SECTION TITLE
INSTRUMENTATION • ELECTRONICS
Istec has a variety of hardware for measuring speed
factor of the size, speed and distance of the target. If the speed is too low, the gear tooth too small or the distance to the target material too big, the signal will be flattened and not usable. On the other hand, if the speed is high, the gear tooth large or the distance is small, the signal will show high pulses (80VRMS). Te application and positioning of VR sensors requires special attention and expertise to function properly. As these types of sensors do not function well with low speed, they are not suitable for low or zero-speed detection.
EDDY CURRENT (PROXIMITY) An eddy current sensor uses an electromagnetic field to measure changes in the distance to an object. As a pole wheel moves past the sensor, it measures a variation in distance; close (tooth) and far (notch). Te rotational speed can be determined based on the time between these events.
ADVANTAGES A major advantage of eddy current sensors is that the measuring principle shows both the pulses and the position with respect to the teeth. Tis provides insight into the set distance to the teeth of the target object. Eddy current sensors are also available with a dynamic current output, which allows for long cabling (up to 1,000m).
20
www.engineerlive.com
Sensors with a dynamic current output are less affected by cable impedance as compared to Hall-effect sensors, eddy current sensors based on voltage signals, and VR sensors.
DISADVANTAGES Te use of eddy current sensors for speed measurements has a disadvantage. At a high speed, saturation may occur, causing the signal shape to flatten increasingly. When the gear teeth move past the sensor at high speed, an eddy current sensor barely detects a difference in distances. Te higher the frequency, the less effective an eddy current sensor will be for speed measurements.
HALL-EFFECT SENSORS A Hall-effect sensor measures changes in magnet’s magnetic field, caused by the ferromagnetic target material. Te sensors have built-in signal conditioners, which generate a clear square wave signal. In contrast to VR sensors, Hall-effect sensors are sensitive to the size of the magnetic flux rather than the speed at which it changes. Hall-effect speed sensors have a broad measurement range and can be used to measure both low-speed or stationary parts and high-speed parts.
ADVANTAGES An advantage of a Hall-effect sensor is that the sensor directly provides a digital
output that is easy to transmit and process. Another advantage is that Hall-effect sensors usually feature internal signal processing. Te signal is digitalised and amplified, making it less susceptible to electromagnetic interference (EMI).
DISADVANTAGES Due to built-in electronics, Hall-effect sensors are limited to applications that operate in temperatures ranging from -40°C to 150°C. Moreover, Hall-effect sensors require a three-wire connection. Also, the trigger level is defined in the Hall-effect sensor and cannot be changed.
Hall-effect sensors provide an easy to transmit digital output
Michel Faas is with Istec.
www.istec.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52
