Micro-Epsilon
With over 45 years experience and more
than 15,000 customers worldwide,
Micro-Epsilon understands the need for
accurate, robust, intelligent sensors and
measurement systems.
www.micro-epsilon.co.uk
The Importance Of Sensor
Triggering In Production And
Process Automation
When measuring the position of moving targets in production and process automation
environments, it is important to understand the different methods of sensor triggering,
their impact on measurement cycle times and the benefits they can offer over continuous
measurement, says Chris Jones, Managing Director at Micro-Epsilon UK.
Triggering is a term often used in
on (initiated) every 5s for a duration
conditions: rising edge (positive edge),
sensing and measurement technology
of 1s. The measurements between
falling edge (negative edge), High level
and includes all the different methods
the target objects are of no interest
(H level) and Low level (L level).
of initiating a measurement or a
and so do not need to be evaluated.
controlled output of measurement
This type of sensor set up provides
Edge triggering
data.
savings in terms of the memory of the
After the triggering edge, provided
evaluation system.
by an initiator switch or PLC, the
Particularly in production and process
automation environments, in order
It is important to understand the
to reduce the system load on any
different triggering methods available
downstream monitoring and control
and their relationship to sensor
units, a permanent measurement
measurement rate and cycle time,
output is often not the best approach.
particularly in fast-moving processes.
Instead, the sensor should wait for a
signal from an external source that
specifies the time for a measurement
to take place, thus initiating the
output of data. Triggering is therefore
often initiated by an external signal.
For example, consider a target object
in a high speed production line, which
passes a sensor every five seconds for
a period of one second. If the sensor
has a trigger function, the output of
the sensor only needs to be switched
10 FDPP - www.fdpp.co.uk
Non-contact laser sensors are
often installed in production and
process automation
environments to measure
displacement, distance
or position. These
sensors can be triggered
both via the ‘edge’ or
the ‘level’ of the trigger
signal. The following are
implemented as trigger
analogue output is updated, or if a
digital output has been selected, only
a digital measurement is output via an
RS422 interface (see Fig 1).