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LB-718T Digital Thermometer with a Resolution of 0.01°C and Modbus RTU Support


Air temperature meter with high precision measurement. It can work in a dusty environment because the sensors are surrounded by a filter. There is a version with an external Pt1000 sensor that can be used for temperature measurements of liquid and solid media.

The device talks with the measuring system using the industrial RS-485 Modbus RTU communication standard.

  • Air temperature, resolution 0.01°C, uncertainty 0.1°C
  • optionally: external temperature probe
  • RS-485 Modbus RTU
  • 7..28V DC 4mA
Operating range:
  • 0..40°C
  • -200..+550°C (external probe)
  • Polymas, ABS, IP65, 170x64x35mm
  • Air temperature (or other medium)
  • robust and dust-proof housing
  • Wide operating temperature range
  • RS-485 interface, MODBUS RTU
  • temperature resolution of 0.01°C
  • PC software - LBX Server (SCADA-type)


The LB-718T digital thermometer is designed for air temperature measurement in rooms or other media in the version with external temperature sensor (TX). It may operate in extremely dusty spaces, thanks to the use of air-tight housing and suitable filter protecting the measuring sensor. It is a small, stationary thermometer, powered by an external source. Measurement data are displayed on a two-line LCD display; they may be displayed with a resolution of 0.01°C.

To make the measurements, the thermometer uses data from the external Pt-1000 temperature sensor. On the basis of the known non-linear characteristics of the temperature sensor and digital calibration data stored during calibration on the device storage memory, the built-in microprocessor calculates the current temperature measurement results. The results are available in a digital form for the supervising data collection system via the RS-485 interface and MODBUS RTU protocol.

The LB-718T thermometer is equipped with a digital RS-485 interface that allows the operation of up to 32 devices on one rail with a total length of up to 1,200 m. Thethermometer integrates the widely-known MODBUS RTU protocol, thanks to which the thermometer may operate in many systems based on this standard. In particular, the LB-718 thermometers may be connected via the DE-311 Ethernet converter with the LBX software, serving as a central point of the LAB-EL monitoring system.

The thermometer is equipped with jumpers used for setting the MODBUS address in the range of 1…32.

The output of the LB-718T digital thermometer is made with screw clamps (4 camps — power, A and B lines), located inside the housing, to which a cable is led through an opening with a diameter of 7 mm.

The thermometer does not feature mechanical calibration elements (e.g. potentiometers). The thermometer calibration includes sending calibration data via a digital interface to the instrument’s permanent storage, obtained from the calibrated climatic conditions. It ensures convenience and high calibration accuracy as well as the stability of the device's metrological parameters over time.

The LB-718T digital thermometer may come in a special "S" version (poured with siliconic compound), which makes the electronics resistant to high levels of humidity. Irrespective of the ("S") version, the instrument may not be subject to direct atmospheric precipitation nor water vapour condensation.

The standard version of the thermometer (without siliconic compound) is fitted for short-term (up to a few hours) measurements within the measuring range limits. In addition to the measurements, the device is to be kept in the recommended continuous operating conditions. In the standard version, the instrument is equipped with a sensor screen (impurities filter), type F3.

Calibration certificates

Each digital thermometer, as per order, may feature an individual calibration certificate provided by LAB-EL Calibration Laboratory.

Dedicated software

This thermometer may additionally come with an advanced software for Windows — the LBX software — enabling:

  • presentation of current readings from devices;
  • alarm monitoring and signalling;
  • presentation of archived data — charts, reports, histograms;
  • data archive management;
  • access for remote clients.

Technical Data

Measurement uncertainty ±0.1°C (1) in the range of 50°C
±0.2°C (1) in the range of 100°C
±0.4°C (1) in the range of 200°C
±1.5°C (1) in the range of 400°C
±3.0°C (1) in the range of 750°C
Measurement range -40…+85°C  
-100…+260°C (2) TX version
-200…+550°C (2) TXE version

(1) Additionally, ±1 last digit
(2) For the LB-718TX/TXE, the actual measurement range: may be limited by the functionalities of the temperature probe. E.g.: -60…+90°C for standard TL2 probe.

Parameter Reading range Resolution
Temperature -200.00…+550.00°C 0.01°C via digital RS-485 interface
-200.0…-100.0°C and +100.0…+550.0°C 0.1°C on the LCD display
-99.99…+99.99°C 0.01°C on the LCD display
Temperature range 0…40°C
Humidity range 20…80%

*) Exceeding the recommended continuous operating conditions (e.g. when installing the device outdoors) requires the use of additional protective measures for the electronic part of the device against the eventuality of water entering the device (protection of the electronics with silicone or usage of additional external housing).

