Description
The TMMB is a surface temperature sensor on a holding magnet, manufacturer type Müller METS-WTM.
It is placed on a pipe or a vessel and holds itself – no drilling, no process connection, no intervention in the medium. The spring-loaded measuring face presses against the surface, the magnet pulls with 66 N.
This device has no display and no keys – it is set exclusively over HART. Otherwise it is identical to the TMMA (METS-WSM), which carries the display. Anyone who wants to read the value on site orders the TMMA.
The input is a Pt100 in 4-wire connection in classes A, B and AA (B 1/3 DIN), with a range of -50 … +200 °C at a smallest span of 50 K; up to -50 … +250 °C on request. The output is 4 … 20 mA with HART in the 2-wire loop, current range 3.8 … 20.5 mA, with 3.6 mA on short circuit and 21 mA on break. Accuracy is 0.3 % of the range at 16 bit, the response time 20 ms, the measuring rate 10 measurements per second, the filter 0 … 99 s.
The two limit contacts are PNP or NPN with 30 VDC / 200 mA, optionally 1000 mA; switching point and hysteresis are adjustable across the whole measuring range, the switching delay from 0.0 to 999.9 s, and failsafe behaviour as well. Supply comes from the HART current loop with 12 … 40 VDC, load R = (UB − 12 V) / 21 mA, with reverse polarity protection.
Mechanically: holding magnet in Alnico 500, measuring face Ø 6 mm spring-loaded with 1.5 mm travel, sensor body stainless steel 1.4571, PBT GF30 housing, connection either at the side or on top, weight approx. 259 g, system pressure PN 25, protection at least IP 65 at the electronics.
Three points the manufacturer leaves open and that belong in the planning. The sensor sits with the magnet directly on the hot surface. The measuring face may reach +200 °C, the electronics in the head only +80 °C – how much heat travels into the head is not documented, and above +85 °C the electronics can be destroyed. The galvanic isolation applies only between the switching outputs and the amplifier, not against the loop and not against the surface the magnet sits on. And how the holding force changes with temperature the source does not say.
Ten electrical connections are available – which one carries how many limit contacts is not a free choice: two contacts are only possible on M12 five- and eight-pin, on MIL and on the cable version; on Deutsch DT04 four-pin and on Super Seal, none. Configuration uses the HART interface with USB and software, order number 01310-00220; when communicating through a HART modem a resistance of 250 Ω has to be taken into account. No CE marking is documented and no declaration of conformity is available.
Advantages at a glance
- Measuring without intervening in the process – holding magnet with 66 N
- Spring-loaded measuring face Ø 6 mm, 1.5 mm travel
- Pt100 4-wire, classes A, B and AA
- Medium -50 to +200 °C, up to +250 °C on request
- 4 … 20 mA with HART, accuracy 0.3 % of the range
- Two limit contacts with adjustable delay
- Sensor body stainless steel 1.4571, magnet Alnico 500
- Protection at least IP 65
- Version with display available as TMMA