Selecting Transducers And Transmitters - ACR Electronics SmartReader Plus Reference Manual

SmartReader Plus Data Loggers
57
WARNING: Using resistors with tolerances looser than 1%, poor temperature
coefficients and long-term drift characteristics will create undesirable
measurement errors.
1.10.5

Selecting Transducers and Transmitters

A transducer is defined as a device that receives energy from one system and retransmits it, in
a different form, to another system. A transmitter is a term usually reserved for transducers in
a current loop circuit. In this section, the terms transducer and transmitter will be used
interchangeably.
For a transducer to be useful, the retransmitted signal must be compatible with standard
instrumentation. For the SmartReader Plus 7 logger, this can be either in the form of an
analog DC voltage or current.
Many compatible transducers exist for measuring such variables as temperature, relative
humidity, pressure, speed, pH and more. You can obtain these from a wide variety of
manufacturers or distributors. An extensive listing of sensors and companies is published
yearly by Sensors Magazine.
To figure out what to look for when choosing transducers, it is helpful to know a few technical
terms and how they relate to use with your SmartReader Plus 7 logger.
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 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 you require a regulated power supply.
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 or loop
Orange 3
Yellow 4
Green 5
Blue 6
Violet 7
Grey 8
White 9
Gold
Silver
None
5% J
10% K
20%
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