Frederiksen Photo Gate. This Photogate Unit is specially designed to be used together with the Electronic Counter or timer FO140110. It can be used as an optical switch, activated when the light beam is broken and for pendulum period measurements, air track timing, measuring period of rotation etc. The unit is made from impact-resistant plastic with threads for vertical and horizontal mounting using the supplied 10 mm diameter support post. The Photogate Unit is supplied with powerful red transmitter diode, in front of which is 1 mm slit, and two LEDs on the sides of the unit (red for transmitter, green for receiver), indicating the function.The Photogate Unit can be connected directly to the DIN sockets of the counter and additional photocells can be daisy-chained and connected to the same counter input, for measurement of acceleration etc.Dimensions: 160 120 28 mm (W H D). Gap width: 90 mm.