Description
The TFMA is a screw-in temperature sensor that sends its reading by radio, manufacturer type Müller METS-WR.
It is built for measuring points no cable reaches: no signal cable, no supply, no cable route through the plant. The sensor runs from a rechargeable battery and transmits in the license-free 868 MHz SRD band.
The input is a Pt100 in 4-wire connection, class A, with a range of -50 … +400 °C. The measuring module works with 16 bit and 0.1 °C resolution at 8 measurements per second; accuracy is 0.15 % of the range, the temperature coefficient 50 ppm/K, the filter 0 … 1 s. The radio module transmits at up to 5 dBm (about 3.2 mW) at 19.2 kb/s.
The range is 20 m with the internal and 100 m with an external antenna – in each case with a clear line of sight; walls, metal and plant components shorten it, and by how much the manufacturer does not say. The external antenna is connected through an SMA plug (option). Two LEDs in red and green under the lens show the state; the device is switched on and off at the top with a magnet.
The lithium-ion battery with 3.6 V and 2600 mAh lasts about six months at one measurement per minute – and about 50 days at six measurements per minute. The measuring rate is therefore the most important setting on this device. Without a connector the battery is swapped for charging; with the four-pin M12×1 connector it charges in the device (24 VDC, max. 1 A, about two hours) or the sensor runs permanently from 24 VDC.
Mechanically: process connection from 1/4" to 1" as well as 1/4NPT to 1/2NPT, protective tube in 1.4571, Ø 6 × 0.5 mm, PBT GF30 housing, PMMA lens with a PA6.6 GF30 screw cap, weight approx. 400 g, system pressure PN 25, protection at least IP 65 with encapsulated boards.
Three points for sizing. The neck tube decides the medium temperature – without one up to 200 °C, with 200 mm up to 400 °C. The battery only charges between 0 and +45 °C, while the device works up to +60 °C; above +45 °C it can therefore measure but not charge. And the ambient temperature is not the medium temperature – the electronics in the head tolerate -20 … +60 °C.
Reading out and remote configuration require the USB-RC transceiver (order number 700-00122); it is transmitter and receiver in one and plugs into the PC. The manufacturer names the ETSI directive and the EMC directive 2014/30/EU but shows no CE marking, and gives no radio approval number; no declaration of conformity is available.
Advantages at a glance
- Radio transmission in the 868 MHz SRD band, no signal cable
- Pt100 4-wire class A, -50 to +400 °C
- Accuracy 0.15 % of the range, 16 bit
- Range 20 m internal, 100 m with an external antenna
- Battery lasting about 6 months at one measurement per minute
- Charging in the device or permanent supply from 24 VDC
- Switched on and off with a magnet
- System pressure PN 25, protection at least IP 65