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LTT measurement technology now available with LVDT sensors


LVDT/carrier-supplied DMS sensors are not commonly used. But when they are, they pose major challenges for measurement technology. This is especially true for large-scale projects with multiple measurement channels. The LTT24 from Labortechniker Tasler GmbH is the market leader for such tasks and many more.


Sometimes DMS and LVDT sensors supplied by carrier frequency would be the best solution...

...if only it were possible to connect them!

They are rarely used in “normal” everyday measurement work and some people don’t even know what they are: DMS and LVDT sensors supplied by carrier frequency. They both rely on a sinusoidal voltage supply. While DMS operate in resistance bridge circuits as resistive voltage dividers, LVDT sensors are constructed as loops and operate inductively. They both generate a sinusoidal output signal for which the amplitude is determined by the physical parameter being measured (e.g. deflection or path).

The advantage of inductive construction is primarily the option of electrically and mechanically separating the receiver coil from the transmission coil, which can be beneficial in potentially explosive areas of use (e.g. fill level measurement in fuel tanks).

The primary distinguishing feature of the two sensor types is that the amplitude-modulated output signals have just one frequency: the exact same signal frequency as the applied sinusoidal supply. No other frequency in the output signal is included in the measurement results. Any disruptions or noise can therefore be removed by analogue or digital filtering, which is not the case for the excitation frequency. As a result, an unbelievably precise measurement signal is still retained even in environments with extremely heavy disruption. This is a huge advantage!

They make use of their full potential in demanding applications. This typically includes applications that depend on a long service life and good reliability (military, aviation, turbines, power plants, factory automation etc.).

Thanks to their robust design with respect to interference susceptibility, extreme operating temperatures, rapid temperature changes and vibrations, they are suitable for demanding applications in all industrial sectors. High IP protection classes and quality housing materials such as stainless steel and titanium make underwater applications possible. Because these position sensors also withstand contact with aggressive chemicals without suffering damage, they are also suited for cleaning or disinfection in machines or food production and packaging plants. Pressure-tight versions of these sensors are installed for control and regulation in hydraulic cylinders, servo valves and pneumatic cylinders.

With multi-channel measurements, however, caution is required: if all connected sensors are supplied with the same excitation frequency, crosstalk may be generated between certain signal components of the connected sensors – and they would not be filtered out because they all have the same frequency. For this reason, it must be ensured that all sensors for multi-channel measurement are supplied with their own sinusoidal excitation frequency (also referred to as carrier frequency).

The slowest carrier frequency that is used determines the available bandwidth of the measurement signal.  Additional measurement channels therefore have to use higher carrier frequencies, which means that the preamplifier has to offer different carrier frequencies for each individual channel, and must also be capable of operating cleanly up to high carrier frequency ranges.

This kind of preamplifier actually doesn’t exist anymore...

...but fortunately the LTT24 has been equipped with this highly useful capacity after a major wave channel project!

Carrier frequencies of up to 125 kHz with a measurement signal dynamic of 140 dB can be configured individually via software on up to 32 measurement channels: this enables practically disruption-free measurement for large wind tunnels, wave channels or other demanding large-scale projects with multiple channels.

The LVDT option is just one of the must-have features of the LTT24!