Temperature data logger

What is a temperature data logger?

Temperature data loggers are processor-controlled, technical devices used for measuring and monitoring temperatures, often humidity as well. The measured data is stored and, depending on the data logger model, can also be passed on directly to other devices such as PLCs via communication interfaces. Temperature data loggers are used in cold chain monitoring, food storage, the production and transport of pharmaceuticals, as well as experimental settings and research. Multifunctional data loggers are often used in place of temperature data loggers. These have programmable analogue and digital inputs that can be used to measure and process a range of other physical values in addition to temperatures.

For what purpose do you need a temperature data logger?

Temperature data loggers are used when specific temperatures need to be maintained or monitored over long periods of time. Examples of this are along cold chains in the food sector and in the pharmaceutical industry. Temperature data loggers are also used in research, experiments and testing, as well as in the drive systems of plant and machinery. Important here is monitoring that ensures that certain limit values are not exceeded, e.g. ensuring that a motor does not overheat. The most well-known application of data loggers is perhaps measuring temperature and relative humidity in indoor spaces such as in offices or homes.

How does a temperature data logger work?

Data loggers that are to measure and record temperatures and/or humidity values are equipped with thermocouples or resistance sensors or are capable of being connected to such sensors. Temperature data loggers used in industrial environments can be universally configured for any thermocouple or resistance sensor via analog inputs.

Delphin Technology's data loggers, the LoggitoLab and the Loggito Logger, are also equipped with high-precision and galvanically isolated 24-bit AD converters and precision internal current sources for reference current supplies, meaning there is no need for standard measuring transformers.

What benefits do temperature data loggers without built-in sensors have?

Many temperature data loggers are equipped with integrated sensors. These data loggers are perfectly suited to private use or for basic measuring tasks. They are, however, only suited to a limited range of applications, i.e. only those that can be serviced by the inbuilt temperature sensors. Delphin Technology's temperature data loggers, on the other hand, generally have no integrated probes or sensors. Delphin data loggers are modular and can therefore be expanded by connecting external sensors and probes to enable multiple simultaneous measurement processes and large quantity structures (i.e. high numbers of analog and digital inputs).

What types of temperature sensors and temperature probes are there and how do they work?

A wide range of different sensors and probes are available for temperature measurement when connected to a data logger.


These include resistance thermometers, thermocouples, special semiconductor circuits, fibre-optic temperature measurement and temperature-dependent differential frequency measurement.


Selecting the right sensor always depends on measurement site requirements. Key factors in the selection are:


  • The measuring range in which temperatures are to be measured.
  • The speed at which temperature changes are to be recorded.
  • Accuracy of the temperature measurements.
  • Environmental influences prevailing at the measurement site.

Thermocouples for data loggers

Thermocouples belong to the top group of temperature sensors and probes. Temperature measurement is made possible by these electrical conductors through the so-called "thermoelectric effect". This thermocouple property is also known as the Seebeck effect and is manifested in the occurrence of a thermoelectric voltage due to a temperature difference along an electrical conductor. Selecting 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 data loggers

In resistance thermometers, electrical resistance changes at different temperatures. Resistance thermometers are made of a specific metal which changes the resistance value in ohms when temperatures change according to the metal's characteristic curve. According to Ohm's law, changing resistance changes applied voltage.


Common resistance thermometers are:


  • Pt100
  • Pt1000
  • PTC
  • NTC
  • Silicon

Characteristic curve for temperature data loggers

Each temperature sensor has a characteristic curve that can be used to determine measured temperature values.


When using temperature data loggers without built-in temperature sensors, the data logger requires teaching as to which thermocouple is currently connected and how to interpret the incoming measured values. The data logger must therefore know the characteristic curve.


Temperature data loggers with analog inputs such as those from Delphin Technology are optimised to be used with any common thermocouple or resistance sensor. Preconfigured characteristic curves and validity ranges allow any type of thermocouple to be connected within minutes. The following temperature sensors, among others, can be used with Delphin data loggers: resistance thermometers, thermocouples, KTY silicon sensors, NTC hot-wire sensors and infrared sensors for high-speed temperature measurement.

Temperature data loggers are also often capable of recording air humidity

Many temperature data loggers are also equipped for measuring humidity, or can be equipped with humidity and temperature sensors. Such "multifunctionality" is due to the close relationship between temperature and humidity: when temperature rises, relative air humidity decreases while the absolute amount of water remains the same. By simultaneously monitoring temperature and humidity, indoor climate conditions can be determined and adjusted to a desired humidity level. Temperature and humidity data loggers are particularly important when storing and transporting moisture-sensitive goods as well as in industrial production and monitoring.

Why are temperature and humidity data loggers often equipped with WLAN?

Digitalisation is making decentralised data collection and continuous monitoring of dispersed measurement locations easier than ever before. By networking temperature and humidity data loggers via WLAN or Ethernet, decentralised measurement networks can be set up cost-effectively and the data obtained can be transferred in real time to the cloud (or to a stationary server). Wireless communication between the data loggers allows flexible scalability and expandability of the data loggers at any time. In combination with the appropriate software, data loggers are then capable of "Measuring and Monitoring Tasks 4.0".

What are USB temperature data loggers?

