Advantech iDAQ-871 handleiding
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iDAQ-871_873 User Manual 14
3.1 Bridge Input Overview
This section gives a brief introduction to the architecture and operation of the bridge
input circuit, which is also called a Wheatstone bridge. In addition, there are several
methods to correct the error in bridge input measurement, including remote sensing,
offset nulling, and shunt calibration, are described.
3.1.1 Wheatstone Bridge
Many sensors, including strain gauges, load cells, pressure sensors, and torque sen-
sors are based on the concept of a Wheatstone bridge. A Wheatstone bridge con-
tains four elements or arms. Although these elements can be resistive or reactive,
they are however almost resistive for sensors previously mentioned.
Figure 3.1 A resistive Wheatstone bridge circuit
Figure 3.1 shows a resistive Wheatstone bridge circuit. It consists of an excitation
voltage source and two voltage dividers. R
B1
and R
B2
form one voltage divider, and
R
B4
and R
B3
form the other voltage divider. The excitation voltage (V
EX
) is connected
to the upper node (junction of R
B1
and R
B4
) and the lower node (junction of R
B2
and
R
B3
), and output voltage (V
O
) is measured between the middle node of two voltage
dividers. When R
B1
= R
B2
and R
B3
= R
B4
, the output voltage is 0 V.
If some of the resistors are replaced by active sensors, whose resistance change
with the physical quantity, V
O
will also change due to these resistance changes. By
measuring the value of this voltage change, the physical quantity can be calculated.
There are three types of active sensor configuration in bridge input circuit: quarter-
bridge, half-bridge, and full-bridge. Refer to Figure 3.1, for quarter-bridge, only R
B1
is
an active sensor; for half-bridge, both R
B1
and R
B2
are active sensors; for full-bridge,
all four resistors are active sensors.
Due to the property of the voltage divider, V
O
will be proportional to V
EX
. When VEX
is used as the voltage reference of an ADC, and V
O
is measured by the ADC, as
shown in Figure 3.2, the measurement result is an unitless ratio between V
O
and
V
EX
, or V
O
/V
EX
. For specified resistances, the measurement result is independent of
the variation in V
EX
. This is called ratiometric measurement.
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Productinformatie
| Merk | Advantech |
| Model | iDAQ-871 |
| Categorie | Niet gecategoriseerd |
| Taal | Nederlands |
| Grootte | 5398 MB |
