Caliper2PC possesses two tachometers, with which the speed of spindles such as of lathes and milling machines can be measured and displayed. The electronic measuring equipment integrated into Caliper2PC has been designed for the use of reflective opto switches. A combination of a simple photo transistor or photo diode and an infra-red LED (a red LED can also be used) serve as sensor. In order to measure the spindle speed, the sensor has to be set up in such a way that the transmitting LED illuminates the rotating spindle. The spindle needs to be marked at least once. Alternatively, the sensor can be mounted inside the gear so that the teeth of a gear wheel are illuminated. The photo transistor, which serves as receiver, measures the light reflected by the rotating element. The alternating intensity of the light is then converted into electronic signals by the photo transistor. The Caliper2PC interface processes the data and determines the time between the edges. Preferably, a dark location should be chosen for the sensor to minimize the influence by foreign sources of light. The Caliper2PC interface supplies the transmitting LED with regulated DC voltage. The measurable spindle speed ranges from 3000 – 300 000 rpm (50 – 5000Hz) (see video).
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fig. 1: Tachometer, Reflective Opto Switch.
If a speed below 3000 rpm needs to be measured, several equally spaced markings can be made. The number of markings can be defined in the software so that the frequency measured is automatically converted and the correct rpm is displayed. Instead of reflective opto switches, slotted opto switches (such as the ones in a mechanic PC mouse) can be used as well. The sensors are connected by 2.5 mm stereo jacks (see fig. 2). Caliper2PC possesses two sockets with which two sensors can be connected.
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fig. 2: pin assignment of optical tachometers for Caliper2PC.
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Copyright © Dipl.-Ing. Tomer Lanzman. All rights reserved.
