Wireless transmitters for load cells and force transducers

With wireless transmitters you read out load cells, force transducers and torque sensors without a signal cable. Transmitter modules at the sensor transmit digitally in the license-free 2.4 GHz band to base stations, handhelds or output modules with analog, relay and interface outputs. Configuration and logging are done with free Windows software.

When wireless load cells or wireless force transducers are the right solution

Wireless transmission is not worthwhile because it looks more modern, but in four clearly defined cases.

The sensor moves. On a crane hook, a rotating shaft, a traveling carriage or a rail vehicle, a cable cannot be routed permanently. Slip rings and drag chains are expensive and wear out.

There is no cable route. There is a road between the silo and the control room, the measuring point is on the hall roof, or the cable would have to cross a fire wall. The cost of the cable route quickly exceeds the extra cost of the wireless modules.

The measurement is temporary. Nobody builds a permanent installation for a load test, a tension test on guy lines or a two-week measurement campaign. Set up, measure, dismantle.

Many distributed measuring points. When twenty points are spread across a site, a wireless network is simpler than twenty cables to a central cabinet.

Arguments against wireless, on the other hand, are safety-related shutdown functions, closed control loops with short response times, and permanently installed weighing points where a short cable and a weight transmitter are the cheaper and more robust solution.

How wireless measurement systems are built

A single device is never enough. You need at least two components, usually three.

The transmitter module sits at the sensor, excites the measuring bridge, digitizes the signal and transmits it. It is battery-powered and available in weatherproof housings, and in a compact design also for integration into the sensor housing.

The receiver determines what happens to the value. The options are base stations for the PC, rugged handheld displays for use on site, and output modules that translate the wireless value back into a conventional signal: analog as 4…20 mA or 0…10 V, as a relay switch point, or via a serial interface into the control system. This lets you connect a wireless sensor to a PLC that does not need to know anything about wireless.

The software is used to configure, scale and calibrate the modules and to log data. An SDK is available for your own applications.

Since all modules work in the same network, several transmitters can be assigned to one receiver, and one value can be output to several receivers at the same time – for example to a handheld for the operator and in parallel to an analog module for the plant.

Estimating range realistically

Range figures apply to a clear line of sight. In practice, steel structures, concrete walls, shelving, full silos and moving machinery attenuate the signal in the 2.4 GHz band considerably, and a transmitter mounted directly on a large metal surface radiates much less well than one with some distance from it.

So plan with a reserve, mount the antennas as high as possible and in sight of each other, and use a repeater for longer distances or buildings with many corners. Also keep in mind that the 2.4 GHz band is shared with Wi-Fi; in environments with dense radio traffic, channel selection is a topic for commissioning.

The advantage of the band: its use requires no registration and no fees, and you do not need a frequency allocation.

Measuring rate and battery life

This is the central trade-off and the point where projects fail if it is not clarified beforehand. The modules can deliver high transmission rates, up to the range of a thousand readings per second. But exactly this rate consumes bandwidth and battery capacity.

For silo monitoring that needs a value every few seconds, transmitter modules with a sleep function run for a very long time on one set of batteries. For a dynamic measurement at a high rate, expect hours to days and plan for battery changes or an external supply. So define the required rate before you choose, and no higher than necessary.

Two more points for dynamic applications: wireless introduces a latency that can be too large for control tasks, and several transmitters do not automatically measure in sync. If you want to combine channels in calculations, for example in multi-axis measurements, clarify synchronization with us in advance.

Typical applications

Load measurement on the crane hook, complementing our crane scales. Rope and guy forces on masts, cable cars and tents. Load tests and acceptance tests on structures and lifting equipment. Test rigs with rotating or traveling assemblies. Tank and silo weighing without a cable route to the control room. Wheel load and axle load measurements on vehicles. Temporary measurement campaigns in service.

Matching components

You will find the sensors under load cells and force transducers, cable-based evaluation under weight transmitters and strain gauge amplifiers, remote displays under large displays, and mobile devices under handheld measuring devices. We calibrate the sensors to ISO 17025 in our own laboratory.

Our engineers will advise you directly on range, measuring rate and system design – gladly based on your floor plan.