Product specifications

Instrumentation Laboratory Exercise 16
2.2 Circuit setup
V
D
will be fed into pin 1 of the DAQ board, and the circuit ground
will be fed into the ground (pin 39) of the DAQ. The diode has a
fixed polarity; it will not work if it is connected in the opposite
direction. The stripe end should be connected to ground.
Once the circuit is connected, confirm that you have +5 V and that V
D
is approximately 0.7 V.
2.3 VEE programming
The voltage V
D
will change slightly with temperature. As the voltage
change is relatively small (a few mV), we should set up the DAQ for
the greatest sensitivity applicable to our measurement. The input can
be measured as bipolar (BIP, allowing both positive and negative
voltages) or unipolar (UNIP, allowing only positive voltages).
In this exercise, V
D
will always be positive, so using unipolar
configuration will allow us twice the resolution of bipolar mode. Also,
the input channels can be configured for various voltage input ranges.
Typically a 10 V input range is used, meaning that the maximum
input voltage is 10 V. In unipolar mode with a 16- bit analog to digital
converter, we then have a voltage resolution of 10 V/(2
16
), or about
0.15 mV. As we know the diode junction voltage will be approximately
0.7 V, we can use an input voltage range of 1.25 V, greatly enhancing
our voltage resolution.
5 V
R
1
D
1
V
D
R1 = 1 kΩ
D1 = Signal Diode