RTA's Blog
Data Historian vs Data Logger
Jan
People in automation misuse words all the time and I am as guilty as anyone. Two terms that are consistently misused are data historian and data logger. A data logger is simply a device that records values over time. A data historian not only stores time-series data in a database, but it also generally provides some analysis capabilities.
Why Do Data Loggers and Data Historians Exist on the Factory Floor?
Data about an application has always been valuable. Data values that are commonly logged include energy data from motor drives, temperatures from loop controllers and job termination statistics.
While most of these devices are connected to a PLC in a control application much of this doesn’t exist in a PLC. To get time series data from a control system you need a tool outside of the PLC.
For example, it’s uncommon to find energy data in a PLC because they are designed to process data, not store it. This means they have limited storage and dedicate their processing power to real-time determinism.
Data loggers and data historians live alongside a PLC and gather data from the PLC and control devices that have not been mapped in the PLC.
What is a Data Logger?
A data logger is simply a device that records values over time. Values can range from how often a bird returns to its nest to pressures, temperatures and machine cycles. Data loggers typically store values in a simple text file, with each set of values marked with a time stamp. Compared to a historian, a data logger is the simpler of the two.
How Do Data Loggers Transfer Data?
Data loggers usually capture data in flat files that are often transferred into worksheets, generally as ASCII values. Data is transferred using a USB stick, FTP (File Transfer Protocol) or other online file transfer if the data logger can be connected to a computer.
A common file format for these files is a CSV (Comma Separated Value) file. A CSV file is nothing more than a set of values separated by commas. For example:
04/14/81 22:10:17,56.2,2345.456,0,Job 11,9X
The ASCII data stored by a data logger contains any alphanumeric character except commas. Since every value is ASCII string data, no quotes are used around the strings.
What is a Data Historian?
Data historians, like data loggers, collect time-stamped, time-series data in machine-readable format and store it in a database. Database data is algorithm-friendly, meaning it can be analyzed more easily to answer performance- or efficiency-related questions in a factory floor environment.
What is the Difference between a Data Logger and a Historian?
The real difference between a data logger and a historian is that historians provide much more detailed information to a manufacturer.
Compared to a data logger that provides flat text files, a data historian provides a database schema with its data for more detailed analysis. A database schema provides a formal, logical blueprint that defines how data is organized, structured, and related within a database. A schema can be read by an application and know what data values are present, how they relate to one another and can even have metadata – additional data that characterizes the data.
In addition, historians often include simple single-value trend charts and dashboards for quick analysis of the data, assisting organizations in identifying inefficiencies, monitoring machine performance and generating information that results in real-time insights into production processes.
| Feature | Data Logger | Data Historian |
|---|---|---|
| Data Format | Simple, time-stamped ASCII strings | Structured schema |
| Data Delivery | Flat files (CSV) | Relational database records |
| Data Analysis | Manual (spreadsheets) | Built-in dashboards, external BI tools |
| Primary Goal | Recording events | Operational intelligence |
Why the Distinction between Data Loggers vs. Data Historian Matters
Like many others, I am guilty of using words without much precision. Data loggers and data historians, while similar, don’t provide the same functionality. Data historians provide more sophisticated storage, offer analysis capabilities and have more sophisticated interfaces to other systems.
Where Do I Get a Historian?
While most data historians are software-based, The Allen-Bradley PLC Historian from RTA is a module for collecting and analyzing data specifically from Allen-Bradley PLCs. There’s no software to download or maintain. A proven, physical historian that can help bridge data from your closed OT network to your IT network. Find out more about the Allen-Bradley PLC Historian or contact an Enginerd at 800-249-1612.
