Data logger

A data logger is a processor- controlled storage unit , which records data in a certain rhythm via an interface and stores it on a storage medium. This can be done using software if the information to be logged is already available in digital form, for example within a computer , and only needs to be processed. If, on the other hand, the information is only available in non-electrical form, the data logger can consist of special hardware combined with sensors that record physical measurement data such as temperatures , voltages and accelerations over a certain period of time . The first digital data loggers appeared in the early sixties of the twentieth century. Analog recorders, on the other hand, have been around for much longer.

Humidity and temperature data logger in the form of a USB stick

Data logger for climate analysis e.g. B. with mold problems

construction

Humidity and temperature curves with the possible display options

A data logger consists of a programmable microprocessor , a storage medium, at least one interface and one or more channels for connecting the data source such as e.g. B. sensors. The data is recorded externally or internally via a manufacturer-dependent interface. An internal interface exists when the data logger is connected to a sensor, e.g. B. a temperature sensor forms a unit. The data is passed on from the sensor directly to the data logger via the internal interface and stored. Each data logger has at least one external interface for recording and transferring data from or to the environment. In the industrial and machine environment, RS232 , CAN and USB are the most common interfaces.

Any external devices, sensors or machines can be connected as a data supplier via connections such as USB, D-Sub , Bluetooth , WLAN or industrial terminals . A data logger is usually also configured for its use via these accesses (e.g. start and end time of the measurement, measurement intervals, etc.). The data type is not initially specified in more detail. Depending on the application, it can be process or sensor data. The storage rhythm depends on the specific use. The storage process can take place at precise time intervals or at the moment of data generation. In any case, the storage process is always fully automatic.

Sensor logger

Data logger Cube (Avisaro 2.0) for storing sensor and process data

For specific applications in sensor technology, data logger and sensor are built into one device. The corresponding measurement data such as temperature, air pressure etc. are recorded via the sensor. An analog-to-digital converter then converts this data into "storage-ready" data and stores it on the storage medium. The type of storage can prevent possible data loss (if the battery is empty). The recorded data is read out via the interfaces (serial interface, USB, LAN, Bluetooth, etc.) and evaluated with suitable software. Depending on the desired measurement parameters, a data logger can have one or more channels in order to be able to connect several sensors at the same time.

Disposable logger

Disposable data loggers have been developed for monitoring transports in order to offer a cost-effective solution for single-use applications. The service life of these devices is usually limited to 1 year and is particularly useful where it would be too costly to return the devices (export shipments). These temperature loggers have a USB interface and therefore do not require any additional hardware. Thanks to the PDF evaluation (see below), no special software is required.

PDF logger

The PDF logger is a special variant of the autonomous data logger. When plugged into a USB interface, this automatically creates a PDF file with a text and a graphic part of the current measurement data. The device then appears to the PC operating system as a standard USB mass storage device . This makes it possible for the recipient worldwide to generate a report without additional software. These devices are used for shipping in the cold chain .

Mini logger

Mini data logger (MSR145) with integrated sensors for temperature, humidity, pressure, acceleration and light

Mini data loggers, often also called USB loggers, are small in size. They are optionally equipped with internal or external sensors for recording various measured variables, but despite their small size they have a large storage capacity. Mini-loggers are used everywhere in industry and science where size is an important criterion: e.g. B. in health care for patient monitoring, where the patient has to wear the data logger for a long time. In research, mini-loggers are used, for example, to measure acceleration forces on the human body (e.g. pilots, parachutists, etc.). In business, it can be a matter of inconspicuously operating transport monitoring with the small logger.

In museums or galleries, on the other hand, mini-loggers are required for climate monitoring. In order to obtain meaningful measured values from the immediate ambient climate of the property, the loggers must be placed very close. Nevertheless, the museum visitors should not see the loggers as much as possible, which speaks for the mini-logger. The measured values of the mini-logger can be transferred to a PC via USB both during the measurements and after they have been completed.

Underwater data logger

In addition to their waterproof housing, underwater data loggers have a larger memory for measured values and are designed to be particularly energy-saving. This means that they can work in hard-to-reach places for months and collect data. After exchanging the memory, the data can simply be read out via the interface as with normal data loggers. Waterproof data loggers are not only used in bodies of water. You will e.g. B. also used in manufacturing processes. The data logger is put into the packaging together with the product and checks whether the parameters important for production, such as B. the pressure or the temperature are maintained.

Vehicle data logger

Vehicle data loggers record the current vehicle status via digital inputs, which record changes in the status of the vehicle (engine on / off, vehicle accelerates, drives, stops) as well as on the vehicle (trailer attached / detached) and vehicle attachments (snow plow up / down, road salt on / off) and can be read out via an interface or mobile. Through the additional acquisition of GPS signals, a specific assignment of the changes in status is possible - using the example of a gritter: When was which road section cleared and how. Vehicle data loggers are usually installed in the vehicle so that they are easily accessible for drivers / service personnel or connected to a base station so that they can also be removed and read out manually if they cannot be accessed via mobile devices.

Some vehicle manufacturers offer their workshops data loggers that are installed in the customer's vehicle in the event of sporadic problems. The driver can press a button while driving and thus trigger data recording, which can then be analyzed afterwards.

Differentiation from the vehicle diagnostic system

Data logger for diesel particle filters. DYNTEST system from CPK Automotive. With temperature and pressure sensor, among other things

The term data logger is often confused with the term vehicle diagnostic system, especially in the automotive industry . Normally, data loggers mainly offer functionality for recording measured values and other data. Vehicle diagnostic systems go beyond this and master data reduction, processing and visualization of the data as well as other functionalities that support the user in the analysis.

Specifications

Professional data logger ( MWS3 ) based on Linux for recording environmental parameters in the ODL measuring network

A distinction has to be made between loggers for "home use" and loggers for professional use. The latter have u. a. has the following properties:

a calibration certificate, traceable to an accredited calibration center
are much more robust
have "Excite" outputs in order to be able to connect active (power-consuming) sensors
have parameterizable inputs
have wide input voltage ranges
have their own precise clock
extended temperature resistance
have one or more alarm outputs
have extensive options for triggering (e.g. event-controlled start of recording)
have options for networking and remote control
if necessary, there is the possibility of remote access
have a high accuracy and long-term stability and a high storage capacity
the inputs / outputs are standardized
have the option of connecting any (manufacturer-independent) sensors
have a battery / accumulator to bridge power failures.

Heartbeat signal

In particularly critical applications, the data logger can be equipped with a heartbeat signal generator so that the monitoring staff is promptly informed of a possible failure. This can e.g. B. be an SMS that is sent via cellular network .

Web links

Commons : data logger - collection of images, videos and audio files

Avisaro AG - Basics of data loggers . January 17, 2013. Archived from the original on October 13, 2012.

Individual evidence

↑ The history of the development of the data logger. July 15, 2016, accessed October 23, 2018 .
↑ Datafox vehicle data logger. June 6, 2017. Retrieved June 6, 2017 .
↑ Volkswagen vehicle EKG receives Automechanika Innovations Award 2008. September 12, 2008, accessed on October 23, 2018 .
^ Long-term data logger, found on February 22, 2010 ( memento from March 25, 2011 in the Internet Archive ).

[1] The history of the development of the data logger. July 15, 2016, accessed October 23, 2018 .

[2] Datafox vehicle data logger. June 6, 2017. Retrieved June 6, 2017 .

[3] Volkswagen vehicle EKG receives Automechanika Innovations Award 2008. September 12, 2008, accessed on October 23, 2018 .

[4] Long-term data logger, found on February 22, 2010 ( memento from March 25, 2011 in the Internet Archive ).