Photoelectric Scanning Head
The SH 11 model scanning head was especially designed both for scanning of the marks on the rotating discs of mechanical meters or simulated disc marks on LCD displays and for detection of light emitting diodes (LED’s) of electronic meters. The choice of operation with mechanical or electronic meters is made by simple rotation of a selection switch. The precision optical lens is designed to make the scan- ning head insensible to external light. Its compact, robust construction makes the head equally suitable for use in stationary test consoles as well as for use with mobile and portable equipment.
The impulse output of the scanning head delivers a positive output pulse of the duration 0.5 ms.
Disc mark detection with mechanical meters
A pulsed green light beam is used to enable the scanning head to detect the optical contrasts on the perimeter of the disc. The marks may be either red or black, and within this colour range may be rough, matt or shiny or otherwise be marked with strobo- scopic markings.
The manually sensibility set-up for the disc or LCD marks is not necessary. The optimal set-up is auto- matically learned by the integrated teach function, which can be activated by the rotary switch or an external control signal.
Light Emitting Diode (LED) impulse detection with electronic meters
The duration of optical impulse signals from electric meters may be detected and evaluated by use of the SH 11 head. The LED signal from the meter under test must fulfil the following conditions:
The impulse length must be ≥ 100 μs and the impulse pause must be ≥ 600 μs
The changeover from dark to light state must take place in ≤ 20 μs and the change from light to dark be ≤ 100 μs
Short impulses or impulses with a 1:1 ratio (with- out modulation or with an 8 kHz modulated switch-on time) and with a frequency of up to 800 Hz may be scanned
The wavelength of the received signal must lie within the range of 500 – 950 nm