heavy

overload and dynamic impulses and vibrations, simply by choosing a far to high loadcell capacity.

1.8 METROLOGY LEGISLATION CE

Based upon the European Legislation, according to EN 45501 the 348-2 is EC approved and certified by Dutch

NMi Certin with nr. - TC 5164 as part of a weighing machine

- T 5170 as a complete not automatic weighing machine

for max. 10,000 divisions and 0.3 µV per division at >

5.6 VAC excitation and > 58 Ohm input impedance.

The length of the loadcell cable is not

limited. No special EMC precautions are required.

The CE marking of the 348-2 is based on EN 50081-1, EN 50082-1, EN 61000-3-2 and EN 45501.

Manual 348-2 V 3.1 Page 6 01-06-2007

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