Chapter3 MakingSignal Connections
6527User Manual 3-8 ni.com
Sensing DC Voltages
Whenyou apply a DC voltage of at least 2 V across the two input t erminals,
the6527 device registers a logic high for that input. If n ovol tage is present
(a voltage difference of 1 V or less), the 6527 device registers a logic low
forthat input. DC voltages between 1 V and 2 V are invalid and r egister an
unreliable value. Thus, you can use the 6527 device to sense a wide range
ofD C signals—from TTL logic levels to DC power supply levels up to
28 V.
Signal Connection Example
Figure 3-3 shows signal connections for a supply and load connected to
an isolated input. In this figure, the 6527 device is being used to sense that
aload is being powered. The load is connected to the power supply by
meansof a switch. This power supply can be any DC voltage within the
6527 device range. When the switch is open, no current flows through the
load and no voltage is applied to the load or to the 6527 device input. The
digital logic of the 6527 device then registers a logic low for the channel.
When the switch is closed, current flows through the LED and the
6527 device registers a logic high for thech annel.
Figure3-3. SignalConnection Example for Isolated Input
0.25W
6527
5211
Optoisolator
Isolation
15k 3k
Load
DigitalLogic
ComputerGround
+5V
DIG+
DIG–
IsolatedGround
Supply
+
–