Historians are electronic data recording products that are typically used for trend style data. Trend data is comprised of measurement samples over a period of time. Prior to automation of this data collection, similar recording was accomplished with electro-mechanical pen and paper recording devices commonly referred to as chart recorders. Chart recorders would typically produce a graph of one or more measured values over a period of time.
Modern presentation of electronically recorded historic data often mimics the appearance of the old style chart records. A graph is produced where the measured value is presented on the vertical axis, with time units presented on the horizontal axis. It is not uncommon for more than one measurement to be presented on a single graph, with each graph or “pen” denoted in a different color.
In a process control system, very common items that are historized include temperature, flow rate, pressure, level and other types of analog data. Increasingly common is the historization of digital data, such as the output or feedback states associated with valves, pumps and other discrete control devices.
Why Historians?
From an electronic storage and retrieval perspective, Historians are designed to capture a lot more data, using a lot less space compared to traditional relational databases such as Microsoft SQL Server or Oracle products.
Compared to paper records, it is much simpler to manage both compliance data and process data electronically. For example you can quickly call up data three years old on a narrow slice of time for any key parameter of interest, compared to sorting through years worth of paper records locked away in file cabinets.
Common Report Usages
Historic trend style data is often combined with traditional log style data in a variety of reports available for process systems. Where trend style data indicates the change of a measurement over time, log style data presents quantitative measurements at a particular point in time.
Examples of log style data might include how much of a particular ingredient was used in a product batch formulation and when the ingredient completed; how many batches of a product were made and when each completed; or when a particular sequence step such as cleaning chemical strength or sterilization temperature was achieve.
Some examples of pairing historic trend and log style data on a single report include Clean in Place (CIP) reports where one or more graphs are presented for temperatures, flow rates and chemical solution strengths, combined with a date/time stamp of each major step in the cleaning sequence indicating when each started and stopped.
In the food industry, pasteurizer reports typically include trends of temperature, flow and pressure through the HTST thermal processor, combined with log data indicating what product was run, how much was processed, when it started and completed, and where the pasteurized product was stored.
Legal and Compliance Verifications
Should something go wrong, there is nothing like historic data to help pinpoint what happened and where. Should there be a product recall such data has been used by our clients to help determine root causes, as well as which products to include in the recall. Common culprits include inadequate cleaning times, low cleaning solution strengths, a device malfunction causing the improper cleaning of a piece of equipment, or low temperature product processing. Historic data trends coupled with some log style data will quickly get you to the answer of what went wrong.
Occasionally there also might be a legal issue concerning a product, where this detailed trend data has provided in-depth system performance analysis used to assist with defense against litigation.
Troubleshooting
Combining trend and log style information can be performed in an ad hoc manner to provide deep insight into the behavior of your process at any given point in time. One real world example from one of our clients involved the case of the missing product.
A full tank of product literally disappeared from a batch tank. The supervisors had no idea what happened. This system historized all digital and analog measurement and control devices in the process. This was coupled with a TriCore product, TCflexTrack, that provides log data on who did what, where and when for all automated operations in the process.
By examining the historic trend data the client was able to quickly pinpoint when level started dropping in the tank. At that point in time they overlaid historic trend data on all the on/off valves around the tank. From this it was clear that the tank drain valve activated, and the date/time it activated, sending a tank full of product to drain. Referencing the TCflexTrack data for that device at this time immediately indicated which operator had manually activated the drain valve causing the product loss.
Author: David McCarthy, President and CEO of systems integrator TriCore, Inc. in Racine, Wis.
