SITRANS TO500 Temperature measuring system

How do I reliably detect hotspots in my tube-bundle reactor?

TO500 Temperature measurement article

Accurate determination of temperature in the catalytic conversion of gases and liquids is a critically important task that often presents operational challenges.

The SITRANS TO500 multipoint measurement system transmits temperatures and temperature profiles reliably and fast. The system is particularly well suited when a very large number of measuring points are required in a tight space with low thermal mass, such as in tube and tube-bundle reactors.

Read how Evonik Industries is optimizing temperature measurement with the TO500.


The SITRANS TO500 multipoint temperature transmitter is used for measuring a large number of temperatures using a very narrow fiber-optic temperature measuring lance. The system consists of the following components: the transmitter, and the measuring lances, which can each be connected to up to 48 temperature sensors on the transmitter at four channels. With up to four measuring probes, 192 measuring points can be processed at the same time by a SITRANS TO500.

The extremely thin sensor measuring probe of < 2 mm is used for measured value transmission. The system is therefore particularly suitable when the user wishes to install a very large number of measuring points in a tight space and with low thermal mass, such as in tube and tube bundle reactors or in capillary or microreactors. The fast and gap-free detection of temperature profiles enables the plant operator to optimize processes in terms of lifetime, quality and output. Local overheating is quickly and accurately detected, thereby preventing damage to the process, plant and environment.

SITRANS TO500 technology is based on fiber Bragg gratings (FBGs) which are arranged at individually defined points on the sensor probe. The transmitter sends light waves to the fiber-optic sensors and evaluates the reflected portions. In the transmitter, light is generated in the wavelength of 1500 to 1600 nm and output to the sensor measuring probe by means of a continuously tunable laser light. Each fiber Bragg grating reflects light of a defined wavelength. The wavelength reflected by the grating varies depending on the temperature. The reflection at the FBGs is thus a measure of the temperature at the respective measuring point. A gas cell with fixed absorption line serves as a reference in the SITRANS TO500 and the wavelength determination is continuously adjusted by it.

The transmitter provides the determined values for analysis in control systems via a Profibus DP interface and makes them available for management of the assets and optimization of the process. The parameters of the SITRANS TO500 are set via the integrated Ethernet interface.


SITRANS TO500 Overview Video

TO500 Video Image

SITRANS TO500 - Fiber-optic temperature transmitter for optimizing processes



TFBG (fiber Bragg grating) temperature measuring probes

4 channels

Measured variable


Input type

FBG sensors (max. 48 per channel)

Characteristic curves



0.1 K

Measuring accuracy

<0.5 K


<0.5 K

Measuring cycle

< 1 s

Measuring range

-292°F to 1472°F (-180°C to +400°C), depending on measuring probe type




Output signal


Power supply

24 V DC ± 20%


Against reverse polarity

Measuring speed
Measurement rate


1 HZ, independent of the number of FBG's

Optical Power

≤ 1 mW per channel

Laser protection class

Class 1

Operating conditions

Ambient temperature

32 to 122°F (0 to +50°C)

Storage temperature

-40 to 185 °F (-40 to +85°C)

Relative humidity

< 80%, non condensing at 122 °F (50°C)

Electromagnetic compatibility

According to EN 61326





5.3 lb (2.4 kg)


9.84 x 5.51 x 4.33 inches (250 x 140 x 110 mm)

DIN rail adapter

At the back



Displays and buttons


"Power-on" (continuous light)
"Status" (flashing during start-up; otherwise continuous light)


"Reset" (system restart or address reset)


  • < 2 mm diameter of the measuring lance for more reactor space due to the smaller protective tube and thus faster response times

  • Gap-free temperature profile due to ta total of 192 measuring points for process optimization

  • Simple insertion of the measuring probe into the protective tube due to the rolled state, as well as low-cost transport and easy installation

  • Flexible, application-specific customer solution through individual positioning of the FBGs on the sensor measuring probe

  • Measured value transfer takes place in the same fiber; no additional cables necessary

  • Especially suitable for applications in which a large number of measuring points are to be installed in a very tight space and with low thermal mass