In the third and final blog post in this series on Modbus we take a look at Vaisala viewLinc, a digital monitoring system that’s especially suited to Modbus due to the communication protocol’s ability to transmit data digitally. Because analog to digital conversion only occurs at the point of measurement, using viewLinc with Modbus allows for extremely accurate collection and storage of data.
Typical viewLinc applicationsVaisala viewLinc Continuous Monitoring System is often used in regulated environments, for instance with pharmaceutical products and medical devices. Adhering to the regulatory requirement to use a separate redundant system for monitoring allows users to demonstrate that processes such as drug storage have been performed within the required specifications. Unlike programmable logic control (PLC) platforms, viewLinc isn’t a control system – it is used to monitor for data collection and storage, send alarms whenever any measured values fall outside of the specification and provide robust historical data to demonstrate that process values have been maintained within the required limits.
In these types of regulated environments, viewLinc is generally used to monitor temperature and humidity in manufacturing and storage areas, where heating, ventilation, and air conditioning (HVAC) systems are typically used as control systems. As these systems don’t have enough sensors to provide the detailed information required for monitoring, viewLinc performs this role. Being an entirely digital system, viewLinc doesn’t deal with any analog data and all analog to digital conversion is carried out by the sensors at or near the point of measurement, from which point the digital data can be accurately transmitted and processed. As digital communication has become the norm for monitoring systems in life sciences environments, long analog cables, and numerous thermocouple networks are now largely a thing of the past.
Using viewLinc for non-digital applications
Although digital data is generally preferable in highly regulated environments, viewLinc also has a universal data logger that accepts analog inputs, allowing facilities to use specialized legacy instruments or older equipment that only outputs analog values for parameters that aren’t otherwise offered by Vaisala’s data loggers. This ability to accept almost any measurement is also beneficial where the parameters being measured minimize the error risks associated with loop calibrations or calibrating in the field. A good example of this in viewLinc is differential pressure measurements, which are often used in cleanrooms; high pressure is used in these areas to ensure constant airflow into the dirtier parts of the facility, keeping the area clean by preventing particles from flowing upstream.
Differential pressure measurements are taken in a panel housed near the data logger, allowing for short wires that reduce the impact of wiring on the analog signal and therefore minimize errors. It’s easy to integrate stable, reliable calibration equipment in the field for differential pressure, and this is the exception rather than the rule in this sense. For cleanroom measurements where it’s inconvenient to perform a loop calibration due to longer wires or issues with your calibration reference standard, or where the device signal is too complicated for an analog signal, digital is more helpful. One example of this is particle counters, which are important for determining how clean the room is.Connecting viewLinc with Modbus
Particle counters provide complicated process data that can’t be easily conveyed with an analog signal and is therefore much better suited to a digital signal. This digital data is ready to travel, so there’s no need to convert it to analog and back again – it just needs a direct digital pathway to the viewLinc system, and the pathway we use is Modbus. To make it easier to convert a Modbus device to viewLinc, we’ve created a library of templates within the system – for example, complicated devices such as particle counters can be added by simply selecting the correct template. It’s also possible to create and save new templates, which you can then use again and again.
Because digital communication remains accurate over long distances, it decreases the number of calibrations needed, increases calibration accuracy, and allows you to simply send the data logger to a calibration lab and replace it with a unit that’s pre-calibrated for your specific process. The viewLinc system has analog sensor capability, but this is only useful in cases where there’s no other option. For this reason, viewLinc uses the Modbus communication protocol wherever possible.
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