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DAQP-CFB2
Excitation Voltage
The excitation voltage is programmable to 1, 2 or 5 V. The carrier frequency is programmable to 0.6,1, 2.5,
3, 5, 10 or 20 kHz. When the module is configured as “stand alone” or as “single” the frequency is based on
a crystal oscillator. When it is switched to external clock a PLL synchronizes the excitation with the external
signal. The EXC+ and EXC- voltage is always balanced around GND. That allows using the ground potential
as shield. For high accuracy strain gage measurement it is recommended using lower frequencies. When
higher bandwidth is required use higher carrier frequencies.
Remote Sense
The DAQP-CFB2 supports remote sense. That means that the excitation voltage loss in the sensor cable is
compensated. The sense line terminals are internally connected to the excitation via a 100 kΩ resistor. For
accurate voltage regulation there has to be also an external connection. Even if the remote sense function is
not required. Sense has to be connected to EXC.
Phase adjustment
In inductive mode the phase of the amplifier needs to be adjusted to compensate the phase shift due to
sensor and wiring. The DAQP-CFB2 is able to compensate ±90° with the phase sensitive rectifier.
Output offset
The output offset can be programmed from positive to negative full scale range. This is useful if the DAQP-
CFB2 is used as an analog signal conditioner.
Input offset
The input offset can be set ±400 % of the input range. It is automatically recalculated when changing the
measurement range. The input offset is automatically determined with the sensor balance function.
Internal Completion Resistors
The DAQP-CFB2 has internal half bridge completion and internal quarter bridge completion wiring for
120 Ω and 350 Ω strain gages. High precision resistors with low temperature drift allow a long-term stable
measurement of almost every strain gage type without using an external completion network.
Internal Shunt
A 50 kΩ and a 100 kΩ shunt resistor can be applied to the bridge internally. This is called “shunt calibration”.
With this technique the whole measurement chain (sensor, amplifier and analog-to-digital conversion) can be
checked. The table below shows the shunt calibration results for typical strain gage resistance values.
Strain gage Resistor
Shunt resistor Result
120 Ω
50 kΩ
0.6 mV/V
120 Ω
100 kΩ
0.3 mV/V
350 Ω
50 kΩ
1.74 mV/V
350 Ω
100 kΩ
0.87 mV/V
The shunt resistor check is not possible in inductive bridge operation mode.
Amplifier balance
Balance amplifier allows eliminating all internal amplifier offsets automatically. It switches the differential
amplifier inputs IN+ and IN- to internal GND. Then the output offset of the module is adjusted to zero for all
ranges. This function takes up to 8 seconds. Previously stored sensor offset values are cleared.
Summary of Contents for DAQP-CFB2
Page 20: ...20 DAQP CFB2 Notes ...
Page 22: ...C2 NOTES ...
