What is a temperature data logger?
Temperature data loggers are processor-controlled, technical devices that are used to measure and monitor temperatures and often also humidity. The measured data is stored and, depending on the data logger version, can also be transferred directly to other devices such as PLCs via communication interfaces. Temperature data loggers are used in the monitoring of cold chains, the storage of food, the production and transportation of pharmaceuticals as well as in test fields and research. Multifunctional data loggers are often used instead of temperature data loggers. These can measure and process various other physical values in addition to temperature thanks to freely configurable analog and digital inputs.
Why do you need a temperature data logger?
A temperature data logger is always required when certain temperatures need to be reliably maintained or monitored over a longer period of time. This is the case, for example, along cold chains in the food sector or in the pharmaceutical industry. A temperature data logger is also used in research, trials and tests or in drive systems of machines or plants. The aim here is to monitor that certain limit values are not exceeded - for example, that a motor does not become too hot. Probably the best-known application of data loggers is the measurement of temperature and relative humidity in indoor spaces such as offices or private homes.
How does a temperature data logger work?
Data loggers that measure and record temperatures and/or humidity values are equipped with thermocouples or resistance sensors or can be connected to these sensors for temperature measurement. In the industrial environment, a temperature data logger is primarily used, which can be universally configured for any thermocouple or resistance sensor via analog inputs.
The data loggers from Delphin Technology, the LoggitoLab or the Loggito Logger are also equipped with high-precision and galvanically isolated 24-bit AD converters and precise internal current sources for a reference current supply, so that otherwise conventional measuring transformers can be dispensed with.
What are the advantages of a temperature data logger without built-in sensors?
Many data loggers for temperature are equipped with integrated sensors. These data loggers can certainly be used for private applications or simple measurement tasks. However, these temperature data loggers are only suitable for a limited range of applications - namely precisely for the applications that the integrated temperature sensor enables. The temperature data loggers from Delphin Technology, on the other hand, are generally designed without integrated probes or sensors. Instead, the data loggers from Delphin Technology can be modularly expanded by connecting external sensors and probes, which enables many simultaneous measurement processes or large quantity structures (high number of analog and digital inputs).
What temperature sensors and temperature probes are available and how do they work?
There are a variety of different sensors and probes for temperature measurement, which measure temperatures when connected to a data logger.
These include resistance thermometers, thermocouples, special semiconductor circuits, fiber optic temperature measurement and temperature-dependent differential frequency measurement.
The selection of the right sensor always depends on the requirements of the measuring point. Decisive for the selection are
- The measuring range in which temperatures are to be measured.
- The speed at which temperature changes are to be detected.
- The accuracy of the temperature measurement.
- The environmental influences that prevail at the location to be measured.
Thermocouples for data loggers
Thermocouples belong to the upper group of temperature sensors and probes. These electrical conductors enable temperature measurement through the so-called "thermoelectric effect". This property of thermocouples, also known as the Seebeck effect, is demonstrated by the occurrence of a thermoelectric voltage due to a temperature gradient along an electrical conductor. The selection of a temperature sensor depends, among other things, on the temperature range to be measured.
- Type K: Material NiCr-Ni. Usual application range: 750 - 1,100° Celsius
- Type J: Material Fe-CuNi. Usual application range: 400 - 600° Celsius
- Type N: Material NiCrSi-NiSi. Usual application range: 850 - 1,200° Celsius
- Type E: Material NiCr-CuNi. Usual application range: 440 - 690° Celsius
- Type T: Material Cu-CuNi. Usual application range: 200 - 300° Celsius
- Type R: Material Pt13Rh-Pt. Usual application range up to 1,400° Celsius
- Type S: Pt10Rh-Pt. Usual application range up to 1,400° Celsius
- Type B: Pt30Rh-Pt6Rh. Usual application range up to 1,500° Celsius
Resistance thermometer for temperature data logger
As the name suggests, the electrical resistance of resistance thermometers changes at different temperatures. The resistance thermometer consists of a specific metal which changes the resistance value in ohms when the temperature changes according to the characteristic curve of the metal. According to the ohmic law, a change in resistance changes the voltage applied.
Common resistance thermometers are:
- Pt100
- Pt1000
- PTC
- NTC
- Silicon
Characteristic curve for temperature data logger
There is a so-called characteristic curve for each temperature sensor, which can be used to determine the measured temperature value.
If a temperature data logger is used in which no temperature sensor is permanently installed, the data logger must be taught which thermocouple is currently connected and how the incoming measured values are to be interpreted. The data logger must therefore know the characteristic curve.
