Description
The EFMF is an OEM transmitter module for strain gauge bridges: load cells, torque transducers, strain gauges, pressure modules and other four-wire bridges. The board measures only 37.5 × 16.8 × 6.6 mm and therefore fits into the sensor housing — turning an ordinary load cell into a wireless load cell.
The input takes the mV/V signal directly and provides 5 V bridge excitation for up to four load cells. The measuring electronics work with 24-bit internal resolution, 4 ppm/°C zero drift and 5 ppm/°C gain drift and can be calibrated by the user at up to nine points — with linearization and output in freely selectable units. It transmits up to 200 readings per second to all receivers of the wireless system: handheld displays, large displays, analog outputs, base stations. The module is compatible with existing T24 systems.
Two versions are available: with an antenna integrated in the radio module and a range of up to 500 m, or with a UFL socket for an external antenna and up to 800 m. Three sensitivities can be ordered: ±3.1 mV/V as standard, plus ±4.5 mV/V and 20 mV/V.
The power-saving modes make long battery operation possible: the module can switch off between transmissions or — from a handheld display or base station — be switched off completely and woken up again. With a pair of AA cells and twelve five-minute measuring sessions per day, about two years of operation can be reached, with D cells about five years. The radio link uses the licence-free 2.4 GHz DSSS band at 10 mW with 128-bit AES encryption.
Benefits at a glance
- Miniature board 37.5 × 16.8 × 6.6 mm for installation in the sensor
- Bridge excitation 5 V DC, bridge resistance 85 to 5000 Ω, up to four 350 Ω bridges in parallel
- Sensitivity ±3.1 mV/V, optionally ±4.5 mV/V or 20 mV/V
- 24-bit internal, up to 200 updates per second, transmission interval 5 ms to 1 day
- Calibration at up to 9 points, stored in the module
- Bidirectional measurement — tension and compression
- Supply 2.1 to 3.6 V DC, quiescent current typically 5 µA
- Range up to 500 m (integrated antenna) or up to 800 m (external antenna) in open field
- 128-bit AES encryption, FCC, ETSI and IC approvals
Please note: the module is not protected against reverse polarity, the maximum voltage is 3.6 V, and the supply must be able to deliver 300 mA briefly at start-up. The cable between module and strain gauge should stay below 3 m, because the voltage drop in the cable affects the factory calibration in four-wire measurement. The bare board has no protection rating — for this there are enclosed versions with IP67, such as the EFMC wireless radio transmitter, and with IP50.
Matching receivers can be found under wireless measurement, load cells to fit them under load cells & force transducers.