Big data from process plants originates at the sensor level, often with a healthy dose of manually entered information. There are four ways for you to collect, store and analyze this data: electronic data recorders, PLCs, HMIs and data historians.
Processes requiring I/O that can connect to sensors, local operator interfaces and data storage are best served by an electronic data recorder. "In many applications, a local operator must keep watch over a batch process, and periodically annotate the acknowledgement of an alarm event with a text comment,” says Steve Byrom, product manager for data acquisition, Yokogawa.
"In FDA program areas, the recording system must support compliance with regulation 21 CFR Part 11, requiring user log-in before granting access to the system. The latest, multi-point, touch-panel recording systems allow users to rapidly log in, acknowledge alarms, enter descriptive text data, and apply electronic signatures by touching screen icons and typing text on-screen. Trend history can be reviewed with a swipe to any area of interest in the saved data records, and data is saved in real time to secure, non-volatile flash memory,” says Byrom.
Many process plants purchase packaged units such as compressors, often with their own PLC-based control system. Modern PLCs can store significant amounts of data locally, and transmit or transfer this data to higher-level computing systems in a variety of ways.
Jeff Payne, product manager for PLCs, I/O and PC-based controls at AutomationDirect, explains. "Many modern PLCs and PACs have built-in data acquisition, data storage and networking capabilities. This allows data to be collected and stored locally and also transmitted to other systems. This can be done by simply connecting an Ethernet port to a network. If no connection is available, data can be pulled from a removable mass storage device such as a USB pen drive.”
Next in sophistication is PC-based HMI software, particularly when coupled with an SQL database installed on the same machine. With a PC with sufficient power and storage space, these platforms often can function as a plant’s sole data collection tool.
"The most common method of data collection is PC-based HMI software like our InduSoft Web Studio,” claims Richard Clark, an engineer with InduSoft. "Process variables and batch information can be trended and stored in a local proprietary or a SQL database. "Sometimes the amount and volume of data needing to be stored is beyond the scope and capability of the HMI or SCADA system, and an external, dedicated plant historian must be connected to the PC.
Take the case of an application for a water treatment plant in Alaska, where a historian was required due to the sheer volume of data and other factors. Working with Dowland-Bach (www.dowlandbach.com), a local Rockwell system integrator, the plant upgraded its control system to improve reporting, data storage capabilities and maintenance efficiencies by installing FactoryTalk Historian software from Rockwell Automation.
Before installing the new system, it took operators six hours to generate one report — a task that needed to be repeated five times per month, at an annual cost of $18,000. Report generation was also frustrating and error-prone, as operators had to manually scroll through each day’s one-minute samples to locate high turbidity points.
The facility is now producing highly accurate 24-hour data trend reports with minimal effort. With the historian software, reports take minutes. Regulatory compliance requires seven years of data on the system, which overworked the original databases and caused breakdowns costing $20,000 annually in maintenance costs alone. Using the historian software, the plant easily stores 25 years of data, eliminating unplanned maintenance and downtime due to failures.