Controls and Functions
Bridge-Volt adjustable (0.5 ....5 volts)
Signal Mode selectable (Normal / Capacitive)
Polarity selectable (Normal / Inverted
Calibration <execute>
Bridge Load adjustable (60.0 >>> 3000 Ω)
Bridge compl. Selectable (1/1, ½, ¼ 120Ω or 1/4 350Ω)
Presentation selectable (default / Output V / Signal V/V / Physical unit)
Functional Description
The first line bridge-volt defines the excitation-voltage of the transducer or straingauges.
Values from 0.5 … 5 volt are possible. There is a 10% margin to compensate cable-losses
when using 6-wire connections (sensing). This allows for (e.g.) 12 Ω total cable-resistance
when using 120 Ω straingauges at 5 volt excitation.
After the value is accepted for bridge-volt, the amplifier will automatically perform a
calibration. It measures the real bridge-voltage using the sense-lines and corrects any
deviation. It is therefore necessary that the sense-lines are connected on the bridge-
connector. When sensing is not used to compensate cable-losses, it is still necessary to
connect the sense-lines on the connector itself.
This calibration can also be done later with the calibration-parameter. It is even necessary
when another sensor or straingauge with different resistance is connected to the amplifier.
Just press the ENTER-button at this line, while the sensor and sense-lines are connected.
Notice that the output voltage of the amplifier will be disturbed during the calibration. Null
and full-scale reference-measurements are done and will be visible in the amplifier output
signal.
The local display will not show any error, because it just does not measure during the
calibration.
The polarity parameter gives an easy method of changing the polarity of the output voltage
without changing the wiring. But use normal if you do not need inverted polarity.
Inverted polarity is the same as a negative gain. When such a negative gain is entered, the
polarity will be on inverted mode.
The signal-mode is usually set to normal. In capacitive mode, the amplifier does not
measure the normal resistive signal from the straingauges but the capacitive, phase-shifted
signal, caused by cable-capacitance and other parasitic causes. Although the amplifier is
designed to distinguish between the desired measurement and error-signals, when this
signal is large (full-scale or more) it can affect the accuracy of the normal measurement.
Capacitive unbalance is mostly observed in quarter-bridge configurations with several
meters of cabling.
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