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Home » Devices » Thermometers » Dual Thermometer LB-714

LB-714 Dual thermometer with probes, LB-714P Wet-and-Dry bulb thermometers


An electronic two-channel temperature meter that can be used as a wet-and-dry bulb thermometer. Precise temperature measurement using Pt1000 probes. The device is adapted for installation in high humidity conditions. Psychrometric measurement works particularly well in places with high humidity. Designed for use in measurements in cold stores, freezers, food storage, halls of cultivation.

The device can participate in a measurement system based on data transfer using the S300 interface. The device works well in an industrial environment, in the presence of high electromagnetic interference, for which the S300 interface is resistant.

  • 2-channel temperature Pt1000, resolution 0.01°C, uncertainty 0.1°C
  • optionally: wet-and-dry bulb temperature, relative humidity, resolution 0.1%, uncertainty 1%
  • 6..24V DC
Operating range:
  • 0..40°C
  • -200..+550°C (external temperature probes)
  • 145x64x35mmm
  • Dual thermometer with external Pt1000 probes
  • Wet-and-dry bulb thermometer as option
  • Wide range of temperature measurement
  • Sensors for various media
  • Temperature resolution of 0.01°C

Description of the thermometer

The LB-714 thermometer with a probe is a stationary device of small dimensions, powered by an external power source. On the basis of the known non-linear characteristics of the temperature sensors and digital calibration data stored during calibration on the thermometer’s storage memory, the instrument’s built-in microprocessor calculates the current two temperature measurements results. The results are sent from the thermometer in a digital form to the mother data collection system. Measurements are displayed on a two-row LCD display, with the resolution of 0.01°C or 0.1°C.

This standard version LB-714 thermometer consists of two sensors (Pt1000 thermometric resistor) for temperature measurement in stainless steel tubes, connected with a measuring converter by means of a cable of 1…10 m in length (depending on the requirements of the ordering party). The LB-714 thermometer is particularly recommended for locations with high humidity (e.g. freezers, cold stores), due to the resistance of the external measuring sensor to humidity. Depending from the design of the sensor, it may be used for temperature measurement in various media in the range of -100…+260°C or -200…+550°C (LB-714E version).

Wet-and-dry bulb thermometer

LB-714P wet-and-dry bulb thermometerWet-and-dry bulb
module LB-714P

Two sensors (Pt1000 thermometric resistors), mounted in a holder of stainless steel and equipped with a vessel for dampening the wick of the wet bulb thermometer constitute a the LB-714P wet-and-dry bulb thermometer. The LB-714 dual-channel thermometer interacting with them is then configured as a wet-and-dry bulb thermometer — the jumpers inside the device must be in place. Then thermometer 1 fulfils the role of a dry bulb thermometer, and thermometer 2 acts as a wet bulb thermometer. In such a case, the dry-bulb thermometer temperature is displayed on the display screen of the wet-and-dry bulb thermometer set, and the relative humidity is calculated. It should be noted that the wet-and-dry bulb thermometer requires individual adjustment in order to set the suitable psychrometric constant. In the memory of the LB-714 thermometer, that was subject to adjustment of the wet-and-dry bulb thermometer, a standard value of the psychrometric constant is stored, that may be unsuitable for a given wet-and-dry bulb thermometer. The wet-and-dry bulb thermometer may be adjusted in the LAB-EL Calibration Laboratory.

The standard length of the cable between the LB-714 panel and the LB-714P wet-and-dry bulb thermometer is 3 m. Other lengths are available per special order.

The advantage of the wet-and-dry bulb thermometer is the precise and stable measurement of high values of relative air humidity, close to 100%. That is why a wet-and-dry bulb thermometer is recommended for monitoring conditions in climatic chambers, where immunological research is conducted, for example. One drawback of the wet-and-dry bulb thermometer is the necessity for maintenance (frequent wick replacement, adding distilled water) and securing a constant speed of air flowing around the sensors — like the one used during calibration of the psychrometric constant.

