Application

Speeds in a straight path can easily be measured to an accuracy of 1% with the speed sensors in the 89100 series. They are used for shock absorber tests, filling checks, vibration investigations in buildings and machines, and in servocontrolled systems. In addition, they are suitable for taking measurements on reciprocating pumps, for determining the creep rates and insertion speed of hydraulic presses, as measuring transducers for computers and as signal sources for seismographs.

To match the needs of a wide range of measurement tasks, many types of speed sensors having varying sensitivities are available, including those with unbreakable magnetic cores. The sensors are universally applicable. They can be used over wide temperature ranges and can operate in hydraulic oil as well as in other non-corrosive liquids. The wide range of measurements (the ratio of the smallest to largest measurable speeds 400,000 : 1), high resolution and absence of hysteresis are further advantages. The output of the speed sensor is not electrically connected to the housing. This provides optimum conditions for connecting to the subsequent electronics.

Description

If a magnet is moved through a coil then, in accordance with Faraday‘s law and Lenz‘s law, a voltage is induced in the coil, proportional to the speed of the magnet and to its field strength. The speed sensors in this series operate according to this principle of magnetic induction.


If the north and south poles of a magnet move axially in a coil, they induce voltages equal in magnitude but opposite in vector, and the resulting output voltage is therefore zero. In order to avoid this effect, the coil is divided into two parts wound in opposite directions, so that the north pole generates a voltage in one half and the south pole generates one in the other half. The coils are connected in series. The addition of the individual voltages gives an output signal that is proportional to the linear speed. It is also possible to access the voltages in the two individual coils.


The maximum speed is limited by the maximum permitted output voltage of 500 V. At the other end, the minimum measurable speed is determined by the sensitivity and the noise background of the subsequent electronics. If any interfering voltages are induced by strong alternating current fields, they can be eliminated through additional screening.