Measurement Computing CIO-EXP-GP - Manual (Page 31)

supply all eight sensors. This is an extreme case but is indicative of the attention you must pay to power
requirements when using bridge sensors.
Also, when selecting the power source for the excitation voltage, consider the voltage you will use for
excitation. The options available are 0.5, 1, 2, 4 and 10V. In general, higher excitation voltages are
better because a higher voltage increases the difference between the balance points of the bridge circuit,
which increases the accuracy of your measurement. The excitation voltage must be less than the source.
+P
EX
T
+
12V
+5
V
JB11
Jumper JB11 (Figure 7-1), located near the bottom edge of the board,
selects the source of the bridge excitation voltage. The three choices are
+5V (the same 5V source chosen for board power above), +12V (from the
PC through the 37 pin connector) or +PEXT (an external power supply
connected at the ±P EXT screw terminal).
Figure 7-1
Output Gain & Power Select
If you choose a separate power supply, it must be a floating, isolated supply (one with three terminals).
Do not tie the GND and
−
V terminal together. It must not exceed +15V.
The +5V and +12V jumpers are only valid with CIO-DAS08 family boards. The +12V jumper is not
valid with the CIO-DAS08-AO and -PGx. For more information on excitation voltages, refer to the
section on bridge sensors.
+5V Excitation Voltage Source
If your choice for the excitation voltage source is +5V, you may choose a 0.5V, 1V, 2V or 4V excitation
voltage for your bridge sensors. The +5V option is always available, since +5V is required to power the
CIO-EXP-GP.
+12V Excitation Voltage Source
If your choice for the excitation voltage source is +12V PC power, you have the choice of 0.5, 1, 2, 4, or
10 volt excitation for your bridge sensors. The option to power from the PC 12 volt supply exists only
with DAS08 family boards, except that +12V is not valid with the CIO-DAS08-AO or PGA.
+PEXT Excitation Voltage Source
An external power supply can be used. If you choose a separate power supply, it must be a floating, or
isolated supply (one with three terminals). Do not tie the GND and -V terminal together). Output voltage
must not exceed +15V. If your power supply is not floating, it is likely that you will create a ground loop
(current flow in the ground lines). A ground loop will induce an error in your reading. Connect the
power supply to the CIO-EXP-GP at the terminals labeled
−
PEXT and +PEXT on the screw terminal
block located adjacent to the 37-pin connector, P2.
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