Description
The EFMF is an OEM transmitter module for strain gauge bridges: load cells, torque transducers, strain gauges, pressure measurement modules and other four-wire bridges. The board measures only 37.5 × 16.8 × 6.6 mm and thus fits into the sensor housing — turning a conventional load cell into a wireless load cell.
The input directly accepts the mV/V signal and provides 5 V bridge excitation for up to four load cells. The measurement electronics operate with 24-bit internal resolution, 4 ppm/°C zero drift and 5 ppm/°C gain drift, and are customer-calibratable over up to nine points — with linearization and output in freely selectable units. Data is transmitted at up to 200 readings per second to all T24 receivers: handheld displays, large displays, analog outputs, base stations.
Two designs are available: T24-SAi with an antenna integrated into the radio module and a range of up to 500 m, T24-SAe with a UFL socket for an external antenna and up to 800 m. Three sensitivities can be ordered: ±3.1 mV/V as the basic version, plus ±4.5 mV/V and 20 mV/V.
The low-power modes enable long battery life: the module can shut down between transmissions or — from a handheld display or base station — be completely switched off and woken up again. With a pair of AA cells and twelve measurement sessions of five minutes per day, approximately two years of operating time can be achieved, and about five years with D cells. The radio link operates on the license-free 2.4 GHz DSSS band with 10 mW and 128-bit AES encryption.
Advantages 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, optional ±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 over 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 (SAi) or up to 800 m (SAe) in open field
- 128-bit AES encryption, FCC, ETSI and IC approvals
Please note: The module is not reverse polarity protected, the maximum voltage is 3.6 V, and the supply must be able to provide 300 mA for a short time at startup. The cable between the module and the measuring grid should remain under 3 m, because the voltage drop in the cable in four-wire measurement affects the factory calibration. The bare board has no protection class — for this, there are the housing versions T24-ACM-SA and T24-ACMi-SA with IP67, and T24-ACMm-SA with IP50.
The suitable receivers can be found under Wireless Measurement Technology, load cells for equipping under Load Cells & Force Transducers.