PECM Issue 21 2016 | Page 38

The Importance of Sensor Triggering in Production and Process Automation W hen measuring the position downstream monitoring and control This type of sensor set up provides savings of moving targets in units, a permanent measurement output in terms of the memory of the evaluation production and process is often not the best approach. Instead, system. automation environments, the sensor should wait for a signal from an it is important to understand the different external source that specifies the time for a It is important to understand the different methods of sensor triggering, their impact measurement to take place, thus initiating triggering methods available and their on measurement cycle times and the the output of data. Triggering is therefore relationship to sensor measurement rate benefits they can offer over continuous often initiated by an external signal. and cycle time, particularly in fast-moving measurement, says Chris Jones, Managing Director at Micro-Epsilon UK. Triggering is a term often used in sensing and measurement technology and includes all the different methods of initiating a measurement or a controlled output of measurement data. Particularly in production and process automation environments, in order to reduce the system load on any 38 PECM Issue 21 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 on (initiated) every 5s for a duration of 1s. The measurements between the target objects are of no interest and so do not need to be evaluated. processes. 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 conditions: rising edge (positive edge), falling edge (negative edge), High level (H level) and Low level (L level).