Data logger

Data loggers are electronic devices with an integrated, processor-controlled memory unit, one or more interfaces and at least one channel for connecting a data source. These are the features that set them apart from basic measurement devices. Data loggers record data over a specified period of time and store it for later use. Data loggers are used to record physical measurement data (temperature, acceleration, pressures, etc.) as well as digital information.

The history of electronic devices dates back to the early 20th century, even when state-of-the-art, high-performance data loggers make this difficult to imagine. Analog recording devices such as data recorders were being used as early as around 1900 to reliably record various measurement variables with minimal time effort. This was happening especially in industry and research.

It was not until after the Second World War that the development of data loggers really took off. The invention of transistors and their further development into the early 1960s "electrified" data recording, which had up to then only been mechanical. During the 1960s, it became possible to mount an increasing number of transistors on increasingly smaller surface areas. As quick-acting switches, transistors can be seen as the origin of digital technology. Consequently, it was not long – in 1965 to be precise – before the first data loggers were being developed that could digitise analogue signals and store them on magnetic tape, the common medium of the time.

Unlike data loggers, magnetic tape was to have no future. The compact cassette replaced the bulky, stationary and space-consuming magnetic tapes by the late 1960s. From 1966 on, compact cassettes were used as storage media for data loggers. For more than a decade, compact cassettes remained the standard storage medium until the advent of "Electrically Erasable Programmable Read-Only Memory" technology, or EEPROM for short. EEPROM's invention represented a technological breakthrough for data loggers. They had previously been dependent on a continuous power supply and therefore not very mobile, but with EEPROM as a storage medium a continuous power supply was no longer necessary. In the 1980s, another innovation emerged that is still used today as a storage medium in data loggers: Flash EEPROM. Flash EEPROM, commonly known as flash memory, stores information persistently, i.e. in a non-volatile way, on a small space and does not require a continuous power supply.

The measurement technology sector also changed permanently with the introduction of the first home computers in the 1980s, such as the Macintosh 128k or the Commodore 64 (C64). The greater availability of processors and programming options meant that from then on it was not only possible to build measuring devices or data loggers that just stored data– they could also record more complex data and simultaneously preprocess it within the device.

Delphin Technology was one of the first companies to successfully build the first data loggers using the MCS6502 processor (based on the C64).With the processor transformation at the core of data loggers, measurement devices and programmable logic controllers (PLCs), a new era in measurement and control technology began.

With the processor transformation at the core of data loggers, measurement devices and programmable logic controllers (PLCs), a new era in measurement and control technology began.

Processors have now become indispensable for any data logger or PLC. Differences between data loggers and a PLC can be blurred. Control and regulation tasks can now also be performed by powerful data loggers. For example, powerful data loggers are used as mini controllers. One example here is the Expert Logger from Delphin for highly precise measurements where control and regulation tasks are also required.

Devices such as the ProfiMessage D are used in the monitoring of large-scale systems with multiple sensors and actuators. ProfiMessage D is a modular, expandable system and can function similarly to a PLC, but with the addition of highly powerful measurement functions.

With the advancement of automation in the 1990s and the increasing availability of large amounts of memory and processor capacity, data loggers could no longer be seen as the sole solution for measurement and control tasks. The focus increasingly moved towards the interplay between measurement data acquisition and powerful DAQ measurement software.

Today, networked data loggers can easily set up a data network spanning a plant or the entire globe, enabling condition monitoring when used with the appropriate software. Software making this possible is the Delphin Data Center in combination with the ProfiSignal 20 measurement software.

Data logger operation always depends on intended use and the type of data recording. Basically, a distinction is made between data recording:

• Digital sources
• Analog sources

Data loggers to be used for recording digital information are directly connected via an interface to the processing unit generating the data. Data recording and storage on the storage medium is software-based.

Data loggers used to acquire and store analog information, such as temperatures, humidity and machine parameters, are connected to sensors via inputs (0-20 mA, 4-20 mA, 0-10 V, ...). These sensors record physical, analog, binary information and forward it to the data logger via an interface. The data is then digitised, processed and stored.