A temperature data logger with analogue inputs such as those from Delphin Technology are optimized for use with all common thermocouples and resistance sensors. Thanks to pre-configured characteristic curves and validity ranges, any type of thermocouple can be connected within minutes. Among others, the following temperature sensors can be used with Delphin data loggers:
Resistance thermometers, thermocouples, KTY silicon sensors, NTC thermistor sensors or infrared sensors for fast, non-sluggish temperature measurement.
A temperature data logger also frequently records humidity
Many temperature data loggers are also equipped to measure humidity - or can be fitted with sensors for humidity and temperature. The reason for the "multifunctionality" of the devices lies in the close relationship between temperature and humidity: the relative humidity of the air decreases while the absolute amount of water remains the same as soon as the temperature rises. By simultaneously monitoring temperature and humidity, the room climate can be determined and adjusted to a desired humidity level. Data loggers for temperature and humidity are particularly relevant in the storage and transportation of moisture-sensitive goods and in industrial production and monitoring.
Why do the temperature and humidity data loggers often have WLAN?
In the course of digitalization, decentralized data acquisition and permanent monitoring of distributed measuring points is easier than ever before. By networking the data loggers for temperature and humidity via WLAN or Ethernet, decentralized measurement networks can be set up cost-effectively and the data collected can be transferred to the cloud (or, of course, to a stationary server) in real time. The wireless communication between the data loggers allows the data loggers to be flexibly scalable and expandable at any time. In combination with the appropriate software, the data loggers are ready to carry out "Measurement and monitoring tasks 4.0".
What are USB temperature data loggers?
For mobile use, many manufacturers have developed data loggers that resemble a USB stick in terms of appearance and size. These data loggers have an integrated sensor and battery and can be read out via the USB interface. The USB stick data loggers are ideal for many applications, such as temperature monitoring in the freight sector. However, USB data loggers for temperature quickly reach their limits when:
- More than one temperature is to be monitored.
- temperatures are to be recorded at rapid intervals.
- The temperature data should be transmitted live.
- The live temperature data should be stored in a cloud.
- The data logger should also perform control functions.
- The measured data must be very accurate.
- In addition to the temperature, for example, a GPS position is also required.
Professional but small multifunctional data loggers can be used as an alternative to classic USB data loggers in USB stick format. The Loggito logger from Delphin is small and at the same time an extremely powerful data logger. It is approx. 7 cm high and has the footprint of a credit card. Equipped with several inputs and outputs, USB, WLAN and connections for GPS (some optional), it is ideal for almost any application.
Is it possible to operate a temperature data logger with an app?
Location- and platform-independent access to measurement data offers maximum flexibility and convenience in daily use. Many temperature data loggers offer the option of transferring measured values to an app. It is important to differentiate here between the context in which a temperature data logger with app is to be used. The requirements of a private individual in terms of the accuracy of measured temperature data and its display often do not correspond to what is required in a professional and industrial environment.
In the professional sector, there are many manufacturers that make it possible to transfer measured values from a data logger to mobile devices, e.g. with Android or Apple. It is important to define the requirements in advance.
- Should the measured values only be transmitted in a local network?
- Is worldwide access to the data via app necessary?
- What data security is required?
- Where should the measurement data be stored - on your own server or in the Internet cloud?
- What accuracy should the measurement data have and how precisely should it be displayed in an app?
- Should several temperature measurements distributed at different locations be recorded in one app?
- Should it also be possible to send a control signal to the data logger via the app?
It is often also possible to display existing data loggers or data from a PLC in an app. An example of this is our complete software ProfiSignal 20. This software provides users with complete platform independence - and simple, intuitive management of the measured values obtained. Measured values can be recorded in ProfiSignal 20 from almost any data source and, if desired, distributed in a local or global cloud. The data can also be made accessible to mobile devices via the internet.
A temperature data logger with alarm function: perfect for limit value monitoring
Data loggers for temperature can be used not only for obtaining measurement data, but also for limit value monitoring. A limit value is a maximum permissible deviation from a setpoint value. The monitoring of temperature limit values is relevant in automation technology, in the storage and transportation of sensitive goods or in solar systems. Data loggers for temperature, which have an alarm function, trigger an alarm when a presettable limit value is exceeded - acoustically, visually or as a digital message - and thus fulfill a protective function.
Data loggers equipped with a control and regulation function offer even greater protection of systems, processes or experiments against temperature or humidity. These data loggers not only record data, but can also control actuators using integrated microprocessors - similar to a PLC.
