Description
The TFMB is a surface temperature sensor with radio transmission on a magnetic base, manufacturer type Müller METS-WRM.
It is attached, not installed: The Alnico 500 magnetic base holds it with 66 N on pipes, motors, and housings where neither drilling nor cabling is possible. The spring-loaded measuring surface Ø 6 mm with 1.5 mm travel presses onto the surface, and the sensor body is made of stainless steel 1.4571. At approximately 514 g and at least IP 65 for the electronics, the mounting position is arbitrary.
There is no signal cable: The measured value is transmitted wirelessly in the SRD band 868 MHz with FSK. The range is 20 m with an internal antenna and 100 m with an external antenna, each with a clear line of sight. The sensor is powered by a 3.6 V / 2600 mAh lithium-ion battery, optionally continuously with 24 VDC; the standby time is approx. 6 months for one measurement per minute and approx. 50 days for six measurements per minute. It is switched on and off with a magnet on top of the lid, and two LEDs indicate the status.
Measurements are taken with a Pt100 in a 4-wire circuit, Class A with 16 bits and a step size of 0.1 °C. The maximum range extends from -50 … +400 °C, the factory setting is -50 … 250 °C according to the order key. The measurement rate is 8 measurements per second, and the accuracy is 0.15 % of the range.
Please note before ordering: The data sheet states the accuracy as 0.15 % of the range, while the feature list on the first page indicates approx. 0.2 %; the data sheet is decisive. The ambient temperature is not the medium temperature – the measuring surface can withstand up to +400 °C, but the electronics in the head only up to +60 °C, and the sensor with the magnet is placed directly on the hot surface; the data sheet does not specify how much heat reaches the head in this process. The range applies to clear line of sight: Walls, metal, and system components shorten it, but by how much, the data sheet does not say – and the magnet places the sensor directly on metal. The battery only charges between 0 and +45 °C, but operation is possible up to +60 °C; above this, measurements can be taken, but the battery cannot be charged. For reading out and remote configuration, the USB transceiver USB-RC (700-00122) is required. A CE mark, a declaration of conformity, a radio approval number, and explosion protection are not documented in the data sheet.
Advantages at a glance
- Attached instead of installed – magnetic base with 66 N made of Alnico 500
- Spring-loaded measuring surface Ø 6 mm, Pt100 4-wire, Class A, up to +400 °C
- Wireless in the SRD band 868 MHz, 20 m internal, 100 m external with clear line of sight
- Accuracy 0.15 % of the range, 16 bits, step size 0.1 °C
- Battery 3.6 V / 2600 mAh, standby time approx. 6 months at 1 measurement per minute
- Sensor body 1.4571, at least IP 65, system pressure PN 25