Chapter 3 Signal Connections
6527 User Manual 3-8 www.ni.com
Sensing DC Voltages
When you apply a DC voltage of at least 2 V across the two input terminals,
the 6527 device registers a logic high for that input. If no voltage is present
(a voltage difference of 1 V or less), the 6527 device registers a logic low
for that input. DC voltages between 1 V and 2 V are invalid and register an
indeterminate value. Thus, you can use the 6527 device to sense a wide
range of DC 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 a
load is being powered. The load is connected to the power supply by means
of 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 the channel.
Figure 3-3. Signal Connection Example for Isolated Input
0.25 W
6527
IL55B
Isolation
15 kΩ 3 kΩ
Load
Digital Logic
Computer Ground
+5 V
DIG+
DIG–
Isolated Ground
Supply
+
–