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5.3
Choosing Transducers
A transducer is defined as a device that receives energy from one system and retransmits it, in a
different form, to another system. For a transducer to be useful, the signal must be compatible with
standard instrumentation. This is analog DC voltage for the OWL DC Voltage logger.
Many compatible transducers exist for measuring such variables as temperature, relative humidity,
pressure, current, voltage, wind speed, pH and more. These can be obtained from many
manufacturers and distributors.
To discern what to look for when choosing transducers, it is helpful to know a few technical terms and
how they relate to measuring voltage.
Excitation Voltage
This term refers to the input voltage that a transducer requires in order for it to work properly. It is
either specified as a range (for example, 9 to 30 volts DC) or as a specific voltage (for example, 10
volts DC). When a range is specified, it means you can use an unregulated power supply (such as a
battery) as long as voltages within the range are provided. Usually, if a specific voltage is required, it
means a regulated power supply is needed.
When an unregulated power supply is specified for the excitation voltage, a regulated one may also be
used. The reverse, however, is not true. Millivolt pressure transducers, for example, usually require
regulated power supplies.
Maximum Impedance
An important consideration when choosing transducers is the requirement for input impedance. This
simply refers to how much resistance the instrumentation (for example, the OWL logger) can have
before it will begin to affect the signal. For voltage inputs, a very high impedance is usually required
(greater than 10k ohms). This prevents the unnecessary draining of current from the transducer circuit.
The OWL DC Voltage logger's input is high impedance (greater than 100k ohm). Check the
specifications for the transducer to ensure the OWL's input impedance is acceptable.
© 2001 ... ACR Systems Inc.
Range
Full Scale
0
121.0 mVDC
1
241.9 mVDC
2
362.9 mVDC
3
483.9 mVDC
4
605.8 mVDC
5
726.8 mVDC
6
848 mVDC
7
969 mVDC
8
1.093 VDC
9
1.214 VDC
10
1.334 VDC
11
1.455 VDC
12
1.577 VDC
13
1.698 VDC
14
1.819 VDC
15
1.940 VDC
OWL DC Voltage Data Logger
Range
Full Scale
16
2.431 VDC
17
4.863 VDC
18
7.294 VDC
19
9.73 VDC
20
12.18 VDC
21
14.61 VDC
22
17.04 VDC
23
19.47 VDC
24
21.96 VDC
25
24.39 VDC
26
26.82 VDC
27
29.25 VDC
28
31.71 VDC
29
34.14 VDC
30
36.57 VDC
31
39.00VDC
23
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