Abstract: The optical reflectance or transmittance concentration analyzer includes an acousto-optical tunable filter (AOTF). The AOTF is tuned by a computer controlled digital-to-analog converter through a tunable sweep oscillator. Tuned beams can be selected according to their direction of propagation or according to their polarization behavior. Therefore, if desired, a pair of crossed polarizers can be used to select one of the tuned monochomatic light beams that pass from a light source through the AOTF. To obtain rapid wavelength change along with electronic chopping or wavelength modulation, the digital-to-analog converter output is combined with the output of a high speed signal generator. The modulated light is conducted directly or through a fiber optic cable to the location of the optical measurement and impinges upon the sample where it is reflected or transmitted. The emerging light is collected onto detector(s).

Abstract: A key telephone system having a plurality of telephone station sets for selective connection to first or second telephone lines. The system includes a control unit which detects the presence of on-hook conditions on the lines, and transmits control signals in selected time slots to each of the station sets over a single control line to indicate the off-hook/on-hook status of the lines. The system may include circuitry at each station set for transmitting additional control signals in other selected time slots over the single control line to identify privacy release of the telephone line connected thereto.

Abstract: A key telephone system having a plurality of telephone station sets for selective connection to a plurality of telephone lines. At least one set having circuitry for transmitting in a selected time slot on a control line, a signal requesting a hold state on the telephone line connected to the set. The system includes a control unit which upon detecting the signal requesting the hold state places a hold network on the telephone line and continues to transmit the signal in the selected time slot. Each of the telephone sets includes circuitry which is responsive to the signal in the selected time slot for indicating the hold status of the telephone line.