The fourth industrial revolution, Industry 4.0 for short, is in full swing. Networking and communicating with plant, machinery and equipment via the internet is at the heart of Industry 4.0. The demands placed on modern data loggers are correspondingly diverse. As part of the IoT (Internet of Things), data loggers need to be adaptable to the respective application areas, while also being network capable and able to communicate with other IoT devices as well as users. The Expert Logger in combination with the ProfiSignal 20 software is Delphin's answer to the needs of networked, digital industrial environments.

The Delphin Expert Logger or Loggito series provide data logger systems that:

• Enable access to measurement values via mobile devices
• Provide 16 to 46 analog inputs for autarchic data acquisition from any sensor
• Enable continuous communication with the company's cloud
• Are also equipped with internal data storage that prevents data loss when the connection to the cloud is interrupted
• Serve as mini controllers or replacement PLCs by using digital and analog outputs

In the Internet of Things, edge devices undertake the transport of data packets between different network structures. Edge devices use processors to handle sensor data directly at the application at the edge of the network, enabling more efficient processing and control of the huge volumes of data that are generated. In Industry 4.0, edge devices undertake connectivity and gateway tasks. This specifically involves converting data from fieldbuses into IP-based data traffic.

Data acquisition is performed via interface(s) in two ways:

• External - the data logger is connected to external sensors via an interface
• Internal - the data logger and the sensor constitute a compact unit

The type of interface used by a data logger is determined by the intended use, with data loggers being capable of having multiple interfaces. In industry and manufacturing, serial interfaces such as RS-232 or RS-485 are common, as are USB connections, mobile data networks (UMTS, LTE, 4G, in future also 5G), WLAN and industrial Ethernet. This variety of interfaces already gives an idea of the many potential applications of data loggers.

Modern data loggers are equipped with different industrial standards for data exchange, depending on the intended use. It is important to distinguish between basic data loggers that are designed only to record a specific value and have little or no communication interfaces. In contrast, state-of-the-art professional and high-precision data loggers are equipped with high-performance processors similar to a PLC and can actively participate in measurement network communications. Common communication protocols include OPC UA (Open Platform Communications Unified Architecture), ProfiNet, CAN Bus and Modbus.

A data logger's power supply depends on its intended use and power consumption during operation. Autarchic data loggers for mobile usage use batteries as a power supply. Stationary data loggers are connected to the mains by means of a cable and a power supply unit. The energy consumption required for data loggers can vary considerably for various reasons. If data loggers with galvanic isolation are used, power consumption will be significantly higher as a result. Connected sensors and the sampling rates required for these can also lead to higher power consumption.

Datal logger inputs and outputs, also referred to as I/Os, are used to record measurement data (inputs) or to control systems or actuators (outputs).

Inputs

Depending on the required application, data loggers may have one or more inputs for connecting sensors. The Loggito from Delphin Technology, for example, provides up to eight multifunctional analog inputs to which different sensors and measured variables can be connected in parallel. For more complex measuring requirements, the Delphin Expert Logger provides up to 46 analog inputs. The current measuring ranges of the devices are 0-20 mA and 4-20 mA .

Outputs

When data loggers are being used to continuously monitor plant and machinery, the devices need to be capable of not just recording and storing data, but also of actively controlling actuators. Data loggers equipped with the appropriate outputs can then significantly increase levels of automation.

Galvanic isolation involves decoupling two conductive objects from each other or isolating the electrical line between two circuits. Galvanic isolation is also sometimes necessary for data loggers:

• Measuring sections with earth reference: earth potential differences that occur here can cause distortions. Earth current loops can cause faulty signal evaluations.
• Linking of multiple measuring circuits: unwanted reference potentials can happen here.
• Applications with long cable distances or in high EMC environments: inductive or capacitive disturbances can occur in the measuring circuit.

Galvanic isolation of inputs and outputs ensures isolation of electrical potentials and potential-free circuits. Galvanic isolation is necessary for reliable measurement data acquisition. You can find out more about galvanic isolation in this article.

