LF-TD 120 air humidity and temperature transmitter

Humidity and temperature measurement in kilns and ducts up to 120 °C

The LF-TD 120 is an industrial transmitter for relative air humidity and temperature, made for continuous operation where the air is hot: in timber drying kilns, supply air ducts, climatic chambers and process lines at temperatures up to 120 °C. It is used in laboratory, air-conditioning and drying technology, in the timber, food and feed industries, in construction, printing and papermaking, in agriculture, biotechnology and the pharmaceutical industry.

In production, processing, storage and transport it is the air humidity that decides whether the material dries evenly, whether condensation appears and whether the batch keeps its quality. A continuous measurement makes it possible to react before the process leaves the intended window.

A 500 mm probe measures where the process happens

The stainless steel sensor tube, 12 mm in diameter and 500 mm long, reaches into the duct or chamber, while the electronics housing stays outside in a cooler place. The sensor cap is screwed on and replaceable - sintered stainless steel and nickel-plated sintered bronze are among the choices, matched to the dust load and the aggressiveness of the atmosphere.

Two 4-20 mA outputs wire straight into the control system

Humidity and temperature leave the transmitter as two independent 4-20 mA current signals: humidity scaled 0 to 100 %, temperature scaled -20 to +120 °C. A signal like that is accepted by any PLC, data logger and analogue input module, without drivers or intermediate software. The device is supplied with 12 to 29 VDC and draws about 18 mA.

Display and digital interfaces to choose from

The optional display with a keypad (art. no. 13731) shows the current humidity and temperature on the device itself, which helps at commissioning and during service. If the reading is to reach a network, the transmitter can be ordered with an RS232, USB or Ethernet interface. Where Profinet is needed, the right device is a separate model of the series, the LF-TD Profinet.

Calibration at six humidity points

Every LF-TD transmitter is calibrated at the factory at six humidity points. The calibration accuracy is ±2 % over the range of 10 to 90 % relative humidity and ±0.3 °C over +10 to +60 °C. A factory calibration certificate with an adjustment report is supplied on request (art. no. 10403), and the sensor can be checked in place with the calibration device for tube probes (art. no. 10006) together with certified ampoules.

Advantages The capacitive humidity sensor keeps its accuracy over years of operation and withstands the usual contamination and contact with many chemicals. It settles quickly after a change of conditions, so it suits processes in which the humidity changes within minutes. relative humidity and temperature measured by one device long-term stability and factory calibration at six points stainless steel probe with replaceable sensor caps 4-20 mA outputs ready to wire into a controller or a data logger aluminium housing with mounting holes, easy to fasten data management in the HumiSenseWare software

Technical data

Technical drawing

Scope of delivery

LF-TD 120 with a 1.9 m connecting cable and a moulded 5-pin sensor plug.

Extended accessories

• Art. no. 13731 - display with a keypad for the LF-TD
• Art. no. 12807 - RS232 interface for the LF-TD
• Art. no. 12808 - USB interface for the LF-TD
• Art. no. 13738 - Ethernet interface for the LF-TD
• Art. no. 13612 - angle bracket for the LF-TD
• Art. no. 12456 - drip guard for LF-TD transmitters
• Art. no. 10249 - sintered stainless steel sensor cap with a sintered filter, for high temperatures and demanding conditions
• Art. no. 13799 - nickel-plated sintered bronze sensor cap
• Art. no. 10006 - calibration device for tube probes
• Art. no. 10352 - certified calibration ampoules, set of 5 at 50 % relative humidity
• Art. no. 10005 - certified calibration ampoules, set of 5: 2 × 35 %, 1 × 50 %, 2 × 80 % relative humidity
• Art. no. 10403 - factory calibration certificate with an adjustment report
• Art. no. 14711 - HumiSenseWare LF-TD, standard Live Trend licence - requires one of the interfaces: RS232 (art. no. 12807), USB (art. no. 12808) or Ethernet (art. no. 13738)
• Art. no. 14712 - HumiSenseWare LF-TD, data management and logging option
• Art. no. 14713 - HumiSenseWare, integration package for 3 additional sensors
• Art. no. 12011 - special version, flat rate to order, regardless of the quantity ordered

For similar applications we also recommend the LF-TD 90 with a smaller temperature range, up to 90 °C, and the LF-TD 150 with a 750 mm probe, working up to 150 °C.