Linear Transducers

Within the various linear measurement rules used in the industry, we have several devices that are quite different at the hardware level. This need is related to the need to adapt the measurements to the various environments and mechanics inherent to the machine.

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Therefore, the most common devices used by us are the following:

• LVDT (Linear Variable Differential Transformer/ Linear Variable Differential Transformer)

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These devices are based on the fact that an inductor circuit consists of a primary and secondary coil, and that through the movement of the central core, a voltage is induced, which will be translated into a voltage variation. This tension variation will be interpreted as a positioning quota. Sectional view of an LVDT (FIGURE 1). The current is applied to the primary coil A, causing a voltage to be induced in each secondary coil B. As can be understood, any influence caused by eddy currents will influence the measurement accuracy. For this reason, several factors must be taken into account when connecting it:

• Ensure that connections to the ground are made;
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• Choose, when possible, the shortest path of the LVDT connection cables (power supply and respective positioning feedback);
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• Try to ensure that the cable that will serve as power supply and LVDT feedback do not intersect with power cables;

• Signal stabilization (when possible they must be connected to these devices, their mesh/ground/ground when available must be connected to the card and not to the machine's common ground);
  

• Some hardware that connects to the respective LVDT analog signal contains power channels.

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The figures represent two different cards to be able to connect an analog device, and the choice of hardware must take into account all these factors, so that the correct value can be measured.

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Linear transducers based on the potentiometer principle

These transducers are based on the voltage divider principle. For this purpose they use the potentiometer concept. When displacements are made, the measuring element on the core of the element will vary the resistance. This resistance variation when we apply a voltage to your terminals will cause the voltage value to vary. That is, if we have applied it to the same 10v, 10v will be the maximum measurement value. As the resistance increases or decreases, the voltage value will vary between 0 and 10 v.

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Connection Example

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In the example on the left, 2 will be the tension value that will vary depending on the cursor position.

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Linear pulse position transducers

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During movement, these transducers provide pulses in their respective channels, generally consisting of 3 channels, two of which will be out of phase between them (with this offset we can understand whether the displacement is in the positive or negative direction) and the third channel (generally Z) is used to increase precision.

They will be linked to a fast pulse chart (High Speed Counter) responsible for counting the number of pulses received. As we have 2 phases out of date, this card will increase or decrease the number of pulses upon detection when the first phase appears.

An example of this type of transducer is an SMC pneumatic with a counter, ce1 or cep1 (the difference is its accuracy).

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Example of a cable from a ce1

In this case we do not have the Z phase but we have the two phases called A- Phase and B-phase, through which we will obtain the respective linear positioning.

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