Voltage range 7…28 V DC  
Power consumption approx. 4 mA without a terminator
External dimensions of the housing  170 x 64 x 35 mm   
Material plastics (polymas, ABS)  
Housing protection class IP 65 additionally limited by the protection class of the filter


RS-485 transmission parameters: 19,200 bps, 8 information bits, parity control — Even, 1 stop bit (19200/8E1) or (configured with a jumper starting with the firmware v1.0.1) 9,600 bps, 8 information bits, no parity control — none, 1 stop bit (9600/8N1)

MODBUS RTU protocol. Interface connection in the form of 4 screw clamps, accessible after removing the device’s cover. Address set with jumpers in the range of 1…32.

Description of available MODBUS registers

The value defined as the register address is the same as the one that should appear in the Modbus data package in the address field. Sometimes the PC software adopts the Modicon convention and requires that the input register address be expanded by 30001 more than the value given in this document — e.g. the DEVID register would then have 30001.
Address Designations TYPE Description
0 DEVID WORD Device type identification 0x0718 (hex format)
1 CPTB WORD Firmware version from the viewpoint of operation via MODBUS. In the event that the user’s software recognises firmware of a newer version (FVER register) than the supported one, it should — while reading this register (CPTB) — confirm that it is able to support the device. The version specified in the CPTB register is possibly the oldest version that the current firmware is backward compatible. Description correct for CPTB = 10000.
2 SNUM WORD Serial number of the device
3 FVER WORD Firmware version in the form of X.Y.Z, where: X — tens of thousands of FVER, Y — hundreds of FVER, Z — units of FVER. E.g.: for FVER = 21203, it is 2.12.3
4 CONFIG WORD The value of a variable set by the manufacturer; meaning of bits:
0: humidity measurement present
1: thermometer featuring wide range of temperature (E version: -200…+550)
2: temperature measurement averaging enabled (for the FLOAT type variable)
3: humidity measurement averaging enabled (for the FLOAT type variable)
4: temperature resolution of 0.01°C
5 STATUS WORD State of the device; meaning of bits:
0: ERROR_T — temperature measurement error
1: ERROR_RH — humidity measurement error
2: CFG_ERR — calibration error
Remaining bits feature no meaning
6.7 T FLOAT Temperature
8.9 RH FLOAT Humidity
10 T_WORD WORD Temperature as a number in U2 code with a resolution of 0.1°C (the read-out value should be divided by 10)
11 T_WORD_AVG WORD Temperature — the same as above, but averaging
12 RH_WORD WORD Humidity as a number in U2 code with the resolution of 0.1% (the read-out value should be divided by 10)
13 RH_WORD_AVG WORD Humidity — the same as above, but averaging
14 CAL_YM WORD Date of the last calibration, LSB: year — 2000, MSB: month
15 CAL_DH WORD Date of the last calibration, LSB: day, MSB: hour
16 CAL_M WORD Date of the last calibration, MSB = 0, LSB: minute
Read Device Identification 43/14 BASIC ID


By special order, the following set-ups are available:

  • The LB-718TS digital thermometer of increased resistance to climatic conditions (in siliconic compound).
  • The LB-718TFn digital thermometer — version of sensors’ cover (according to description), the version is given if it is not F3.
  • The LB-718TX digital thermometer — fitted for connecting an external temperature sensor.
  • The LB-718TXE digital thermometer — fitted for the connection of an external temperature sensor working in the range of -200…+550°C.


LB-718T devices may be connected to the DE-311 converter, thanks to which the measurement data may be monitored by the LBX software via Ethernet.
Connection of the LB-718 with the DE-311 should be made according to the following table:

DE-311 LB-718T DC 7…28 V power unit Signal description
3 A   Data + (B)
4 B   Data - (A)
5 - - Power - / GND
  + + Power +

Microswitch of the DE-311 converter should be in the RS-485 position:


Other versions of the LB-718 thermometer

  • LB-718 digital thermometer/hygrometer
See also
See also
Thermometer LB-710ATThermometer LB-710AT
Precise electronic thermometer. Internal or external temperature sensor. Wide range of measurement.
Dual Thermometer LB-714Dual Thermometer LB-714
A double thermometer with a psychrometer function. Temperature and humidity measurement. Wide range of measurement.
Thermohygrometer LB-520 Thermohygrometer LB-520
Thermohygrometer is a relative humidity and temperature recorder, powered by the long-lasting lithium battery; it uses Pt-1000 and capacitive sensors.