The transducers are elements that change the physical dimension to another, ie.

• physical magnitude of angular velocity can be changed to a physical scale voltage.

• current physical magnitude to voltage changes.

• Physical quantity of angular movement is changed to sinusoidal voltages.

Between the transducers used to measure speed are:

A) ENCODER

The encoder are divided into two groups: incremental and absolute. Incremental Encoder, have simply moved from one division of the circle and deliver pulsed outputs that can store account and know the direction of rotation. This method is known as system output "A quad B" and shown in Figure 12.

Figure 12

In this method, the rotation is deduced from the presence of the fronts of the pulse trains A and B. A transition from 0 to 1 in "A" occurs before a transition in the same way "B" in a direction of rotation, and the opposite happens if the money is in the opposite direction, see figure 13.

During rotation of the shaft, each time it goes through the zero position pulse is generated synchronously with A and B. Incremental encoders produce these pulses from photoelectric devices.

The advantage of the incremental encoder is that the position is not known at the time of the launch.

Figure 13

Some nominal values ​​are incremental encoder: 1024 pulses per revolution, 300 pulses per revolution, and so on.

Absolute Encoder, provide a parallel digital output is generated by a pattern located on a rotating disk attached to the shaft. The sensors used in this case can be electrical contact or photoelectric system. Different codes can be used, with the binary and Gray the most common and may reach very high resolutions and details of the order of 16 bits (20 arcseconds) and above.

This method has the disadvantage of high cost and presents the problem of transmitting data in parallel if the encoder is far from the electronic measuring system.

B) RESOLUTION

Resolve is a rotary transformer analog output voltage which is related only to the angle of its axis. It is, therefore, an absolute position transducer with a rotation angle from 0 to 360 °. See Figure 14.

The resolve to transducer angle measure has several advantages. First, is a mechanical device that can withstand rugged harsh environments of dust, oil, temperature extremes and radiation. Second, because it introduces a transformer signal separation and natural rejection of common mode electrical interference.

Figure 14

This feature, combined with the fact that only four wires are needed for data transmission angular ago by solving unique angle measurement and ideally suited to operate in harsh environmental conditions typical of heavy industry and aerospace. Currently available brushless resolvers, which need not make any contact with the rotor, which greatly increases the durability and reliability of the device.

C) TACHOMETER

Tachometer (Tach) or Dynamo Tachometer (DT) is a DC electric machine that converts mechanical energy into electrical energy, ie as a generator DC.

Its parts are:

Stator consists of a permanent magnet provides the magnetic flux 0F, and

Rotor made ​​of a slotted laminated core, on which windings are copper wires, which end on the commutator and brushes needed to transform the available output voltage induced in DC. See Figure 15.

Figure 15

The shaft of the tachometer is coupled to the motor shaft which is to take the measure of speed. Turning the motor, its shaft drives the tachometer, which responds at its output a DC voltage proportional to motor speed. Consider the following equation relating the input speed n (rpm) and the voltage Vout output DC Tachometer

Ecu 2.3

D) AC CURRENT TRANSFORMER

Consisting of a laminated core around which toroidal winding is induced which becomes secondary. On the toroidal core hole is the power cord to measure (Iprimario), this current is AC, the output current is called Isecundario, and also AC but a lower value, according to the transformation ratio by nameplate. The secondary current must be rectified by diode bridge and converted to volts as shown in Figure 2-13.

Figure 2-13

It has the following relationship:

Ecu 2.4

Where k1 is the ratio of (I _PRIMARY / _SECONDARY I) nominal and R is the resistance of current to voltage conversion. The current transformer is placed in the AC power line to the power stage and its purpose is to measure it indirectly consumes DC current armor.

E) DC CURRENT TRANSFORMER

It is based on the phenomenon of "Hall effect" in which the charge carriers moving through a magnetic field are forced to one side of the middle of the driver, then the nonuniform distribution of load produces a potential difference side by side, which is called the Hall voltage. Figure 2-14 shows an application flow as a measure of power.

Figure 2-14

F) SHUNT RESISTANCE

Comprised of a copper or bronze, which is placed in series with the driver which you want to measure DC current. See Figure 2-15.

Figure 2-15

It is based on the principle of voltage drop that produces a resistance to be traversed by a current (Ohm's Law).

The equation representing the relationship is:

2.-5 Ecu

Where k2 is the ratio of mV / Ampere ratings given on the nameplate of the shunt resistance.

It is specified as follows: k2 = 20mV/50A, k2 = 50mV/50A, etc. This means, for the first case, passing a maximum current of 50ADC there a voltage drop equal to 20mV at the terminals of the shunt resistor.

Its advantage is the economic cost.

The disadvantage is that no isolation between power stage and control stage, it is also necessary to amplify the output signal of the order of mV to V

In some applications, to maintain isolation between power stage and control, using a converter card DC / DC which also fulfills the function of amplifying the signal proportional to the current stage is to receive control.