Specifications

74 Control and Automation Solutions Guide
Analog Communication
A sensor communicates its “sensed”
information with analog or digital
techniques. Analog techniques are based
on either voltage signals or current
loops. The analog voltage signal range
is typically from 0 to +10V, but can be
as wide as -15V to +15V. Current loops
are from 0 or 420mA. Analog signals
go through an A/D converter (described
in the Analog Input Functions section
of the Programmable Logic Controllers
(PLCs) chapter) and are digitized for
the host controller to process.
Digital Communication
Binary
Binary sensors are digital sensors that
only transmit single-bit information.
The signal reads either as on/o, true/
false, open/closed represented by a 1
and 0, and are typically unidirectional.
The presence or absence of an object
is detected and communicated with
a logic level. For example, when an
object like a piston in a valve reaches
a predened critical position, the
sensor detects and communicates this
to the PLC system through a binary
interface. Industrial binary signals are
often 0V and 24V. This high voltage
swing provides good noise immunity.
Digital
The other type of unidirectional
digital sensor can generate a range of
digital values where each digital value
represents a dierent measured level.
For example, a digital ow meter sensor
will output a higher digital value for fast
ow and a lower one for a slower ow.
For bidirectional sensor communication,
IO-Link is an emerging standard
that enables a sensor to be more
intelligent through conguring and
monitoring over a standard 3-wire
cable. Digital information is also
communicated through CAN, RS-485,
and other serial data interfaces.
Because industrial environments
are harsh, sensor interfaces need
to be robust to counter all forms
of mishandling and EMI. Maxim
oers a broad portfolio of industrial
transceivers that integrates industry
leading protection circuitry to handle
fault, overvoltage, and ESD.
When selecting a sensor communica-
tions interface, consider the following:
• Distance analog signal must travel to
digitizer
• Drive capabilities of analog or digital
sensors
• Distance digitized signal must travel
• Unidirectional or bidirectional data
and control flow
• Whether half-duplex or full-duplex
data is required
• Data rates required
• Response time required between
sensor signal and system controller
• ESD, EMI/RFI, overvoltage, and other
fault protection and fault response
• Power consumption
• Solution size
• Ease of installation
• Network topology
Sensor Communications Interface