Data loggers are available in various designs and are configured differently depending on the application. For example, especially small, compact and inexpensive single-use data loggers are optimised for one-time use in the transport sector, while larger multichannel data loggers, which are more expensive to purchase, can measure and store different values. Other data loggers have integrated sensors or are waterproof (enclosed).

Other distinguishing features can be found in the storage. Autarchic data loggers (for transport monitoring or similar) are usually equipped with a module for storing acquired data. Stationary data loggers directly connected to a computer do not need this capability - the data is generated by the data logger and immediately passed on to the connected computer.

Some data loggers are capable of not only acquiring and storing data, but also of being used as an ICA device/controller. ICA (instrumentation, control, automation) devices are capable of recording data through powerful integrated processors and a wide range of connection options for sensors, and capable of using this data to control plant and machinery. A simple example of an application here is a heating system. When a sensor detects that temperatures are above or below a certain level, the heating is automatically increased or decreased accordingly. Industrial data loggers with PLC functions are used to improve plant availability, reduce energy consumption and increase operating times.

Multifunctional data loggers

Multifunctional data loggers feature multiple interfaces, e.g. to enable the monitoring of dispersed measuring locations. Multifunctional data loggers are able to acquire data via different types of sensors and are ideal for the cost-effective set-up of decentralised measurement networks. All data loggers manufactured by Delphin Technology can be classified as high-precision, multifunctional data loggers. They provide all the functions of the data loggers listed below. They also perform excellently as PLC replacements.  

Temperature data loggers

Temperature data loggers are primarily used in industry for monitoring temperature-sensitive environments, e.g. the drive systems of machine tools.

Temperature and humidity data loggers

Temperature and humidity data loggers record both temperature and humidity conditions thereby significantly expanding their potential areas of application.

GPS data loggers

GPS data loggers permanently transmit their location via a dedicated module and log any events that occur. In addition to the benefit of determining locations, GPS can also be used to synchronise data acquisition times down to the nearest millisecond. Many of the data loggers for general measurement applications can also be equipped with a GPS module.

LTE, 4G, 5G, mobile communications data loggers

These data loggers use the fast LTE, 4G or 5G data standards to transmit acquired data. LTE 4G 5G data loggers are ideal for location-independent use in logistics, industry and construction. The data loggers, which are capable of autarchic operation, enable high-speed data transfer, e.g. for assessing measuring locations from a desk via remote maintenance.

Vibration data loggers

Data loggers for vibrations are used, for example, to optimise and monitor plant, machinery and vehicles. Recording oscillations and vibration creates a data baseline to optimise motors, bearings and drive spindles. Data loggers for vibrations are often used in condition monitoring.

Vehicle/transport data loggers

Vehicle/transport data loggers enable detecting and logging of vibration or shock events during the transport of goods and commodities, as well as the tracking of vehicles.

Photovoltaic data loggers

Photovoltaic data loggers are used to monitor solar installations. These data loggers are able to provide information on solar power production, the condition of a system and the charge level of batteries.

Vaccine data loggers

Vaccine data loggers are indispensable in monitoring refrigerators and freezers for vaccine storage.

Climate mapping data loggers

Climate mapping data loggers are highly specialised devices that log temperature distributions and humidity within a predefined range.

High-temperature data loggers

High-temperature data loggers are capable of operating in areas with very high temperatures. Depending on the equipment and intended use, high-temperature data loggers can be used at temperatures of up to 400° C and above.

Shock data loggers

Shock data loggers record shock events. Shock data loggers are used, for example, on transport routes to detect extreme shocks that products are subjected to during transport.

Pressure data loggers

Pressure data loggers are used to monitor pressures, e.g. water pressures or compressed air pressures. Pressure data loggers are used, e.g. for leak testing, fault analysis in pipelines and monitoring air pressure system functioning.

Pharma data loggers

Pharma data loggers are optimised to meet the high demands of the pharmaceutical industry. Pharma data loggers are used for process monitoring and high-precision monitoring of manufacturing processes.

