Data logging is an offshoot of data monitoring. Often, the same data being monitored by the HMI is also sent to a Data historian for logging. This works great except for remote sites or when the data is very important. In these cases, you want to have a local datalogger. The protocol that is used the most in these applications is Modbus.

The reasons why Modbus is so popular for these applications is that Modbus is:

      • Easy to implement in the device.
      • Does not take very much CPU power or resources.
      • Data can be pulled at long intervals.
      • Universally supported.

We will now look at two applications.

Application Example 1:

A customer has a gas analyzer that needs to have its values logged every minute. It is in a remote part of the plant that is inspected once per month. The gas analyzer is old and only supports Modbus RTU over RS-485.


Use an EasyLog by 4next Technology Systems to collect and store the data. This family of devices can pull data from either a Modbus TCP slave over ethernet or a Modbus RTU slave over RS-485. The data is stored in either Comma-Separated-Variable (CSV) or JSON format on a micro-SD RAM card in EasyLog.

The logs can be accessed via FTP, HTTP REST, MQTT or by reading the micro-SD RAM card directly.

The setup is easy:

      • Wire the gas analyzer directly to the EasyLog via RS-485.
      • Using a web browser, set the Modbus RTU parameters to match the analyzer.
      • Set up what variables you want to pull from the gas analyzer and how often.
      • Select how you want to get the files or have them sent to you.

datalogging application with 4Next EasyLog

In this case, the site has to be inspected once a month. The service technician will connect to the EasyLog with an Ethernet cable and using the web browser download the monthly log during these visits.


Application Example 2:

In this application example, you have a site with three power meters that all have Modbus TCP onboard. You need to log several parameters from each meter every minute. The site is away from the main location. You have a satellite Ethernet connection to the site, but sometimes, dropouts occur. The customer therefore wanted a backup system on site in case of interruptions.


For this application, we will use an EasyLog by 4next wired into a Helmholz unmanaged switch. Also plugged into the switch are the three power meters. We then set up the EasyLog to pull the data from each power meter via Modbus TCP.

Process instruments connected to a 4Next EasyLog for remote datalogging

The EasyLog can be used as a backup or as a data concentrator in this case. There is a version of this called EasyLog UA that has OPC UA built in, which would make data retrieval very easy. In this variant, the setup would be the same except now the HMI would pull all the data from the EasyLog. In the case of an interruption, the EasyLog would act as a data buffer ensuring that no data is lost.


Data logging is easy using Modbus and the EasyLog by 4next Technology Systems. One of the best aspects of this product is that it is also very cost-effective.

If any of these datalogging applications interest you or if you have your own application that you want to discuss with us, please contact us at or give us a call at 705-868-8745.

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