Food & Drink Process & Packaging Issue 9 2016 - Page 10

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).