Acceleration data loggers

Acceleration data loggers are used to evaluate mechanical-dynamic loads on an object. They are equipped with acceleration sensors that record the acceleration currently acting on the sensors in shock or vibration events.

CO2 data loggers

CO2 data loggers are used for air quality checks in work or recreation rooms in offices or schools. CO2 data loggers measure and record the amount of carbon dioxide in the ambient air.

Single-use data loggers

Single-use data loggers are low-cost data loggers designed for one-off usage. Single-use data loggers are used, among other things, to monitor goods during transport and storage.

Multichannel data loggers

Multichannel data loggers are capable of controlling different sensors and therefore measuring and recording different information in one device.

Data logger accuracy is determined by how much a measurement-generated value deviates from the actual value.
The smaller the deviation, the more accurate a data logger measures. Devices from Delphin Technology's Loggito series provide the following accuracies:

• Resistance measurement: 0.01% of full scale for 4-wire connection, 0.1% of full scale for 3-wire connection
• RTDs: 0.1 K for 4-wire connection, 1K for 3-wire connection

Data logger speed or sampling rate indicates the time intervals at which a measurement is taken. The higher the sampling rate, the finer the resolution of an event. However, too high a measurement speed can also be a disadvantage, because it automatically leads to increased data volumes which a data logger may be unable to manage over the long term. The DAQ measurement data software connected to the measurement network may also not be designed for the volume of data transferred. High sampling rates also increase a data logger’s power consumption, which might restrict operating times, especially for mobile devices using batteries.

Data loggers from Delphin are equipped with high-speed CPUs that can process the acquired data directly in the device thereby avoiding excessive data volumes. Adaptive storage is used for this purpose. Adaptive storage means only data that differs from previous data is fully stored. The procedure compresses the measurement data without any data loss and stores it in a compact format.

A sensor is a technical component which can be used to record measurement values that are physical or chemical properties or the condition of an environment. A sensor detects measurement values occurring through biological, chemical or physical processes and converts them into electrical signals. Data loggers can be used in a wide variety of applications, so the range of sensors is correspondingly extensive. Widely used data logger sensors are:

• Temperature sensors
• Material humidity electrodes
• Climate sensors for temperature and humidity
• CO2 sensors
• Insertion sensors
• Shock sensors
• Air pressure sensors
• Acceleration sensors
• Vibration sensors

With modern measurement data software such as ProfiSignal 20 from Delphin Technology, measurement values acquired by data loggers can be analysed and visualised intuitively and platform-independently, allowing processes to be effortlessly monitored and controlled.

As part of the ongoing digitalisation of industry, software solutions are required that also centralise management of data acquired from plant, machinery and measuring systems. All-round solutions are required, especially for continuous condition monitoring. The solutions must provide a wide range of interfaces, cross-system user administration and maximum scalability and expandability. The Delphin Data Center (DDC) is one of the most powerful DAQ measurement data software solutions for networking, monitoring and analysing dispersed measurement data sources.

Its open data pool structure enables the Delphin Data Center to standardise, archive and monitor measurement and process data - either locally or via global access. The Delphin Data Center has the added advantage that almost all data in a plant network can be recorded and processed in a structured way, whether the data originates from Delphin devices, from a PLC or other data loggers. Common standards such as OPC UA, Modbus, ProfisNet, ProfiBus, CAN, ... are supported.

To ensure that measurement values recorded by data loggers are as precise as possible, data loggers undergo calibration.

How often calibration should occur depends on the manufacturer and the device, as well as on the operational requirements. It is recommended to recalibrate data loggers at least once a year, especially for complex or critical applications.
Depending on operational usage, regular calibration of data loggers is required for reasons of liability.

Calibration is performed by comparing the data loggers with a reference measuring device and calibrating them on site or in a certified laboratory.

A calibration certificate records the values recorded by the reference measuring device at the measuring location, the values recorded by the data logger at the same measuring location, and the difference between the two values.

Do you want to find out more about data loggers from Delphin Technology or do you have a question about a specific application? Then call us now. We look forward to the opportunity to impress you with the wide range of possibilities offered by our products.