Numerous manufacturers have developed data loggers for mobile use that resemble a USB stick in appearance and size. These data loggers are equipped with an integrated measuring sensor and battery and can be read out via the USB interface. USB stick data loggers are ideal for many applications such as temperature monitoring in the freight sector. However, USB temperature data loggers soon reach their limits when:


  • More than one temperature is to be monitored.
  • Temperatures are to be recorded at short intervals.
  • Temperature data is to be transmitted live.
  • Temperature data is to be stored live in the cloud.
  • Data loggers also need to perform control functions.
  • Measured data needs to be highly accurate.
  • GPS location is required in addition to the temperature.

As an alternative to classic USB data loggers, professional, compact multifunctional data loggers can be used. The Loggito Logger from Delphin is both a compact and extremely powerful data logger. It is approx. 7cm high and has the surface area of a credit card. It is equipped with multiple inputs and outputs, USB, WLAN, and optional connections for GPS or LTE, making it ideal for almost any application.

Can you operate a temperature data logger with an app?

Having access to measurement data independent of location and platform provides maximum flexibility and convenience for routine tasks. Many temperature data loggers provide the option of transferring measured values to an app. It is important to distinguish between the different uses of a temperature data logger with an app. The accuracy of temperature data measured and the way it is displayed for personal use are different to what is required in professional and industrial environments.

In the professional sector, many manufacturers enable measured values from a data logger to be transferred to mobile devices, e.g. with Android or Apple. Specifying needs in advance is important here.


  • Do the measured values only require transmission within a local network?
  • Is worldwide access to the data via app required?
  • What data security is required?
  • Where should the measurement data be stored - inhouse server or internet cloud?
  • How accurate does the measurement data need to be and how precisely does it need to be displayed in an app?
  • Do temperature measurements from multiple locations need to be recorded in one app?
  • Does a control signal also need to be sent to the data logger via the app?


Existing data loggers or data from a PLC can often also be displayed in an app. ProfiSignal 20 from Delphin Technology is able to do this. This software provides users with complete platform independence - and simple, intuitive management of the acquired measurement values. Measurement values can be recorded in ProfiSignal 20 from almost any data source and shared across a local or global cloud if required. The data can also be made accessible to mobile devices via the internet.

Temperature data logger with alarm function: Ideal for limit value monitoring

Temperature data loggers can be used for monitoring limits as well as for obtaining measurement data. A limit value refers to a maximum permissible deviation from a setpoint. Monitoring temperature limits is important in automation technology, in storing and transporting sensitive goods, and also in solar installations. When a preset limit value has been exceeded, temperature data loggers with alarm functions trigger an alarm - acoustically, visually or as a digital message - thereby providing a protective function.


Even greater protection against temperature or humidity for industrial plant, processes or experiments is provided by data loggers equipped with control and regulation functions. These data loggers not only record data, but can also control actuators through integrated microprocessors - similar to a PLC.

What are the benefits of temperature data loggers with external sensors?

Temperature and/or humidity data loggers equipped with external probes provide a much wider measuring range than devices with integrated probes only. All common thermocouples, Pt100 / Pt1000 sensors and NTC sensors can be used with data loggers from Delphin Technology. Each sensor has its own advantages and disadvantages:


  • Thermocouples only have a small mass. They are therefore quick to react to temperature fluctuations. Very broad measuring and high temperature ranges are manageable due to the wide variety of available materials. However, thermocouples do not offer the accuracy of other sensors.
  • Pt100/Pt1000 sensors are widely used in industrial environments. These sensors offer highly accurate measurement over wide measuring ranges and can also be used at low temperatures. 3 or 4-wire connections can be made with these sensors to deliver extremely accurate measurement.
  • NTC sensors are especially popular for measuring temperatures in a fixed, limited range of typically -40° to +80° Celsius. The drawback of the smaller measuring ranges in NTC sensors is made up for by their lower purchase price and high accuracy.

When measurements are required with minimal inaccuracies, it is advisable to equip the sensors with transducers.

What are the distinguishing features of temperature data loggers for industry?

Data loggers performing measurements in industry have to meet completely different needs than devices used in private environments. One key criterion for high-quality data loggers is the quality of the installed components. Temperature data loggers for industry need to withstand large temperature differences as well as dusty and humid environments while also being capable of recording precise measurements. They sometimes need to operate 24/7 for many years and not permitted any downtimes. Industrial data loggers are also designed to perform complex measurement tasks not only at one but usually at several locations simultaneously within a plant. Professional temperature data loggers are therefore equipped with interfaces commonly used in industry (RS232, Ethernet, WLAN, OPC UA, Modbus, CAN, ProfiNet, ProfiBus, ...). The variety of connections, interfaces and transmission standards enable industrial temperature data loggers to perform even the most complex measurement tasks.

Is there an upper limit to the number of inputs on a data logger?

No, there is no (physical) upper limit regarding the number of inputs and thus the number of potential sensors and probes that can be connected. For example, Delphin Technology's largest data logger, the Expert Logger 300, has "only" 46 analogue inputs for temperature or other measurements and therefore might seem limited in terms of connections. However, its modular design allows the number of inputs to be expanded almost infinitely. This is done by simply adding another Expert Logger or a "slave" device to the data logger. In combination with the powerful Delphin Data Center (DDC) software, all inputs can be recorded and stored, fully independent of the number of sensors or connected devices.

ProfiMessage D from Delphin can be used when several hundreds or even thousands of inputs and outputs are required. The device is almost infinitely expandable and can be compared to a large PLC, with ProfiMessage D's measurement accuracy and structured data collection offering clear advantages over a PLC.


Are you interested in finding out more about the wide range of opportunities that data loggers from Delphin Technology offer you in your day-to-day work? Or do you have any questions about our products? Call us now and let our experts advise you personally and without obligation.