Chapter 3
Signal Conditioning
3-10
ni.com
Building Attenuators (Voltage Dividers)
Attenuators or voltage dividers allow voltage measurements larger than the
maximum input range of DAQ devices. For example, voltage signals in the
±20 V range can be measured by building a 2:1 voltage divider circuit.
You can connect attenuators to the analog inputs of the BNC-2090A when
the inputs from its DAQ device are in differential or single-ended mode.
Caution
Do
not
connect input voltages greater than 42.4 V
pk
/60 VDC to the BNC-2090A.
The BNC-2090A is not designed for any input voltages greater than 42.4 V
pk
/60 VDC,
even if a user-installed voltage divider reduces the voltage to within the input range of the
DAQ device. Input voltages greater than 42.4 V
pk
/60 VDC can damage the BNC-2090A,
all devices connected to it, and the host computer. Overvoltage can also cause an electric
shock hazard for the operator. National Instruments is
not
liable for damage or injury
resulting from such misuse.
The gain in differential mode,
G
DIFF
, of this attenuator is given by the
Equation 3-2.
(3-2)
The gain in single-ended mode,
G
SE
, of this attenuator is given by the
Equation 3-3.
(3-3)
Therefore, the input to the DAQ device (
V
MIO
) for Equation 3-2 or 3-3 is as
follows:
V
MIO
=
V
in
⋅
G
(3-4)
where
V
in
is the voltage applied to the BNC connectors of the BNC-2090A.
The accuracy of this gain equation depends on the tolerances of the
resistors used.
Figure 3-9 shows a resistor circuit for attenuating voltages at the
differential inputs of the BNC-2090A. It also shows the placement of the
resistors on the open-component positions for channel 1.
G
DIFF
R
E
R
C
R
D
R
E
+
+
(
)
-------------------------------------
=
G
SE
R
F
R
C
R
F
+
-------------------
=
