TB20, strain gauge weighing module | Edition 1 | 21.12.2018
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TB20, strain gauge weighing module
5.1
Purpose
The weighing module serves the purpose of measuring and processing
signals from weight, torque, or force sensors. The weighing module
enables the direct connection of a load cell in the strain gauge full bridge
circuit (voltage-fed bridge circuit).
The feed voltage of the bridge is generated from the back wall bus of the
TB20 and amounts to 5 V with a maximum 70 mA load. The voltage
output is protected with an internal, reversible fuse against overload and
short circuit. Load cells with a minimum of 72
can be connected. The
external bridge feed of the load cell is possible.
The bridge voltage can be measured on the load cell with 6-wire
connection. The measured value is incorporated into the calculation of the
measurement value. Controlled by the application, wire break detection
can also take place by feeding test current into the measurement channel.
The input channels have a resolution of 24 bits. Measurement values are
issued configurable in mV/V or in kg.
With adjustable sample rates, interference voltages and mechanical
fluctuations in the measurement can be suppressed. Disruptions from a series of measurement values
can be smoothed out using a moving mathematical average. A zero point comparison of the load cell
can be carried out with the offset, or measurement with a definite value can be commenced with.
Linearity deviations of the measuring instruments can be linearized with up to 5 sampling points.
The measurement inputs have overvoltage protection relating to the 24 V potential and possess
electrical isolation with 500 V dielectric strength.
5.2
Measurement values
The measuring ranges are calibrated to the specified precision upon delivery. The weighing module
cannot be gauged.
5.2.1
Measurement value for conversion rate
The conversion rate can be configured to suppress interference frequencies. Separate operating modes
of 50 or 60 Hz are not required.
Conversion rates for 50 Hz interference frequencies: 6.25/s; 12.5/s; 25/s; 50/s
Conversion rates for 60 Hz interference frequencies: 7.5/s; 15/s; 30/s; 60/s
5.2.2
Averaging
A moving arithmetical average with the number n: 1 … 255 can be formed. After the start of the load
cell module or the reconfiguring of the parameter, a correctly averaged measurement value is first
available at the TB20 bus when the configured number of measurement values has been configured.
No averaging takes place for the number 1.