Thermometer — the wet-and-dry bulb thermometer is equipped with the LAB-EL S300 digital current interface, with runtimes analogues with the RS232C standard. Recordings of subsequent measurement results are sent from the instrument approx. every 2 seconds. Except for data transmission, the output interface is used also to power the thermometer — to this end, a two-wire line (e.g. telephone type) is used, with the provision that the polarity of interface wires connection is at the user’s discretion.

This instrument may be connected to any given supervisory system, e.g. LB-722 climate regulator; LB-480, LB-489 or LB-856 hubs (establishing a temperature monitoring system); LB-755A panel and (with the use of the LB-371 converter) to the RS232C interface, or (with the use of the LB-375 converter) to the USB interface of any PC. It enables remote and automatic collection of temperature data.

Some older types of the instruments may not support the LB-714 format, that is why this dual-channel thermometer/wet-and-dry bulb thermometer is usually equipped with a configuration jumper; when inserted, the measurement results are sent in a format compatible with the LB-711 or LB-710 thermometers (in the configuration as a wet-and-dry bulb thermometer), which can connect the thermometer with devices and systems that enable interaction with the LB-714 format. It must be noted that in such a case, the transmission resolution of the measured temperature is only 0.1°C.

Thermometer calibration

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

Each thermometer or wet-and-dry bulb thermometer may feature an individual calibration certificate issued by the LAB-EL Calibration Laboratory.

The LB-714 thermometer is a light (no humidity sensor) version of the LB-710 thermo hygrometer, awarded approval No. RP T 95 77, issued by the Chairman of the Central Office of Measures in Warsaw.

Technical Data

 Metrological data
Temperature measurement Maximum measurement range -100…+260°C — for LB-714
-200…+550°C — for LB-714E
Measurement uncertainty for single-point calibration *1) ±0.2°C,
±1 final digit
Measurement uncertainty for two-point calibration *1) ±0.1°C,
±1 final digit
Measurement resolution 0.01°C — for LB-714
0.1°C — for the LB-714E or a format compatible with the LB-711 or LB-710
Humidity measurement — with the LB-714P wet-and-dry bulb thermometer Maximum measurement range 5…100% of relative humidity
Measurement uncertainty
(after calibration)
±1.0% (above 60%)
±1.5% (in the range of 20…60%)
± 2.5% (below 20%)
Measurement resolution 0.1% RH
Operating temperature range of measuring converter -40…+80°C
of temperature sensor (standard) -60…+90°C
(with the exception of the connection cable)
of temperature sensor (special) -200…+550°C
(depends on the sensor version)
Data read-out on an integrated display Temperature with a resolution of 0.01°C — for the range of -99.99…+99.99°C
0.1°C — in the remaining range and for LB-714E
Serial number of the instrument  
Technical condition of the instrument  

*1) within the interval of 50°C

Recommended continuous operating conditions *2)
Temperature range 0…40°C
Humidity range 20…80%
Degree of environmental corrosivity, according to PN-71/H-04651 B

*2) Exceeding the recommended continuous operating conditions 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, e.g. when installing the device in an open space).

Power supply
Voltage range 6…24 V DC  
Power consumption 1 mA average
25 mA maximum

Thermometer INTERFACE

Transmission parameters: according to RS232C, 300 bauds, 7 information bits, without parity control, 1 stop bit operating in the standard of the so-called S300 digital current loop.

  • TXD — constant transmission of measurement results and power to the thermometer;
  • RXD — recording instrument’s calibration data in its permanent storage.


  • measuring converter:  145 x 64 x 35 mm,
  • standard TL-2 sensor:   diameter — 6 mm, length — 100 mm,
  • special sensors: as per individual agreement.
C01 CONNECTIONC01 connection


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

  • LB-714Y wet-and-dry bulb thermometer — with C01 connection (instead of clamps inside the cover).
See also
See also
Thermometer LB-710ATThermometer LB-710AT
Precise electronic thermometer. Internal or external temperature sensor. Wide range of measurement.
Thermometer LB-718TThermometer LB-718T
Digital Thermometer with High Resolution and MODBUS RTU Support
Regulator LB-474A3Regulator LB-474A3
Universal PID climate regulator, operating with two Pt-1000 or Pt-100 platinum thermometers, or with four analogue 0–10 V, 0–1 V or 4–20 mA inputs.
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.