User manual

Product information32
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Some simple scaling examples:
Example 1: Interfacing a Resistive sensor
Notes:
Light-dependent resistor (LDR) can be
used in conjunction with a fixed
resistor to measure light level. A
suitable LDR sensor can be obtained
from Maplin Electronics (part number
N53AY). A resistor (R) of around 500k
is suitable.
Example 2: Measuring 4-20 mA Current
Notes:
4-20 mA output is the industry
standard for interfacing between a
control centre (data logger) and a
remote process such as a sensor. For
this reason 4-20 mA sensors are very
common.
For relatively small currents a simple
shunt resistor can be used to convert
the current into voltage which the
DrDAQ can then measure.
A suitable resistor (R) for the USB
DrDAQ is 120 ohms. This would give
(using Ohm's Law):
0.4 volts at 4 mA
2.4 volts at 20 mA
P = VxI
Therefore >50 mW resistor required.