What are the advantages of a temperature data logger with external sensors?
Data loggers for temperature and/or humidity that are equipped with external sensors offer a significantly wider measuring range than devices that only have an integrated sensor. All common thermocouples, Pt100/Pt1000 sensors or NTC sensors can be used with the data loggers from Delphin Technology. Each sensor has specific advantages and disadvantages:
- Thermocouples have a low mass. As a result, they react quickly to temperature fluctuations. A wide range of materials is available to cover very wide measuring ranges and high temperature ranges. However, thermocouples do not offer the accuracy of other sensors.
- Pt100/Pt1000 sensors are frequently used in industrial environments. These sensors offer very accurate measurement over a wide measuring range and can also be used at low temperatures. For a particularly accurate measurement, a 3- or 4-wire circuit can be carried out with these sensors.
- NTC sensors are particularly popular when temperatures need to be measured in a fixed, small range of typically -40° to +80° Celsius. The disadvantage of the small measuring range is compensated for by the low purchase price and high accuracy of NTC sensors.
If measurements are required in which inaccuracies are to be excluded as far as possible, it is advisable to equip the sensors with transducers.
What characterizes a temperature data logger for industry?
Data loggers that carry out measurements in an industrial environment are subject to completely different requirements than devices used in a private environment. One of the most important criteria for a high-quality data logger is the quality of the installed components. A data logger temperature for industry must not only withstand large temperature differences, sometimes dusty environments or those with high humidity, but also carry out precise measurements. In some cases, they have to work 24/7 for years and must not fail at any time. In addition, the industrial data loggers should not only perform complex measurement tasks at one location, but usually at several locations in a system simultaneously. This is why professional temperature data loggers are equipped with interfaces that are commonly used in industry (RS232, Ethernet, WLAN, OPC UA, Modbus, CAN, ProfiNet, ProfiBus, ...). Thanks to the variety of connections, interfaces and transmission standards, temperature data loggers for industry enable even highly complex measurement tasks to be carried out.
Is there actually an upper limit to the number of inputs on a data logger?
In a nutshell: No, there is no (physical) upper limit when it comes to the number of inputs and therefore the number of sensors and probes that can be connected. For example, the largest data logger from Delphin Technology, the Expert Logger 300, "only" has 46 analog inputs for temperature or other measurements and is therefore limited in terms of connections at first glance. However, thanks to its modular design, the number of inputs can be expanded almost infinitely. To do this, simply attach another Expert Logger or a "slave" device to the data logger. In combination with the powerful software Delphin Data Center (DDC), all inputs can be recorded and saved - regardless of the number of sensors used or the connected devices.
If several hundred or even thousands of inputs and outputs are required, the ProfiMessage D of Delphin can be used. It is almost infinitely expandable and comparable to a large PLC. However, the measuring accuracy of the ProfiMessage D and the structured data collection offer clear advantages over a PLC.
The right software for your measurement and testing solution
Data acquisition and analysis
With ProfiSignal Go you can display online data from the Message and Expert hardware in diagram form. Numerous analysis functions, such as zoom, cursor, movable axes, flags, ASCII export and calculation channels, enable fast display of measured values and post-processing.
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Operating and monitoring
ProfiSignal Basic combines the functions of ProfiSignal Go with operating and monitoring elements of process visualisations, e.g. digital and analogue displays, switches, buttons and signal lamps. With Basic, you can create everything from simple visualisation diagrams to complex visualisation systems.
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Automate and control
ProfiSignal Klicks supplements ProfiSignal Basic with functions for process automation. Structural diagrams for mapping the process as well as a script language (completely operable with the mouse) enable even the non-informatician to create complex test stand and automation applications with automatic report generation.
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Fast project planning and analysis of measurement data
With ProfiSignal 20 Go you can visualise your measurement data in just a few steps, both online and offline, in various diagram types, monitor, analyse, archive as a measurement file or export directly in the appropriate file format.
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Visualisation and operation
With ProfiSignal 20 Basic you can create individual diagrams using a wide range of operating and monitoring elements. Both continuous processes (e.g. production data acquisition) and discontinuous measurement tasks (e.g. test measurements) can be visualised, operated and monitored without any programming effort. You can create the operating and monitoring diagrams by assembling and configuring the prefabricated elements.
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Central measurement data management
The Delphin Data Center is the solution used for the worldwide measurement networking and control of plants, machines and test stands.
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